Exposure risks of trace metal(loid)s on little egrets in a restored polymetallic mining area in eastern China

Abstract

Trace metal(loid) pollution from mining activities is a widespread environmental problem, which has stimulated restoration efforts over the world. Tongling is a non-ferrous metal mining area in China with a long history of mining activities. To restore the environment polluted by mining after the 1950 s, local government has implemented numerous measures since the 1990 s, but the effectiveness on wildlife remains largely unknown. In this study, we measured contents of metal(loid)s (As, Cd, Cr, Cu, Pb and Zn) in eggshells of little egrets Egretta garzetta collected near a restored mining wasteland in Tongling, and compared them to those collected in two control areas where there are no mining histories, i.e. Chizhou and Mingguang in Anhui Province. The contents of trace metal(loid)s and isotopes (δ15N and δ13C) in main food of little egrets were also measured to assess exposure risk of trace metal(loid)s for the species. Compared with the two control areas, Cd (0.005 μg/g) was lower but Cr (0.861 μg/g), Pb (0.585 μg/g) and Zn (3.420 μg/g) were higher in the eggshells in Tongling. Pb showed biomagnification (trophic magnification factor = 1.29) from food to eggshell; Cr and Cu showed biodilution, while As, Cd and Zn did not show transfer trends. The risk assessment indicated that little egrets faced lowered levels of exposure risks for most metal(loid)s after the environmental restoration, but they were still threatened by relatively high levels of Pb and Zn. Our findings suggested that the environmental restoration of mining wastelands in Tongling might significantly reduce the exposure risks of most metal(loid)s for waterbirds. The study provides important implications for restoration of metal(loid) pollution in polymetallic contaminated area.

Keywords

• Trace metal(loid)
• Little egret
• Ecological restoration
• Risk assessment