Tracing arsenic and antimony in mining-impacted environments: New insights from antimony isotopes

Arsenic (As) contamination is a common issue at mine sites worldwide, posing significant risks to both the environment and human health. Advances in metal stable isotope techniques over the last two decades have led to improved environmental assessment of other metal contaminants, but tracing the sources and geochemical processes controlling As in complex and multi-source environments remains challenging due to the lack of multiple stable isotopes of As. Antimony (Sb) is a contaminant of emerging concern that shares similar geochemistry and behaviour with As, often co-occurring in sources and sinks in mining-impacted environments. Unlike As, Sb has two stable isotopes which have recently been the focus of intense study as environmental tracers, making Sb isotopes possible proxies for tracing As. In this review, we examine the possibility for Sb isotopes to track As cycling in mining-impacted environments by synthesizing recent advances in the rapidly growing field of Sb isotope geochemistry, with emphasis on the geochemical processes controlling both As and Sb in the environment that result in Sb isotope fractionation (ore formation, weathering, redox changes, adsorption). Although Sb isotopes may have potential for tracing some As-related geochemical processes like weathering and leaching, differences in As and Sb geochemistry during other processes like oxidation/reduction and adsorption are highly dependent on site-specific environmental conditions, making it difficult to predict the suitability of Sb isotopes as proxies for As without dedicated experimental and field-based studies.