Characteristics of Ligands for the Ah Receptor and Sex Steroid Receptors in Hepatic Tissues of Fish Exposed to Bleached Kraft Mill Effluent

Male white sucker (Catostomus commersoni) from a population exposed to effluent from a bleached kraft mill and from a reference site were held in effluent or clean water for 4 d. To investigate bioavailable bioactive compounds, hepatic tissues were extracted and fractionated according to octanol−water partition coefficient (K ow) using reverse phase HPLC. Fractions were tested in vitro for the presence of compounds functioning as ligands for (i) the aryl hydrocarbon receptor (AhR) using mixed function oxygenase (MFO) induction in H4IIE cells, (ii) the estrogen receptor (ER) isolated from rainbow trout (Oncorhynchus mykiss) liver, (iii) the androgen receptor (AR) isolated from goldfish (Carassius auratus) testes, and (iv) sex steroid binding protein (SSBP) isolated from goldfish plasma. Polychlorinated dioxins and furans accounted for MFO activity of liver contaminants of log K ow > 5 but multiple nondioxin AhR ligands of log K ow 2 to 5 also caused significant induction. Compounds of log K ow 2 to 5 in livers of exposed fish exhibited significant competition for the AR, ER, and SSBP, indicating potential effects on hormone signaling and transport. The absence of most ligands for the AhR and sex steroid receptors in tissues of preexposed fish held in clean water demonstrates clearance of these compounds after short-term removal from effluent. This study demonstrates the utility of using wild fish tissue burdens to study the lipophilicities and the pharmacokinetic properties of bioavailable compounds functioning as ligands for the AhR and sex steroid hormone receptors.