LAUSR

Geothermal waters often are enriched in trace metal(loid)s, like arsenic, antimony, molybdenum, and tungsten. Presence of sulfide can lead to formation of thiolated anions, however, their contributions to total element concentrations typically remain unknown because non-suitable sample stabilization and chromatographic separation methods convert them to oxyanions. Here, the concurrent widespread occurrence of thioarsenates, thiomolybdates, thiotungstates, and thioantimonates, in sulfide-rich hot springs from Yellowstone National Park and Iceland is shown. More thiolation was generally observed at higher molar sulfide to metal(loid) excess (Iceland>Yellowstone). Thioarsenates were the most prominent and ubiquitous thiolated species, with trithioarsenate typically dominating arsenic speciation. In some Icelandic hot springs, arsenic was nearly quantitatively thiolated. Also for molybdenum, thioanions dominated over oxyanions in many Icelandic hot springs. For tungsten and antimony, oxyanions typically dominated and thioanions were observed less frequently, but still contributed up to a few tens of percent in some springs. This order of relative abundance (thioarsenates>thiomolybdates>thiotungstates≈thioantimonates) was also observed when looking at processes triggering transformation of thioanions like mixing with non-geothermal waters or H2S-degassing and oxidation with increasing distance from a discharge. Even though to different extents, thiolation contributed substantially to speciation of all four elements studied, indicating their analysis is required when studying geothermal systems.