Quantification of the relationship between multiple metal(loid) distribution and integrated effect of internal-external factors in riverbed sediments across Xijiang River basin, South China.

Understanding the integrated effect of external factors (e.g., human activities) and internal factors (e.g., hydrodynamics, sediment properties) on metal(loid) distributions is necessary for relevant decision-makers to develop river basin management strategies. In attempts to understand the possible causes of the distribution of nine target metal(loid)s in riverbed sediments across Xijiang River basin in China, we grouped and portrayed the multiple metal(loid) distributions by calculating metal(loid)'s normalised-and-weighted average concentrations, and then canonical correlation analysis combined with a series of statistical operations, collectively called optimized CCA analysis, was applied to quantify the strength of relationship between multiple metal(loid) distribution and integrated effect of internal-external factors. Results showed that the target metal(loid)s can be divided into three groups according to their distribution patterns: Group A (including Zn, As, Cd, Sb and Pb), Group B (including Cr, Ni and Cu) and Group C (including Tl). Among them, metal(loid)s in Group A was significantly enriched in comparison with the reference values of Chinese sediments, and the wide-ranging accumulation of Cd and Sb in the whole study area needs paying great attention to. For those metals in natural states (e.g., metals in Group B), the affinity of sediment (e.g., Fe and Mn oxides) is responsible for their distributions. By contrast, when metal(loid)s (e.g., metal(loid)s in Group A and Group C) had obvious anthropogenic sources, the interferences of anthropogenic inputs (e.g., non-ferrous metal enterprises' waste-discharging activities) and the specific sedimentary characteristics (e.g. karst topography and low-energy hydrodynamic depositional conditions) in study area can weaken the correlation between the binding affinity of sediment and the contents of metal(loid)s. The optimized CCA analysis can be an alternative and advantageous statistical operation for determining the main types of causes of multiple metal(loid) distribution in the case of observations with relatively low case-per-variable ratios.

Distribution and migration of heavy metals in soil and crops affected by acid mine drainage: Public health implications in Guangdong Province, China.

Acid mine drainages (AMD) contain high concentrations of heavy metals, and their discharges into streams and rivers constitute serious environmental problems. This article examines the effects of AMD on soil, plant and human health at Dabaoshan mine in Guangdong Province, China. Although the large scale mining was stopped in 2011, the heavy metal pollution in soil continues to endanger crops and human health in that region. The objectives of this study were to elucidate distribution and migration of Cd, Cu, Zn, As and Pb and associated health implications to local inhabitants. We collected and analyzed 74 crop samples including 28 sugarcane, 30 vegetables, 16 paddy rice and the corresponding soil samples, used correlation and linear relationship for transformation process analysis, and applied carcinogenic and non-carcinogenic risk for hazard evaluation. Results showed that the local soils were heavily polluted with Cd, Cu and As (especially for Cd) and the mean Igeo value was as high as 3.77. Cadmium, Cu, and Zn in rice and vegetables were comparable with those found four years ago, while As and Pb in edible parts were 2 to 5 times lower than before. The root uptake of Cd and Zn contributed mainly to their high concentrations in crops due to high exchangeable fraction of soil, while leafy vegetables accumulated elevated As and Pb contents mainly due to the atmospheric deposition. Metal concentrations in sugarcane roots were higher than those in rice and vegetable roots. The risk assessment for crops consumption showed that the hazard quotients values were of 21 to 25 times higher than the threshold level for vegetables and rice, indicating a potential non-carcinogenic risk to the consumers. The estimated mean total cancer risk value of 0.0516 more than 100 times exceeded the USEPA accepted risk level of 1×10(-4), indicating unsuitability of the soil for cultivating the food crops. Therefore, the local agricultural and the land-use policies need to be reevaluated.