Accumulation, spatio-temporal distribution, and risk assessment of heavy metals in the soil-corn system around a polymetallic mining area from the Loess Plateau, northwest China

To investigate the heavy metal concentrations in soil-corn system, 30 pairs of soil (0-20 cm) and corn grain samples were collected from Baiyin City, China, a typical industrial oasis in Loess Plateau. The results indicated that the mean concentrations of Cu, Zn, Cd and Pb in agricultural soils from the Dongdagou and Xidagou stream valleys exceeded the soil background concentrations of Gansu Province, China. Correlation analysis showed that the correlation among the total Cu, Zn, Cd and Pb in soils were significant at P < 0.01. Results showed that only a fraction of Cd and Pb in the corn grain samples exceeded the limits of eight elements in cereals, legume, tubes and its products and the maximum levels of contaminants in foods in China. The spatial distribution pattern of Cd in corn grains was highly similar to that in sampled soils. Correlation analysis revealed that the main source of Zn, Cd and Pb in corn grains was soils. Temporal distribution of heavy metals showed that heavy metal content in soils was still high, and the Cu, Cd, Pb content in corn grains showed a decreasing trend over 20 years. The values of pollution index (PI) and Nemerow integrated pollution index (NIPI) indicated that the heavy metal pollution level was Cd > Zn > Cu > Pb, and Cu, Zn, Cd and Pb belong to safe to heavy pollution. The results of hazard quotient (HQ) indicated that there was no obvious adverse health effect for children and adults.