HR: 14:00h
AN: H43D-03    [Abstracts]
TI: Tracing Cadmium in the Environment: an Evolving Stable Isotope Approach
AU: * Bullen, T D
EM: tdbullen@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Bouse, R M
EM: rmbouse@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Brown, C L
EM: clbrown@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Croteau, M
EM: mcroteau@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Luoma, S N
EM: snluoma@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Topping, B R
EM: btopping@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: Cadmium (Cd) is a trace constituent in rocks and waters, and like many transition metals is an essential dietary nutrient at low levels but highly toxic in elevated doses. In many respects, cadmium behaves chemically like calcium (Ca) and thus substitutes for Ca in liquid-solid partitioning reactions and generally follows Ca through biogeochemical cycles and metabolic processes. Cd is comprised of 8 stable isotopes, and given the isotopic systematics of environmental Ca it is likely that variations in the stable isotope composition of Cd in natural materials will result from both inorganic and biologic processes. In order to assess the potential of Cd isotope variations to reveal information about sources, metabolic and biogeochemical pathways and fates of environmental Cd, we have initiated a broad study of the stable isotope composition of Cd in a variety of natural and anthropogenically-influenced systems. As an example, here we report the results of the first systematic study of the stable isotope composition of Cd in biologic materials. We focused on the isotopic variability of Cd in tissues of two species of clam collected from the San Francisco Bay estuary, Potamocorbula amurensis which resides in brackish water and Corbicula fluminea which resides in fresh and slightly brackish water. Both clam species concentrate Cd in their soft and hard tissues. During both low-flow conditions in August and high-flow conditions in April, δ¹¹⁶Cd of soft tissues of Potamocorbula was consistently negative and increased down-estuary with increasing salinity (δ¹¹⁶Cd is defined as the per mil difference of the ¹¹⁶Cd/¹¹⁰Cd ratio between a sample and our standard, igneous rock BIR-1). Samples collected in August were systematically displaced to higher δ¹¹⁶Cd than those collected in April. Soft tissues of Corbicula collected in both August and April from upstream, fully fresh-water sampling sites had identical δ¹¹⁶Cd, while soft tissues of Corbicula collected from our site at the fresh water-brackish water interface had variable δ¹¹⁶Cd that was approximately 0.4‰ less negative than that of co-sampled Potamocorbula. These results point to a variety of potential controls on the isotopic distribution of Cd, including differences in aqueous speciation of Cd in saline and fresh waters, species-specific and temporal variations of nutritional sources and distribution of Cd between soft and hard tissues, and changing influences of Cd contamination to the ecosystem.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2005 Joint Assembly