Spatial distribution and human health risk assessment of soil heavy metals based on sequential Gaussian simulation and positive matrix factorization model: A case study in irrigation area of the Yellow River

The content of Cd, Cu, Pb, Zn, Cr, Ni and As from 250 soil samples was measured in agricultural soil of Ningxia section of the Yellow River. Positive matrix factorization (PMF) was to identify the main sources of these heavy metals; Sequential Gaussian Simulation (SGS) was to identify their spatial distribution and high-risk areas; and Human Health risk (HHR) model was to measure the health risk. Results showed that the average content of Cd and As exceeds the risk screening value of ''Soil Environmental Quality-Agricultural Land Soil Pollution Risk Control Standard'' (GB 15618-2018), which belongs to slight-level pollution. Although the content of other types of HMs (Cu, Pb, Zn, Cr, Ni) is below the risk screening value, they are still included heavily in the soil (except Cr). PMF indicated that mixed sources of agriculture and industry accounted for 27.06%, natural sources accounted for 14.12%, industrial sources accounted for 23.04%, traffic sources accounted for 21.50%, and Yellow River sedimentary sources accounted for 14.28%. PMF-HHR showed that the mixed sources of agriculture and industry are the most important factor causing non-carcinogenic risk (HI) to children (accounting for 55.75%). Industrial sources and traffic sources were the two main factors that cause HI to adults (industrial sources accounted for 25.16%, and traffic sources accounted for 28.78%). Mixed sources of agriculture and industry and natural sources were the two main factors that cause carcinogenic risk (CR) (mixed sources of agriculture and industry account for 35.34%, and natural sources account for 33.23%). SGS indicated that 0.64% and 9.32% of the total areas were posing as higher HI areas to children and adults respectively; in particular, 0.68% and 1.12% of the areas were identified as higher HI of As and Cr areas at a critical probability of 0.9.