Toxicological studies are often hampered by concerns of fish residency in the industrial effluent being evaluated. Contaminants in muscle or visceral tissue are useful indicators of recent exposure, but depuration, metabolic transformation, and tissue recompartmentalization of contaminants makes their use as temporal markers tenuous. Otoliths are metabolically stable and can provide temporal resolution for exposure to some elements that are incorporated into their calcified structure, including the divalent cations Sr, Zn, and Mn. Here we provide the first determinations of selenium, an anion in biological systems, in the otoliths of rainbow trout captured from a site receiving runoff with elevated selenium from a coal mine operation. Concentrations of selenium in annual growth zones of otoliths suggest that fish from the mine-impacted system are recent immigrants from nearby reference streams not receiving selenium-bearing effluent. Read less