Bioaccumulation and trophic transfer of selenium in a large oligotrophic river

In flowing waters with elevated selenium concentrations, fish are often considered to be at risk from selenium toxicity owing to dietary exposure and accumulation in ovarian tissues and subsequent deformities in developing larvae. We studied selenium throughout components of the aquatic food webs at geomorphically distinct locations along the oligotrophic Kootenai River (Montana and Idaho, USA), a river with moderately elevated dissolved selenium concentrations (∼ 1 µg/L). Components included water, sediment, freshly accrued biofilms, in situ periphyton, sestonic detritus, aquatic invertebrates, and fish, with spring and fall sampling. Selenium concentrations were similar among the sediment, biofilm, periphyton, and detritus samples. Among the aquatic invertebrates, the highest selenium concentrations were observed in Paraleptophlebia sp. mayflies and oligochaetes. No consistent concentration patterns with season or feeding traits were observed. Fish tissue selenium concentrations were highly variable among species and tissue type. Selenium in fish tissues tended to be highest in livers of rainbow trout and mountain whitefish relative to ovarian, muscle, and carcass tissues. With northern pikeminnow, redside shiner, and slimy sculpin, selenium concentrations tended to be highest in ovarian tissues. The trophic transfer factors of selenium from particulates to invertebrates and fish was higher in the lotic sites than in the lentic site. The results question the validity of the lotic/lentic risk paradigm for selenium beyond the small stream versus wetland/pond settings from which the paradigm was developed. Potential alternative monitoring approaches are illustrated using aquatic invertebrates or the food web monitoring results to derive monitoring targets for selenium in water or invertebrate tissue that could avoid the need to kill fish to assess whether fish protection guidelines are met.