The effects of temperature and salinity on 17-α-ethynylestradiol uptake and its relationship to oxygen consumption in the model euryhaline teleost (Fundulus heteroclitus)

The synthetic estrogen 17-α-ethynylestradiol (EE2), a component of birth control and hormone replacement therapy, is discharged into the environment via wastewater treatment plant (WWTP) effluents. The present study employed radiolabeled EE2 to examine impacts of temperature and salinity on EE2 uptake in male killifish (Fundulus heteroclitus). Fish were exposed to a nominal concentration of 100 ng/L EE2 for 2 h. The rate of EE2 uptake was constant over the 2 h period. Oxygen consumption rates (MO2), whole body uptake rates, and tissue-specific EE2 distribution were determined. In killifish acclimated to 18 °C at 16 ppt (50% sea water), MO2 and EE2 uptake were both lower after 24 h exposure to 10 °C and 4 °C, and increased after 24 h exposure to 26 °C. Transfer to fresh water (FW) for 24 h lowered EE2 uptake rate, and long-term acclimation to fresh water reduced it by 70%. Both long-term acclimation to 100% sea water (32 ppt) and a 24 h transfer to 100% sea water also reduced EE2 uptake rate by 50% relative to 16 ppt. Tissue-specific accumulation of EE2 was highest (40–60% of the total) in the liver plus gall bladder across all exposures, and the vast majority of this was in the bile at 2 h, regardless of temperature or salinity. The carcass was the next highest accumulator (30–40%), followed by the gut (10–20%) with only small amounts in gill and spleen. Killifish chronically exposed (15 days) to 100 ng/L EE2 displayed no difference in EE2 uptake rate or tissue-specific distribution. Drinking rate, measured with radiolabeled polyethylene glycol-4000, was about 25 times greater in 16 ppt-acclimated killifish relative to FW-acclimated animals. However, drinking accounted for less than 30% of gut accumulation, and therefore a negligible percentage of whole body EE2 uptake rates. In general, there were strong positive relationships between EE2 uptake rates and MO2, suggesting similar uptake pathways of these lipophilic molecules across the gills. These data will be useful in developing a predictive model of how key environmental parameter variations (salinity, temperature, dissolved oxygen) affect EE2 uptake in estuarine fish, to determine optimal timing and location of WWTP discharges

► Both ethynylestradiol (EE2) uptake and oxygen consumption increased with increasing temperatures in Fundulus heteroclitus.
► Salinity altered EE2 uptake in Fundulus from reference conditions (18 °C, 16 ppt).
► EE2 accumulation was observed in the gut, liver and gall bladder after acute 2-h exposures, however this tissue specific pattern of uptake was not similar in rainbow trout (Oncorhynchus mykiss).