Concentrations, Bioavailability, and Spatial Distribution of Soil Heavy Metals in a Long- Term Wastewater Irrigation Area in North China

Heavy metal contamination in a long-term wastewater irrigation area in north China was investigated. The highest concentrations of Cr, Cd, Pb, As, Zn, and Cu in topsoil were 113.58, 3.78, 13.91, 14.44, 90.75, and 95.53mg/kg, respectively. The Nemerow's synthetical pollution index was below 0.7, suggesting that this area belonged to a safe domain. The bioavailable concentrations of the heavy metals in this area were also maintained at low level. The correlation between Al (or Fe) and other heavy metals proved that concentrations of Pb, As, and Zn in soil might be mainly affected by the soil natural material. Spatial distributions analysis of heavy metals in this area indicated that the sewage irrigation might also have influence on heavy metals pollution in this long-term wastewater irrigation area. The vertical profile of heavy metals concentrations in this area showed that all the heavy metals in surface soil layer were in the highest concentration and began to decrease with the increase in soil depth. The low concentration of heavy metals in wastewater and soil suggested a potential sustainability of the long-term wastewater irrigation area where the good quality wastewater was available for agricultural usage.