Implementing the tissue-based selenium standard in Gilbert Bay, Great Salt Lake: A case study of challenges and opportunities
Great Salt Lake’s Gilbert Bay has a numeric criterion for selenium to protect waterfowl, shore birds and other water-oriented wildlife including their necessary foodchain. The selenium criterion is a geometric mean of 12.5 mg/kg dry weight in bird eggs as determined by at least five eggs collected over a nesting season. While this criterion is appropriately protective—as determined by expert consensus—the implementation of an egg criterion within water quality programs brings unique challenges.
The extent to which birds are exposed to selenium is mediated by several complex physical and biological processes. Exposures starts as organisms encounter selenium in the water or sediment and is subsequently transferred up through intermediate steps in the food web and ultimately to birds. The available data relating the selenium concentrations in water to bird eggs is highly variable and difficult to interpret. In addition, current assessment methods require collection of bird eggs, which is time-consuming and invasive.
Birds by nature are quite mobile, which confounds efforts to determine the precise sources of selenium exposure. The Utah Division of Water Quality’s has ongoing efforts to refine implementation procedures of the tissue based standard to improve linkages to water quality programs, particularly to establish appropriate discharge permit limits that must be expressed as water concentrations. Extensive monitoring efforts are also ongoing to better understand selenium dynamics within Great Salt Lake. These ongoing efforts to evaluate threats of selenium to Great Salt Lake species will be discussed.