Thin Layer Chromatographic Studies on Depletion of Some Herbicides in Two Soil Ecosystems

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.