Contamination from historic metal mines and the need for non-invasive remediation techniques: a case study from Southwest England

Abstract

The UK is legally required by the EU Water Framework Directive (WFD) to improve the environmental quality of inland and coastal waters in the coming years. Historic metal mine sites are recognised as an important source of some of the elements on the WFD priority chemicals list. Despite their contamination potential, such sites are valued for their heritage and for other cultural and scientific reasons. Remediating historic mining areas to control the contamination of stream waters, whilst also preserving the integrity of the mine site, is a challenge but might be achieved by novel forms of remediation. In this study, we have carried out environmental monitoring at a historic, and culturally-sensitive, lead–silver mine site in southwest England and have undertaken a pilot experiment to investigate the potential for a novel, non-invasive remediation method at the site. Concentrations of Pb and Zn in mine spoil were clearly elevated with geometric mean concentrations of 6,888 and 710 μg g⁻¹, respectively. Mean concentrations of Pb in stream waters were between 21 and 54 μg l⁻¹, in exceedance of the WFD environmental quality standard (EQS) of 7.2 μg l⁻¹ (annual average). Mean Zn concentrations in water were between 30 and 97 μg l⁻¹, compared to the UK EQS of 66.5 μg l⁻¹ (average). Stream sediments within, and downstream from, the mining site were similarly elevated, indicating transport of mine waste particles into and within the stream. We undertook a simple trial to investigate the potential of hydroxyapatite, in the form of bonemeal, to passively remove the Pb and Zn, from the stream waters. After percolating through bonemeal in a leaching column, 96–99% of the dissolved Pb and Zn in stream water samples was removed.