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New Approach to Evaluating Selenium Toxicity in the Environment

Cove of the November 15, 2009, issue of Environmental Science and Technology
USGS scientists Samuel N. Luoma's and Theresa S. Presser's article Emerging opportunities in management of selenium contamination: Integrating the chemistry of selenium with its biology and ecotoxicology gives indications on how to regulate its environmental levels. was the feature article in the November 15, 2009, issue of Environmental Science and Technology. (Cover image published by ACS Publications.

ecological risk assessment for a specific predator species must consider all three factors involved in toxicity:

  1. the likelihood of high exposures of the organism in the environment as determined by its feeding habits (viz does its prey efficiently bioaccumulate Se?);
  2. the inherent sensitivity of the species relative to concentrations in its reproductive tissues as accumulated from diet; and
  3. the demographics of the organism in terms of susceptibility to a reproductive toxicant."

Luoma and Presser, 2009

A new unified approach to evaluating the toxicity of selenium could help ecologists faced with varied and inconsistent approaches to assessing the toxicity of selenium in rivers, estuaries, and other water bodies. A team of U.S. Geological Survey (USGS) scientists proposed an ecosystem-scale model of the fate of selenium in the environment. The model quantifies how selenium is transferred from water and into predatory fish and birds through dietary uptake. The model integrates the chemistry of biological and geological systems and the physiological factors that control how various animals within food webs bioaccumulate selenium.

From Water To Predators: It's the Pathway That's Important

The approach shows that environmentally safe concentrations of selenium dissolved in water vary among ecosystems because the factors that affect whether selenium reaches toxic levels in fish and birds depends on the unique ecological and chemical conditions in each ecosystem. For example, the amount of selenium transferred within a local food web will differ depending on the species involved because different species bioaccumulate selenium at different rates and amounts. The unified approach is implemented in a computer model. The model provides a tool that ecologists, regulators, water resource managers, and other environmental professionals can use to:

  • assess a site-specific ecological problem or occurrence of selenium exposure, and
  • develop sound policies and guidelines regarding the ecological fate of selenium in the environment.

What Makes the Model Unique?

The model is unique because it integrates:

  • the environmental chemistry of different forms of selenium (speciation),
  • the transformation of dissolved selenium to particulate material,
  • how much selenium enters the food web at its very base,
  • the bioavailability of selenium,
  • the bioaccumulation of selenium in aquatic invertebrates (animals without backbones), and
  • the transfer of selenium from organism to organism (trophic transfer) within food webs all the way to predatory fish and birds.

Each trophic level (the placement of an organism within a food web or what an organism eats and what eats it) in the model is assigned a trophic transfer factor. These factors are different for each organism in the simulated food web. For example, a clam bioaccumulates selenium at a different rate than an insect, but both are prey for fish and birds. The model has been validated using 29 case studies. The development of the model is part of collaborative investigations with the U.S. Environmental Protection Agency and U.S. Fish and Wildlife Service.


Luoma, S.N., and Presser, T.S., 2009, Emerging opportunities in management of selenium contamination: Environmental Science & Technology, v. 43, no. 22, p. 8483-8487, doi:10.1021/es900828h.

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