| There are many types of pollutants in agricultural environment.Heavy metal mercury,metalloid arsenic,and persistent organic pollutants Polybrominated diphenyl ethers?PBDEs?are typical pollutants.In recent years,antibiotic resistance genes?ARGs?have received widespread attention.As emerging pollutants,they brought new challenges to agricultural environmental protection.It's worth noting that many typical pollutants play important roles in promoting ARGs abundance in the environment.With the rampant development of China,these pollutants were continuously introduced into agricultural environment,posing adverse impacts to ecosystems and human health.Currently,there has been limited information on the distribution characteristics and impact factors of ARGs in the agricultural soils at national scale.The concentration characteristics of typical pollutants and the environmental effects of compound pollution?typical pollutants-ARGs?in actural environment were unknown.Therefore,in this study,we carried out a systematic sampling campaign to collect soil and tree bark samples around farmland across China in different year.All sampling sites were away from pollution sources.We aimed to?a?reveal the distribution characteristics of emerging pollutant ARGs in agricultural soils;?b?clarify concentration characteristics of three typical pollutants in agricultural environment;?c?discuss influence posing by different typical pollutants on the horizontal transfer of ARGs and possible mechanism;?d?assess the potential ecological risks and human health risks of typical pollutants.Those topics have extremly important scientific and practical signification in the field of controlling and reducing pollution,and environmental health.The main research results are as follows.?1?Sulfanilamide?sul?and tetracycline?tet?resistance genes widely occurred in agricultural soils,with relative abundance of 10-8-10-2 gene copies/16S r RNA gene copies.The distribution characteristics of sul and tet genes in soils were significantly different.Northeast China was the hot spot of sul genes,with the highest abundance of1.85×10-3 gene copies/16S r RNA gene copies.The abundance of tet genes was higher in Liaoning,Hubei,Jiangsu,Shandong and Hunan provinces,ranging from 1.4×10-2-3.9×10-2 gene copies/16S r RNA gene copies.Analysis showed meteorological parameters and sewage irrigation well explained the geographical distribution of sul genes,showing a gradually decreasing pattern from north to south.Tet genes were more closely related with soil properties and manure application in agricultural practice.?2?The concentrations of mercury in agricultural soil ranged from 0.06 to 0.78mg/kg.The total mercury storage of Chinese surface agricultural soil was 4.1×104 tons,and the annual emission of mercury from agricultural soil to air was 107 tons.High mercury concentration was found in East China and South China.The vertical distribution showed a slight enrichment on the surface soil.The geological accumulation index(Igeo)and CA emphasizes the effect of rapid economic growth and energy consumption on soil mercury concentration between 2011 and 2016.Soil organic matter,high temperature and heavy precipitation could promote the accumulation and sedimentation of mercury into soil.Compared with other metals?Pb,Cd,Cr,Zn,Ni,Ca,Mg,Co,Mn?,the influences of mercury and copper on ARGs were more significant.The SOS response of bacteria and co-resistance may be the main mechanism.In contrast,sul genes was more sensitive to heavy metal pollution than tet genes,confirming sul genes could be used as an effective indicator of heavy metal pollution.The Hakanson index showed mercury in agricultural soils posed considerable ecological risks,emphasizing that mercury should be one of the priority metal on ecological control.The mean hazard index?HI?linked to non-carcinogenic risks was below 1,suggesting an absence of non-carcinogenic risks of mercury in agricultural soils.?3?The concentrations of arsenic in agricultural soil ranged from 1.93 to 36.0mg/kg.The total storage of arsenic in Chinese surface agricultural soil was estimated to be 3.72×106 tons.The higher arsenic level was found in South and Northeast China.Igeo and PCA showed concentration characteristics of arsenic were mainly affected by soil parent materials.Soil arsenic content showed an upward trend from 2006 to 2016,which may be the result of the application of fertilizer in agricultural practice,especially phosphate fertilizer.Soil p H played an important role in the distribution and migration of soil arsenic.Soil arsenic may promote the horizontal transfer of sul2 gene.This may be the result of co-resistance.In addition,a negative correlation between arsenic and tet M were found.The influence of arsenic on the microbial community carrying tet genes may be the reason for the inhibition.The Hakanson index indicated the potential ecological risk of arsenic in agricultural soil was low.In general,arsenic in agricultural soils didn't pose non-carcinogenic risk to human and the carcinogenic risk was at a low level.?4?The concentrations of PBDEs in agricultural soil ranged from 2.26 to 16.9 ng/g.East China and South China had the highest PBDEs concentration.BDE-209contributed mostly to PBDEs in soil.BDE-209 in tree bark was possibly origined from the usage of Deca-BDEs,while low-brominated PBDEs possibly came from the historical usage of PBDEs and the degradation of PBDEs in the environment.soil organic matter and p H played important roles in PBDEs concentration characteristic.Low-brominated PBDEs could promoted the horizontal transfer of ARGs.The co-resistance and cross-resistance were likely to be the mechanism.?5?The concentration of PBDEs in tree bark around farmlands ranged from 0.398to 13.8 ng/g dw.Highest concentration was found in East China.BDE-209 was the main component of PBDEs in tree bark.Tree bark had the similar source of PBDEs to soil.The concentration of PBDEs were significantly related with regional atmospheric PM2.5,population density,and economic indicators?PCGRP,GDP?,highlighting the important role of atmospheric fine particulates in long-distance transportation of PBDEs,and emphasizing socioeconomic development maight exacerbate environmental PBDEs pollution.?6?The estimated concentration of PBDEs in the atmosphere around farmland ranged from 0.923 to 423 pg/m3,which was predicted by tree bark/atmosphere distribution model.The PBDEs concentrations in tree bark,soil,and air were significantly correlated,indicating different environmental media in agricultural environment may have similar source of PBDEs,and thet were closely related.The ff values of PBDEs were all less than 0.3,indicating a stong trend of transmission from air to soil.This process could be affected by regional temperatre and precipitation.Based on the non-dietary exposure pathways of soil intake,skin contact and air inhalation,the average exposure dose of PBDEs in different age groups shows the trend as toddlers>infants>children>teenagers>adults.PBDEs didn't pose non-carcinogenic risk to human and the carcinogenic risk was at a very low level. |
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