Research On The Strong Reduction And Remediation Of Soil 666 In Pesticide-contaminated Sites And Its Mechanism

Pesticides play an important role in agricultural production,but with their increasing usage,pesticide pollution has become a global environmental problem.Once these pollutants enter the food chain,they will directly affect human health and destroy the ecological balance.Organochlorine pesticides are defined as one of the most dangerous pesticides by the World Health Organization(WHO),and are recognized as persistent organic pollutants in the“Stockholm Convention on Persistent Organic Pollutants”.China is one of the major producers of pesticide chemicals,and its output ranks first in the world,accounting for more than one-third of the world.It was estimated that there were more than 1200 pesticide-contaminated sites and some of them urgently need to be remediated according to the"Thirteenth Five-Year Development Plan for the Pesticide Industry"and the"Soil Pollution Prevention and Control Action Plan"in China.Reductive Soil Disinfestation(RSD)remediation technology is mainly used to repair continuous cropping obstacles,but has rarely been used for the remediation of organic pollutants-contaminated soils.In this study,the response surface method was used to screen out the optimal process for the degradation of HCH in the RSD treatment,including organic materials,temperature and moisture contents.The changes of soil physicochemical properties,HCH removal efficiency,microbial community,and environmental toxicity of HCH during the optimal RSD process was investigated.The main research conclusions were as follows:(1)Within a certain range,the increase of organic material dosage,temperature and moisture content resulted in the enhancement of HCH degradation.Through single-factor experiments,the optimal conditions were:1.0?2.0%of organic material dosage,temperature 30?40?,and moisture content of 100?200%.According to the experimental data obtained from the Box-Behnken Design(BBD)in the response surface method,the optimal RSD process were as follows:for?-HCH,1.53%of organic material dosage,temperature 36.8?,151%of moisture content;and for?-HCH,1.49%of organic material dosage,temperature 37.1?,186%of moisture content.(2)It was found that both HCH-contaminated soils were initially acidic,but the soil pH tended to become neutral after RSD treatment,indicating that RSD treatment effectively improved the degree of soil acidification.The soil Eh decreased during the RSD treatment,and the final soil Eh was below-100 mV.The EC values of the two HCH-contaminated soils were reduced,indicating that RSD treatment effectively reduced soil salinity and improved soil salinization.The Cl^–content of the soil increased to a certain extent during the RSD process,and the leached Cl^–content followed a similar trend.The RSD treatment could also effectively remove SO₄^2–and NO₃^–from the soil,and the content of SO₄^2–and NO₃^–in the leachate also showed a decreasing trend.Under the optimal conditions,the HCH degradation rate increased after RSD treatment,and the experimental result of the HCH degradation could be well estimated by the response surface method.(3)According to the results of soil surface morphology observation,specific surface area and pore size analysis,Fourier infrared spectroscopy analysis and total organic carbon determination and characterization,the RSD process did not noticeably changed soil properties,and the soil structure were similar to the original soil.Compared to the original soil,the specific surface area of treated soil was reduced by0.57?3.34 m²/g,the TOC content was reduced by 0.001?0.036 g/kg.The soil total nitrogen and available potassium increased by 0.3?1.9 g/kg and 27.5?86.4 mg/kg,respectively.But the available phosphorus content decreased by 0.25?12.2 mg/kg.(4)The diversity and richness of soil bacterial communities decreased after RSD treatment.In the control test,the diversity of Shannon of?-HCH and?-HCH were decreased by 0.43 and 0.26,and the abundance of Chao was decreased by 3195 and244,respectively.In comparison,the diversity of Shannon of?-HCH and?-HCH was reduced by 0.54 and 1.08,respectively,and the abundance of Chao was reduced by 805and 1136,respectively,in the RSD treatment.The diversity of Shannon of soil fungal communities did not change much in the blank test,with only 0.03 for both?-HCH and?-HCH.However,the diversity of Shannon of soil fungal communities was significantly reduced in the RSD treatment,by 1.80 and 1.97 for?-HCH and?-HCH,respectively.Compared with the original soil,the abundance of Chao after RSD treatment was reduced to different extents.In the blank test,?-HCH and?-HCH were reduced by 10.66 and 52.97,respectively;but they became 223 and 32,respectively,when organic materials were added.(5)It was found that the soil leachater was more clearer with increasing the RSD treatment time.The toxicity of the soil leachate to the photobacterium gradually decreased with the increase of treatment time.After 16 days of treatment,the toxicity of?-HCH and?-HCH to the photobacterium was reduced by 30.7?36.7%and38.0?44.0%,respectively,indicating that the RSD treatment effectively reduced the toxicity of HCH-contaminated soils,and adding organic materials coule accelerate this process.The toxic effects of soil leachate for zebrafish and earthworms appeared with the increase of exposure time.However,after RSD treatment,the toxicity of soil leachate to zebrafish and earthworms continued to decrease,and the seed germination rate gradually increased.And finally,almost non-toxic performance was observed for earthworms,the average number of dead earthworms decreased from 3?5 to 1?3,and the seed germination rate of?-HCH and?-HCH increased by 13.0%and 14.8?18.5%.