Quantifying influences of interacting anthropogenic-natural factors on trace element accumulation and pollution risk in karst soil

This study quantified influences of interactions between anthropogenic and natural factors on trace element accumulation and pollution risk in karst soils at regional and local scales and identified the dominant interacting factors. A total of 513 soil samples were collected from Hechi, southern China to measure concentrations of arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb), which were compared with published background values. Descriptive statistics and occurrence characteristics were developed with geostatistical methods and the comprehensive pollution risk was calculated using the Nemerow pollution index (NPI). Geo-detector models were used to further examine and quantify the influence of 14 factors (5 anthropogenic and 9 natural) on trace element concentrations and NPI, both individually and interacting with the other 13 factors. The results clearly demonstrate that anthropogenic factors interact with natural factors to enhance nonlinearly and significantly trace element accumulation in karst soils. Watershed was the natural factor that most enhanced trace element accumulation when interacting with anthropogenic factors. Land use and smelting industry were the anthropogenic factors that most enhanced trace element accumulation when interacting with natural factors. Land use-watershed interaction accounted for 56% of Cd accumulation and smelting industry-watershed interaction for 19% of As accumulation. Land use-watershed, land use-lithology, and pH-watershed interactions accounted for 51%, 19%, and 15%, respectively of NPI values. The findings indicate that changing land use and reducing pollutant discharge from the smelting industry should be considered.