The estrogenic effect of butylparaben was investigated in a rainbow trout Oncorhynchus mykiss test system. Butylparaben was administered orally to sexually immature rainbow trout every second day for up to 10 days in doses between 4 and 74 mg kg(-1) 2 d(-1) and in the water at 35 and 201 microgram l(-1) for 12 days. Plasma vitellogenin was measured before and during the exposures and the concentrations of butylparaben in liver and muscle were determined at the end of experiments. Increases in average plasma vitellogenin levels were seen at oral exposure to 9 mg butylparaben kg(-1) 2 d(-1). The ED50 values for increase in vitellogenin synthesis were 46, 29 and 10.5 mg butylparaben kg(-1) 2 d(-1), respectively, at day 3, 6 and 12. Exposure to 201 microgram butylparaben l(-1) increased vitellogenin synthesis, but exposure to 35 microgram l(-1) did not. Butylparaben showed little tendency to bioaccumulation in rainbow trout; less than 1 per thousand of the total amount of butylparaben administered orally at 51 mg kg(-1) 2 d(-1) over the 12 days experimental period was retained in liver at the end of the experiment. After 12 days exposure to 35 and 201 microgram butylparaben l(-1), plasma concentrations were 9 and 183 microgram l(-1), respectively, and for the fish exposed to 201 microgram l(-1) there was a positive correlation between concentrations of vitellogenin and butylparaben in the plasma. On the assumption that butylparaben removed from the water phase during water exposure were taken up into the fish, butylparaben uptake rates in the fish exposed to 35 and 201 microgram butylparaben l(-1) were 13 and 78 mg kg(-1) day(-1), respectively.

Previous studies conducted in the Elk River watershed showed that selenium concentrations are higher in aquatic biota in lentic compared to lotic habitats of the system having similar water selenium concentrations. Studies have also shown that water selenium concentrations have increased over time (∼10% per year) and recent annual average concentrations have ranged up to 0.044 mg/L in areas downstream from mine discharges. For the present study, trophic transfer of selenium was characterized in lotic versus lentic habitats using concentrations measured in field‐collected samples and assuming a three‐step food chain of water to the base of the food web (biofilm), to benthic invertebrates, and then to westslope cutthroat trout (WCT) ovaries. Food chain models were developed for each habitat type (lotic and lentic) by combining linear regression equations for the three transfer relationships, allowing for prediction of fish ovary concentrations from water concentrations. Greater accumulation of selenium in lentic areas was mostly attributable to greater uptake at the base of the food chain compared to lotic areas. Enrichment/trophic transfer factors for selenium at all levels of the lotic and lentic food chains decreased and then became near constant as exposure concentrations increased. The lotic model predicted little increase in WCT ovary selenium concentrations over an eightfold increase in water concentrations (∼0.005–0.040 mg/L), accounting for the lack of observed increase in within‐area fish tissue concentrations over time despite increasing trends in water concentrations. Environ. Toxicol. Chem. 2012;31:672–680. © 2011 SETAC