Integrated assessment of sediment metal pollution in Pb/Zn mining districts

This study assessed two Pb/Zn mining districts in northern Spain using a weight-of-evidence framework based on a reference condition approach integrating three lines of evidence (LOE): sediment chemistry, chronic sediment toxicity, and metal bioaccumulation in field biomonitors.

We studied seven sites in Arditurri (n = 5) and Reocín (n = 2). In the absence of Spanish sediment quality guidelines, ecological backgrounds and thresholds for Cd, Pb, and Zn were derived from 31 to 55 reference sites across northern Spain. Toxicity was measured with a 28-day Tubifex tubifex whole-sediment bioassay; effective tissue residues were also obtained from laboratory tests. An overall weight-of-evidence approach was performed based on alterations measured across the three LOEs.

The proposed ecological thresholds for Cd, Pb, and Zn are comparable to values reported for other regions. Sediment Cd, Pb, and Zn exceeded background by more than six to ten times across mining sites. All three lines of evidence indicated impairment driven by sediment chemistry and chronic toxicity at all test sites, and hazardous bioaccumulation levels were not reached at only one site.

Ecological Thresholds represent a useful tool for pollution assessment in mining areas. Concordant evidence from chronic toxicity tests and biomonitor´s effective residues indicate sediment-borne metals pose risk to benthic communities and ecological integrity through toxicity and bioaccumulation at most sites. Effective tissue residues obtained here are relevant candidates for deriving environmental quality standards. Overall, the assessment supports implementing management actions to reduce metal sources at these sites.