Environ Monit Assess (2010) 170:45–58
DOI 10.1007/s10661-009-1213-1
Effect of humic deposit (leonardite) on degradation
of semi-volatile and heavy hydrocarbons and soil quality
in crude-oil-contaminated soil
Oguz Can Turgay · Esin Eraydın Erdogan ·
Ayten Karaca
Received: 18 August 2008 / Accepted: 9 October 2009 / Published online: 4 November 2009
© Springer Science + Business Media B.V. 2009
Abstract In order to investigate the bioremedial
potential of humic deposit (leonardite), the effects
of the treatments of leonardite and a commercial
bioaugmentation agent on the degradation of a va-
riety of petroleum hydrocarbons (C13–C31) and
soil enzyme activities (urease acid-alkaline phos-
phatase and dehydrogenase) were tested within a
soil incubation experiment lasting 120 days. Ex-
perimentally crude-oil-contaminated soil (2.5%)
was regulated to a C:N:P ratio (100:15:1; Oilcon),
amended with 5% of leonardite and regulated
to the same C:N:P ratio (Oilcon-L) or mixed with
a commercial bioaugmentation product (Oilcon-
B), respectively. In the short period of incuba-
tion (60 days), Oilcon and Oilcon-B treatments
showed higher hydrocarbon degradations, where-
as Oilcon-L showed higher hydrocarbon degrada-
tion over Oilcon and Oilcon-B treatments in the
long-term (120 days). Applying contaminated soil
with leonardite increased urease (LSD, 4.978,
*P < 0.05) and dehydrogenase (LSD, 0.660,
*P < 0.05) activities. However, acid and alkaline
phosphatase activities showed no certain inclina-
tion between different treatments. Dehydroge-
nase seemed to be more related to hydrocarbon
O. C. Turgay (
B
) · E. E. Erdogan · A. Karaca
Department of Soil Science,
Agriculture Faculty of Ankara University,
Ankara, Turkey
e-mail: turgay@agri.ankara.edu.tr
degradation process. Overall results showed that
leonardite enhanced biodegradation of petroleum
hydrocarbons and also stimulated soil ecological
quality measured as soil enzyme activities.
Keywords Humic substances · Leonardite ·
Biostimulation · Hydrocarbon degradation ·
Soil enzyme activities
Introduction
The process of soil bioremediation simply im-
plies degradation activities of soil microorgan-
isms to decrease the concentration of hazardous
wastes (Boopathy 2000) and it basically in-
volves two main approaches: bioaugmentation
and biostimulation. Bioaugmentation of contam-
inated soils involve the inoculation of exogenous
or indigenous microorganisms for the enrichment
of hydrocarbon-degrading microbial populations
(Richard and Vogel 1999; Barathi and Vasudevan
2001) whereas biostimulation can be obtained by
regulating vital soil characteristics, i.e., moisture
content, aeration, nutrient addition, and pH for
stimulating native hydrocarbon degrading micro-
bial biomass (Margesin et al. 2000a; Elektorowicz
1994; Piehler et al. 1999; Rhykerd et al. 1999).
Biostimulation has been extensively studied both
in situ and in vitro experiments under optimal
conditions (Bossert and Bartha 1984; Leahy and