Guidance on assessing the potential impacts of selenium in freshwater ecosystems.

This article focuses on current approaches and best practices for monitoring and assessing ecological risks of environmental selenium (Se) contamination in North American freshwater systems. It emphasizes that Se bioaccumulates primarily through dietary exposure, with reproductive impairment in fish—mediated by maternal transfer of Se to eggs—being the most sensitive endpoint for ecological risk assessment. The article outlines criteria for selecting sentinel fish species based on dietary pathways, reproductive biology, and habitat use, and discusses the use of mature eggs as the most reliable tissue for Se toxicity evaluation, while also reviewing alternative tissues and juvenile monitoring. Additionally, it addresses the role of abiotic (water, sediment) and lower trophic level (macroinvertebrates, biofilm) sampling to complement fish tissue data or serve as proxies when fish sampling is not feasible, highlighting the importance of site-specific factors such as habitat type and Se speciation in designing effective monitoring programs.