Contamination Assessment And Source Apportionment Of Heavy Metals In Agricultural Soil In Hexi Corridor

The contamination of soil by heavy metal in China has become a significant concern due to the rapid and extensive development of society and economy.Heavy metal contamination in farmland has attracted great attention recently for its risk to food safety and human health.Hexi Corridor,located in key parts of the northwestern regions of the ‘Silk Road Economic Belt',is the most important base of commodity grain and producing area for cash crops.However,the rapid development of agriculture and industry has inevitably led to heavy metal contamination in the soils in this region.In order to understand the levels of heavy metals and their source apportionment for agricultural soil in Hexi Corridor wholly and partly,twice samplings were conducted in October 2016 and October 2017,respectively.This study will be helpful to prevent and control heavy metal pollution in agricultural soil,meanwhile provide theoretical basis for rational and sustainable use of arable land.In October 2016,124 agricultural topsoil samples were collected and analyzed to determine their heavy metal concentrations(including Co,Cr,Cu,Mn,Ni,Pb,Ti,V,W and Zn).The results showed that the average concentrations of Cr,Cu,Ni,Pb and Zn were lower than the secondary standard of soil environmental quality;however,the concentrations of eight metals(Cr,Cu,Mn,Ni,Pb,Ti,V and Zn)were higher than background values,and their corresponding enrichment factor values were significantly greater than 1.Different degrees of heavy metal pollution occurred in the agricultural soils;specifically,Ni had the most potential for impacting human health.The results from the multivariate statistical analysis and GIS-based geostatistical methods indicated both natural sources(Co and W)and anthropogenic sources(Cr,Cu,Mn,Ni,Pb,Ti,V and Zn).To better identify pollution sources of heavy metals in the agricultural soils of Hexi Corridor,the PMF model was applied.Further source apportionment revealed that enrichments of Pb and Zn were attributed to traffic sources;Cr and Ni were closely related to industrial activities,including mining,smelting,coal combustion,iron and steel production and metal processing;Zn and Cu originated from agricultural activities;and V,Ti and Mn were derived from oil-and coal-related activities.In October 2017,376 soil samples were collected and analyzed for heavy metal content.Geochemical baseline value(GBV),single factor pollution(PI)and potential ecological risk index(RI)were used to assess pollution degree.Finally,geostatistical analysis,positive matrix factorization(PMF)and health risk assessment model were used to determine main pollution source and priority control source.The results showed that mean heavy metal concentration was higher than GBV.Although mean heavy metal concentration did not exceed national Grade II value,some samples of Ni and As exceeded the criteria.PI and RI revealed that farmland soil was moderately polluted and had low ecological risk,and was the least polluted in the center.Based on PMF,Factor 1 represented metal processing;Factor 2 represented a mixed source of electroplating and smelting in the west and center,while a mixed source of mining and agricultural activities in the east;Factor 3 was ascribed to agriculture;Factor 4 was a mixed source of atmospheric deposition and traffic emission.The main pollution source(Factor 4 in the west and east,Factor 2 in the center)had highest percent proportion to total metals and priority pollution source contributed most to carcinogenic risk(Factor 2 in the west,Factor 3 in the center and east)and non-carcinogenic risk(Factor 4 for adults and Factor 2 for children in the west respectively,Factor 3 in the center and east)respectively.In short,farmland soil heavy metal pollution was caused by human,but pollution degree was low.