| The Yangtze River Delta is one of the most developed areas of industrial and agricultural economy in China.Excessive heavy metals has entered and enriched in the farmland soil through anthropogenic activities,such as agricultural production,industrial production,and transportation.The concentrations of heavy metals in farmland soil have accumulated year by year and the Yangtze River Delta has suffered increasingly complicated heavy metals pollution,which has threatened the safety of agricultural production,and may pose irreversible damage on human health.The Taige canal valley,a typical agricultural region of Taihu Lake Basin in the Yangtze River Delta,was the target study area.118 soil topsamples were collected from the Taige canal valley's farmland soil by the mesh points method,and concentrations of Cr,Hg,As,Cu,Zn,Ni,Pb and Cd were analysed.Single factor index,nemerow index,geo-accumulation index and potential ecological risk index were used to assess farmland soil heavy metals pollution and potential ecological risk with the soil background value of the Taihu Lake Basin as the evaluation standard.The health risk assessment?HRA?of the US EPA was used to identify the health risk,which posed by heavy metals.The multivariate statistical analysis,spatial analysis,and positive matrix factorization model?PMF?was combined to identify the pollution sources and hot spots of farmland soil heavy metals,and clarify the spatial distribution characteristics of heavy metals in farmland soil.The results showed that:?1?The average concentrations of Cr,Hg,As,Cu,Zn,Ni,Pb,and Cd were 63.25,0.25,7.83,35.24,77.25,31.48,38.37,and 0.16 mg·kg-1,respectively.Heavy metals exceeded the background value of the Taihu Lake Basin by 48.31%?Cr?,81.36%?Hg?,33.05%?As?,99.15%?Cu?,45.76%?Zn?,57.63%?Ni?,96.61%?Pb?,66.95%?Cd?,respectively.Hg,Cu,Zn,Pb,and Cd exceeded the risk screening values of soil contamination of agricultural land by 0.85%,0.85%,0.85%,3.39%,and 5.08%,respectively.All heavy metals in farmland soil met the soil environmental requirements of the edible agricultural products.The results indicated that the soil environment was suitable for agricultural production,while heavy metals in farmland soil has represented obvious enrichment phenomenon in the study area.?2?The nemerow index of all farmland soil samples exceeded the warning value.The average value nemerow index was 1.85 and the overall pollution situation was light.The geo-accumulation index of Pb was the highest and showed slightly polluted.The mean value of potential ecological risk index was 137.66,and the percentage of soil samples presented severe and strong ecological risk level was 1.69%and 0.85%,respectively,which indicated the potential ecological risk was slight.?3?In the study area,for adults and children,the mean non-carcinogenic risk was1.13×10-1 and 7.88×10-1,respectively,and the mean carcinogenic risk was 7.07×10-6and 1.24×10-5,respectively.Both of them were less than the safety threshold,and indicated the health risk for people in the study area was acceptable.The HRA demonstrated that ingestion was the main exposure pathways and As was the most important element for health risk.The downstream of Taige canal had centralized hot spots and faced the relatively high health risks,due to anthropogenic activities and soil parent materials.?4?Owing to the production of industrial points source,Cr,Ni and As had more obvious spatial clustering and spatial abnormal points,which indicated spatial clustering phenomenon were obvious.The high values of Cr and Ni were concentrated in the upper and middle reaches of the south and downstream of the north in the Taige canal,where were industrially dense areas.Affected by agricultural activities such as farming time,the concentrations of Hg and Cu in the north of the canal were significantly higher than that in the south.The concentrations of As in the downstream of the canal were obviously higher than that in the upstream,which was the result of the distribution of soil parent materials.Due to the large scale of cultivation and livestock breeding,the concentrations of Zn in the middle of the canal were comparatively high.The overall spatial distribution of Cd and Pb was more uniform,because of pesticide and fertilizer application and atmospheric deposition.?5?Heavy metals of farmland soil in the study area were mainly originated from industrial activities,soil parent materials,atmospheric sedimentation and agricultural activities.The contribution rates of various pollution sources were 29.51%,27.91%,22.85%,and 19.73%,respectively,which indicated the anthropogenic activities dominated the sources of heavy metals in farmland soil in Taige canal valley. |
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