Degradation Of Herbicides In Soils And Their Effect On Biological Indicators For Soil Quality

The soils in some areas of China were contaminated by herbicide application, with thecharacteristic of big mass, lager scope and scattered. Atrazine, butachlor and metsulfuron-methyl are three kinds of herbicides that have been mostly used in China. The physico-chemical and biological behavior of these three herbicides have been evaluated by many researchers, but the studies related to the herbicide decomposition and their influence on soil microbiological indicators are very little. Atrazine, butachlor and metsulfuron-methyl herbicides were chosen to evaluate their dynamic characters of decomposition in contaminated soil, and the response of biological indicators to explain the process and mechanism of their relationship for remediation of contaminated soils. The main results are summarized as follows:1. Degradation of atrazine under controlled environmental conditions(1) The changes of total amount of atrazine's residue with time satisfied kinetics formula C=C0e-kt, when the soil water holding capacity (WHC) is 40% and incubation constant temperatures are 15℃,25℃ and 35℃, respectively. In this experiment the rate of degradation for atrazine increased and half-life decreased with increase in temperature. The half-life of atrazine was 15.2 days to 59.2 days, 15.0 days to 25.6 days and 10.5 days to 32.7 days under 15℃,25℃ and 35 ℃ temperature, respectively. This indicated that the residues of atrazine degraded faster at high temperature than at low temperature.(2) Incubation at 25 "C, the degradation rate of atrazine increased with increasing WHC from 40% to 60%. It means that he activity of microbes and also the degradation of herbicide were improved by regulating soil water content and soil temperature.2. Degradation of butachlor under controlled environmental conditions(l)During the incubation time the degradation rate of butachlor at 40% of water holding capacity (WHC) increased with increased in incubation temperature from 15℃ to 35℃. It was found that there was a steady loss of butachlor in soils with time and can be explained by thefirst-order equation. But the range of half-life for butachlor was different under different temperatures. The half-life of butachlor under 15"C, 25癈 and 35'C were 15.2 day .to 59.2 day, 15.0 day to 25.6 day and 10.5 day to 32.7 day, respectively. It was found that the residues of butachlor degraded faster at high temperature than at low temperature. The microbial bioactivity and soil properties can influence the degradation rate of butachlor(2) The degradation rate of butachlor under 35 癈 incubation increased with increase of the WHC from 40% to 60%. The half-life of butachlor were 16.2d, 10.5d and 32.7d when WHC was 40% ,and IS.lday, 9.9day and 13.5day when WHC was 60% in different type of soil ( paddy field on Quaternary red soil, blue clayed paddy soil and paddy field on desalting muddy polder).3. Influence of herbicides contamination on soil microbial indicatorsThe results indicated that the microbial indicators was significantly affected by three herbicides application to soil at the rate of lOmg kg"1. The soil microbial biomass was largely influenced by herbicide and this influence decreased with the time.(1) The soil microbial biomass C content decreased apparently at starting stages. Different herbicides showed different degree of influence on soil microbial biomass C. The order of influence on microbial biomass C in different soils by atrazine application was: paddy field on desalting muddy polder>blue clayed paddy soil>paddy field on Quaternary red soil. The sequence of influence on microbial biomass C in different soils by butachlor application was: paddy field on desalting muddy polder>paddy field on Quaternary red soil>blue clayey paddy soil. For this the order of influence of metsulfuron-methyl application microbial biomass C in different soils was: blue clayed paddy soil>paddy field on desalting muddy polder>paddy field on Quaternary red soil. The three herbicides' influenced the soil microbial biomass C i...