AN ASSESSMENT OF TELLURIUM IN SEMI-ARID MINE TAILINGS AT DELAMAR, NEVADA: IMPLICATIONS FOR HUMAN AND ECOSYSTEM HEALTH

Tellurium (Te) is a rare metalloid (~ 3 µg kg^-1 average upper crustal abundance) that has been classified as a (near-) critical element that is increasingly used in highly efficient solar panels. As such, extensive use of Te during the growth of alternative energy technologies will result in geographic concentration and increased potential for human and ecosystem exposure. Specifically, Te can be enriched up to hundreds of parts per million in Au/Ag deposits. Since it is generally not recovered, significant amounts of Te remain in mine tailings exposed to the environment. Tellurium is toxic to humans; Te(IV) is more toxic than Te(VI), Se(IV), or As(III). Chemically, it behaves similarly to Se, so the effects of Te deposition on the ecosystem may similarly be of concern. The weathering of Te-bearing mine tailings in surficial environments can transform Te and have implications for human and environmental health, which can serve as a model for improper end-of-use disposal of Te-based photovoltaics.

Our goal is to determine whether Te-rich historic mine tailings pose a health risk to surrounding ecosystems and communities. The historic Delamar mining district, located in semi-arid Lincoln County, NV, was mined for Au from 1891 to 1938 and produced at least 450,000 tons of mine tailings containing elevated concentrations of Te (up to 267 mg kg^-1). Circum-neutral (pH 7.4-8.3) tailings piles were sampled as a function of depth. Bulk fits modeling Te speciation via X-ray absorption spectroscopy suggest the predominance of Te(VI), the less toxic form of Te. Micro-focused X-ray fluorescence mapping and electron microscopy indicate the enrichment of Te in small particles associated with S and iron (oxy)hydroxides. Tellurium and other toxic metal(loid)s (e.g. Pb, Bi, Cu, and As) are enriched in surficial tailings, likely present as bioaccessible efflorescent salts, and may be susceptible to dispersion by wind or surface water erosion. Strong semi-arid wind and rainfall events can greatly impact metal transport. Roughly 50% of particles by weight have diameters below the wind transportable threshold of 37 µm. It is thus plausible that these tailings may be dispersed to local populations supported by HYSPLIT modeling. Taken together, these results lend insight into the potential health and environmental impacts of Te.