Toxicity of Mining-Contaminated Lake Sediments to Lumbriculus variegatus

Boreal lakes with soft water and low buffering capacity are susceptible to excess ion loading resulting from metal mining. The impact of two Finish mining sites in downstream lakes was assessed with a chronic sediment toxicity test using a laboratory-reared freshwater Lumbriculus variegatus (Oligochaeta). The test organisms were exposed to mining-contaminated natural lake sediments and hypolimnion water (HLW) or artificial freshwater (AFW) as overlying water in two independent experimental setups. In both test setups, growth and reproduction of L. variegatus were lower in sediments from the lakes receiving high amount of mining effluents from the mines nearby. In the biomining site, the main contaminants in the recipient lakes were the ore metals Ni and Zn, while in the lakes affected by the conventional underground mine, they were Cu and Zn. These metals accumulated in L. variegatus especially in the setup with natural HLW above the sediment. Growth and reproduction were lower in the HLW than in the AFW setup. The mining-contaminated sediments did not support optimum growth or reproduction of L. variegatus in comparison to the local reference sediments. Decline of pH in the unbuffered natural sediments brought up challenges in the assessment of metal-contaminated lake sediments with high sulfur content, and a need to develop new tools for their risk assessment.