17 alpha-ethynylestradiol (EE2) is a synthetic estrogen that is an endocrine disruptive toxicant in aquatic environments. The aim of this study was to determine whether metabolic rate influenced EE2 uptake in male killifish (Fundulus heteroclitus), based on the hypothesis that the mechanism of EE2 uptake at the gills is similar to that of oxygen. F. heteroclitus were exposed to 100 ng/L radiolabeled [H-3]EE2 for 2 h while swimming at 0, 15, and 40 cm/s. A positive linear correlation between the rates of oxygen consumption (MO2) and EE2 accumulation was seen (r(2) = 0.99,p < 0.01), with more EE2 taken up at higher swimming speeds, suggesting that oxygen uptake predicts EE2 uptake. EE2 tended to accumulate in the liver (where lipophilic toxicants are metabolized), the gall bladder (where metabolized toxicants enter bile), and the gut (where bile is received). In a subsequent experiment killifish were exposed to both hypoxic and hyperoxic conditions (PO2 = 70-80 Torr, and PO2 = 400-500 Torr respectively). Despite significant decreases in MO2 during hypoxia, EE2 uptake rates increased only slightly with hypoxia, but in individual fish there was still a significant correlation between MO2 and EE2 uptake. This correlation was lost during hyperoxia, and EE2 uptake rates did not change significantly in hyperoxia. Marked influences of salinity on EE2 uptake rate occurred regardless of the oxygen condition, with higher uptake rates in 50% seawater than in freshwater or 100% seawater. Tissue distribution of EE2 in these exposures may have been influenced by changes in tissue blood flow patterns and oxygen supply. These data will be useful in eventually constructing a predictive model to manage the optimal timing for discharge of EE2 from sewage treatment plants into receiving waters. (C) 2013 Elsevier B.V. All rights reserved.
