Characteristics Of Residual Pyrethroids Contamination And Their Effects On Soil Enzyme Activity In The Hilly And Plain Region: A Case From Wutongqiao County In Sichuan

Pyrethroid pesticides,as the substitute for HCHs and DDTs,were widely used in agriculture,forestry,food safety and human health,and in turn played a vital role in increasing yield and income.However,recent studies pointed out that the pyrethroid residues had threat on human health and ecological security to a certain extent,implying that deep studies on the characteristics of the degradation and migration of pyrethroid pesticides in soil-plant systems and their effects on soil enzyme activity are of importance on agriculture and forestry production safety and human health.Little information is as yet available on the degradation characteristics of pyrethroid pesticides in different soil-plant systems and their effects on soil enzyme activity.The content of pyrethroid pesticides in the representative plants were therefore investigated in order to obtain an understanding of the residual characteristics of pyrethroid pesticides in plants of the typical hilly and plain area(Wutongqiao County) in Sichuan,which was a densely populated area in 2007,based on optimizing the method of pyrethroid pesticide measurement by gas chromatography. Meanwhile,the content of pyrethroid pesticides in nine soil-plant systems which included the combinations of alluvial soil,calcareous purple soil and acid purple with sponge (Acacia),poplar(Populus spp) and maize(Zea mays L.) was measured to understand the degradation and migration characteristics of pyrethroid pesticides in different soil-plant systems,employing the methods of gas chromatography in combination with controlled environmental chambers and pot experiment.Furthermore,dynamics on the activities of polyphenol oxidase,dehydrogenase,urease and nitrate reductase in soils under nine soil-plant systems were measured in order to understand the effects of pyrethroid pesticides on soil microbial activity.The objectives of this study were to provide a scientific basis on the safe production for agriculture and forestry as well as ecological risk assessment on pyrethroid pesticides.The recovery rate varied from 95%to 89%and the extraction effect was ideal when the ratio of petroleum ether/acetone(V/V) was 1:1.The separation effect of RTX-5 column, N₂ for the carrier gas,and ECD detection was efficient,which the minimum of detection was 5×10^-10g,the minimum detection concentration was 0.012mg.kg^-1,the recovery rate varied from 85%to 105%,and the variation coefficient ranged from 2.5%to 3.4%, respectively.In addition,GC ECD detector could detect the residual pyrethroid pesticides in the soil and plant,and showed the characteristics of good repeatability,simple operation, and high sensitivity,accuracy and precision which could make the needs of residual pesticides detection.Among the studied 9 kinds of herbages,Hemarthria altissima had higher residual fenpropathrin and cyhalothrin which was 0.46mg.kg^-1 and 0.09mg.kg^-1,respectively. Meanwhile,Canna edulis,Astragalus sinicus and Cyclosrus parasiticus had higher contents of residual cypermethrin,deltamethrin and fenvalerate,which were 0.12mg.kg^-1, 0.38mg.kg^-1,and 0.07mg.kg^-1,respectively.Similarly,among the studied 7 shrubs and trees,Eucalyptus grandis had higher content of residual fenpropathrin which was 0.21mg.kg^-1,Populus adenopoda had higher contents of residual cypermethrin, deltamethrin and fenvalerate which were 0.33mg.kg^-1,0.71mg.kg^-1 and 0.26mg.kg^-1, respectively,while Vernicia fordii had higher content of residual cyhalothrin which was 0.11mg.kg^-1.Among the studied 8 vegetables,Solanum tuberosu had higher contents of residual fenpropathrin,cypermethrin and cyhalothrin and the corresponding values were 0.14mg.kg^-1,0.11mg.kg^-1 and 0.06mg.kg^-1,respectively.Glycine max and Cucurbita moschata had higher contents of residual deltamethrin fenvalerate,and the corresponding values were 0.27mg.kg^-1 and 0.08mg.kg^-1,respectively.The results of the cluster analysis indicated that cyhalothrin and fenvalerate had similar residual mechanisms in plants,while the residual mechanism on fenpropathrin in plants was different from other 4 pyrethroid pesticides.The residual pyrethroid pesticides in soils were strongly influenced by poplar tree which had higher accumulation capacity on the pyrethroid pesticides,while those were weak influenced by maize resulting from smaller accumulation capacity.The degradation rate of pyrethroid pesticides was higher in calcareous purple soil due to the alkaline condition was favorable for the degradation of pyrethroid pesticides in comparison with other soils.The contents of cypermethrin and deltamethrin in soils changed little over 105 days,while the contents of other pyrethroid pesticides in soils increased at first and thereafter decreased,depending on soil-plant systems.Soil types had significantly influenced on the ability of sponge tree to accumulate the pyrethroid pesticide,but not significantly influenced on the capacity of poplar tree.Pyrethroid pesticides had influenced the activities of polyphenol oxidase, dehydrogenase,urease and nitrate reductase in soils at different levels,depending on soil types,soil-plant systems and enzymes.The activity of polyphenol oxidase in soils varied with soil types,the short-term increase of pyrethroid pesticides in soils increased the activity of polyphenol oxidase in soils,while the long-term residual pyrethroid pesticides in soils inhibited the activity of polyphenol oxidase in soils.In short term,pyrethroid pesticides increased the activity of dehydrogenase in soils under the soil-sponge tree systems,but inhibited the activity of dehydrogenase in soils under the soil-poplar and soil-maize systems,while in long term,the effects of promotion or inhibition weakened. Alter 105 days of pyrethroid pesticides supply,the activity of urease in soil increased in different soil-plant systems except for calcareous purple soil-maize system.The pyrethroid content was positively correlated with the activity of nitrate reductase in alluvial soil and acid purple soil,and negatively with that in calcareous purple soil.Alter 105 days of pyrethroid pesticides supply,the activity nitrate reductase in acid purple soil increased.