The Toxicity Of Midazolinone Herbicides To Microorganisms And Earthworm And Its Environmental Behaviors

Midazolinone herbicides have high efficiency, broad spectrum and selectivity and low toxicity with non-target organism advantages. They were mainly used for prevention leguminous crops and they also uesd to control the annual gramineae and broadleaf weeds. But the persistence of the herbicides was showed in soil. The massive and continuous use of the pesticides in agriculture would pollute the environment, be harm to rotational crops and threat to the non-target organisms. The herbicides on the toxicity of microorganisms and earthworms were determinate and thedegradation dynamics and the adsorption of imazapic in soil were investigated. The main results of this paper were summarized as follows:1. The effects of the midazolinone herbicides on microorganisms in soil and the toxicity of imazapic on earthworms were discussed in this paper. The results showed that the imazapic has the biggest inhibitory effect on soil respiration and as the concentration of the pesticides increases, the higher inhibitory effects on soil microorganisms were detected. After60days of imazapic in soil, the mounts of microorganisms are same as ck. The LC50of imazapic on earthworms is0.3775mg/cm2. The joint toxicity of imazapic and chlorpyrifos is higher than anyone of them on earthworms. The LC50of imazapic increased1187.2times.2. The extracting agents, pH, type of SPE and the elution volumes were compared in this study. The optimum conditions were that using the acetonitrile-water (5:3, V/V) as the extracting agent and using the phosphoric acid adjust the pH equal to3. The SAX cartridge was uesd to clean the impurities and the analyte was eluted with methanol. The residue was re-constituted in methanol and then filtered through a0.22μm filer before HPLC analysis. The recoveries of four imidazolinone herbicides in three spiked soils were between86.0～108.8%(RSD≤3.3%, n=5). Under the optimized conditions limits of detection for imazapyr、imazapic and imazethapyr were all0.02mg/kg, imazamethabenz-methyl was0.04mg/kg (S/N=3).3. The degradation dynamics of imazapic in three different soils under laboratory conditions were studied in this paper. The factors affecting the degradation such as soil types, soil microbial, soil moisture and temprature were discussed. They were complied with first order kinetics equation in the degradation process. The half-times of degradation in GuangXi NanNing A, ShanDong QingDao and JiLin ChangChun are133.3,121.6and101.9d, respectively. Soil microorganisms were the dominant position in the degradation process. In a certain range, as the temperature and soil moisture content increased, the half-times of degradation will be earlier than before.4. The adsorption and desorption of imazapic by nine differernt soils were studied in this paper. The adsorption order of imazapic in differernt soils are GuangXi NanNing A>GuiZhou GuiYang>GuangXi NanNing C>HeiLong jiang HaEr bing> JiLin ChangChun> ShanDong QingDao> GuangXi NanNing B> HeNan XinXiang. The adsorption isotherm of imazapic is belonged to L-type. The results show that the imazapic adsorption is strongly affected by the pH and the content of organic matters.