ENVIRONMENTAL IONIZING RADIATION DOSE OUTDOOR IN AN INHABITED AREA WITH A HIGH CONCENTRATION OF URANO-PHOSPHATE IN NORTHEAST OF BRAZIL

ENVIRONMENTAL IONIZING RADIATION DOSE OUTDOOR IN AN INHABITED AREA WITH A HIGH CONCENTRATION OF... Abstract A marine phosphorus region with high concentrations of phosphate, coastwise of Pernambuco, Northeast of Brazil, is densely inhabited. Rock phosphate deposits naturally contain uranium ore that produces ionizing radiation from it and its natural descendants, furthermore, its thorium and potassium concentrations are comparable to those usually found in soils. Radiological monitoring of this environment is important to verify the occurrence of harmful effective doses for the adjacent population. This study aimed at the in situ radiometric monitoring in four cities of the north of the Metropolitan Region of Recife—Pernambuco, estimating the effective environmental dose to which the local population is subject. In total, 91 points were monitored with a discriminator-type detector. The outdoor environmental effective dose rates ranged from 1.99 ± 0.09 to 7.59 ± 0.36 mSv y−1, with an average of 2.60 ± 0.69 mSv y−1. INTRODUCTION The environmental radioactivity exposes humans to ionizing radiation. This exposure can be detected in several compartments of the ecosystem, coming from rocks, soils, air, water, building materials and foods(1, 2). Environmental radioactivity, for the most part, has its origin from natural radionuclides classified as primordial, present in the earth’s crust since its formation, from the cosmic origin and from some anthropic radionuclides(3, 4). The most important terrestrial sources of exposure are the radioisotopes such as 40K and those of the natural series of the 238U and 232Th(5). Currently, there is evidence of cancer risk due to exposure to low doses, especially doses below current recommended limits for protection of radiation workers and the general public(6–8). The phosphate rocks is an example of ore that may be of concern to researchers in terms of radiation protection due to association with natural radioisotopes. It is used worldwide for manufacturing phosphoric acid and chemical fertilizers(9) and may exhibit 238U concentrations ranging from 30 to 3000 Bq/kg(5, 10), and concentrations of 226Ra, from the 238U, ranging from 100 to 10 000 Bq/kg has been reported yet(11). Iran and Brazil are two examples of countries of high radioactive background because they present high concentrations of radioactive minerals. In Ramsar, northern Iran, background radiation produces absorbed dose up to 260 mSv y−1(12). Studies conducted in the semiarid region of the state of Rio Grande do Norte, Northeastern Brazil, using computer codes, have analyzed the potential public dose, in a future installation of a phosphoric acid production plant for fertilizers, and found an estimated value of 2.8 mSv y−1(9). A phosphate sedimentary rock region, associated with uranium ore, is located from the coast of the state of Pernambuco to the border of Paraíba with Rio Grande do Norte, northeast of Brazil. It has an extension of ~150 km with an average width of 4 km. The thickness of the deposits ranges from decimeters up to ~4 m. The highest uranium concentration layer was at an average depth of 6 m, with a mean concentration ranging from 150 to 200 μg/g of U3O8, depending on the investigated deposit, being among the highest concentrations found in this type of ore when compared to other world occurrences(13). With the evident anthropic changes due the demographic expansion, the region with uranium concentrations in the range of 10–530 μg/g of U3O8 in phosphate samples(14, 15) is currently inhabited, and considering that most of the area’s ore will not be extracted due to the advancement of housing developments, it was observed the need for new comparative and complementary studies of this area, aiming to establish an in situ radiometric monitoring of the region after the occupation to assess the degree of exposure of the local population. In this study, four cities located in the northern area of the Metropolitan Region of Recife (Região Metropolitana do Recife—RMR) were prioritized, due to the fact that they were the most exploited localities at the time of phosphate extraction, in the 1940 decades, and because of their high population density, namely, Abreu e Lima, Igarassu, Olinda and Paulista. In these cities, the external gamma exposure outside the residences was evaluated and the authors constructed a current radiometric profile of the region. MATERIALS AND METHODS The study area The research area is located in the coastal region of the State of Pernambuco, Brazil, comprising four cities in the RMR: Abreu e Lima, Igarassu, Olinda and Paulista. A map of the area (Figure 1), where the radiometry monitoring study was carried out, easily identify this important locality near the Federal Highway BR101 and the State Highway PE15. It is a densely inhabited region with houses, small properties destined to family agriculture, industries, commerce and cultural tourism. Close to very crowded beaches, the region is currently very different in relation to the time of the phosphate exploitation due to the disorderly urban expansion Figure 1. View largeDownload slide Map representing the Brazilian Northeast and detailing, shades of grey, the area of study with the cities of the RMR in Pernambuco State. Figure 1. View largeDownload slide Map representing the Brazilian Northeast and detailing, shades of grey, the area of study with the cities of the RMR in Pernambuco State. Figure 1 shows the map representing the Brazilian Northeast and detailing, shades of grey, the area of study with the cities of the RMR in Pernambuco State. According to the census conducted by the Brazilian Institute of Geography and Statistics (Instituto Brasileiro de Geografia e Estatística—IBGE)(16) (2010), these four cities have a total of 874 695 inhabitants, with the city of Olinda having the highest number with 377 779 inhabitants, followed by the city of Paulista with ~300 466 inhabitants, Igarassu with a population of 102 021 and Abreu e Lima with 94 429 inhabitants. The total value of the population of these four cities represents ~10% of the Pernambuco state. The population distribution occurred totally irregularly, without any planning and concern with the occurrence of phosphate deposits. Considering the whole extension of the phosphate rock region evaluated in this study, only in Olinda was possible to perceive that the extraction of the ore, that occurred in the 1940s, left traces. In some isolated points, in private areas, even in present days, it is possible to verify the presence of inactive excavations of phosphate mines no longer exploited. These large holes are completely abandoned and covered by vegetation and accumulated garbage. The presence of the researchers in the mentioned wastelands was not authorized, which made it impossible to determine the current depth and the risks to the local population. In short, the study site consists of already exploited and unexploited areas with phosphate residues arising at several points. The measurement system The measurement system used to evaluate the effective dose rate outdoor is composed of a portable discriminator gamma detector with a combined probe; model Gamma Surveyor®, manufactured by GF Scientific Instruments. Specifically, the system consists of a control unit, with dimensions of 25.6 × 9.0 × 6.0 cm3 and mass of 0.5 kg, coupled to a gamma probe with dimensions of 9.0 × 12.0 × 29.0 cm3, handle height of 18.0 cm and mass of 1.6 kg. The system control unit has a maximum storage capacity of 32 Mbit for data and can be connected to a computer via a USB cable and to a GPS system. The system probe, in turn, consists of a scintillation material consisting of a single crystal of sodium iodide [NaI(Tl)], of cylindrical in shape but with a planar surface, activated with a low concentration of thallium (~0.094 g) and optically coupled to the photocathode of a photomultiplier tube. To extend the range of energy detection, another scintillation material of higher density of bismuth germanate oxide [BGO (Bi4Ge3O12)] is coupled to the NaI(Tl) too. The volumes of these materials are 350 cm3 (3″ × 3″ or ~75 × 75 mm2) and 103 cm3 (2″ × 2″ or ~51 × 51 mm2), respectively, providing greater efficiency in the detection of gamma radiation. This probe registers a maximum counting rate of 250 000 pulses per second, covers an energy range of 100 keV–3 MeV and has a multichannel analyzer with 512 channels. The instrument allows the measurement of environmental dose rates and determines the concentrations of K (%), 238U (μg/g) and 232Th (μg/g). The concentration of K is determined directly by the gamma emission of the 40K. However, the concentrations of 238U and 232Th are determined based on the detection of 214Bi and 208Tl, respectively, present in their radioactive series. This detector still has the Search Mode function which allows the rapid search of radiation sources or radioactive anomalies present in the field, providing the characterization of an anomalous region with their values of the absorbed dose rate in situ. The measurements taken are stored in the equipment memory and can then be transferred and processed in computer systems. The monitored points In an RMR area, specifically where are located the cities of Olinda, Paulista, Abreu e Lima and Igarassu, there is a formation of discontinuous segments of the phosphate ore due to the partial erosion of the phosphate band. The monitored points of the study area were selected in a systematic way using previous works highlighted here: Amaral(14, 15) and Lima(13), and, furthermore, prioritizing the areas where there are the highest population densities (Figures 2–5). A total of 91 points were selected and analyzed in triplicate in these cities divided as follows: 18 points at Abreu e Lima, 30 points at Igarassu, 28 points at Olinda and 15 points at Paulista. The measurements were taken in the air at 1 m from the soil surface and considering 0.2 a maximum occupancy factor recommended by the UNSCEAR to the outdoors environment(17). The distribution by cities of the monitored points, geographical coordinates and estimated effective doses for a period of one year was all related in Tables 1–4 in Results and Discussion. Thus, with the geographical coordinates, it is possible to search and locate the measurement points, all very close to a large number of residences, businesses and schools along two major roads the State Road PE15 and Federal Highway BR101. Figure 2. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Abreu e Lima. Figure 2. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Abreu e Lima. Figure 3. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Igarassu. Figure 3. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Igarassu. Figure 4. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Olinda. Figure 4. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Olinda. Figure 5. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Paulista. Figure 5. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Paulista. Table 1. Location and obtained results in the monitoring of the Abreu e Lima City. Points Coordinates Effective dose rates (mSv y−1) S W P01 7°54′27.5″ 34°54′01.9″ 2.94 ± 0.14 P02 7°54′27.5″ 34°54′07.3″ 3.08 ± 0.15 P03 7°53′48.8″ 34°54′01.6″ 4.93 ± 0.23 P04 7°52′21.4″ 34°52′42.6″ 2.16 ± 0.10 P05 7°54′01.7″ 34°54′06.6″ 2.01 ± 0.10 P06 7°53′54.3″ 34°54′05.0″ 2.52 ± 0.12 P07 7°53′49.3″ 34°53′56.6″ 2.18 ± 0.10 P08 7°53′43.0″ 34°53′55.3″ 2.21 ± 0.10 P09 7°53′30.3″ 34°53′47.4″ 2.68 ± 0.13 P10 7°53′25.3″ 34°53′42.7″ 2.22 ± 0.11 P11 7°53′34.8″ 34°53′56.4″ 2.11 ± 0.10 P12 7°53′12.5″ 34°54′14.2″ 2.31 ± 0.11 P13 7°51′27.9″ 34°54′28.9″ 2.34 ± 0.11 P14 7°54′39.4″ 34°54′06.1″ 2.44 ± 0.12 P15 7°54′37.8″ 34°54′07.4″ 2.20 ± 0.10 P16 7°54′47.8″ 34°54′02.2″ 2.59 ± 0.12 P17 7°54′55.2″ 34°54′01.2″ 2.15 ± 0.10 P18 7°55′13.6″ 34°53′43.8″ 2.13 ± 0.10 Points Coordinates Effective dose rates (mSv y−1) S W P01 7°54′27.5″ 34°54′01.9″ 2.94 ± 0.14 P02 7°54′27.5″ 34°54′07.3″ 3.08 ± 0.15 P03 7°53′48.8″ 34°54′01.6″ 4.93 ± 0.23 P04 7°52′21.4″ 34°52′42.6″ 2.16 ± 0.10 P05 7°54′01.7″ 34°54′06.6″ 2.01 ± 0.10 P06 7°53′54.3″ 34°54′05.0″ 2.52 ± 0.12 P07 7°53′49.3″ 34°53′56.6″ 2.18 ± 0.10 P08 7°53′43.0″ 34°53′55.3″ 2.21 ± 0.10 P09 7°53′30.3″ 34°53′47.4″ 2.68 ± 0.13 P10 7°53′25.3″ 34°53′42.7″ 2.22 ± 0.11 P11 7°53′34.8″ 34°53′56.4″ 2.11 ± 0.10 P12 7°53′12.5″ 34°54′14.2″ 2.31 ± 0.11 P13 7°51′27.9″ 34°54′28.9″ 2.34 ± 0.11 P14 7°54′39.4″ 34°54′06.1″ 2.44 ± 0.12 P15 7°54′37.8″ 34°54′07.4″ 2.20 ± 0.10 P16 7°54′47.8″ 34°54′02.2″ 2.59 ± 0.12 P17 7°54′55.2″ 34°54′01.2″ 2.15 ± 0.10 P18 7°55′13.6″ 34°53′43.8″ 2.13 ± 0.10 View Large Table 1. Location and obtained results in the monitoring of the Abreu e Lima City. Points Coordinates Effective dose rates (mSv y−1) S W P01 7°54′27.5″ 34°54′01.9″ 2.94 ± 0.14 P02 7°54′27.5″ 34°54′07.3″ 3.08 ± 0.15 P03 7°53′48.8″ 34°54′01.6″ 4.93 ± 0.23 P04 7°52′21.4″ 34°52′42.6″ 2.16 ± 0.10 P05 7°54′01.7″ 34°54′06.6″ 2.01 ± 0.10 P06 7°53′54.3″ 34°54′05.0″ 2.52 ± 0.12 P07 7°53′49.3″ 34°53′56.6″ 2.18 ± 0.10 P08 7°53′43.0″ 34°53′55.3″ 2.21 ± 0.10 P09 7°53′30.3″ 34°53′47.4″ 2.68 ± 0.13 P10 7°53′25.3″ 34°53′42.7″ 2.22 ± 0.11 P11 7°53′34.8″ 34°53′56.4″ 2.11 ± 0.10 P12 7°53′12.5″ 34°54′14.2″ 2.31 ± 0.11 P13 7°51′27.9″ 34°54′28.9″ 2.34 ± 0.11 P14 7°54′39.4″ 34°54′06.1″ 2.44 ± 0.12 P15 7°54′37.8″ 34°54′07.4″ 2.20 ± 0.10 P16 7°54′47.8″ 34°54′02.2″ 2.59 ± 0.12 P17 7°54′55.2″ 34°54′01.2″ 2.15 ± 0.10 P18 7°55′13.6″ 34°53′43.8″ 2.13 ± 0.10 Points Coordinates Effective dose rates (mSv y−1) S W P01 7°54′27.5″ 34°54′01.9″ 2.94 ± 0.14 P02 7°54′27.5″ 34°54′07.3″ 3.08 ± 0.15 P03 7°53′48.8″ 34°54′01.6″ 4.93 ± 0.23 P04 7°52′21.4″ 34°52′42.6″ 2.16 ± 0.10 P05 7°54′01.7″ 34°54′06.6″ 2.01 ± 0.10 P06 7°53′54.3″ 34°54′05.0″ 2.52 ± 0.12 P07 7°53′49.3″ 34°53′56.6″ 2.18 ± 0.10 P08 7°53′43.0″ 34°53′55.3″ 2.21 ± 0.10 P09 7°53′30.3″ 34°53′47.4″ 2.68 ± 0.13 P10 7°53′25.3″ 34°53′42.7″ 2.22 ± 0.11 P11 7°53′34.8″ 34°53′56.4″ 2.11 ± 0.10 P12 7°53′12.5″ 34°54′14.2″ 2.31 ± 0.11 P13 7°51′27.9″ 34°54′28.9″ 2.34 ± 0.11 P14 7°54′39.4″ 34°54′06.1″ 2.44 ± 0.12 P15 7°54′37.8″ 34°54′07.4″ 2.20 ± 0.10 P16 7°54′47.8″ 34°54′02.2″ 2.59 ± 0.12 P17 7°54′55.2″ 34°54′01.2″ 2.15 ± 0.10 P18 7°55′13.6″ 34°53′43.8″ 2.13 ± 0.10 View Large Table 2. Location and obtained results in the monitoring of the Igarassu City. Points Coordinates Effective dose rates (mSv y−1) S W P19 7°53′04.2″ 34°54′06.8″ 3.41 ± 0.16 P20 7°52′18.5″ 34°54′16.2″ 2.88 ± 0.14 P21 7°52′19.9″ 34°54′10.2″ 2.79 ± 0.13 P22 7°52′21.4″ 34°54′04.0″ 2.83 ± 0.13 P23 7°52′25.5″ 34°54′10.2″ 2.83 ± 0.13 P24 7°52′18.2″ 34°54′21.6″ 2.14 ± 0.10 P25 7°52′05.6″ 34°54′14.9″ 2.89 ± 0.14 P26 7°51′56.0″ 34°54′12.8″ 3.08 ± 0.15 P27 7°52′02.5″ 34°54′08.6″ 2.68 ± 0.13 P28 7°52′10.5″ 34°54′39.1″ 2.90 ± 0.14 P29 7°52′07.6″ 34°54′35.0″ 2.50 ± 0.12 P30 7°52′11.2″ 34°54′37.0″ 2.85 ± 0.14 P31 7°52′14.0″ 34°54′38.3″ 2.96 ± 0.14 P32 7°54′18.2″ 34°54′40.3″ 3.00 ± 0.14 P33 7°52′18.8″ 34°54′43.4″ 2.65 ± 0.13 P34 7°52′29.6″ 34°54′50.7″ 3.00 ± 0.14 P35 7°52′26.2″ 34°54′46.1″ 3.21 ± 0.15 P36 7°52′23.2″ 34°54′40.8″ 2.79 ± 0.13 P37 7°52′16.8″ 34°54′34.1″ 2.70 ± 0.13 P38 7°52′11.2″ 34°54′30.7″ 3.04 ± 0.14 P39 7°52′06.8″ 34°54′27.6″ 2.86 ± 0.14 P40 7°52′16.3″ 34°54′28.0″ 2.88 ± 0.14 P41 7°52′20.0″ 34°54′26.3″ 2.84 ± 0.13 P42 7°52′27.0″ 34°54′26.1″ 2.64 ± 0.13 P43 7°52′30.6″ 34°54′27.4″ 2.76 ± 0.13 P44 7°52′29.7″ 34°54′24.4″ 2.50 ± 0.12 P45 7°52′30.2″ 34°54′36.0″ 2.95 ± 0.14 P46 7°52′41.2″ 34°54′33.3″ 2.58 ± 0.12 P47 7°52′36.1″ 34°54′29.0″ 2.57 ± 0.12 P48 7°53′07.7″ 34°54′17.0″ 2.53 ± 0.12 Points Coordinates Effective dose rates (mSv y−1) S W P19 7°53′04.2″ 34°54′06.8″ 3.41 ± 0.16 P20 7°52′18.5″ 34°54′16.2″ 2.88 ± 0.14 P21 7°52′19.9″ 34°54′10.2″ 2.79 ± 0.13 P22 7°52′21.4″ 34°54′04.0″ 2.83 ± 0.13 P23 7°52′25.5″ 34°54′10.2″ 2.83 ± 0.13 P24 7°52′18.2″ 34°54′21.6″ 2.14 ± 0.10 P25 7°52′05.6″ 34°54′14.9″ 2.89 ± 0.14 P26 7°51′56.0″ 34°54′12.8″ 3.08 ± 0.15 P27 7°52′02.5″ 34°54′08.6″ 2.68 ± 0.13 P28 7°52′10.5″ 34°54′39.1″ 2.90 ± 0.14 P29 7°52′07.6″ 34°54′35.0″ 2.50 ± 0.12 P30 7°52′11.2″ 34°54′37.0″ 2.85 ± 0.14 P31 7°52′14.0″ 34°54′38.3″ 2.96 ± 0.14 P32 7°54′18.2″ 34°54′40.3″ 3.00 ± 0.14 P33 7°52′18.8″ 34°54′43.4″ 2.65 ± 0.13 P34 7°52′29.6″ 34°54′50.7″ 3.00 ± 0.14 P35 7°52′26.2″ 34°54′46.1″ 3.21 ± 0.15 P36 7°52′23.2″ 34°54′40.8″ 2.79 ± 0.13 P37 7°52′16.8″ 34°54′34.1″ 2.70 ± 0.13 P38 7°52′11.2″ 34°54′30.7″ 3.04 ± 0.14 P39 7°52′06.8″ 34°54′27.6″ 2.86 ± 0.14 P40 7°52′16.3″ 34°54′28.0″ 2.88 ± 0.14 P41 7°52′20.0″ 34°54′26.3″ 2.84 ± 0.13 P42 7°52′27.0″ 34°54′26.1″ 2.64 ± 0.13 P43 7°52′30.6″ 34°54′27.4″ 2.76 ± 0.13 P44 7°52′29.7″ 34°54′24.4″ 2.50 ± 0.12 P45 7°52′30.2″ 34°54′36.0″ 2.95 ± 0.14 P46 7°52′41.2″ 34°54′33.3″ 2.58 ± 0.12 P47 7°52′36.1″ 34°54′29.0″ 2.57 ± 0.12 P48 7°53′07.7″ 34°54′17.0″ 2.53 ± 0.12 View Large Table 2. Location and obtained results in the monitoring of the Igarassu City. Points Coordinates Effective dose rates (mSv y−1) S W P19 7°53′04.2″ 34°54′06.8″ 3.41 ± 0.16 P20 7°52′18.5″ 34°54′16.2″ 2.88 ± 0.14 P21 7°52′19.9″ 34°54′10.2″ 2.79 ± 0.13 P22 7°52′21.4″ 34°54′04.0″ 2.83 ± 0.13 P23 7°52′25.5″ 34°54′10.2″ 2.83 ± 0.13 P24 7°52′18.2″ 34°54′21.6″ 2.14 ± 0.10 P25 7°52′05.6″ 34°54′14.9″ 2.89 ± 0.14 P26 7°51′56.0″ 34°54′12.8″ 3.08 ± 0.15 P27 7°52′02.5″ 34°54′08.6″ 2.68 ± 0.13 P28 7°52′10.5″ 34°54′39.1″ 2.90 ± 0.14 P29 7°52′07.6″ 34°54′35.0″ 2.50 ± 0.12 P30 7°52′11.2″ 34°54′37.0″ 2.85 ± 0.14 P31 7°52′14.0″ 34°54′38.3″ 2.96 ± 0.14 P32 7°54′18.2″ 34°54′40.3″ 3.00 ± 0.14 P33 7°52′18.8″ 34°54′43.4″ 2.65 ± 0.13 P34 7°52′29.6″ 34°54′50.7″ 3.00 ± 0.14 P35 7°52′26.2″ 34°54′46.1″ 3.21 ± 0.15 P36 7°52′23.2″ 34°54′40.8″ 2.79 ± 0.13 P37 7°52′16.8″ 34°54′34.1″ 2.70 ± 0.13 P38 7°52′11.2″ 34°54′30.7″ 3.04 ± 0.14 P39 7°52′06.8″ 34°54′27.6″ 2.86 ± 0.14 P40 7°52′16.3″ 34°54′28.0″ 2.88 ± 0.14 P41 7°52′20.0″ 34°54′26.3″ 2.84 ± 0.13 P42 7°52′27.0″ 34°54′26.1″ 2.64 ± 0.13 P43 7°52′30.6″ 34°54′27.4″ 2.76 ± 0.13 P44 7°52′29.7″ 34°54′24.4″ 2.50 ± 0.12 P45 7°52′30.2″ 34°54′36.0″ 2.95 ± 0.14 P46 7°52′41.2″ 34°54′33.3″ 2.58 ± 0.12 P47 7°52′36.1″ 34°54′29.0″ 2.57 ± 0.12 P48 7°53′07.7″ 34°54′17.0″ 2.53 ± 0.12 Points Coordinates Effective dose rates (mSv y−1) S W P19 7°53′04.2″ 34°54′06.8″ 3.41 ± 0.16 P20 7°52′18.5″ 34°54′16.2″ 2.88 ± 0.14 P21 7°52′19.9″ 34°54′10.2″ 2.79 ± 0.13 P22 7°52′21.4″ 34°54′04.0″ 2.83 ± 0.13 P23 7°52′25.5″ 34°54′10.2″ 2.83 ± 0.13 P24 7°52′18.2″ 34°54′21.6″ 2.14 ± 0.10 P25 7°52′05.6″ 34°54′14.9″ 2.89 ± 0.14 P26 7°51′56.0″ 34°54′12.8″ 3.08 ± 0.15 P27 7°52′02.5″ 34°54′08.6″ 2.68 ± 0.13 P28 7°52′10.5″ 34°54′39.1″ 2.90 ± 0.14 P29 7°52′07.6″ 34°54′35.0″ 2.50 ± 0.12 P30 7°52′11.2″ 34°54′37.0″ 2.85 ± 0.14 P31 7°52′14.0″ 34°54′38.3″ 2.96 ± 0.14 P32 7°54′18.2″ 34°54′40.3″ 3.00 ± 0.14 P33 7°52′18.8″ 34°54′43.4″ 2.65 ± 0.13 P34 7°52′29.6″ 34°54′50.7″ 3.00 ± 0.14 P35 7°52′26.2″ 34°54′46.1″ 3.21 ± 0.15 P36 7°52′23.2″ 34°54′40.8″ 2.79 ± 0.13 P37 7°52′16.8″ 34°54′34.1″ 2.70 ± 0.13 P38 7°52′11.2″ 34°54′30.7″ 3.04 ± 0.14 P39 7°52′06.8″ 34°54′27.6″ 2.86 ± 0.14 P40 7°52′16.3″ 34°54′28.0″ 2.88 ± 0.14 P41 7°52′20.0″ 34°54′26.3″ 2.84 ± 0.13 P42 7°52′27.0″ 34°54′26.1″ 2.64 ± 0.13 P43 7°52′30.6″ 34°54′27.4″ 2.76 ± 0.13 P44 7°52′29.7″ 34°54′24.4″ 2.50 ± 0.12 P45 7°52′30.2″ 34°54′36.0″ 2.95 ± 0.14 P46 7°52′41.2″ 34°54′33.3″ 2.58 ± 0.12 P47 7°52′36.1″ 34°54′29.0″ 2.57 ± 0.12 P48 7°53′07.7″ 34°54′17.0″ 2.53 ± 0.12 View Large Table 3. Location and obtained results in the monitoring of the Olinda City. Points Coordinates Effective dose rates (mSv y−1) S W P49 7°58′31.8″ 34°51′54.8″ 2.61 ± 0.12 P50 7°58′47.1″ 34°51′33.7″ 2.30 ± 0.11 P51 7°59′59.2″ 34°51′23.4″ 2.65 ± 0.13 P52 8°00′41.7″ 34°51′38.6″ 2.30 ± 0.11 P53 8°00′36.5″ 34°51′46.4″ 2.33 ± 0.11 P54 8°00′56.3″ 34°51′41.3″ 2.34 ± 0.11 P55 8°00′48.0″ 34°51′51.7″ 2.25 ± 0.11 P56 8°00′57.9″ 34°51′46.5″ 2.44 ± 0.12 P57 8°00′38.9″ 34°52′17.9″ 2.43 ± 0.12 P58 8°00′42.7″ 34°51′27.2″ 2.49 ± 0.12 P59 7°58′58.4″ 34°51′20.0″ 2.37 ± 0.11 P60 8°00′20.8″ 34°52′42.8″ 2.77 ± 0.13 P61 6°47′24.8″ 36°50′32.1″ 2.24 ± 0.11 P62 8°00′49.4″ 34°52′06.9″ 2.15 ± 0.10 P63 8°00′49.5″ 34°52′06.8″ 2.22 ± 0.11 P64 8°00′37.3″ 34°52′08.1″ 2.02 ± 0.10 P65 8°00′34.3″ 34°52′09.1″ 1.99 ± 0.09 P66 8°00′28.3″ 34°52′06.6″ 2.20 ± 0.10 P67 8°00′18.9″ 34°52′00.8″ 2.10 ± 0.10 P68 8°00′14.1″ 34°52′07.0″ 2.05 ± 0.10 P69 8°00′25.5″ 34°52′05.4″ 2.30 ± 0.11 P70 8°00′32.9″ 34°52′07.4″ 2.08 ± 0.10 P71 8°00′23.9″ 34°52′40.5″ 3.73 ± 0.18 P72 8°00′23.9″ 34°52′40.5″ 7.59 ± 0.36 P73 8°00′27.7″ 34°52′37.7″ 2.08 ± 0.10 P74 8°00′26.5″ 34°52′38.1″ 3.48 ± 0.17 P75 8°00′22.3″ 34°52′42.4″ 2.46 ± 0.12 P76 8°00′20.3″ 34°52′43.4″ 2.59 ± 0.12 Points Coordinates Effective dose rates (mSv y−1) S W P49 7°58′31.8″ 34°51′54.8″ 2.61 ± 0.12 P50 7°58′47.1″ 34°51′33.7″ 2.30 ± 0.11 P51 7°59′59.2″ 34°51′23.4″ 2.65 ± 0.13 P52 8°00′41.7″ 34°51′38.6″ 2.30 ± 0.11 P53 8°00′36.5″ 34°51′46.4″ 2.33 ± 0.11 P54 8°00′56.3″ 34°51′41.3″ 2.34 ± 0.11 P55 8°00′48.0″ 34°51′51.7″ 2.25 ± 0.11 P56 8°00′57.9″ 34°51′46.5″ 2.44 ± 0.12 P57 8°00′38.9″ 34°52′17.9″ 2.43 ± 0.12 P58 8°00′42.7″ 34°51′27.2″ 2.49 ± 0.12 P59 7°58′58.4″ 34°51′20.0″ 2.37 ± 0.11 P60 8°00′20.8″ 34°52′42.8″ 2.77 ± 0.13 P61 6°47′24.8″ 36°50′32.1″ 2.24 ± 0.11 P62 8°00′49.4″ 34°52′06.9″ 2.15 ± 0.10 P63 8°00′49.5″ 34°52′06.8″ 2.22 ± 0.11 P64 8°00′37.3″ 34°52′08.1″ 2.02 ± 0.10 P65 8°00′34.3″ 34°52′09.1″ 1.99 ± 0.09 P66 8°00′28.3″ 34°52′06.6″ 2.20 ± 0.10 P67 8°00′18.9″ 34°52′00.8″ 2.10 ± 0.10 P68 8°00′14.1″ 34°52′07.0″ 2.05 ± 0.10 P69 8°00′25.5″ 34°52′05.4″ 2.30 ± 0.11 P70 8°00′32.9″ 34°52′07.4″ 2.08 ± 0.10 P71 8°00′23.9″ 34°52′40.5″ 3.73 ± 0.18 P72 8°00′23.9″ 34°52′40.5″ 7.59 ± 0.36 P73 8°00′27.7″ 34°52′37.7″ 2.08 ± 0.10 P74 8°00′26.5″ 34°52′38.1″ 3.48 ± 0.17 P75 8°00′22.3″ 34°52′42.4″ 2.46 ± 0.12 P76 8°00′20.3″ 34°52′43.4″ 2.59 ± 0.12 View Large Table 3. Location and obtained results in the monitoring of the Olinda City. Points Coordinates Effective dose rates (mSv y−1) S W P49 7°58′31.8″ 34°51′54.8″ 2.61 ± 0.12 P50 7°58′47.1″ 34°51′33.7″ 2.30 ± 0.11 P51 7°59′59.2″ 34°51′23.4″ 2.65 ± 0.13 P52 8°00′41.7″ 34°51′38.6″ 2.30 ± 0.11 P53 8°00′36.5″ 34°51′46.4″ 2.33 ± 0.11 P54 8°00′56.3″ 34°51′41.3″ 2.34 ± 0.11 P55 8°00′48.0″ 34°51′51.7″ 2.25 ± 0.11 P56 8°00′57.9″ 34°51′46.5″ 2.44 ± 0.12 P57 8°00′38.9″ 34°52′17.9″ 2.43 ± 0.12 P58 8°00′42.7″ 34°51′27.2″ 2.49 ± 0.12 P59 7°58′58.4″ 34°51′20.0″ 2.37 ± 0.11 P60 8°00′20.8″ 34°52′42.8″ 2.77 ± 0.13 P61 6°47′24.8″ 36°50′32.1″ 2.24 ± 0.11 P62 8°00′49.4″ 34°52′06.9″ 2.15 ± 0.10 P63 8°00′49.5″ 34°52′06.8″ 2.22 ± 0.11 P64 8°00′37.3″ 34°52′08.1″ 2.02 ± 0.10 P65 8°00′34.3″ 34°52′09.1″ 1.99 ± 0.09 P66 8°00′28.3″ 34°52′06.6″ 2.20 ± 0.10 P67 8°00′18.9″ 34°52′00.8″ 2.10 ± 0.10 P68 8°00′14.1″ 34°52′07.0″ 2.05 ± 0.10 P69 8°00′25.5″ 34°52′05.4″ 2.30 ± 0.11 P70 8°00′32.9″ 34°52′07.4″ 2.08 ± 0.10 P71 8°00′23.9″ 34°52′40.5″ 3.73 ± 0.18 P72 8°00′23.9″ 34°52′40.5″ 7.59 ± 0.36 P73 8°00′27.7″ 34°52′37.7″ 2.08 ± 0.10 P74 8°00′26.5″ 34°52′38.1″ 3.48 ± 0.17 P75 8°00′22.3″ 34°52′42.4″ 2.46 ± 0.12 P76 8°00′20.3″ 34°52′43.4″ 2.59 ± 0.12 Points Coordinates Effective dose rates (mSv y−1) S W P49 7°58′31.8″ 34°51′54.8″ 2.61 ± 0.12 P50 7°58′47.1″ 34°51′33.7″ 2.30 ± 0.11 P51 7°59′59.2″ 34°51′23.4″ 2.65 ± 0.13 P52 8°00′41.7″ 34°51′38.6″ 2.30 ± 0.11 P53 8°00′36.5″ 34°51′46.4″ 2.33 ± 0.11 P54 8°00′56.3″ 34°51′41.3″ 2.34 ± 0.11 P55 8°00′48.0″ 34°51′51.7″ 2.25 ± 0.11 P56 8°00′57.9″ 34°51′46.5″ 2.44 ± 0.12 P57 8°00′38.9″ 34°52′17.9″ 2.43 ± 0.12 P58 8°00′42.7″ 34°51′27.2″ 2.49 ± 0.12 P59 7°58′58.4″ 34°51′20.0″ 2.37 ± 0.11 P60 8°00′20.8″ 34°52′42.8″ 2.77 ± 0.13 P61 6°47′24.8″ 36°50′32.1″ 2.24 ± 0.11 P62 8°00′49.4″ 34°52′06.9″ 2.15 ± 0.10 P63 8°00′49.5″ 34°52′06.8″ 2.22 ± 0.11 P64 8°00′37.3″ 34°52′08.1″ 2.02 ± 0.10 P65 8°00′34.3″ 34°52′09.1″ 1.99 ± 0.09 P66 8°00′28.3″ 34°52′06.6″ 2.20 ± 0.10 P67 8°00′18.9″ 34°52′00.8″ 2.10 ± 0.10 P68 8°00′14.1″ 34°52′07.0″ 2.05 ± 0.10 P69 8°00′25.5″ 34°52′05.4″ 2.30 ± 0.11 P70 8°00′32.9″ 34°52′07.4″ 2.08 ± 0.10 P71 8°00′23.9″ 34°52′40.5″ 3.73 ± 0.18 P72 8°00′23.9″ 34°52′40.5″ 7.59 ± 0.36 P73 8°00′27.7″ 34°52′37.7″ 2.08 ± 0.10 P74 8°00′26.5″ 34°52′38.1″ 3.48 ± 0.17 P75 8°00′22.3″ 34°52′42.4″ 2.46 ± 0.12 P76 8°00′20.3″ 34°52′43.4″ 2.59 ± 0.12 View Large Table 4. Location and obtained results in the monitoring of the Paulista City. Points Coordinates Effective dose rates (mSv y−1) S W P77 7°55′07.7″ 34°53′16.5″ 2.63 ± 0.12 P78 7°55′28.9″ 34°53′27.9″ 2.58 ± 0.12 P79 7°55′42.1″ 34°53′16.3″ 2.31 ± 0.11 P80 7°55′52.0″ 34°53′11.1″ 2.45 ± 0.12 P81 7°56′14.2″ 34°52′43.3″ 2.27 ± 0.11 P82 7°56′42.9″ 34°52′42.9″ 2.29 ± 0.11 P83 7°56′56.2″ 34°52′41.8″ 2.33 ± 0.11 P84 7°57′12.6″ 34°52′38.0″ 2.47 ± 0.12 P85 7°57′35.5″ 34°52′15.7″ 2.44 ± 0.12 P86 7°57′57.9″ 34°52′05.2″ 2.14 ± 0.10 P87 7°58′25.0″ 34°51′47.6″ 2.18 ± 0.10 P88 7°58′04.3″ 34°52′02.0″ 2.34 ± 0.11 P89 7°57′33.8″ 34°52′14.4″ 2.08 ± 0.10 P90 7°57′13.4″ 34°52′32.6″ 2.29 ± 0.11 P91 7°56′03.6″ 34°52′42.5″ 2.06 ± 0.10 Points Coordinates Effective dose rates (mSv y−1) S W P77 7°55′07.7″ 34°53′16.5″ 2.63 ± 0.12 P78 7°55′28.9″ 34°53′27.9″ 2.58 ± 0.12 P79 7°55′42.1″ 34°53′16.3″ 2.31 ± 0.11 P80 7°55′52.0″ 34°53′11.1″ 2.45 ± 0.12 P81 7°56′14.2″ 34°52′43.3″ 2.27 ± 0.11 P82 7°56′42.9″ 34°52′42.9″ 2.29 ± 0.11 P83 7°56′56.2″ 34°52′41.8″ 2.33 ± 0.11 P84 7°57′12.6″ 34°52′38.0″ 2.47 ± 0.12 P85 7°57′35.5″ 34°52′15.7″ 2.44 ± 0.12 P86 7°57′57.9″ 34°52′05.2″ 2.14 ± 0.10 P87 7°58′25.0″ 34°51′47.6″ 2.18 ± 0.10 P88 7°58′04.3″ 34°52′02.0″ 2.34 ± 0.11 P89 7°57′33.8″ 34°52′14.4″ 2.08 ± 0.10 P90 7°57′13.4″ 34°52′32.6″ 2.29 ± 0.11 P91 7°56′03.6″ 34°52′42.5″ 2.06 ± 0.10 View Large Table 4. Location and obtained results in the monitoring of the Paulista City. Points Coordinates Effective dose rates (mSv y−1) S W P77 7°55′07.7″ 34°53′16.5″ 2.63 ± 0.12 P78 7°55′28.9″ 34°53′27.9″ 2.58 ± 0.12 P79 7°55′42.1″ 34°53′16.3″ 2.31 ± 0.11 P80 7°55′52.0″ 34°53′11.1″ 2.45 ± 0.12 P81 7°56′14.2″ 34°52′43.3″ 2.27 ± 0.11 P82 7°56′42.9″ 34°52′42.9″ 2.29 ± 0.11 P83 7°56′56.2″ 34°52′41.8″ 2.33 ± 0.11 P84 7°57′12.6″ 34°52′38.0″ 2.47 ± 0.12 P85 7°57′35.5″ 34°52′15.7″ 2.44 ± 0.12 P86 7°57′57.9″ 34°52′05.2″ 2.14 ± 0.10 P87 7°58′25.0″ 34°51′47.6″ 2.18 ± 0.10 P88 7°58′04.3″ 34°52′02.0″ 2.34 ± 0.11 P89 7°57′33.8″ 34°52′14.4″ 2.08 ± 0.10 P90 7°57′13.4″ 34°52′32.6″ 2.29 ± 0.11 P91 7°56′03.6″ 34°52′42.5″ 2.06 ± 0.10 Points Coordinates Effective dose rates (mSv y−1) S W P77 7°55′07.7″ 34°53′16.5″ 2.63 ± 0.12 P78 7°55′28.9″ 34°53′27.9″ 2.58 ± 0.12 P79 7°55′42.1″ 34°53′16.3″ 2.31 ± 0.11 P80 7°55′52.0″ 34°53′11.1″ 2.45 ± 0.12 P81 7°56′14.2″ 34°52′43.3″ 2.27 ± 0.11 P82 7°56′42.9″ 34°52′42.9″ 2.29 ± 0.11 P83 7°56′56.2″ 34°52′41.8″ 2.33 ± 0.11 P84 7°57′12.6″ 34°52′38.0″ 2.47 ± 0.12 P85 7°57′35.5″ 34°52′15.7″ 2.44 ± 0.12 P86 7°57′57.9″ 34°52′05.2″ 2.14 ± 0.10 P87 7°58′25.0″ 34°51′47.6″ 2.18 ± 0.10 P88 7°58′04.3″ 34°52′02.0″ 2.34 ± 0.11 P89 7°57′33.8″ 34°52′14.4″ 2.08 ± 0.10 P90 7°57′13.4″ 34°52′32.6″ 2.29 ± 0.11 P91 7°56′03.6″ 34°52′42.5″ 2.06 ± 0.10 View Large The calculation of the outdoor dose rate The calibration of the detector was executed at the Laboratory of Ionizing Radiation Metrology (Laboratório de Metrologia das Radiações Ionizantes—LMRI), under certification in 6490/0911, of the Nuclear Energy Department of the Federal University of Pernambuco. The LMRI is accredited by a governmental body. From the established calibration procedure, it was possible to construct a calibration line relating to the indication of the instrument and the dose rate in the air. And with the response graph of the portable gamma spectrometer, it was possible to obtain the angular coefficient of 1.92 and the linear coefficient of 1430.8. To calculate an occupancy factor for the inhabitants of the analyzed areas it was considered that they are exposed to an outdoor dose for 24 h during 365.25 days multiplied by a conversion factor of dose 0.7 Sv/Gy which returns 6136.2. This last value multiplied by a factor of 10−6 to convert from nGy to mGy results in 6.14 × 10−3. Equation 1 was determined with the previous values where ‘ Ḋ’ represents the experimental measurements performed in nGy h−1 or the absorbed dose rate outdoor in the environment and, ‘ ḢE’ corresponds to the environmental effective dose rate outdoor. ḢE=(1.92×Ḋ−1430.87)×6.14x10−3 (1) The triplicate measurements for each point were performed in the air at 1 m from the soil surface and using a count time of 190 s, which was defined according to the local radioactivity levels and to the count statistic. The obtained results were absorbed dose rate (nGy h−1). However, through the equation of conversion (Equation 1), with the necessary parameters, the effective environmental dose rates were obtained in mSv y−1(18). RESULTS AND DISCUSSION A sequence of 04 tables was constructed with the results of the effective dose rate measurements (mSv y−1) performed in the municipalities of Abreu and Lima, Igarassu, Olinda and Paulista. The first column of each table refers to the identification of each measurement point in the form of the letter P and a sequential number, the second and third columns identify the South and West geographical coordinates of the sites studied and the last column is the value of the effective dose rate obtained in mSv y−1 (Tables 1–4). For the municipality of Abreu and Lima (Table 1), 18 measurements were identified as points P1–P18 among which we can highlight the point P3 with a value of 4.93 ± 0.23 mSv y−1. This point is located on a residential street in a low-income neighborhood, and also close to restaurants, churches and small markets. The Federal Highway BR101, that in this stretch is identified as Governor Mário Covas, is located to few meters (Figure 2). In the municipality of Igarassu, 30 measurements were made and the points were identified in the range of P19–P48 (Table 2). The maximum effective dose occurred at point 19 (P19) with a value of 3.41 ± 0.16 mS y−1. This measurement was performed in a vacant lot near low-income households. The Federal Highway BR101 is located nearby, as well as gas stations, restaurants and small businesses (Figure 3). In Olinda, with 28 measurements (P49–P76) (Table 3), occurred to the value of greatest concern in terms of radiological protection. The point 72 (P72) is in a poor neighborhood with a disorderly occupation of urban space, with a value of 7.59 ± 0.36 mSv y−1 well above the values of background radiation (Figure 4). The measurement point occurred in a dug-out land and near an industrial chimney probably remnants of phosphate production occurred in the 1940s until 1960s. The measurement P77 resulted in a maximum value in Paulista city of 2.63 ± 0.12 mSv y−1. Only 15 measurements (P77–P91) were made for this county (Table 4). The point 77 was a measurement in a forest area but close to a hospital, a very busy bus station and some residential areas (Figure 5). A descriptive statistical analysis of the complete set of values obtained from the measurements of the 91 points of 04 of the cities that form the RMR and that present a formation of sedimentary rocks rich in phosphate associated with the uranium ore was carried out (Table 5). Table 5. Summary with descriptive statistics of all measurements by cities. Statistic descriptive Effective dose rates (mSv y−1) Abreu e Lima Igarassu Olinda Paulista Number of measurements 18 30 28 15 Minimum 2.01 2.14 1.99 2.06 First quartile 2.16 2.66 2.19 2.22 Median 2.26 2.83 2.31 2.31 Arithmetic mean 2.51 2.80 2.59 2.32 Standard deviation 0.67 0.24 1.05 0.17 Third quartile 2.57 2.94 2.51 2.44 Maximum 4.93 3.41 7.59 2.63 Amplitude 2.92 1.27 5.6 0.57 Statistic descriptive Effective dose rates (mSv y−1) Abreu e Lima Igarassu Olinda Paulista Number of measurements 18 30 28 15 Minimum 2.01 2.14 1.99 2.06 First quartile 2.16 2.66 2.19 2.22 Median 2.26 2.83 2.31 2.31 Arithmetic mean 2.51 2.80 2.59 2.32 Standard deviation 0.67 0.24 1.05 0.17 Third quartile 2.57 2.94 2.51 2.44 Maximum 4.93 3.41 7.59 2.63 Amplitude 2.92 1.27 5.6 0.57 Table 5. Summary with descriptive statistics of all measurements by cities. Statistic descriptive Effective dose rates (mSv y−1) Abreu e Lima Igarassu Olinda Paulista Number of measurements 18 30 28 15 Minimum 2.01 2.14 1.99 2.06 First quartile 2.16 2.66 2.19 2.22 Median 2.26 2.83 2.31 2.31 Arithmetic mean 2.51 2.80 2.59 2.32 Standard deviation 0.67 0.24 1.05 0.17 Third quartile 2.57 2.94 2.51 2.44 Maximum 4.93 3.41 7.59 2.63 Amplitude 2.92 1.27 5.6 0.57 Statistic descriptive Effective dose rates (mSv y−1) Abreu e Lima Igarassu Olinda Paulista Number of measurements 18 30 28 15 Minimum 2.01 2.14 1.99 2.06 First quartile 2.16 2.66 2.19 2.22 Median 2.26 2.83 2.31 2.31 Arithmetic mean 2.51 2.80 2.59 2.32 Standard deviation 0.67 0.24 1.05 0.17 Third quartile 2.57 2.94 2.51 2.44 Maximum 4.93 3.41 7.59 2.63 Amplitude 2.92 1.27 5.6 0.57 Considering only the arithmetic means, Igarassu is the locality with the highest mean value for the effective dose rate (2.80 mSv y), despite the measurements of points P72 (Olinda: 7.59 0.36 mSv y−1) and P03 (Abreu and Lima: 4.93 0.23 mSv y−1) were considerably high relative to background radiation. This fact can be explained by the values of the third quartile of these two municipalities. Olinda has 75% of the measured values below 2.51 mSv y−1 and Abreu e Lima has 75% of its measurements below 2.57 mSv y−1. For Igarassu, the third quartile was calculated as 2.94 mSv y−1 explaining the reason for an average value higher than the other three cities. Paulista was the municipality that did not show peaks of effective dose rates. A representation through a line chart (Figure 6), where the horizontal axis represents the points of the measurements and the effective dose rates measured on the vertical axis, shows the behavior by municipalities point-to-point. Abreu and Lima and Olinda had the highest dose values found, 4.93 and 7.59 mSv y−1, respectively, differing only in that the Abreu and Lima peak occurred in the first measurements and Olinda in the last values obtained. However, excluding the two peaks, the values of both municipalities remained close to 2.5 mSv y−1. The representative graph of the measurements in the municipality of Igarassu shows values considered above the background radiation in a range between 2.5 and 3.5 mSv y−1, although there are no dose peaks occurring in the region. It is possible to confirm that in the city of Paulista the first values are slightly above 2.5 mSv y−1, but decrease and remain below this value until the last measurement. Figure 6. View largeDownload slide Graphs of the measurement points and respective measured values of the dose rate. Figure 6. View largeDownload slide Graphs of the measurement points and respective measured values of the dose rate. The authors observed that generally lower values were found at sites with landfills made with soils from other regions or at public roads with artificial paving, which contributed to the reduction of effective dose rates at various points in the region. The point of greatest value (7.59 mSv y−1), on the other hand, located in the city of Olinda, was obtained inside a semi-destroyed masonry structure, which would probably be one of the kilns used to process the phosphate extracted in the region. This value is considered isolated and with much importance to identify a remnant area of the period of the ore exploration and processing that occurred in a period prior to disordered occupation, but not as an estimator of the RMR radiometry and can be observed in the graphical representation (Figure 6—Olinda) since it differs clearly from the others. A major real estate venture has been implemented on the site and currently, the entrance to this area is not permitted, thus, it is not possible to do any kind of radioactive monitoring at this point. CONCLUSIONS The authors, based on the radiometric monitoring performed in the municipalities of Abreu e Lima, Igarassu, Olinda and Paulista, concluded that, in general, the average annual effective dose equivalent rate found is above the values for normal background radiation. It is possible concluded that the use of landfills with soil from regions without radioactive anomalies and the paving of public roads contributed to the reduction of effective dose rates at various points in the region. These events make unfeasible the resumption of phosphate extraction, so the researchers assume that these dose levels will remain constant. However, it is important to continue radiologically mapping this large region in search of anomalies that may endanger the health of the population. This work allowed the identification of the remaining facilities of the phosphate ore exploration and processing in Olinda city that is being evaluated in more detail. Acknowledgements The authors are grateful to the Coordination for the Improvement of Higher Education Personnel (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—CAPES) for the financial assistance granted and to the Federal University of Pernambuco (Universidade Federal de Pernambuco—UFPE), Department of Nuclear Energy (Departamento de Energia Nuclear—DEN)/Graduate Program in Energy and Nuclear Technologies (Programa de Tecnologias Energéticas e Nucleares—PROTEN), for the structure available for the development of this work. REFERENCES 1 Vasconcelos , W. E. Aplicação de técnicas de inteligência artificial na avaliação da dose de populações de regiões de alto background natural. Tese (Doutorado em Ciências Nucleares), Programa de Pós-Graduação em Tecnologias Energéticas e Nucleares, Universidade Federal de Pernambuco, Recife ( 2009 ). 2 Malanca , A. , Gaidolfi , L. , Pessina , V. and Dallara , G. Distribution of 226Ra, 232Th, and 40K in soils of Rio Grande do Norte (Brazil) . J. Environ. Radioact. 30 ( 1 ), 55 – 67 ( 1995 ). Google Scholar CrossRef Search ADS 3 Melo , N. M. P. Avaliação da dose interna devida ao 226Ra, 228Ra e 210Pb nos suprimentos de água para abastecimento público da Região Metropolitana do Recife. Dissertação (Mestrado em Ciências Nucleares), Programa de Pós-Graduação em Tecnologias Energéticas e Nucleares, Universidade Federal de Pernambuco, Recife ( 2008 ). 4 United Scientific Committee on the Effects of Atomic Radiations . Sources and effects of ionizing radiation. UNSCEAR Report 2000, v. 1, annex B, United Nations Publications, New York ( 2000 ). 5 International Atomic Energy Agency . Exposure of the public from large deposits of mineral residues. TecDoc-1660, 49 p, ( 2011 ). 6 International Commission on Radiological Protection . Low-dose extrapolation of radiation-related cancer risk. ICRP Publication 99 . Ann. ICRP 35 ( 4 ), 142 ( 2005 ). 7 Brenner , D. J. et al. . Cancer risks attributable to low doses of ionizing radiation: assessing what we really know . Proc. Natl. Acad. Sci. USA 100 ( 24 ), 13761 – 13766 ( 2003 ). Google Scholar CrossRef Search ADS 8 Hendry , J. H. , Simon , S. L. , Wojcik , A. , Sohrabi , M. , Burkart , W. , Cardis , E. , Laurier , D. , Tirmarche , M. and Hayata , I. Human exposure to high natural background radiation: what can it teach us about radiation risks? J. Radiol. Prot. 29 , A29 – A42 ( 2009 ). Google Scholar CrossRef Search ADS PubMed 9 Glória dos Reis , R. and da Costa Lauria , D. The potential radiological impact from a Brazilian phosphate facility . J. Environ. Radioact. 136 , 188 – 194 ( 2014 ). Google Scholar CrossRef Search ADS PubMed 10 Mortvedt , J. J. Plant and soil relationships of uranium and thorium decay series radionuclides nuclides; a review . J. Environ. Qual. 23 , 643 – 650 ( 1994 ). Google Scholar CrossRef Search ADS 11 Rossler , C. E. , Smith , Z. A. , Bolch , W. E. and Prince , R. J. Uranium and radium-226 in Florida phosphate materials . J. Health Phys. 37 , 269 – 277 ( 1979 ). Google Scholar CrossRef Search ADS 12 Ghiassi-nejad , M. , Mortazavi , S. M. , Cameron , J. R. , Niroomand-rad , A. and Karam , P. A. Very high background radiation areas of Ramsar, Iran: preliminary biological studies . Health Phys. 82 ( 1 ), 87 – 93 ( 2002 ). Google Scholar CrossRef Search ADS PubMed 13 Lima , R. A. Avaliação da dose na população da região urano-fosfática do nordeste que utiliza os recursos hídricos da região. Tese (Doutorado em Ciências), Instituto de Pesquisas Energéticas e Nucleares, Universidade de São Paulo, São Paulo ( 1996 ). 14 Amaral , R. S. Dose na População da região urano-fosfática pernambucana, devida à presença de urânio e 226Ra nos cultivares. Tese (Doutorado em Tecnologia Nuclear), Instituto de Pesquisas Energéticas e Nucleares, Universidade de São Paulo, São Paulo ( 1994 ). 15 Amaral , R. S. Determinação de urânio na fosforita por meio de medidas radiométricas e análise por ativação. Dissertação (Mestrado em Ciências e Tecnologia Nuclear), Departamento de Energia Nuclear, Universidade Federal de Pernambuco, Recife ( 1987 ). 16 Instituto Brasileiro de Geografia Estatística . Available on http://www.ibge.gov.br/cidadesat/xtras/uf.php?coduf=26 (17 September 2013, date last accessed). 17 United Scientific Committee on the Effects of Atomic Radiations . Sources and effects of ionizing radiation. UNSCEAR report 2008, v. 1, annex B, United Nations Publications, New York ( 2008 ) 18 Nazário , M. , Khoury , H. and Hazin , C. Calibração de equipamentos de radioproteção com radiação gama no Laboratório de Metrologia das Radiações Ionizantes—DEN—UFPE. Metrologia 2003. Recife, setembro 2003. Sociedade Brasileira de Metrologia ( 2003 ). © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Protection Dosimetry Oxford University Press

ENVIRONMENTAL IONIZING RADIATION DOSE OUTDOOR IN AN INHABITED AREA WITH A HIGH CONCENTRATION OF URANO-PHOSPHATE IN NORTHEAST OF BRAZIL

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com
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0144-8420
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1742-3406
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10.1093/rpd/ncy005
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Abstract

Abstract A marine phosphorus region with high concentrations of phosphate, coastwise of Pernambuco, Northeast of Brazil, is densely inhabited. Rock phosphate deposits naturally contain uranium ore that produces ionizing radiation from it and its natural descendants, furthermore, its thorium and potassium concentrations are comparable to those usually found in soils. Radiological monitoring of this environment is important to verify the occurrence of harmful effective doses for the adjacent population. This study aimed at the in situ radiometric monitoring in four cities of the north of the Metropolitan Region of Recife—Pernambuco, estimating the effective environmental dose to which the local population is subject. In total, 91 points were monitored with a discriminator-type detector. The outdoor environmental effective dose rates ranged from 1.99 ± 0.09 to 7.59 ± 0.36 mSv y−1, with an average of 2.60 ± 0.69 mSv y−1. INTRODUCTION The environmental radioactivity exposes humans to ionizing radiation. This exposure can be detected in several compartments of the ecosystem, coming from rocks, soils, air, water, building materials and foods(1, 2). Environmental radioactivity, for the most part, has its origin from natural radionuclides classified as primordial, present in the earth’s crust since its formation, from the cosmic origin and from some anthropic radionuclides(3, 4). The most important terrestrial sources of exposure are the radioisotopes such as 40K and those of the natural series of the 238U and 232Th(5). Currently, there is evidence of cancer risk due to exposure to low doses, especially doses below current recommended limits for protection of radiation workers and the general public(6–8). The phosphate rocks is an example of ore that may be of concern to researchers in terms of radiation protection due to association with natural radioisotopes. It is used worldwide for manufacturing phosphoric acid and chemical fertilizers(9) and may exhibit 238U concentrations ranging from 30 to 3000 Bq/kg(5, 10), and concentrations of 226Ra, from the 238U, ranging from 100 to 10 000 Bq/kg has been reported yet(11). Iran and Brazil are two examples of countries of high radioactive background because they present high concentrations of radioactive minerals. In Ramsar, northern Iran, background radiation produces absorbed dose up to 260 mSv y−1(12). Studies conducted in the semiarid region of the state of Rio Grande do Norte, Northeastern Brazil, using computer codes, have analyzed the potential public dose, in a future installation of a phosphoric acid production plant for fertilizers, and found an estimated value of 2.8 mSv y−1(9). A phosphate sedimentary rock region, associated with uranium ore, is located from the coast of the state of Pernambuco to the border of Paraíba with Rio Grande do Norte, northeast of Brazil. It has an extension of ~150 km with an average width of 4 km. The thickness of the deposits ranges from decimeters up to ~4 m. The highest uranium concentration layer was at an average depth of 6 m, with a mean concentration ranging from 150 to 200 μg/g of U3O8, depending on the investigated deposit, being among the highest concentrations found in this type of ore when compared to other world occurrences(13). With the evident anthropic changes due the demographic expansion, the region with uranium concentrations in the range of 10–530 μg/g of U3O8 in phosphate samples(14, 15) is currently inhabited, and considering that most of the area’s ore will not be extracted due to the advancement of housing developments, it was observed the need for new comparative and complementary studies of this area, aiming to establish an in situ radiometric monitoring of the region after the occupation to assess the degree of exposure of the local population. In this study, four cities located in the northern area of the Metropolitan Region of Recife (Região Metropolitana do Recife—RMR) were prioritized, due to the fact that they were the most exploited localities at the time of phosphate extraction, in the 1940 decades, and because of their high population density, namely, Abreu e Lima, Igarassu, Olinda and Paulista. In these cities, the external gamma exposure outside the residences was evaluated and the authors constructed a current radiometric profile of the region. MATERIALS AND METHODS The study area The research area is located in the coastal region of the State of Pernambuco, Brazil, comprising four cities in the RMR: Abreu e Lima, Igarassu, Olinda and Paulista. A map of the area (Figure 1), where the radiometry monitoring study was carried out, easily identify this important locality near the Federal Highway BR101 and the State Highway PE15. It is a densely inhabited region with houses, small properties destined to family agriculture, industries, commerce and cultural tourism. Close to very crowded beaches, the region is currently very different in relation to the time of the phosphate exploitation due to the disorderly urban expansion Figure 1. View largeDownload slide Map representing the Brazilian Northeast and detailing, shades of grey, the area of study with the cities of the RMR in Pernambuco State. Figure 1. View largeDownload slide Map representing the Brazilian Northeast and detailing, shades of grey, the area of study with the cities of the RMR in Pernambuco State. Figure 1 shows the map representing the Brazilian Northeast and detailing, shades of grey, the area of study with the cities of the RMR in Pernambuco State. According to the census conducted by the Brazilian Institute of Geography and Statistics (Instituto Brasileiro de Geografia e Estatística—IBGE)(16) (2010), these four cities have a total of 874 695 inhabitants, with the city of Olinda having the highest number with 377 779 inhabitants, followed by the city of Paulista with ~300 466 inhabitants, Igarassu with a population of 102 021 and Abreu e Lima with 94 429 inhabitants. The total value of the population of these four cities represents ~10% of the Pernambuco state. The population distribution occurred totally irregularly, without any planning and concern with the occurrence of phosphate deposits. Considering the whole extension of the phosphate rock region evaluated in this study, only in Olinda was possible to perceive that the extraction of the ore, that occurred in the 1940s, left traces. In some isolated points, in private areas, even in present days, it is possible to verify the presence of inactive excavations of phosphate mines no longer exploited. These large holes are completely abandoned and covered by vegetation and accumulated garbage. The presence of the researchers in the mentioned wastelands was not authorized, which made it impossible to determine the current depth and the risks to the local population. In short, the study site consists of already exploited and unexploited areas with phosphate residues arising at several points. The measurement system The measurement system used to evaluate the effective dose rate outdoor is composed of a portable discriminator gamma detector with a combined probe; model Gamma Surveyor®, manufactured by GF Scientific Instruments. Specifically, the system consists of a control unit, with dimensions of 25.6 × 9.0 × 6.0 cm3 and mass of 0.5 kg, coupled to a gamma probe with dimensions of 9.0 × 12.0 × 29.0 cm3, handle height of 18.0 cm and mass of 1.6 kg. The system control unit has a maximum storage capacity of 32 Mbit for data and can be connected to a computer via a USB cable and to a GPS system. The system probe, in turn, consists of a scintillation material consisting of a single crystal of sodium iodide [NaI(Tl)], of cylindrical in shape but with a planar surface, activated with a low concentration of thallium (~0.094 g) and optically coupled to the photocathode of a photomultiplier tube. To extend the range of energy detection, another scintillation material of higher density of bismuth germanate oxide [BGO (Bi4Ge3O12)] is coupled to the NaI(Tl) too. The volumes of these materials are 350 cm3 (3″ × 3″ or ~75 × 75 mm2) and 103 cm3 (2″ × 2″ or ~51 × 51 mm2), respectively, providing greater efficiency in the detection of gamma radiation. This probe registers a maximum counting rate of 250 000 pulses per second, covers an energy range of 100 keV–3 MeV and has a multichannel analyzer with 512 channels. The instrument allows the measurement of environmental dose rates and determines the concentrations of K (%), 238U (μg/g) and 232Th (μg/g). The concentration of K is determined directly by the gamma emission of the 40K. However, the concentrations of 238U and 232Th are determined based on the detection of 214Bi and 208Tl, respectively, present in their radioactive series. This detector still has the Search Mode function which allows the rapid search of radiation sources or radioactive anomalies present in the field, providing the characterization of an anomalous region with their values of the absorbed dose rate in situ. The measurements taken are stored in the equipment memory and can then be transferred and processed in computer systems. The monitored points In an RMR area, specifically where are located the cities of Olinda, Paulista, Abreu e Lima and Igarassu, there is a formation of discontinuous segments of the phosphate ore due to the partial erosion of the phosphate band. The monitored points of the study area were selected in a systematic way using previous works highlighted here: Amaral(14, 15) and Lima(13), and, furthermore, prioritizing the areas where there are the highest population densities (Figures 2–5). A total of 91 points were selected and analyzed in triplicate in these cities divided as follows: 18 points at Abreu e Lima, 30 points at Igarassu, 28 points at Olinda and 15 points at Paulista. The measurements were taken in the air at 1 m from the soil surface and considering 0.2 a maximum occupancy factor recommended by the UNSCEAR to the outdoors environment(17). The distribution by cities of the monitored points, geographical coordinates and estimated effective doses for a period of one year was all related in Tables 1–4 in Results and Discussion. Thus, with the geographical coordinates, it is possible to search and locate the measurement points, all very close to a large number of residences, businesses and schools along two major roads the State Road PE15 and Federal Highway BR101. Figure 2. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Abreu e Lima. Figure 2. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Abreu e Lima. Figure 3. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Igarassu. Figure 3. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Igarassu. Figure 4. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Olinda. Figure 4. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Olinda. Figure 5. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Paulista. Figure 5. View largeDownload slide Map representing the point of the highest measured value of effective dose outdoor in the municipality of Paulista. Table 1. Location and obtained results in the monitoring of the Abreu e Lima City. Points Coordinates Effective dose rates (mSv y−1) S W P01 7°54′27.5″ 34°54′01.9″ 2.94 ± 0.14 P02 7°54′27.5″ 34°54′07.3″ 3.08 ± 0.15 P03 7°53′48.8″ 34°54′01.6″ 4.93 ± 0.23 P04 7°52′21.4″ 34°52′42.6″ 2.16 ± 0.10 P05 7°54′01.7″ 34°54′06.6″ 2.01 ± 0.10 P06 7°53′54.3″ 34°54′05.0″ 2.52 ± 0.12 P07 7°53′49.3″ 34°53′56.6″ 2.18 ± 0.10 P08 7°53′43.0″ 34°53′55.3″ 2.21 ± 0.10 P09 7°53′30.3″ 34°53′47.4″ 2.68 ± 0.13 P10 7°53′25.3″ 34°53′42.7″ 2.22 ± 0.11 P11 7°53′34.8″ 34°53′56.4″ 2.11 ± 0.10 P12 7°53′12.5″ 34°54′14.2″ 2.31 ± 0.11 P13 7°51′27.9″ 34°54′28.9″ 2.34 ± 0.11 P14 7°54′39.4″ 34°54′06.1″ 2.44 ± 0.12 P15 7°54′37.8″ 34°54′07.4″ 2.20 ± 0.10 P16 7°54′47.8″ 34°54′02.2″ 2.59 ± 0.12 P17 7°54′55.2″ 34°54′01.2″ 2.15 ± 0.10 P18 7°55′13.6″ 34°53′43.8″ 2.13 ± 0.10 Points Coordinates Effective dose rates (mSv y−1) S W P01 7°54′27.5″ 34°54′01.9″ 2.94 ± 0.14 P02 7°54′27.5″ 34°54′07.3″ 3.08 ± 0.15 P03 7°53′48.8″ 34°54′01.6″ 4.93 ± 0.23 P04 7°52′21.4″ 34°52′42.6″ 2.16 ± 0.10 P05 7°54′01.7″ 34°54′06.6″ 2.01 ± 0.10 P06 7°53′54.3″ 34°54′05.0″ 2.52 ± 0.12 P07 7°53′49.3″ 34°53′56.6″ 2.18 ± 0.10 P08 7°53′43.0″ 34°53′55.3″ 2.21 ± 0.10 P09 7°53′30.3″ 34°53′47.4″ 2.68 ± 0.13 P10 7°53′25.3″ 34°53′42.7″ 2.22 ± 0.11 P11 7°53′34.8″ 34°53′56.4″ 2.11 ± 0.10 P12 7°53′12.5″ 34°54′14.2″ 2.31 ± 0.11 P13 7°51′27.9″ 34°54′28.9″ 2.34 ± 0.11 P14 7°54′39.4″ 34°54′06.1″ 2.44 ± 0.12 P15 7°54′37.8″ 34°54′07.4″ 2.20 ± 0.10 P16 7°54′47.8″ 34°54′02.2″ 2.59 ± 0.12 P17 7°54′55.2″ 34°54′01.2″ 2.15 ± 0.10 P18 7°55′13.6″ 34°53′43.8″ 2.13 ± 0.10 View Large Table 1. Location and obtained results in the monitoring of the Abreu e Lima City. Points Coordinates Effective dose rates (mSv y−1) S W P01 7°54′27.5″ 34°54′01.9″ 2.94 ± 0.14 P02 7°54′27.5″ 34°54′07.3″ 3.08 ± 0.15 P03 7°53′48.8″ 34°54′01.6″ 4.93 ± 0.23 P04 7°52′21.4″ 34°52′42.6″ 2.16 ± 0.10 P05 7°54′01.7″ 34°54′06.6″ 2.01 ± 0.10 P06 7°53′54.3″ 34°54′05.0″ 2.52 ± 0.12 P07 7°53′49.3″ 34°53′56.6″ 2.18 ± 0.10 P08 7°53′43.0″ 34°53′55.3″ 2.21 ± 0.10 P09 7°53′30.3″ 34°53′47.4″ 2.68 ± 0.13 P10 7°53′25.3″ 34°53′42.7″ 2.22 ± 0.11 P11 7°53′34.8″ 34°53′56.4″ 2.11 ± 0.10 P12 7°53′12.5″ 34°54′14.2″ 2.31 ± 0.11 P13 7°51′27.9″ 34°54′28.9″ 2.34 ± 0.11 P14 7°54′39.4″ 34°54′06.1″ 2.44 ± 0.12 P15 7°54′37.8″ 34°54′07.4″ 2.20 ± 0.10 P16 7°54′47.8″ 34°54′02.2″ 2.59 ± 0.12 P17 7°54′55.2″ 34°54′01.2″ 2.15 ± 0.10 P18 7°55′13.6″ 34°53′43.8″ 2.13 ± 0.10 Points Coordinates Effective dose rates (mSv y−1) S W P01 7°54′27.5″ 34°54′01.9″ 2.94 ± 0.14 P02 7°54′27.5″ 34°54′07.3″ 3.08 ± 0.15 P03 7°53′48.8″ 34°54′01.6″ 4.93 ± 0.23 P04 7°52′21.4″ 34°52′42.6″ 2.16 ± 0.10 P05 7°54′01.7″ 34°54′06.6″ 2.01 ± 0.10 P06 7°53′54.3″ 34°54′05.0″ 2.52 ± 0.12 P07 7°53′49.3″ 34°53′56.6″ 2.18 ± 0.10 P08 7°53′43.0″ 34°53′55.3″ 2.21 ± 0.10 P09 7°53′30.3″ 34°53′47.4″ 2.68 ± 0.13 P10 7°53′25.3″ 34°53′42.7″ 2.22 ± 0.11 P11 7°53′34.8″ 34°53′56.4″ 2.11 ± 0.10 P12 7°53′12.5″ 34°54′14.2″ 2.31 ± 0.11 P13 7°51′27.9″ 34°54′28.9″ 2.34 ± 0.11 P14 7°54′39.4″ 34°54′06.1″ 2.44 ± 0.12 P15 7°54′37.8″ 34°54′07.4″ 2.20 ± 0.10 P16 7°54′47.8″ 34°54′02.2″ 2.59 ± 0.12 P17 7°54′55.2″ 34°54′01.2″ 2.15 ± 0.10 P18 7°55′13.6″ 34°53′43.8″ 2.13 ± 0.10 View Large Table 2. Location and obtained results in the monitoring of the Igarassu City. Points Coordinates Effective dose rates (mSv y−1) S W P19 7°53′04.2″ 34°54′06.8″ 3.41 ± 0.16 P20 7°52′18.5″ 34°54′16.2″ 2.88 ± 0.14 P21 7°52′19.9″ 34°54′10.2″ 2.79 ± 0.13 P22 7°52′21.4″ 34°54′04.0″ 2.83 ± 0.13 P23 7°52′25.5″ 34°54′10.2″ 2.83 ± 0.13 P24 7°52′18.2″ 34°54′21.6″ 2.14 ± 0.10 P25 7°52′05.6″ 34°54′14.9″ 2.89 ± 0.14 P26 7°51′56.0″ 34°54′12.8″ 3.08 ± 0.15 P27 7°52′02.5″ 34°54′08.6″ 2.68 ± 0.13 P28 7°52′10.5″ 34°54′39.1″ 2.90 ± 0.14 P29 7°52′07.6″ 34°54′35.0″ 2.50 ± 0.12 P30 7°52′11.2″ 34°54′37.0″ 2.85 ± 0.14 P31 7°52′14.0″ 34°54′38.3″ 2.96 ± 0.14 P32 7°54′18.2″ 34°54′40.3″ 3.00 ± 0.14 P33 7°52′18.8″ 34°54′43.4″ 2.65 ± 0.13 P34 7°52′29.6″ 34°54′50.7″ 3.00 ± 0.14 P35 7°52′26.2″ 34°54′46.1″ 3.21 ± 0.15 P36 7°52′23.2″ 34°54′40.8″ 2.79 ± 0.13 P37 7°52′16.8″ 34°54′34.1″ 2.70 ± 0.13 P38 7°52′11.2″ 34°54′30.7″ 3.04 ± 0.14 P39 7°52′06.8″ 34°54′27.6″ 2.86 ± 0.14 P40 7°52′16.3″ 34°54′28.0″ 2.88 ± 0.14 P41 7°52′20.0″ 34°54′26.3″ 2.84 ± 0.13 P42 7°52′27.0″ 34°54′26.1″ 2.64 ± 0.13 P43 7°52′30.6″ 34°54′27.4″ 2.76 ± 0.13 P44 7°52′29.7″ 34°54′24.4″ 2.50 ± 0.12 P45 7°52′30.2″ 34°54′36.0″ 2.95 ± 0.14 P46 7°52′41.2″ 34°54′33.3″ 2.58 ± 0.12 P47 7°52′36.1″ 34°54′29.0″ 2.57 ± 0.12 P48 7°53′07.7″ 34°54′17.0″ 2.53 ± 0.12 Points Coordinates Effective dose rates (mSv y−1) S W P19 7°53′04.2″ 34°54′06.8″ 3.41 ± 0.16 P20 7°52′18.5″ 34°54′16.2″ 2.88 ± 0.14 P21 7°52′19.9″ 34°54′10.2″ 2.79 ± 0.13 P22 7°52′21.4″ 34°54′04.0″ 2.83 ± 0.13 P23 7°52′25.5″ 34°54′10.2″ 2.83 ± 0.13 P24 7°52′18.2″ 34°54′21.6″ 2.14 ± 0.10 P25 7°52′05.6″ 34°54′14.9″ 2.89 ± 0.14 P26 7°51′56.0″ 34°54′12.8″ 3.08 ± 0.15 P27 7°52′02.5″ 34°54′08.6″ 2.68 ± 0.13 P28 7°52′10.5″ 34°54′39.1″ 2.90 ± 0.14 P29 7°52′07.6″ 34°54′35.0″ 2.50 ± 0.12 P30 7°52′11.2″ 34°54′37.0″ 2.85 ± 0.14 P31 7°52′14.0″ 34°54′38.3″ 2.96 ± 0.14 P32 7°54′18.2″ 34°54′40.3″ 3.00 ± 0.14 P33 7°52′18.8″ 34°54′43.4″ 2.65 ± 0.13 P34 7°52′29.6″ 34°54′50.7″ 3.00 ± 0.14 P35 7°52′26.2″ 34°54′46.1″ 3.21 ± 0.15 P36 7°52′23.2″ 34°54′40.8″ 2.79 ± 0.13 P37 7°52′16.8″ 34°54′34.1″ 2.70 ± 0.13 P38 7°52′11.2″ 34°54′30.7″ 3.04 ± 0.14 P39 7°52′06.8″ 34°54′27.6″ 2.86 ± 0.14 P40 7°52′16.3″ 34°54′28.0″ 2.88 ± 0.14 P41 7°52′20.0″ 34°54′26.3″ 2.84 ± 0.13 P42 7°52′27.0″ 34°54′26.1″ 2.64 ± 0.13 P43 7°52′30.6″ 34°54′27.4″ 2.76 ± 0.13 P44 7°52′29.7″ 34°54′24.4″ 2.50 ± 0.12 P45 7°52′30.2″ 34°54′36.0″ 2.95 ± 0.14 P46 7°52′41.2″ 34°54′33.3″ 2.58 ± 0.12 P47 7°52′36.1″ 34°54′29.0″ 2.57 ± 0.12 P48 7°53′07.7″ 34°54′17.0″ 2.53 ± 0.12 View Large Table 2. Location and obtained results in the monitoring of the Igarassu City. Points Coordinates Effective dose rates (mSv y−1) S W P19 7°53′04.2″ 34°54′06.8″ 3.41 ± 0.16 P20 7°52′18.5″ 34°54′16.2″ 2.88 ± 0.14 P21 7°52′19.9″ 34°54′10.2″ 2.79 ± 0.13 P22 7°52′21.4″ 34°54′04.0″ 2.83 ± 0.13 P23 7°52′25.5″ 34°54′10.2″ 2.83 ± 0.13 P24 7°52′18.2″ 34°54′21.6″ 2.14 ± 0.10 P25 7°52′05.6″ 34°54′14.9″ 2.89 ± 0.14 P26 7°51′56.0″ 34°54′12.8″ 3.08 ± 0.15 P27 7°52′02.5″ 34°54′08.6″ 2.68 ± 0.13 P28 7°52′10.5″ 34°54′39.1″ 2.90 ± 0.14 P29 7°52′07.6″ 34°54′35.0″ 2.50 ± 0.12 P30 7°52′11.2″ 34°54′37.0″ 2.85 ± 0.14 P31 7°52′14.0″ 34°54′38.3″ 2.96 ± 0.14 P32 7°54′18.2″ 34°54′40.3″ 3.00 ± 0.14 P33 7°52′18.8″ 34°54′43.4″ 2.65 ± 0.13 P34 7°52′29.6″ 34°54′50.7″ 3.00 ± 0.14 P35 7°52′26.2″ 34°54′46.1″ 3.21 ± 0.15 P36 7°52′23.2″ 34°54′40.8″ 2.79 ± 0.13 P37 7°52′16.8″ 34°54′34.1″ 2.70 ± 0.13 P38 7°52′11.2″ 34°54′30.7″ 3.04 ± 0.14 P39 7°52′06.8″ 34°54′27.6″ 2.86 ± 0.14 P40 7°52′16.3″ 34°54′28.0″ 2.88 ± 0.14 P41 7°52′20.0″ 34°54′26.3″ 2.84 ± 0.13 P42 7°52′27.0″ 34°54′26.1″ 2.64 ± 0.13 P43 7°52′30.6″ 34°54′27.4″ 2.76 ± 0.13 P44 7°52′29.7″ 34°54′24.4″ 2.50 ± 0.12 P45 7°52′30.2″ 34°54′36.0″ 2.95 ± 0.14 P46 7°52′41.2″ 34°54′33.3″ 2.58 ± 0.12 P47 7°52′36.1″ 34°54′29.0″ 2.57 ± 0.12 P48 7°53′07.7″ 34°54′17.0″ 2.53 ± 0.12 Points Coordinates Effective dose rates (mSv y−1) S W P19 7°53′04.2″ 34°54′06.8″ 3.41 ± 0.16 P20 7°52′18.5″ 34°54′16.2″ 2.88 ± 0.14 P21 7°52′19.9″ 34°54′10.2″ 2.79 ± 0.13 P22 7°52′21.4″ 34°54′04.0″ 2.83 ± 0.13 P23 7°52′25.5″ 34°54′10.2″ 2.83 ± 0.13 P24 7°52′18.2″ 34°54′21.6″ 2.14 ± 0.10 P25 7°52′05.6″ 34°54′14.9″ 2.89 ± 0.14 P26 7°51′56.0″ 34°54′12.8″ 3.08 ± 0.15 P27 7°52′02.5″ 34°54′08.6″ 2.68 ± 0.13 P28 7°52′10.5″ 34°54′39.1″ 2.90 ± 0.14 P29 7°52′07.6″ 34°54′35.0″ 2.50 ± 0.12 P30 7°52′11.2″ 34°54′37.0″ 2.85 ± 0.14 P31 7°52′14.0″ 34°54′38.3″ 2.96 ± 0.14 P32 7°54′18.2″ 34°54′40.3″ 3.00 ± 0.14 P33 7°52′18.8″ 34°54′43.4″ 2.65 ± 0.13 P34 7°52′29.6″ 34°54′50.7″ 3.00 ± 0.14 P35 7°52′26.2″ 34°54′46.1″ 3.21 ± 0.15 P36 7°52′23.2″ 34°54′40.8″ 2.79 ± 0.13 P37 7°52′16.8″ 34°54′34.1″ 2.70 ± 0.13 P38 7°52′11.2″ 34°54′30.7″ 3.04 ± 0.14 P39 7°52′06.8″ 34°54′27.6″ 2.86 ± 0.14 P40 7°52′16.3″ 34°54′28.0″ 2.88 ± 0.14 P41 7°52′20.0″ 34°54′26.3″ 2.84 ± 0.13 P42 7°52′27.0″ 34°54′26.1″ 2.64 ± 0.13 P43 7°52′30.6″ 34°54′27.4″ 2.76 ± 0.13 P44 7°52′29.7″ 34°54′24.4″ 2.50 ± 0.12 P45 7°52′30.2″ 34°54′36.0″ 2.95 ± 0.14 P46 7°52′41.2″ 34°54′33.3″ 2.58 ± 0.12 P47 7°52′36.1″ 34°54′29.0″ 2.57 ± 0.12 P48 7°53′07.7″ 34°54′17.0″ 2.53 ± 0.12 View Large Table 3. Location and obtained results in the monitoring of the Olinda City. Points Coordinates Effective dose rates (mSv y−1) S W P49 7°58′31.8″ 34°51′54.8″ 2.61 ± 0.12 P50 7°58′47.1″ 34°51′33.7″ 2.30 ± 0.11 P51 7°59′59.2″ 34°51′23.4″ 2.65 ± 0.13 P52 8°00′41.7″ 34°51′38.6″ 2.30 ± 0.11 P53 8°00′36.5″ 34°51′46.4″ 2.33 ± 0.11 P54 8°00′56.3″ 34°51′41.3″ 2.34 ± 0.11 P55 8°00′48.0″ 34°51′51.7″ 2.25 ± 0.11 P56 8°00′57.9″ 34°51′46.5″ 2.44 ± 0.12 P57 8°00′38.9″ 34°52′17.9″ 2.43 ± 0.12 P58 8°00′42.7″ 34°51′27.2″ 2.49 ± 0.12 P59 7°58′58.4″ 34°51′20.0″ 2.37 ± 0.11 P60 8°00′20.8″ 34°52′42.8″ 2.77 ± 0.13 P61 6°47′24.8″ 36°50′32.1″ 2.24 ± 0.11 P62 8°00′49.4″ 34°52′06.9″ 2.15 ± 0.10 P63 8°00′49.5″ 34°52′06.8″ 2.22 ± 0.11 P64 8°00′37.3″ 34°52′08.1″ 2.02 ± 0.10 P65 8°00′34.3″ 34°52′09.1″ 1.99 ± 0.09 P66 8°00′28.3″ 34°52′06.6″ 2.20 ± 0.10 P67 8°00′18.9″ 34°52′00.8″ 2.10 ± 0.10 P68 8°00′14.1″ 34°52′07.0″ 2.05 ± 0.10 P69 8°00′25.5″ 34°52′05.4″ 2.30 ± 0.11 P70 8°00′32.9″ 34°52′07.4″ 2.08 ± 0.10 P71 8°00′23.9″ 34°52′40.5″ 3.73 ± 0.18 P72 8°00′23.9″ 34°52′40.5″ 7.59 ± 0.36 P73 8°00′27.7″ 34°52′37.7″ 2.08 ± 0.10 P74 8°00′26.5″ 34°52′38.1″ 3.48 ± 0.17 P75 8°00′22.3″ 34°52′42.4″ 2.46 ± 0.12 P76 8°00′20.3″ 34°52′43.4″ 2.59 ± 0.12 Points Coordinates Effective dose rates (mSv y−1) S W P49 7°58′31.8″ 34°51′54.8″ 2.61 ± 0.12 P50 7°58′47.1″ 34°51′33.7″ 2.30 ± 0.11 P51 7°59′59.2″ 34°51′23.4″ 2.65 ± 0.13 P52 8°00′41.7″ 34°51′38.6″ 2.30 ± 0.11 P53 8°00′36.5″ 34°51′46.4″ 2.33 ± 0.11 P54 8°00′56.3″ 34°51′41.3″ 2.34 ± 0.11 P55 8°00′48.0″ 34°51′51.7″ 2.25 ± 0.11 P56 8°00′57.9″ 34°51′46.5″ 2.44 ± 0.12 P57 8°00′38.9″ 34°52′17.9″ 2.43 ± 0.12 P58 8°00′42.7″ 34°51′27.2″ 2.49 ± 0.12 P59 7°58′58.4″ 34°51′20.0″ 2.37 ± 0.11 P60 8°00′20.8″ 34°52′42.8″ 2.77 ± 0.13 P61 6°47′24.8″ 36°50′32.1″ 2.24 ± 0.11 P62 8°00′49.4″ 34°52′06.9″ 2.15 ± 0.10 P63 8°00′49.5″ 34°52′06.8″ 2.22 ± 0.11 P64 8°00′37.3″ 34°52′08.1″ 2.02 ± 0.10 P65 8°00′34.3″ 34°52′09.1″ 1.99 ± 0.09 P66 8°00′28.3″ 34°52′06.6″ 2.20 ± 0.10 P67 8°00′18.9″ 34°52′00.8″ 2.10 ± 0.10 P68 8°00′14.1″ 34°52′07.0″ 2.05 ± 0.10 P69 8°00′25.5″ 34°52′05.4″ 2.30 ± 0.11 P70 8°00′32.9″ 34°52′07.4″ 2.08 ± 0.10 P71 8°00′23.9″ 34°52′40.5″ 3.73 ± 0.18 P72 8°00′23.9″ 34°52′40.5″ 7.59 ± 0.36 P73 8°00′27.7″ 34°52′37.7″ 2.08 ± 0.10 P74 8°00′26.5″ 34°52′38.1″ 3.48 ± 0.17 P75 8°00′22.3″ 34°52′42.4″ 2.46 ± 0.12 P76 8°00′20.3″ 34°52′43.4″ 2.59 ± 0.12 View Large Table 3. Location and obtained results in the monitoring of the Olinda City. Points Coordinates Effective dose rates (mSv y−1) S W P49 7°58′31.8″ 34°51′54.8″ 2.61 ± 0.12 P50 7°58′47.1″ 34°51′33.7″ 2.30 ± 0.11 P51 7°59′59.2″ 34°51′23.4″ 2.65 ± 0.13 P52 8°00′41.7″ 34°51′38.6″ 2.30 ± 0.11 P53 8°00′36.5″ 34°51′46.4″ 2.33 ± 0.11 P54 8°00′56.3″ 34°51′41.3″ 2.34 ± 0.11 P55 8°00′48.0″ 34°51′51.7″ 2.25 ± 0.11 P56 8°00′57.9″ 34°51′46.5″ 2.44 ± 0.12 P57 8°00′38.9″ 34°52′17.9″ 2.43 ± 0.12 P58 8°00′42.7″ 34°51′27.2″ 2.49 ± 0.12 P59 7°58′58.4″ 34°51′20.0″ 2.37 ± 0.11 P60 8°00′20.8″ 34°52′42.8″ 2.77 ± 0.13 P61 6°47′24.8″ 36°50′32.1″ 2.24 ± 0.11 P62 8°00′49.4″ 34°52′06.9″ 2.15 ± 0.10 P63 8°00′49.5″ 34°52′06.8″ 2.22 ± 0.11 P64 8°00′37.3″ 34°52′08.1″ 2.02 ± 0.10 P65 8°00′34.3″ 34°52′09.1″ 1.99 ± 0.09 P66 8°00′28.3″ 34°52′06.6″ 2.20 ± 0.10 P67 8°00′18.9″ 34°52′00.8″ 2.10 ± 0.10 P68 8°00′14.1″ 34°52′07.0″ 2.05 ± 0.10 P69 8°00′25.5″ 34°52′05.4″ 2.30 ± 0.11 P70 8°00′32.9″ 34°52′07.4″ 2.08 ± 0.10 P71 8°00′23.9″ 34°52′40.5″ 3.73 ± 0.18 P72 8°00′23.9″ 34°52′40.5″ 7.59 ± 0.36 P73 8°00′27.7″ 34°52′37.7″ 2.08 ± 0.10 P74 8°00′26.5″ 34°52′38.1″ 3.48 ± 0.17 P75 8°00′22.3″ 34°52′42.4″ 2.46 ± 0.12 P76 8°00′20.3″ 34°52′43.4″ 2.59 ± 0.12 Points Coordinates Effective dose rates (mSv y−1) S W P49 7°58′31.8″ 34°51′54.8″ 2.61 ± 0.12 P50 7°58′47.1″ 34°51′33.7″ 2.30 ± 0.11 P51 7°59′59.2″ 34°51′23.4″ 2.65 ± 0.13 P52 8°00′41.7″ 34°51′38.6″ 2.30 ± 0.11 P53 8°00′36.5″ 34°51′46.4″ 2.33 ± 0.11 P54 8°00′56.3″ 34°51′41.3″ 2.34 ± 0.11 P55 8°00′48.0″ 34°51′51.7″ 2.25 ± 0.11 P56 8°00′57.9″ 34°51′46.5″ 2.44 ± 0.12 P57 8°00′38.9″ 34°52′17.9″ 2.43 ± 0.12 P58 8°00′42.7″ 34°51′27.2″ 2.49 ± 0.12 P59 7°58′58.4″ 34°51′20.0″ 2.37 ± 0.11 P60 8°00′20.8″ 34°52′42.8″ 2.77 ± 0.13 P61 6°47′24.8″ 36°50′32.1″ 2.24 ± 0.11 P62 8°00′49.4″ 34°52′06.9″ 2.15 ± 0.10 P63 8°00′49.5″ 34°52′06.8″ 2.22 ± 0.11 P64 8°00′37.3″ 34°52′08.1″ 2.02 ± 0.10 P65 8°00′34.3″ 34°52′09.1″ 1.99 ± 0.09 P66 8°00′28.3″ 34°52′06.6″ 2.20 ± 0.10 P67 8°00′18.9″ 34°52′00.8″ 2.10 ± 0.10 P68 8°00′14.1″ 34°52′07.0″ 2.05 ± 0.10 P69 8°00′25.5″ 34°52′05.4″ 2.30 ± 0.11 P70 8°00′32.9″ 34°52′07.4″ 2.08 ± 0.10 P71 8°00′23.9″ 34°52′40.5″ 3.73 ± 0.18 P72 8°00′23.9″ 34°52′40.5″ 7.59 ± 0.36 P73 8°00′27.7″ 34°52′37.7″ 2.08 ± 0.10 P74 8°00′26.5″ 34°52′38.1″ 3.48 ± 0.17 P75 8°00′22.3″ 34°52′42.4″ 2.46 ± 0.12 P76 8°00′20.3″ 34°52′43.4″ 2.59 ± 0.12 View Large Table 4. Location and obtained results in the monitoring of the Paulista City. Points Coordinates Effective dose rates (mSv y−1) S W P77 7°55′07.7″ 34°53′16.5″ 2.63 ± 0.12 P78 7°55′28.9″ 34°53′27.9″ 2.58 ± 0.12 P79 7°55′42.1″ 34°53′16.3″ 2.31 ± 0.11 P80 7°55′52.0″ 34°53′11.1″ 2.45 ± 0.12 P81 7°56′14.2″ 34°52′43.3″ 2.27 ± 0.11 P82 7°56′42.9″ 34°52′42.9″ 2.29 ± 0.11 P83 7°56′56.2″ 34°52′41.8″ 2.33 ± 0.11 P84 7°57′12.6″ 34°52′38.0″ 2.47 ± 0.12 P85 7°57′35.5″ 34°52′15.7″ 2.44 ± 0.12 P86 7°57′57.9″ 34°52′05.2″ 2.14 ± 0.10 P87 7°58′25.0″ 34°51′47.6″ 2.18 ± 0.10 P88 7°58′04.3″ 34°52′02.0″ 2.34 ± 0.11 P89 7°57′33.8″ 34°52′14.4″ 2.08 ± 0.10 P90 7°57′13.4″ 34°52′32.6″ 2.29 ± 0.11 P91 7°56′03.6″ 34°52′42.5″ 2.06 ± 0.10 Points Coordinates Effective dose rates (mSv y−1) S W P77 7°55′07.7″ 34°53′16.5″ 2.63 ± 0.12 P78 7°55′28.9″ 34°53′27.9″ 2.58 ± 0.12 P79 7°55′42.1″ 34°53′16.3″ 2.31 ± 0.11 P80 7°55′52.0″ 34°53′11.1″ 2.45 ± 0.12 P81 7°56′14.2″ 34°52′43.3″ 2.27 ± 0.11 P82 7°56′42.9″ 34°52′42.9″ 2.29 ± 0.11 P83 7°56′56.2″ 34°52′41.8″ 2.33 ± 0.11 P84 7°57′12.6″ 34°52′38.0″ 2.47 ± 0.12 P85 7°57′35.5″ 34°52′15.7″ 2.44 ± 0.12 P86 7°57′57.9″ 34°52′05.2″ 2.14 ± 0.10 P87 7°58′25.0″ 34°51′47.6″ 2.18 ± 0.10 P88 7°58′04.3″ 34°52′02.0″ 2.34 ± 0.11 P89 7°57′33.8″ 34°52′14.4″ 2.08 ± 0.10 P90 7°57′13.4″ 34°52′32.6″ 2.29 ± 0.11 P91 7°56′03.6″ 34°52′42.5″ 2.06 ± 0.10 View Large Table 4. Location and obtained results in the monitoring of the Paulista City. Points Coordinates Effective dose rates (mSv y−1) S W P77 7°55′07.7″ 34°53′16.5″ 2.63 ± 0.12 P78 7°55′28.9″ 34°53′27.9″ 2.58 ± 0.12 P79 7°55′42.1″ 34°53′16.3″ 2.31 ± 0.11 P80 7°55′52.0″ 34°53′11.1″ 2.45 ± 0.12 P81 7°56′14.2″ 34°52′43.3″ 2.27 ± 0.11 P82 7°56′42.9″ 34°52′42.9″ 2.29 ± 0.11 P83 7°56′56.2″ 34°52′41.8″ 2.33 ± 0.11 P84 7°57′12.6″ 34°52′38.0″ 2.47 ± 0.12 P85 7°57′35.5″ 34°52′15.7″ 2.44 ± 0.12 P86 7°57′57.9″ 34°52′05.2″ 2.14 ± 0.10 P87 7°58′25.0″ 34°51′47.6″ 2.18 ± 0.10 P88 7°58′04.3″ 34°52′02.0″ 2.34 ± 0.11 P89 7°57′33.8″ 34°52′14.4″ 2.08 ± 0.10 P90 7°57′13.4″ 34°52′32.6″ 2.29 ± 0.11 P91 7°56′03.6″ 34°52′42.5″ 2.06 ± 0.10 Points Coordinates Effective dose rates (mSv y−1) S W P77 7°55′07.7″ 34°53′16.5″ 2.63 ± 0.12 P78 7°55′28.9″ 34°53′27.9″ 2.58 ± 0.12 P79 7°55′42.1″ 34°53′16.3″ 2.31 ± 0.11 P80 7°55′52.0″ 34°53′11.1″ 2.45 ± 0.12 P81 7°56′14.2″ 34°52′43.3″ 2.27 ± 0.11 P82 7°56′42.9″ 34°52′42.9″ 2.29 ± 0.11 P83 7°56′56.2″ 34°52′41.8″ 2.33 ± 0.11 P84 7°57′12.6″ 34°52′38.0″ 2.47 ± 0.12 P85 7°57′35.5″ 34°52′15.7″ 2.44 ± 0.12 P86 7°57′57.9″ 34°52′05.2″ 2.14 ± 0.10 P87 7°58′25.0″ 34°51′47.6″ 2.18 ± 0.10 P88 7°58′04.3″ 34°52′02.0″ 2.34 ± 0.11 P89 7°57′33.8″ 34°52′14.4″ 2.08 ± 0.10 P90 7°57′13.4″ 34°52′32.6″ 2.29 ± 0.11 P91 7°56′03.6″ 34°52′42.5″ 2.06 ± 0.10 View Large The calculation of the outdoor dose rate The calibration of the detector was executed at the Laboratory of Ionizing Radiation Metrology (Laboratório de Metrologia das Radiações Ionizantes—LMRI), under certification in 6490/0911, of the Nuclear Energy Department of the Federal University of Pernambuco. The LMRI is accredited by a governmental body. From the established calibration procedure, it was possible to construct a calibration line relating to the indication of the instrument and the dose rate in the air. And with the response graph of the portable gamma spectrometer, it was possible to obtain the angular coefficient of 1.92 and the linear coefficient of 1430.8. To calculate an occupancy factor for the inhabitants of the analyzed areas it was considered that they are exposed to an outdoor dose for 24 h during 365.25 days multiplied by a conversion factor of dose 0.7 Sv/Gy which returns 6136.2. This last value multiplied by a factor of 10−6 to convert from nGy to mGy results in 6.14 × 10−3. Equation 1 was determined with the previous values where ‘ Ḋ’ represents the experimental measurements performed in nGy h−1 or the absorbed dose rate outdoor in the environment and, ‘ ḢE’ corresponds to the environmental effective dose rate outdoor. ḢE=(1.92×Ḋ−1430.87)×6.14x10−3 (1) The triplicate measurements for each point were performed in the air at 1 m from the soil surface and using a count time of 190 s, which was defined according to the local radioactivity levels and to the count statistic. The obtained results were absorbed dose rate (nGy h−1). However, through the equation of conversion (Equation 1), with the necessary parameters, the effective environmental dose rates were obtained in mSv y−1(18). RESULTS AND DISCUSSION A sequence of 04 tables was constructed with the results of the effective dose rate measurements (mSv y−1) performed in the municipalities of Abreu and Lima, Igarassu, Olinda and Paulista. The first column of each table refers to the identification of each measurement point in the form of the letter P and a sequential number, the second and third columns identify the South and West geographical coordinates of the sites studied and the last column is the value of the effective dose rate obtained in mSv y−1 (Tables 1–4). For the municipality of Abreu and Lima (Table 1), 18 measurements were identified as points P1–P18 among which we can highlight the point P3 with a value of 4.93 ± 0.23 mSv y−1. This point is located on a residential street in a low-income neighborhood, and also close to restaurants, churches and small markets. The Federal Highway BR101, that in this stretch is identified as Governor Mário Covas, is located to few meters (Figure 2). In the municipality of Igarassu, 30 measurements were made and the points were identified in the range of P19–P48 (Table 2). The maximum effective dose occurred at point 19 (P19) with a value of 3.41 ± 0.16 mS y−1. This measurement was performed in a vacant lot near low-income households. The Federal Highway BR101 is located nearby, as well as gas stations, restaurants and small businesses (Figure 3). In Olinda, with 28 measurements (P49–P76) (Table 3), occurred to the value of greatest concern in terms of radiological protection. The point 72 (P72) is in a poor neighborhood with a disorderly occupation of urban space, with a value of 7.59 ± 0.36 mSv y−1 well above the values of background radiation (Figure 4). The measurement point occurred in a dug-out land and near an industrial chimney probably remnants of phosphate production occurred in the 1940s until 1960s. The measurement P77 resulted in a maximum value in Paulista city of 2.63 ± 0.12 mSv y−1. Only 15 measurements (P77–P91) were made for this county (Table 4). The point 77 was a measurement in a forest area but close to a hospital, a very busy bus station and some residential areas (Figure 5). A descriptive statistical analysis of the complete set of values obtained from the measurements of the 91 points of 04 of the cities that form the RMR and that present a formation of sedimentary rocks rich in phosphate associated with the uranium ore was carried out (Table 5). Table 5. Summary with descriptive statistics of all measurements by cities. Statistic descriptive Effective dose rates (mSv y−1) Abreu e Lima Igarassu Olinda Paulista Number of measurements 18 30 28 15 Minimum 2.01 2.14 1.99 2.06 First quartile 2.16 2.66 2.19 2.22 Median 2.26 2.83 2.31 2.31 Arithmetic mean 2.51 2.80 2.59 2.32 Standard deviation 0.67 0.24 1.05 0.17 Third quartile 2.57 2.94 2.51 2.44 Maximum 4.93 3.41 7.59 2.63 Amplitude 2.92 1.27 5.6 0.57 Statistic descriptive Effective dose rates (mSv y−1) Abreu e Lima Igarassu Olinda Paulista Number of measurements 18 30 28 15 Minimum 2.01 2.14 1.99 2.06 First quartile 2.16 2.66 2.19 2.22 Median 2.26 2.83 2.31 2.31 Arithmetic mean 2.51 2.80 2.59 2.32 Standard deviation 0.67 0.24 1.05 0.17 Third quartile 2.57 2.94 2.51 2.44 Maximum 4.93 3.41 7.59 2.63 Amplitude 2.92 1.27 5.6 0.57 Table 5. Summary with descriptive statistics of all measurements by cities. Statistic descriptive Effective dose rates (mSv y−1) Abreu e Lima Igarassu Olinda Paulista Number of measurements 18 30 28 15 Minimum 2.01 2.14 1.99 2.06 First quartile 2.16 2.66 2.19 2.22 Median 2.26 2.83 2.31 2.31 Arithmetic mean 2.51 2.80 2.59 2.32 Standard deviation 0.67 0.24 1.05 0.17 Third quartile 2.57 2.94 2.51 2.44 Maximum 4.93 3.41 7.59 2.63 Amplitude 2.92 1.27 5.6 0.57 Statistic descriptive Effective dose rates (mSv y−1) Abreu e Lima Igarassu Olinda Paulista Number of measurements 18 30 28 15 Minimum 2.01 2.14 1.99 2.06 First quartile 2.16 2.66 2.19 2.22 Median 2.26 2.83 2.31 2.31 Arithmetic mean 2.51 2.80 2.59 2.32 Standard deviation 0.67 0.24 1.05 0.17 Third quartile 2.57 2.94 2.51 2.44 Maximum 4.93 3.41 7.59 2.63 Amplitude 2.92 1.27 5.6 0.57 Considering only the arithmetic means, Igarassu is the locality with the highest mean value for the effective dose rate (2.80 mSv y), despite the measurements of points P72 (Olinda: 7.59 0.36 mSv y−1) and P03 (Abreu and Lima: 4.93 0.23 mSv y−1) were considerably high relative to background radiation. This fact can be explained by the values of the third quartile of these two municipalities. Olinda has 75% of the measured values below 2.51 mSv y−1 and Abreu e Lima has 75% of its measurements below 2.57 mSv y−1. For Igarassu, the third quartile was calculated as 2.94 mSv y−1 explaining the reason for an average value higher than the other three cities. Paulista was the municipality that did not show peaks of effective dose rates. A representation through a line chart (Figure 6), where the horizontal axis represents the points of the measurements and the effective dose rates measured on the vertical axis, shows the behavior by municipalities point-to-point. Abreu and Lima and Olinda had the highest dose values found, 4.93 and 7.59 mSv y−1, respectively, differing only in that the Abreu and Lima peak occurred in the first measurements and Olinda in the last values obtained. However, excluding the two peaks, the values of both municipalities remained close to 2.5 mSv y−1. The representative graph of the measurements in the municipality of Igarassu shows values considered above the background radiation in a range between 2.5 and 3.5 mSv y−1, although there are no dose peaks occurring in the region. It is possible to confirm that in the city of Paulista the first values are slightly above 2.5 mSv y−1, but decrease and remain below this value until the last measurement. Figure 6. View largeDownload slide Graphs of the measurement points and respective measured values of the dose rate. Figure 6. View largeDownload slide Graphs of the measurement points and respective measured values of the dose rate. The authors observed that generally lower values were found at sites with landfills made with soils from other regions or at public roads with artificial paving, which contributed to the reduction of effective dose rates at various points in the region. The point of greatest value (7.59 mSv y−1), on the other hand, located in the city of Olinda, was obtained inside a semi-destroyed masonry structure, which would probably be one of the kilns used to process the phosphate extracted in the region. This value is considered isolated and with much importance to identify a remnant area of the period of the ore exploration and processing that occurred in a period prior to disordered occupation, but not as an estimator of the RMR radiometry and can be observed in the graphical representation (Figure 6—Olinda) since it differs clearly from the others. A major real estate venture has been implemented on the site and currently, the entrance to this area is not permitted, thus, it is not possible to do any kind of radioactive monitoring at this point. CONCLUSIONS The authors, based on the radiometric monitoring performed in the municipalities of Abreu e Lima, Igarassu, Olinda and Paulista, concluded that, in general, the average annual effective dose equivalent rate found is above the values for normal background radiation. It is possible concluded that the use of landfills with soil from regions without radioactive anomalies and the paving of public roads contributed to the reduction of effective dose rates at various points in the region. These events make unfeasible the resumption of phosphate extraction, so the researchers assume that these dose levels will remain constant. However, it is important to continue radiologically mapping this large region in search of anomalies that may endanger the health of the population. This work allowed the identification of the remaining facilities of the phosphate ore exploration and processing in Olinda city that is being evaluated in more detail. Acknowledgements The authors are grateful to the Coordination for the Improvement of Higher Education Personnel (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—CAPES) for the financial assistance granted and to the Federal University of Pernambuco (Universidade Federal de Pernambuco—UFPE), Department of Nuclear Energy (Departamento de Energia Nuclear—DEN)/Graduate Program in Energy and Nuclear Technologies (Programa de Tecnologias Energéticas e Nucleares—PROTEN), for the structure available for the development of this work. REFERENCES 1 Vasconcelos , W. E. Aplicação de técnicas de inteligência artificial na avaliação da dose de populações de regiões de alto background natural. Tese (Doutorado em Ciências Nucleares), Programa de Pós-Graduação em Tecnologias Energéticas e Nucleares, Universidade Federal de Pernambuco, Recife ( 2009 ). 2 Malanca , A. , Gaidolfi , L. , Pessina , V. and Dallara , G. Distribution of 226Ra, 232Th, and 40K in soils of Rio Grande do Norte (Brazil) . J. Environ. Radioact. 30 ( 1 ), 55 – 67 ( 1995 ). Google Scholar CrossRef Search ADS 3 Melo , N. M. P. Avaliação da dose interna devida ao 226Ra, 228Ra e 210Pb nos suprimentos de água para abastecimento público da Região Metropolitana do Recife. Dissertação (Mestrado em Ciências Nucleares), Programa de Pós-Graduação em Tecnologias Energéticas e Nucleares, Universidade Federal de Pernambuco, Recife ( 2008 ). 4 United Scientific Committee on the Effects of Atomic Radiations . Sources and effects of ionizing radiation. UNSCEAR Report 2000, v. 1, annex B, United Nations Publications, New York ( 2000 ). 5 International Atomic Energy Agency . Exposure of the public from large deposits of mineral residues. TecDoc-1660, 49 p, ( 2011 ). 6 International Commission on Radiological Protection . Low-dose extrapolation of radiation-related cancer risk. ICRP Publication 99 . Ann. 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