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University of Washington

Superfund Research Program

Arsenic in Shallow Unstratified and Seasonally Stratified Urban Lakes: Mobility, Bioaccumulation and Ecological Toxicity

Project Leader: Rebecca B. Neumann
Grant Number: P42ES004696
Funding Period: 2015-2023
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Project Summary (2015-2017)

Arsenic, a priority Superfund contaminant, neurotoxicant and carcinogen, is a ubiquitous metalloid polluting many urban surface water bodies. However, the ecological implications of this contamination are unclear due to an incomplete understanding of arsenic bioavailability in urban waters, which are typically affected by nutrient- and organic-rich conditions. The objective of the project is to quantify spatiotemporal patterns and primary drivers of arsenic mobility, bioavailability and ecological toxicity in urban lakes.

The South-Central Puget Sound Lowland region offers an exceptional environment to study the environmental health impacts of urban metal(loid)-impacted aquatic ecosystems because it hosts an array of densely settled lakes with arsenic-contaminated waters that display remarkably different redox behaviors: seasonally stratified and anoxic to well mixed and oxic. Although elevated levels of arsenic usually occur in anoxic waters at the bottom of thermally-stratified lakes during the summer, a lake in the study region maintains elevated aqueous arsenic concentrations under oxic conditions. The situation raises questions about the physical and geochemical processes controlling arsenic chemistry in oxic waters of shallow, unstratified lakes, and also about the resulting bioavailability of arsenic to aquatic life. The typical isolation of elevated arsenic concentrations to deep, anoxic waters may act to minimize biological exposure to arsenic, whereas contamination throughout an oxic, unstratified lake may enhance biological exposure.

Within this context, researchers are:

  • Determining the physical and biogeochemical conditions that promote arsenic mobilization from sediments and maintain elevated aqueous concentrations within shallow, unstratified oxic lakes;
  • Identifying the physical and chemical factors that control arsenic bioaccumulation in both stratified and unstratified lakes; and
  • Assessing toxicity of arsenic within both stratified and unstratified lakes using established molecular biomarkers indicating arsenic injury.


The research team is using phytoplankton, the base of the aquatic food web, as an indicator species for assessing biological exposure to and ecotoxicity of arsenic. They hypothesize that arsenic contamination in oxic waters of unstratified lakes is promoted and maintained by anthropogenic inputs of nutrients and organic matter, and that ecological toxicity is enhanced in oxic unstratified lakes compared to seasonally stratified lakes. Researchers are explicitly linking measurements of physical, chemical, and biological lake properties with investigations of arsenic bioaccumulation and ecological toxicity in phytoplankton. This approach combines biogeochemical and eco-toxicological methods and uses molecular biomarkers to identify arsenic injury. Results from this project will provide information needed to establish effective water quality criteria, develop robust lake management strategies, and foster adoption of biomarker techniques.

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