Metal/metalloid bioavailability considerations in addressing site risk and remediation in mine closure

摘要

Current best mining practices call for mine closure planning throughout the lifecycle of a mining project, and many countries have specific guidance for developing mine closure plans. These guidelines (country-specific) are intended to address the footprint left behind from historical mining and processing activities and ensure that the post-closure condition does not represent a health risk to current or future communities and the environment (biodiversity). Among many other aspects, the closure plan should provide an approach for evaluating post-closure risk that incorporates the best available site data, including environmental (e.g., physical, chemical, biological, end-use and social data) - all of which are important for developing a site-specific post-closure risk assessment and protective site remediation levels. A key issue in characterising potential chemical exposure and risk from a closed mine site is understanding the chemical and physical processes affecting site environmental media (e.g., tailings, contaminated soil, surface water, etc.) as these characteristics influence chemical (metal/metalloid) mobility and bioavailability. Important fate characteristics influencing bioavailability include pH, soil cation exchange capacity, organic carbon content, acid volatile sulphides and redox potential. Reduced bioavailability as a result of site and media-specific physical/chemical characteristics translates to a reduction in organism (human, ecological) toxicity potential and, as illustrated for human health, in the development of more-realistic (and site-specific) remediation levels. Accordingly, understanding mine site environmental conditions affecting bioavailability is important in preparing a scientifically robust mine closure risk assessment and in developing site-specific remediation levels protective of site end uses.