| Pengzhou is one of the famous vegetable-bases in Sichuan and even China,owing to its fertile farmland.With urbanization development traditional agriculture is gradually replaced by intensive agriculture that leading to a large number of agro-chemicals were applied to farmland.As a result,agricultural environmental degradation increasingly,especially the issue on soil contaminated by heavy metal is more prominent.However,concerning soil polluted by heavy metals in the vegetable-bases,it has no been comprehensively monitored and systematically evaluated until now.In particular,contaminated characteristics and spatial distribution of heavy metal in soils of the vegetable-base are not well known,and the targeted control measures for heavy metals pollution and the quality and safety of assessment agricultural products are also more deficiency.Therefor,the purpose of this study is to reveal the pollution characteristics and spatial distribution of heavy metals in the vegetable-base soils,and to evaluate potential human health risk caused by heavy metals contaminated.A survey was carried out about soils and vegetables of Pengzhou,heavy metal concentration in both soils and vegetables were determined.Combined geostatistics,GIS techniques and health risk assessment were used to achieve the goal.The results can provide basic data for the governance of soil heavy metal pollution and the layout of agricultural industry.Main results are as follows:1.The average content of Cu,Pb,Zn,Mn,Cr,Hg,Cd and As in the surface soil were 28.906,50.799,88.944,214.777,71.937,1.183,0.373 and 5.880 mg/kg,respectively.Compared with the background values,all the metals in soils exhibited certain accumulation,except for Mn.Hg and Cd content in soils exceeded the maximum permissible limits set by the soil environmental quality standard of China(GB 15618-1995).Concentrations of Pb,Hg,Cd and As in surface soils exhibited a positively skewness distribution;Cu,Zn,Mn and Cr is normal distribution.Concentrations of Pb,Hg,Cd,As in soils is of high variability,and that of Cu,Zn,Mn,Cr is moderate variation.2.Ordinary Kriging interpolation have performed the lowest errors and the highest correlation to predict heavy metal levels in non-sampling sites,compared with Inverse distance weighting(IDW).the spatial distribution patterns of elements Cu,Pb,Zn,Mn,Cr,Hg,Cd were closely related to human activities,while As was mainly affected by soil parent material.3.The highest ratio of DTPA-extractable speciation to total for Cd was 47.3%,followed by As,Cu,Hg,Pb,Mn,Zn and Cr,which were 28.4%,13.1%,13.0%,5.2%,4.9%,3% and 2.3%,respectively.The concentration of total heavy metals and DTPA-extractable speciation in soils were positively correlated with the total heavy metals in vegetables,but their correlations were not significant.4.Mean concentrations of Cd and Pb in edible parts of vegetable exceeded the maximum permissible limits(MPL)set by GB 2762-2012,and the rest metals was below the MPL.Bio-accumulation factor(BAF)of Zn in vegetable was the highest and that of Cr was the lowest.Bio-accumulation factor of heavy metals tended to be in the order of Zn > Hg > Cu > Cd > Mn > Pb > As > Cr.The estimated daily intake(EDI)of Pb via consumption of vegetables for adults and children in the study area exceeded the oral reference dose(Rf D)recommended by USEPA and other agencies.The target hazard quotients(THQ)of Pb for adults who consumed vegetables per day achieved 1.785,while the THQ values of Pb and Hg for children were 2.178 and 1.210,respectively,these THQ values were above 1,indicating that have a potential health risk to local residents.Health risk that intake of heavy metals via vegetables consumption for children was more higher than adults.Main conclusions as follows:Concentrations of Cu,Pb,Zn,Cr,Hg,Cd and As in surface soils of the study area all have an enrichment trend when compare to the background values.of which the concentration of Hg and Cd in soils showed more markedly exceeding the standard of the soil environmental quality of China(GB 15618-1995).The spatial distribution of heavy metals in the vegetable-base soils showed uneven distribution patterns,which mirrored the different land use characteristics in some extent,and human activities imposed more obvious influence on the distribution of heavy metals in soil.No significant correlation between the concentration of heavy metals in vegetables and DTPA-extractable speciation or total amount of heavy metals in the soils,indicating that heavy metals in vegetables would not be predicted by DTPA-extractable speciation or total heavy metal.The vegetables from the research area showed to be contaminated by Pb and Hg that would lead to a higher health risk for local residents,they intake metals via vegetables consumption had overtaken the oral reference dose recommended by USEPA and other agencies,and the THQ value had overrode the health advice that imply a potential health risk.The amount of heavy metal ingested by vegetables consumed by the children was more than that of adults,the children in the study area would be a higher health risk. |
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