Predicting plant metal bioaccessibility at the historic wheal maid tailings lagoons, Cornwall, UK

Abstract

Abandoned mine sites with their metal-rich substrates pose significant challenges to naturally colonizing plants. In this study, the abandoned Sn-Cu tailings lagoons at Wheal Maid (Cornwall, UK) have been investigated to establish the bioaccessibility of metals and metalloids (As, Cd, Cu, Pb, Sb, Zn) in exposed tailings and wastes using a new plant bioaccessibility test. Four main substrate types were sampled: (1) mine waste used to construct the lagoons, a relatively uncontaminated material with variable particle size; (2) granular capping material used in the upper lagoon to cover the tailings and relatively uncontaminated; (3) grey tailings a fine to medium grained material with visible sulfides and white secondary salts, extremely high in near-total Zn concentrations; and (4) marbled tailings a fine grained brown/red/yellow material with extremely high near-total As concentrations. The analytical quality of results produced by a new plant bioaccessibility test was monitored using blanks, spiked solutions and repeat analyses. The grey tailings had the highest bioaccessible metal and metalloid content. As this material oxidizes, it will release As, Cd, Cu, Sb, Zn and to a lesser extent Pb in a form which will be more available to plants. This will inevitably delay re-vegetation at the site. The new bioaccessibility test is recommended for sulfidic rocks and waste samples and should be employed at an early mine-life stage to allow appropriate waste classification and improve mine closure outcomes.