Heavy metals accumulation and risk assessment in a soil-maize (Zea mays L.) system around a zinc-smelting area in southwest China

Smelting of nonferrous metals causes significant concerns because of its emissions of heavy metals (HMs) into surface soil, and its potential threat to human health through the food chain. To investigate the HMs concentrations in a soil-maize system, a total of 41 paired soil-maize samples were collected from a typical indigenous zinc-smelting area of northwestern Guizhou Province, China. Results showed that the concentrations of the targeted HMs in the soil were significantly higher than their corresponding background values of Guizhou Province. Results obtained of the geo-accumulation index (I) and the potential ecological risk factor of an individual metal revealed that Cd and Pb were identified as the top-priority control HMs in the study area. The mean concentrations in maize grain decreased in the order of Zn>Pb>Cu>Cd. Bio-accumulation factor (BAF) indicated a strong ability for Cd to be accumulated in the maize root. Translocation factor (TF) and Fourier transform infrared (FTIR) spectroscopy revealed that the maize root played an important role in reducing the mobilization of HMs to stem, except for Zn. Kriging interpolation results illustrated that the spatial distribution patterns of HMs in the maize grain were generally similar to those in sampled soil, and the higher concentrations for the investigated HMs were partially overlapping between soil and maize grain. The average hazard quotient (HQ) of the investigated HMs for both children and adults were all lower than the threshold value (HQ=1). The total hazard index (HI) was 5.51E-01 and 4.24E-01 for the two population groups, respectively, implying no potential non-carcinogenic risk for local maize-consumers. Sensitivity analysis demonstrated that the oral ingestion rate (IngR) of grain was the predominated contribution to the output of the risk assessment.