Short-term fluctuations in heavy metal concentrations during flood events through abandoned metal mines, with implications for aquatic ecology and mine water treatment

The variability in heavy metal concentrations and physico-chemical parameters during rain-fed river floods that pass through abandoned metal mines is poorly understood due to the difficulties of sampling these events. Such information is essential for the characterisation of contaminant dynamics and for investigations of contaminant/ecosystem relations and the effectiveness of remediation. This study investigates the role of flood flows in contaminant mobilisation and temporary increases in toxicity at an abandoned metal mine in central Wales, UK. Flood events substantially increase the potential toxicity of river water. The principal contaminants are dissolved Pb, mobilized by increased acidity resulting from the dissolution and flushing of efflourescent salts accumulated on the surface of mine spoil. The implications of flood runoff and contaminant mobilisation for aquatic ecology and mine water treatment are discussed.