Research On The Effects Of Glyphosate On Soil Ecology And Toxicology

In the past few decades,concerns have been directed to the accumulation of pesticide residues in soil,because of their potential threats to non-target soil organisms.Due to excellent efficiency for a broad-spectrum of herbs,glyphosate(N-(phosphonomethyl)glycine)becomes a most widely used non-selective organophosphorus herbicide in agricultural practices.Although different soil extraction and analytical methods have been reported,there is lack of an accurate and well established methods for determination of glyphosate.Besides,the inhibitory effects on soil fungi and the toxicity of glyphosate on soil earthworms have been documented in previous studies.However,the effects of glyphosate on the whole soil ecological environment and its degradation in soils with different acidity and alkalinity have not been systematically studied.In this study,the responses of ecotype Eisenia foetidaand soil bacterial and fungal microorganisms to glyphosatewere investigated inlaboratory batch incubation experiments,in an effort to reveal,the effects of glyphosate on soil animalsand microbial ecology.The degradation characteristics of glyphosate in different acidity and alkalinity soils and water content were determined by liquid chromatography;The effects of glyphosate on the abundance and diversity of bacteria and fungi in soil were discussed and analyzed from the perspective of microbial ecology by Miseq high-throughput sequencing;The growth characteristics of earthworms in glyphosate-contaminated soils were observed by applying glyphosate to soil;The toxicity mechanism of glyphosate to soil earthworms was discussed by measuring the related enzymes in earthworms.The main results of the research work are as follows:(1)A simple pretreatment method was established for the determination of glyphosate in soil by pre-column derivative liquid chromatography.For glyphosate in theconcentration range of 2μL·mL-1-100μL·mL-1,the coefficient of determination,R2,of the standard working curve is above 0.999,the average recovery is 75%～96.49%,and the relative standard deviation is less than 15%.(2)Soil pH and water contentaffected the degradation of glyphosate in soil.Overall,degradation of glyphosatewas affected by soil pH to a larger extent.Under acidic and neutral conditions,60%water content was more favorable for degradation of glyphosate,which may be ascribed to enhanced soil microbial activities in soil with adequate soil aeration.However,in alkaline conditions,degradation of glyphosate was not favored with 60%soil moisture,but was facilitatedat 100%soil moisture.(3)Upon glyphosate addition,bacterial diversity was inhibited in acidic and neutral soils but promoted in alkaline soils.Growth of Bacillus in three soils,was promoted in three glyphosatespiked soils,which enhanced glyphosate degradation due toBacillus cereus in Bacillus.In addition to Bacillus,Streptomyces in acidic soils could use glyphosate as carbon and nitrogen sources for themselves and thus glyphosate in acidic soils is more easily degraded.Thus,degradation of glyphosate in soilwas more dependent on bacteria than fungi.The existence of two kinds of glyphosate-degrading microorganisms in acidic soilresulted in greater glyphosatedegradation.(4)The mortality of earthworms in soils was followed the order of acidic<alkaline<neutralsoils.The body weight of earthworms was not affected by glyphosate concentration.The addition of glyphosate in acidic soil decreases the content of soluble protein in earthworms;the specific activities of SOD and POD and CAT are affected to different extents under different glyphosate concentrations.The addition of glyphosate in neutral soil decreases the soluble protein content,but the specific activity of SOD increases withglyphosate concentrations;the specific activity of POD increases first and then decreases;the CAT activity increasesto its maximum at the 12th day of incubtion and then decreases,and the higher the concentration appears,the greater the change of CAT activity shows.In alkaline soil,the soluble protein content increased with time in the first 16 days after glyphosate was added,and decreased thereafter,with no signicant difference between glyphosate treatment and control;the specific activity of SOD fluctuated with no obvious trend;the POD specific activityin earthworms was always at a high level with high glyphosate concentrations;CAT activity decreased with the increase of glyphosate concentration,indicating the inhibition effects of glyphosate.