The Effect Of Carbosulfan On Cotton Field Soil Microflora And Its Degradation Regularity In Soil

Objective: As the largest cotton area of China, Xinjiang’s cotton seedlings often sufferred from spider mite s, aphids and other pests. Phorate dressing is the most effective protection measure, however, it’s highly toxic. With the consideration of environment, carbosulfan was used to dress seed in many areas instead of phorate. In order to guide the proper use of pesticides and to maintain healthy and sustainable development of soil ecosystem, carbosulfan toxicological effects on soil microbial ecology, degradation dynamics in soil and carbosulfan biodegradation were mainly studied in this paper.Method: Under indoor simulation and pot conditions, Plate count method was used to determine the number of microorganisms and the effect of carbosulfan on cotton seedlings was tested; Soil enzyme activity was measured using Guansongyin’s method. We used Biolog ECO tested the carbosulfan’ impact on soil microbial community functional diversity. The carbosulfan residues and degradation regulation was determined by using HPLC. Pesticide-degrading bacteria was screened by enrichment culture.Results: 1) Cotton seedling biomass was not significant affected by different concentrations carbosulfan,but chlorophyll content was decreased under 20 and 50 mg/kg concentrations treatment and the content of proline and MDA which are associated with stress resistance grew.2) In the simulation test, carbosulfan residue inhibited actinomycetes growing significantly, had slightly impact on bacteria and fungi growing. Pot experiments result showed each concentration treatment on the number of rhizosphere soil fungi was "suppression-promoting-suppression" trends. Low concentrations of carbosulfan residue inhibited bacteria growing, but high concentrations promoted bacteria multiplication.And different concentrations of carbosulfan residue on actinomycetes showed "activation- inhibition-restore" trends.3) In the simulation test, the activity of sucrose was promoted by 2, 8 and 20 mg/kg concentration of Carbosulfan residue, but it was restrained by 50 mg/kg concentration. The activities of urease、alkaline and catalase phosphatase were inhibited by all the concentration of Carbosulfan residue. Pot experiment showed that activity of low concentrations of carbosulfan residual on soil invertase is “suppression-recovery” changing trend, and mainly appeared inhibition with the concentration of 50mg/kg; the activity on soil urease is “suppression- promote- trends recovery ” changing trend; various concentrations of residual has slight inhibition effect on alkaline phosphatase, but the difference was not significant; the activity of 8mg/kg residual concentration on catalase is “promote first and then suppress”, and the activity of 2, 20 and 50mg/kg residual concentration on catalase is mainly suppression.4) In the simulation test, After 7d treatment, the AWCD value of low Carbosulfan residual concentrations was lower than CK, but the AWCD value of high concentrations was higher than CK. After 14 d it returned to CK level. The Shannon indexes for each treatment group were different from CK at 7d, and they went back to CK level at 14 d. The Simpson indexes were always same as CK at 7d and 14 d. Mc Intosh value of50 mg/kg concentration was higher than CK. After 7d treatment, the microbial AWCD values of 20 and 50mg/kg concentration were lower than control. Whereas, after 14 d treatment, the high concentration carbosulfan made the microbial AWCD values was higher than control. The change trend of Shannon and Simpson indexes for each treatment group is the same with simulation test. Mc Intosh index for each treatment group was lower than control after 7d, and under 20 and 50 mg/kg carbosulfan residual, it was higher than controls after 14 d.5) Using HPLC to determine carbosulfan residues in soil is reliable, as the recovery rate were from 84.6%to 87.4% and the lowest detectable concentration was 0.01 mg/kg, it was in line with the requirements of pesticide residue analysis. After 7d, degradation rate was about 50%; and after 30 d, it was over 90%.carbosulfan residues in soil increased as the concentration increased, but the half-life decreased, were 6.05-8.53 d.6) We isolated and domesticated one carbosulfan degrading bacteria strain ZJ-11, which was identified as Pseudomonas aeruginosa. It was able to degraded more than half of 500mg/L concentration of carbosulfan in 5d. Carbofuran was detected in the degradation biodegradation production by Shanghai Micro-spectrum Chemical Technology Services Ltd. But this degradation was not complete, reducing carbosulfan residual,but produced a new pollutant carbofuran.Conclusion: Different concentrations of carbosulfan residue will affect microbial activity in soil environment, changing community structure, but the change and the impact are temporary, some even return to control levels as the time of application extends. Carbosulfan will be degraded in the soil environment, and the degradation half-life is between 6.05 and 8.53 days. By enrichment culture approach,a degrading bacterium strain ZJ-11 is selected, and more than half of the concentration of carbosulfan that with the concentration of 500mg/L will be degraded in five days.