Abstract:
Depletion rates of three triazine herbicides, atrazine, simazine and ametryne and
two urea base herbicides, diuron and metobromuron, under laboratory conditions
have been investigated in soil samples collected from GAEC, a coastal savannah
soil, and KNUST, a forest zone soil. Two hundred grammes of the soil samples
were treated with herbicides standard solution to generate herbicide-soil
concentration of 10 pg/g and incubated at room temperature for 12 weeks. TLC
methodology was used to monitor the decline of the herbicides from the soil and
the result showed that the decline of the chemicals was comparatively faster in
the KNUST soil than the GAEC soil. After two weeks of soil treatment and
incubation, atrazine, simazine and metobromuron had depleted more than half of
the initial amount applied. In all, the rate of depletion of metobromuron was found
to be the highest and at the end of the experiment, it declined to about 2.42 %
and 4.38 % of the initial concentration in the KNUST and the GAEC soils
respectively. The results obtained, indicated that the kinetics involved in the
process of depletion of the herbicides to a higher degree could be described by
first order reaction kinetics. The half-lives of the herbicides in the GAEC soil were
in the range of 14.8 - 32.2 days and 13.3-31.1 days in the KNUST soil. Soil
moisture and organic matter content were found to facilitate the depletion of the
chemicals from the soils. Out of the various solvents systems tried for the
extraction of the herbicides, acetone, acetonitrile and acetone/hexane mixture
(4:1) were found to be efficient for the recovery of the chemicals in the soil
ecosystems studied. With the photosynthesis inhibition method used for the
detection of the herbicides, the detectability for the unclean extracts was in the
range of 0.004 - 0.008 (jg/g and that of the clean-up extracts was in the range of
0.024 - 0.162 pg/g.
