PNNL

Abstract

It is well known that endocrine disrupting compounds (EDCs) present in wastewater treatment plant (WWTP) effluents interfere with reproduction in fish, including altered gonad development and induction of vitellogenin, a female-specific egg yolk protein precursor produced in the liver. As a result, studies have focused on the effects of EDC exposure on the gonad and liver. However, impacts of environmental EDC exposure at higher levels of the hypothalamic-pituitary-gonad (HPG) axis are less well understood. In this study, the effects of WWTP effluent exposure on pituitary gonadotropin (Gth) mRNA expression were investigated in juvenile coho salmon (Oncorhynchus kisutch). First, a controlled 72-hr exposure to 17a-ethynylestradiol (EE2) and trenbolone (TREN) was performed to evaluate the response of juvenile coho salmon to EDC exposure. Second, juvenile coho salmon were exposed to 0, 20 or 100% effluent from 8 WWTPs from the Puget Sound, WA region for 72 hrs. Juvenile coho salmon exposed to 2.5 and 12 ng EE2/L had 16-fold and 184-fold higher lhb mRNA levels relative to control fish. In contrast, vtg mRNA levels were dramatically increased 5,929-fold, but only in response to 12 ng EE2/L and fshb mRNA levels were not altered by any of the treatments. Similarly, in the WWTP effluent exposures, lhb mRNA levels were significantly elevated in fish exposed to 5 of the WWTP effluents. Transcript levels of vtg, on the other hand, were not affected by any of the WWTP effluent exposures. In addition, mean levels of natural and synthetic estrogens in fish bile were consistent with pituitary lhb expression, suggesting that the observed lhb induction may be due to estrogenic activity of the WWTP effluents. These results suggest that lhb gene expression may be a more sensitive index of exposure to estrogenic chemicals than hepatic vtg under short-term exposure studies with juvenile coho salmon. Further work is needed on the kinetics and specificity of lhb induction to evaluate its utility as a potential indicator of estrogen exposure in immature fish.