Occupational and Environmental Medicine

Li, C Y; Thériault, G; Lin, R S

doi: 10.1136/oem.53.8.505pmid: 8983460

OBJECTIVES: To appraise epidemiological evidence of the purported association between residential exposure to power frequency magnetic fields and adult cancers. METHODS: Literature review and epidemiological evaluation. RESULTS: Seven epidemiological studies have been conducted on the risk of cancer among adults in relation to residential exposure to power frequency magnetic fields. Leukaemia was positively associated with magnetic fields in three case-control studies. The other two case-control studies and two cohort studies did not show such a link. Brain tumours and breast cancer have rarely been examined by these studies. Based on the epidemiological results, the analysis of the role of chance and bias, and the criteria for causal inferences, it seems that the evidence is not strong enough to support the putative causal relation between residential exposure to magnetic fields and adult leukaemia, brain tumours, or breast cancer. Inadequate statistical power is far more a concern than selection bias, information bias, and confounding in interpreting the results from these studies, and in explaining inconsistencies between studies. CONCLUSIONS: Our reviews suggested that the only way to answer whether residential exposure to magnetic fields is capable of increasing the risks of adult cancers is to conduct more studies carefully avoiding methodological flaws, in particular small sample size. We also suggested that the risk of female breast cancer should be the object of additional investigations, and that future studies should attempt to include information on exposure to magnetic fields from workplaces as well as residential exposure to estimate the effects of overall exposure to magnetic fields.

Bonde, J P; Giwercman, A; Ernst, E

doi: 10.1136/oem.53.8.511pmid: 8983461

Malfunction of the male reproductive system might be a sensitive marker of environmental hazards, the effects of which may extend beyond reproductive function. The testis is more vulnerable to heat and ionising radiation than any other organ of the body and several xenobiotics are known to disrupt spermatogenesis after low level exposure. Studies of environmental impact on human health are often most informative and accurate when carried out in the workplace where exposures can be high and easy to document. Semen analysis provides readily obtainable information on testicular function. The main advantages in comparison with functional measures such as fertility rates and time taken to conceive are the possibilities to examine men independently of marriage and pregnancy, to find changes of fecundity with different exposures within the same person and to detect adverse effects when no alteration of fertility is yet taking place. In the implementation of an occupational sperm study considerable attention must be paid to logistic issues. A mobile laboratory unit for initial semen preparation and processing may in some situations increase worker compliance and the quality of sperm cell motility. The cross sectional design which has been used in almost all male reproductive studies so far has several severe limitations including selection bias because of differential participation, difficulties in defining a suitable reference group, and lack of information about the time dimension of the cause-effect relation. The longitudinal design deals adequately with most of these constraints. Semen samples are collected before, during, and possibly after exposure to the risk factor of interest and causal inferences are based upon change of semen variables within a man over time rather than upon differences between men. The logistics of the longitudinal study may benefit from pre-employment health examinations to enrol newly hired workers and require fewer participants to obtain comparable statistical power. In conclusion, andrological methods and epidemiological designs are available for the implementation of valid studies concerned with environmental impact on human testicular function. Occupational sperm studies should probably not be the first choice when the objective is initial screening of environmental impact on fertility but should be implemented when their is a need to corroborate or refuse earlier evidence that specific exposures have impact on testicular function.

Beach, J R; Spurgeon, A; Stephens, R; Heafield, T; Calvert, I A; Levy, L S; Harrington, J M

doi: 10.1136/oem.53.8.520pmid: 8983462

OBJECTIVES: Organophosphates are effective pesticides which are frequently used in several agricultural settings. Although their acute effects are well characterised, it remains unclear whether long term exposure can damage the human nervous system. This study sought to investigate their long term effects by comparing abnormalities on neurological examination between groups of workers exposed to organophosphates and an unexposed group. METHODS: 146 exposed sheep farmers and 143 unexposed quarry workers were recruited into a cross sectional study of symptoms and neuropsychological effects of long term exposure to organophosphates in sheep dip. From a symptom questionnaire given immediately after dipping the 10 most symptomatic and 10 least symptomatic farmers were selected. Several months later each of these, along with 10 of the unexposed quarry workers, underwent a standardised neurological examination similar to that which might be used in clinical practice, at at time as remote as possible from recent exposure to organophosphates so as to exclude any acute effects. RESULTS: All 30 selected subjects agreed to participate. The components of the examination which showed a significant difference were two point discrimination on the dorsum of the hand (symptomatic farmers 22 mm; asymptomatic farmers 13 mm; quarry workers 8 mm) and the dorsum of the foot (symptomatic farmers 34 mm; asymptomatic farmers 10 mm; quarry workers 11 mm), and mean calf circumference (symptomatic farmers 35.0 cm; asymptomatic farmers 36.3 cm; quarry workers 38.6 cm). Overall the prevalence of neurological abnormalities was low. CONCLUSIONS: The differences in neurological examination detected between groups were subtle and their clinical significance was unclear. However, they do suggest evidence of an adverse neurological effect from exposure to organophosphates. Further, larger scale studies will be required before it is possible to confirm or refute the differences detected.

Rodvall, Y; Ahlbom, A; Spännare, B; Nise, G

doi: 10.1136/oem.53.8.526pmid: 8983463

OBJECTIVES: The aim of the study was to analyse whether any job titles, industrial codes, and certain occupational exposures were associated with an increased risk of glioma. METHODS: A population based case-control study of incident primary brain tumours in adults was carried out in Uppsala, Sweden in the period 1987-90. The study included 192 cases of glioma and 192 matched controls. It also included cases with other tumours of the central nervous system with matched controls. Information from all 343 controls was used in this study. Information was collected by means of a questionnaire that was sent to all subjects. An occupational hygienist reviewed the questionnaires for self reported exposures to substances and assessed whether these reported exposures were plausible or not in the corresponding occupation. RESULTS: The kappa coefficient for those classified by the two methods ranged between 0.46 and 0.88, and they were almost the same for cases and controls. For men exposed to solvents a relative risk (RR) of 2.6 (95% CI 1.3 to 5.2) was found. For men exposed to pesticides the RR was 1.8 (95% CI 0.6 to 5.1), and for plastic materials the RR was 3.6 (95% CI 1.0 to 12.4). For men employed in forestry and logging the RR was 2.2 (95% CI 0.9 to 5.3) and in basic metal industries 2.0 (95% CI 1.0 to 4.0). CONCLUSION: An increased risk of glioma was associated with use of solvents, pesticides, and plastic materials but this should be interpreted with some caution.

Clavel, J; Conso, F; Limasset, J C; Mandereau, L; Roche, P; Flandrin, G; Hémon, D

doi: 10.1136/oem.53.8.533pmid: 8983464

OBJECTIVES: The role of occupational exposures in hairy cell leukaemia (HCL) was investigated through a multicentre, hospital based, case-control study. This paper analyses the role of exposure to benzene in HCL. METHODS: A population of 226 male cases of HCL and 425 matched controls were included in the study. Benzene exposure was evaluated by expert review of the detailed data on occupational exposures generated by case-control interviews. RESULTS: No association was found between HCL and employment in a job exposed to benzene (odds ratio (OR) 0.9 (95% confidence interval (95% CI) 0.6-1.3)). The sample included 125 subjects, 34 cases (15%), and 91 controls (21%) who had been exposed to benzene, as individually assessed by the experts, for at least one hour a month during one of their jobs. Benzene exposure was not associated with a risk of HCL (OR 0.8 (0.5-1.2)). No trend towards an increase in OR was detected for increasing exposures, the percentage of work time involving exposure to > 1 ppm, or the duration of exposure. No findings suggested a particular risk period, when the OR associated with the time since first or last exposure, or since the end of exposure, were examined. CONCLUSIONS: In conclusion, with the low exposures prevalent in the sample, the study did not show any association between benzene exposure and HCL.

Hobbesland, A; Kjuus, H; Thelle, D S

doi: 10.1136/oem.53.8.540pmid: 8983465

OBJECTIVES: Concern about the health hazards of exposure to workers in the ferroalloy industry has initiated this historical cohort study. The aim was to examine the mortality pattern among male employees in 12 Norwegian ferroalloy plants. METHODS: All men employed for at least six months who started their first employment during 1933-91 were eligible for the cohort. Deaths observed during 1962-90 were compared with expected figures calculated from national mortalities. Internal comparisons of rates were performed by Poisson regression analysis. The final cohort comprised 14,730 male employees who were observed for 288,886 person-years. RESULTS: Mortality from all causes of death was slightly increased (3390 deaths, standardised mortality ratio (SMR) 1.08, 95% confidence interval (95% CI) 1.04-1.11). Regression analysis of total mortality showed a significant negative trend for the rate ratios with increasing duration of employment. An increased mortality was found among employees in urban plants compared with employees in rural plants (rate ratio (RR) 1.21, 95% CI 1.13-1.29). Excess deaths from cancer (SMR 1.11) and sudden death (SMR 1.47) were found among employees with at least three years of employment. Mortality from accidents, poisonings, and violence was increased among all employees (SMR 1.28). Excess deaths from this cause were however only found for the time after the end of employment in this industry and not during employment (SMR 0.90). CONCLUSIONS: The increased mortality from cancer and sudden death could be related to work exposures, at least in subgroups, and these results warrant further studies. The excess deaths from accidents, poisonings, and violence were probably not related to work exposures. The mortality results for short term workers and other information indicate that systematic errors contribute to the increased overall mortality.

Edward, A T; Whitaker, D; Browne, K; Pooley, F D; Gibbs, A R

doi: 10.1136/oem.53.8.547pmid: 8983466

OBJECTIVES: To find the numbers of mesotheliomas in Calderdale over the period 1966-94 and determine their relation to asbestos exposure, pathology, and mineral fibre burden within the lungs of affected subjects. METHODS: Cases were entered into the study if the subject has been diagnosed with mesothelioma after postmortem and histopathological examinations. Occupational data were obtained mainly from the case records of the Cape Asbestos medical officer, hospital, and medical practitioner and from death certificates. Analyses of the mineral fibres were performed with transmission electron microscopy and energy dispersive x ray spectrometry. RESULTS: 73 mesotheliomas were diagnosed from 1966 to 1994. Forty four were associated with exposure at the Acre Mill factory, which manufactured asbestos products. Concentrations of amphibole asbestos fibres were found to be raised above controls in 31 out of 32 cases associated with Acre Mill exposure, in 10 out of 12 other cases exposed to asbestos and eight out of 17 cases not exposed to asbestos. CONCLUSIONS: There was a high number of mesotheliomas in Calderdale. More than half of the cases were associated with occupation at the Acre Mill factory and were associated with exposure to amphibole asbestos, predominantly crocidolite. No cases associated with neighbourhood exposure to asbestos were identified.

Churg, A; Vedal, S

doi: 10.1136/oem.53.8.553pmid: 8983467

OBJECTIVE: To evaluate the extent to which human airway carinas accumulate ambient atmospheric particles, a newly developed technique was used to micro-dissect and analyse particle concentration in tubular segments and carinas of the large airways of 10 necropsy lungs from non-smokers from the general population of Vancouver. METHODS: Ratios of the particle concentrations on the carinas to the tubular segment immediately preceding it were measured with analytical electron microscopy for the mainstem bronchus, upper and lower lobe bronchi, and four different segmental or subsegmental bronchi--that is, Weibel generations 1 to about 5. A total of 119 carinal-tubular pairs was evaluated. RESULTS: Over all cases, both carinal and tubular particle concentrations increased with increasing airway generation; the median ratio of carinal to tubular particle concentration was 9:1 and did not show any trend with airway generation. The ratio was > 5 in 71% of carinal-tubular pairs, > 10 in 42% of pairs, > 20 in 31% of pairs, and > 100 in 9% of pairs. Some subjects showed a notable tendency to high ratios, with many ratios > 100, and other subjects had a tendency toward low ratios. The predominant mineral species in both carinas and tubular airway segments was crystalline silica and the relative proportion was similar in both sites; however, mean particle diameter was consistently less in the carinal tissues. CONCLUSIONS: These findings suggest that the ratio of carinal to tubular retained particles in the large airways in non-smokers is higher than might be supposed from data generated in airway casts, and that there is considerable variation in this ratio between subjects. This finding is of potential interest in models of carcinogen, toxin, and dose of fibrogenic agent to the large airways as it suggests high and sometimes extreme concentrations of toxic particles at carinas, and thus reinforces the notion that carinas may be sites of initiation of disease.

Peelen, S J; Heederik, D; Dimich-Ward, H D; Chan-Yeung, M; Kennedy, S M

doi: 10.1136/oem.53.8.559pmid: 8983468

OBJECTIVES: Four previously conducted epidemiological studies in more than 1200 grain workers were used to compare exposure-response relations between exposure to grain dust and respiratory health. METHODS: The studies included Dutch workers from an animal feed mill and a transfer grain elevator and Canadian workers from a terminal grain elevator and the docks. Relations between forced expiratory volume in one second (FEV1) and exposure were analysed with multiple regression analysis corrected for smoking, age, and height. Exposure variables examined included cumulative and current dust exposure and the numbers of years a subject was employed in the industry. Sampling efficiencies of the Dutch and Canadian measurement techniques were compared in a pilot study. Results of this study were used to correct slopes of exposure-response relations for differences in dust fractions sampled by Dutch and Canadian personal dust samplers. RESULTS: Negative exposure-response relations were shown for regressions of FEV1 on cumulative and current exposure and years employed. Slopes of the exposure-response relations differed by a factor of three to five between industries, apart from results for cumulative exposure. Here the variation in slopes differed by a factor of 100, from -1 to -0.009 ml/mg.y/m3. The variation in slopes between industries reduced to between twofold to fivefold when the Dutch transfer elevator workers were not considered. There was evidence that the small exposure-response slope found for this group is caused by misclassification of exposure and a strong healthy worker effect. Alternative, but less likely explanations for the variation in slopes were differences in exposure concentrations, composition of grain dust, exposure characteristics, and measurement techniques. CONCLUSION: In conclusion, this study showed moderately similar negative exposure-response relations for four different populations from different countries, despite differences in methods of exposure assessment and exposure estimation.

Yu, R C; Rappaport, S M

doi: 10.1136/oem.53.8.567pmid: 8983469

OBJECTIVES: To test the validity of a Michaelis-Menten-like kinetic model of pulmonary clearance of insoluble dusts. METHODS: Data were investigated from studies of pulmonary clearance in F344 rats exposed to antimony trioxide (Sb2O3), photocopy test toner, polyvinyl chloride powder (PVC), and diesel exhaust particles. The Michaelis-Menten-like model was used to develop a relation in which the pulmonary clearance half time was a linear function of lung burden. After combining all data, linear regression techniques were applied to investigate the underlying relations. With the estimated intercepts and slopes, the Michaelis-Menten-like kinetic parameters kmax (maximal clearance rate) and m1/2 (a characteristic lung burden at which kmax is reduced by 50%) were derived for the four dusts. RESULTS: The experimental data fit the linear regression very well (R2 = 0.989), suggesting that pulmonary clearance for the four dusts followed Michaelis-Menten-like kinetics. Values of the intercept terms were not significantly different among the four dusts (P = 0.294), indicating that the intrinsic clearance rates of F344 rats were the same among the four experiments. The intrinsic clearance half time was estimated to be 77.8 days, leading to an estimated kmax of 0.0089 day-1. However, the slopes of the linear relations were significantly different among the four dusts (P < 0.001). Values of m1/2 were ranked in the order of: Sb2O3 (0.69 mg) < photocopy test toner (0.97 mg) < diesel exhaust (2.49 mg) congruent to PVC (2.90 mg). CONCLUSION: This study suggests that the Michaelis-Menten-like kinetic model reasonably describes the kinetic behavior of pulmonary clearance in F344 rats. The parameters m1/2 can be used to differentiate the potency of a particular dust for impairing pulmonary clearance.