| The soil organic pollution becomes extremely serious as a result of the rapid development of industrialization and agriculture,among which the farmland soil pollution is most harmful for people’s life.Jilin Province,as an important agricultural province in China,has found organic pollution in some farmland soil,which gravely threatens the yield and quality of maize.However,the distribution and enrichment characteristics of the organic pollutants are still unclear.In addition,Jilin Province has put forward policies to encourage the conservation tillage based on straw returning,greatly changed the physicochemical property of soil organic carbon,which made the understanding of the organic pollutants distribution further unclear.In this research,we studied 50 maize fields and 7 kinds of maize fields with different cultivation ways.We analyzed these physicochemical properties,the content and composition of organic chlorine pesticides,organophosphorus pesticides and PAHs respectively.The enrichment characteristics of organic pollutants and its influence on conservation tillage was revealed.And risks of the three contaminants was also evaluated.Furthermore,the influence of conservation tillage methods on health risks was discussed.The results of the paper have great significance for the systematic assessment of human health risks caused by soil pollution and food security in Jilin Province,providing scientific data for comprehensive monitoring of conservation tillage.The specific study conclusions are shown as follows:（1）Organochlorine pesticide concentrations ranged from 12.94 to 170.59μg/kg,with DDTs,HCHs,and heptachloride being the most prevalent,the distribution of which was high concentration in eastern region and low in western region.Among entire country,the residual content of organochlorine pesticides in maize fields of Jilin Province is at a medium level.Source analysis showed that DDTs pesticide maybe utilized recently,while HCHs pesticide is a mixture of new and old sources.The organophosphorus pesticides concentrations ranged from 169.44 to 657.73μg/kg,mainly diazinon and malathion,which is higher than other agricultural regions.The two contaminants were concentrated in mid-east region of Jilin Province but sparse in mid-west region.The content of PAHs was 398.54 to 4530.73μg/kg,mainly low rings（40%of 3 ring）and high rings（41%of 5～6 ring）,intensively distributed at middle region while sparsely distributed at mid-west region.The retention of PAHs in agricultural soil was higher than other areas of China.The major sources of PAHs in soil are coal,diesel,natural gas and biomass combustion.Moreover,traffic emissions also play an important role which is affected by oil sources.（2）Soil organic matter has significant correlation with organic pesticide species only methamidophos（r=0.403,P<0.01）.Organic pesticides with poor hydrophobicity,such as dimethoate and endosulfan,have a significant positive correlation with particle size.PAHs have a significant positive correlation with powder and clay particles,but no correlation with organic matterwhich shows that the single physical and chemical properties of soil is not the main factor that determine the amount of organic pollutants.The distribution of most pesticides is significantly correlated with precipitation,elevation,and slope,while PAHs are also significantly and positively correlated with elevation and precipitation,indicating that geographical environmental factors are important factors affecting the accumulation and distribution of organic pollutants in soil.（3）Conservation tillage by straw returning way will cause significant changes of the physicochemical property of soils.Because we found that soil macroaggregates,average grain size,and water content in protective maize fields were significantly higher than those in traditional maize fields（P<0.05）.Thus,there was no consistent pattern that the straw turnover cannot affect the change of the total amount of the three organic pollutants significantly.Research on each pollutant shows that PAHs were more likely to respond to protection than organic pesticides,and high-ring PAHs tended to accumulate in protective plots with higher soil organic carbon content.The response of methamidophos in organophosphorus pesticides to conservation tillage was related to soil organic matter,while organophosphorus pesticides with weak hydrophobicity showed significant differences between conservation plots and traditional plots（P<0.05）.The response of organochlorine pesticides to straw turnover was the smallest.Therefore,protective measures for straw turnover will affect the change of organic pollutants by affecting soil physical and chemical properties,but the response behavior for different pollutants to conservation tillage was not consistent.（4）Value of carcinogenic risk for organochlorine pesticides was 4.42×10-8to 5.83×10-7,and the non-carcinogenic risk value was 4.60×10-5to 5.77×10-4,but the childhood carcinogenic risk value ranged from 1.04×10-4to 9.26×10-4,which is the moderate risk level(>10–4).Value of carcinogenic risk for organophosphate pesticides was 5.79×10-7to0.23×10-5and non-carcinogenic 6.74×10-5to 1.30×10-3,but children ranged from 1.34×10-3to5.12×10-3,already at a higher risk level(>10–3).The carcinogenic risk value of PAHs ranged from1.53×10-9to 1.94×10-8,and the non-carcinogenic risk value ranged from 3.40×10-5to3.46×10-4,indicating that soil PAHs in corn fields in Jilin Province do not have human health threaten.For conservation and traditional tillage,there was no significant difference of health risks threaten,indicating that conservation tillage based on straw turnover does not increase the health risks of organic pollutants. |
