Toxic elements in the stream sediments of an urbanized basin, Eastern China: urbanization greatly elevates their adverse biological effects.

The concentration of toxic elements (Hg, Cd, Cr, Cu, Pb, Zn, Ni and As) was measured in the sediments of the Qinhuai River in Eastern China along a rural to urban gradient. Multiple approaches were undertaken to evaluate the degree of enrichment and adverse biological effects of these elements. The results showed that the concentration of Hg, Cd, Zn, Cu and Pb increased exponentially from the agricultural headwater to the urbanized downstream, which reflects a severe anthropogenic influence. In addition, area-specific references, such as the local soil background (LSB) and upper continental crust (UCC) derived from the Yangtze craton, were more applicable for evaluating the enrichment of toxic elements in the Qinhuai River than was global UCC. In addition, Cd and Hg had the highest enrichment factor values (EF, with averages of 9.18 and 7.14, respectively); Zn, Pb and Cu had moderate EFs (averages from 1.52 to 2.40), while the average EFs of Ni, Cr and As were approximately equal to 1. Based on consensus-based sediment quality guidelines (SQGs), the contamination characteristics of all of the samples studied were associated with low to moderate priority of adverse biological effects (ABEs) in the rural upstream area, while it was associated with a high to moderate priority of ABEs in the urban sections of the Qinhuai River. Our results suggest that the adverse biological effects of elevated levels of toxic elements were strongly related to the degree of anthropogenic pollution.