Bioavailability and uptake of smelter emissions in freshwater zooplankton in northeastern Washington, USA lakes using Pb isotope analysis and trace metal concentrations.

The upper Columbia River and associated valley systems are highly contaminated with metal wastes from nearby smelting operations in Trail, British Columbia, Canada (Teck smelter), and to a lesser extent, Northport, Washington, USA (Le Roi smelter). Previous studies have investigated depositional patterns of airborne emissions from these smelters, and documented the Teck smelter as the primary metal contamination source. However, there is limited research directed at whether these contaminants are bioavailable to aquatic organisms. This study investigates whether smelter derived contaminants are bioavailable to freshwater zooplankton. Trace metal (Zn, Cd, As, Sb, Pb and Hg) concentrations and Pb isotope compositions of zooplankton and sediment were measured in lakes ranging from 17 to 144 km downwind of the Teck smelter. Pb isotopic compositions of historic ores used by both smelters are uniquely less radiogenic than local geologic formations, so when zooplankton assimilate substantial amounts of smelter derived metals their compositions deviate from local baseline compositions toward ore compositions. Sediment metal concentrations and Pb isotope compositions in sediment follow significant (p < 0.001) negative exponential and sigmoidal patterns, respectively, as distance from the Teck smelting operation increases. Zooplankton As, Cd, and Sb contents were related to distance from the Teck smelter (p < 0.05), and zooplankton Pb isotope compositions suggest As, Cd, Sb and Pb from historic and current smelter emissions are biologically available to zooplankton. Zooplankton from lakes within 86 km of the Teck facility display isotopic evidence that legacy ore pollution is biologically available for assimilation. However, without water column data our study is unable to determine if legacy contaminants are remobilized from lake sediments, or erosional pathways from the watershed.

A positive test of East Antarctica-Laurentia juxtaposition within the Rodinia supercontinent.

The positions of Laurentia and other landmasses in the Precambrian supercontinent of Rodinia are controversial. Although geological and isotopic data support an East Antarctic fit with western Laurentia, alternative reconstructions favor the juxtaposition of Australia, Siberia, or South China. New geologic, age, and isotopic data provide a positive test of the juxtaposition with East Antarctica: Neodymium isotopes of Neoproterozoic rift-margin strata are similar; hafnium isotopes of approximately 1.4-billion-year-old Antarctic-margin detrital zircons match those in Laurentian granites of similar age; and a glacial clast of A-type granite has a uraniun-lead zircon age of approximately 1440 million years, an epsilon-hafnium initial value of +7, and an epsilon-neodymium initial value of +4. These tracers indicate the presence of granites in East Antarctica having the same age, geochemical properties, and isotopic signatures as the distinctive granites in Laurentia.