Residual Characteristics And Dietary Risk Assessments Of Typical Pesticides In Main Areas Of Three Types Of Grains Production In China

Wheat,maize,and rice are three main types of grains in China.Pesticides,as effective agricultural inputs for ensuring grain output,their residues in agricultural products and environment have caused extensive concern.Hence,it is of great significance to understand the occurrences of pesticides in grains production areas.The grain planting span in China is large and scattered,and the previous studies were mostly carried out in local areas,which was certain limited.In this thesis,to explore the occurrences of pesticides in grains production areas,three main areas of wheat production,three main areas of maize production,and four main areas of rice production in China were selected,and the dietary risk assessments were conducted.The main results are as follows:The phenomenon of multiple pesticides residues existed in soil and agricultural product samples.At least 16 target pesticides could be detected in all soil samples,and at least 2 target pesticides were detected in agricultural products.The higher residue values were concentrated in a few pesticides.In soil samples from main areas of wheat production,the average concentrations of cyhalothrin,imidacloprid,and cypermethrin were the highest,with 44.12μg/kg,27.08μg/kg and 23.31μg/kg,respectively.In soil samples from main areas of maize production,the average concentrations of atrazine and nicosulfuron were the highest,with 226.07μg/kg and 138.25μg/kg,respectively.In soil samples from main areas of rice production,the average concentrations of chlorantraniliprole and mesotrione were the highest,with73.80μg/kg and 72.70μg/kg.The residual levels of different types of pesticides in soil samples were different.In general,the residual levels of insecticides in soil samples from main areas of wheat production were relatively higher,and the residual levels of herbicides in soil samples from main areas of maize production were relatively higher,and the residual levels of insecticides and herbicides in soil samples from main areas of rice production were relatively higher.The total residual concentrations of 26 pesticides in soil samples from main areas of wheat production ranged from 6.57μg/kg to 1633μg/kg,with average concentration of 195.74μg/kg.The total residual concentrations of 24 pesticides in soil samples from main areas of maize production ranged from187.63μg/kg to 3163μg/kg,with average concentration of 879.35μg/kg.The total residual concentrations of 26 pesticides in soil samples from main areas of rice production ranged from 118.30μg/kg to 1205μg/kg,with average concentration of 537.60μg/kg.In addition,the residual levels of target pesticides in the farmland soils of three grains have shown regional and temporal differences.In main areas of wheat production,the total residual level of target pesticides in soil samples in Shandong province was the highest,whilst Inner Mongolia Autonomous was the lowest（mean value）.In main areas of maize production,the total residual levels of target pesticides in soil samples were basically as follows:The Huang-Huai-Hai Summer Maize Production Area>the Northern China Spring Maize Production Area>the Southern China Summer Maize Production Area（mean value）.In main areas of rice production,the total residual levels of target pesticides in soil samples were basically as follows:The Northeast China Rice Production Area>the Southern China Rice Production Area>the Huang-Huai-Hai Rice Production Area>Middle and lower Yangtze River Rice Production Area（mean value）.In order to assess the risks of pesticide application accurately,this study paid attention to the residue level differences between chiral pesticides enantiomers.For the chiral pesticides tebuconazole and myclobutanil,their enantiomers residual levels in farmland soils are different.ER_{S-tebuconazole/R-tebuconazole}and ER_{（+）-myclobutanil/（-）-myclobutanil} in soils were in the range of 0.57-1.49 and 0.49-1.65,respectively.ER_{S-tebuconazole/R-tebuconazole} in wheat samples was in the range of 0.54-0.73.In addition,we also paid more attention to the occurrences of pesticides that have adverse impact on subsequent crops.In this study,the long-residual herbicide atrazine was detected in all soil samples from wheat fields.The concentrations of atrazine ranged from 0.03-296.49μg/kg,of which the residue levels were mainly in the range≥LOQ-50μg/kg（88%）.Concentrations of atrazine in 15 wheat soil samples were higher than 100μg/kg,which may pose risks to the normal growth of afterreap crop wheat plant.In addition,although myclobutanil was not registered on rice,the contributions of myclobutanil to both paddy soil and brown rice fungicide pollution were the highest.The result most likely was due to the unscientific use of myclobutanil in paddy fields.Additionally,the study also has found that pesticides usually undergo metabolic processes after entering the environment.The detection rates of the five metabolites of imidacloprid,acetamiprid,and thiamethoxam in the soil samples were 100%,and the average total residue concentrations was 2.4 times that of the total of the three parent compounds.Therefore,more attention should be paid to pesticide metabolites in the further monitoring work.The residual levels of the target pesticides in the three types of agricultural products were all relatively low（<MRLs）.The total concentrations of 26 pesticides in wheat samples ranged from 2.81-95.27μg/kg,and the average concentration of cyhalothrin was the highest（8.68μg/kg）.The total concentrations of 24 pesticides in maize samples ranged from 3.27 to 15.20μg/kg,and the average concentration of emamectin benzoate was the highest（2.06μg/kg）.The total concentrations of 26pesticides in brown rice samples ranged from 1.81-26.74μg/kg,and the average concentration of chlorantraniliprole was the highest（4.94μg/kg）.The%ARf D value and%ADI value of target pesticides in three types of agricultural products were in the range of 1.23×10^-6%-5.32×10^-1%and 5.28×10^-6%-9.54×10^-2%,respectively,which were far lower than 100%,indicating a low dietary risk to human health.