Superfund Research Program
Arsenic in Shallow Unstratified and Seasonally Stratified Urban Lakes: Mobility, Bioaccumulation and Ecological Toxicity
Final Progress Reports
This project has completed a full year of sampling in urban lakes impacted by the ASARCO copper smelter. The smelter operated in Tacoma, Washington for nearly 100 years and closed 31 years ago. Arsenic emitted by the smelter is still found in soils and lake sediments. Arsenic is a neurotoxic and carcinogenic chemical, and ranks at the top of contaminants of concern for human health. In impacted lakes, arsenic can move out of contaminated sediments into overlying water where it can then be taken up by aquatic organisms. Over the year, this project sampled water, sediment, and plankton in two stratified lakes (Angle Lake and North Lake) and two unstratified lakes (Lake Killarney and Steel Lake). In stratified lakes, arsenic mobilized from sediments remained sequestered in deep anoxic waters while in unstratified lakes, mobilized arsenic was mixed throughout the oxygenated water column. Since aquatic organisms primarily congregate in oxygenated waters, there was more spatial overlap between arsenic contamination and aquatic life in unstratified lakes. Consequently, phytoplankton and zooplankton in unstratified lakes accumulated almost an order of magnitude more arsenic than plankton in stratified lakes. Water quality guidelines set to protect human and environment health are currently based on maximum aqueous arsenic concentrations measured within a water body. These results indicate that arsenic concentrations in oxic water, rather than maximum concentrations (which occur in the bottom anoxic waters of stratified lakes), may serve as a more relevant metric for assessing arsenic bioavailability in aquatic systems.