[Source Apportionment and Ecological Risk of Soil Heavy Metals in Typical Vanadium-titanium Magnetite Mining Areas...

A total of 895 surface soil samples （0-20 cm） and five road-dust samples were collected in a typical vanadium-titanium magnetite mining area of Hongqi-Damiao catchment in the Chengde City and analyzed for 12 heavy metals （Cu, Ni, Cd, Cr, Pb, Zn, Hg, V, Ti, Mn, As, and Co） and their chemical speciation. The accumulation and ecological risk characteristics of soil heavy metals （HMs） were clarified by geological accumulative index, potential ecological risk index （RI）, risk assessment coding （RAC）, and modified Nemerow integrated ecological risk index （mNIER）. Multiple statistical methods including principal component analysis, correlation analysis, cluster analysis, redundancy analysis, and GIS spatial analysis were used to investigate the spatial variation response of soil HMs to the environmental impact factors （distance to the road network, land use, and soil parent material types）. The sources of HMs were quantitatively analyzed using a positive matrix factorization （PMF） model. The results showed that the over-standard rates of Cu, Cr, Cd, Ni, Pb, and Zn were 5.70%, 2.79%, 1.01%, 0.67%, 0.11%, and 0.11%, respectively, in comparison to China's soil environmental quality standard risk screening values （GB15618-2018）. The average accumulation index of soil HMs followed the order of Cu>Ti>Cr>V>Co>Ni>Cd>Zn>Mn>As>Hg>Pb, while the average accumulation index of Cu was 1.23 and categorized as moderate accumulation. The accumulation of Cu, Zn, Cr, Mn, V, Ti, Co, and Ni gradually decreased within a distance of 200 m, while the content of Cd in soil was relatively stable within the distance from 25 m to 800 m to the road network, and the accumulation index of Pb, Hg, and As in soil was highest at the 200 m buffer zone. The average RAC value of 12 HMs followed the order of Cd>Mn>Ni>Zn>Hg>Co>Pb>Cu>As>Cr>V>Ti. The average RAC value of the Cd element was 46.45%, showing high biological activity, while the bioavailability RAC value of other elements was generally categorized as low-risk or risk-free level. The potential ecological risk of HMs in soil was relatively low with the RI value range between 51.48 to 1 152.39 （average of 131.2） and the mNIER value range between 10.32 to 745.57, with an average value of 32.85, in which 97.43% of the samples were classified as light to moderate risk. Based on the PMF model, 44.82%, 33.45%, 32.27%, and 24.35% of Pb, Hg, Cd, and Zn in surface soil were contributed by intensive transportation activities, respectively. The main sources of 12 HMs in the study area were the combined sources of natural sources （soil parent materials）, weathering sources of V-Ti-Fe-P deposits, dust deposition from industrial and mining activities and coal combustion, agricultural sources, and traffic sources, with their contribution rates of 27.46%, 21.12%, 19.29%, 17.05%, and 15.08%, respectively.