Effects of exposure to municipal wastewater in situ on the reproductive physiology of the fathead minnow (Pimephales promelas)

Effects of representative central Michigan wastewater treatment plant (WWTP ) effluents on the reproductive physiology of fathead minnows (Pimephales p romelas) were assessed in situ by measuring plasma concentrations of vitell ogenin (VTG), 17 beta-estradiol (E2), and testosterone (T), and evaluating gonad histology and male secondary sex characteristics. Caged adult male an d female fathead minnows were exposed for 3 weeks to WWTP effluent. One riv erine site and one lacustrine site were included as references for comparis on to WWTP sites. Plasma concentrations of VTG, E2, and T in female fish, q uantified by enzyme-linked immunosorbent assay (ELISA), were greater at the lacustrine site than the riverine site or WWTP sites. None of the male fis h had mean plasma VTG concentrations similar to that observed in females. M ost VTG concentrations in male fish were less than the VTG ELISA detection limit. Female plasma concentrations of E2 were similar among riverine and W WTP sites. Plasma concentrations of E2 in male fish were greater than the r iverine site at all WWTP sites except the Williamston site, but were not si gnificantly different from the lacustrine site. Concentrations of T in fema le and male fish were similar among riverine and exposure sites. No trends in hormone concentrations, male secondary sex characteristics, or gonad his tology could be attributed to putative endocrine disrupter exposure in WWTP effluent. The results indicate that the risk for estrogen agonist exposure below these central Michigan WWTPs is small.