Points Along the Reaction Path: Complementary Approaches to Understanding Arsenic Transitions in Two Surficial Environments Impacted by Mining Activities
Abstract
In natural settings that exhibit chemical and hydrologic complexity, As concentration and speciation depend on system characteristics that respond to seasonal events and/or anthropogenic influences. As arsenic-bearing minerals decompose, As may be introduced to aqueous solutions with potential for human exposure or ecological impacts. This transformation may be attenuated by sorption, or precipitation of other phases. Two examples illustrate how laboratory experiments, field observations, spectroscopy, and geochemical modeling synergistically contribute to predictions of temporal change in mine-impacted environments. In both cases X-ray absorption spectroscopy (XAS) has proven valuable for determining As-mineral associations, which are critical to As release and transport pathways. Field and analytical/spectroscopic observations at a high-As pit lake at the Jamestown Mine (Tuolumne County, California) have informed development of an integrated hydrogeochemical model of pit lake evolution. Water fluxes in the pit lake exhibit strong seasonal variation, and pit wall characteristics also change as efflorescent salts build up and are eroded in response to seasonal differences in temperature and rainfall. The model incorporates lake stratification and mixis events as well as interaction with the pit wall rock in the context of water fluxes from ground water, precipitation, and evaporation. The use of XAS to determine As associations in smelter-impacted soils on Vashon-Maury Island, Washington has provided insight into the potential for As mobilization in the vadose zone. Arsenic associations with Al-oxyhydroxides and/or phyllosilicates such as clinochlore imply that As initially released from the smelter as particulate As(III) and As(V) oxides was oxidized, dissolved, and adsorbed onto soil minerals and colloids. Physical transport of As oxide particles and As adsorbed on soil colloids may account for limited downward migration of As within the soil column.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.H24C..03S
- Keywords:
-
- 1845 Limnology;
- 1875 Unsaturated zone;
- 1030 Geochemical cycles (0330);
- 1045 Low-temperature geochemistry;
- 1065 Trace elements (3670)