Geochemical assessment of arsenic toxicity in mine site along the proposed Mineral Tramway Project, Camborne, Cornwall

Abstract

Many abandoned mine sites in Cornwall, UK, are characterised by elevated concentrations of arsenic which can cause contamination of surrounding soil and water resources. Often these sites have important historical and cultural value that requires access to be maintained, despite the potential toxicity of As. In west Cornwall, the potential for As contamination has been recognized within the Industrial World Heritage site focused on the Mineral Tramway and mining sites mines in the Gwennap and Camborne mining districts. The major abandoned mine sites, arsenic calciner and milling sites along a proposed tourist route in this area have been assessed for As toxicity and bioavailability taking into account the proximity of footpaths to areas of potential contamination. Arsenic concentrations up to 3.3% were found in soils along the proposed footpaths and exposed mine spoil, with 55% of all total As values above the UK criteria for contaminated industrial soil of 640 mg/kg in surface soil. Using a Physiologically Based Extraction Test (PBET), the maximum amount of As observed to be bioavailable varied from 4 mg/kg through to a maximum of 9,000 mg/kg with a positive correlation between total As concentrations and bioavailable As concentrations. Mineralogical and selective extraction evaluation identified that the PBET-released As is not so much associated with total As concentrations, but is positively correlated to As held within the weak ‘ionic-held’ As, strongly adsorbed As, As associated with amorphous iron and calcium oxide phases, and poorly crystallized As(V) salts. The data reported here have been used to develop a risk assessment of the sites and propose management strategies to mitigate these risks.