The effects of persistent and pseudopersistent pollutants on reproduction in Ceriodaphnia dubia and fish

I studied several persistent and pseudopersistent pollutants and their effects on reproduction in fish and invertebrates. The persistent pollutants, methylmercury (MeHg) and polychlorinated biphenyls (PCBs), are both found at levels of concern in fish tissues and are implicated as endocrine disrupting compounds. I examined the reproductive effects of exposure to MeHg or PCBs on reproduction in fathead minnows (Pimephales promelas). Dietary exposure to MeHg, at environmentally relevant concentrations, reduced fathead minnow reproduction by decreasing the number of breeding pairs that spawned during a 21 day period. I also saw a significant increase in oocytes undergoing atresia in female ovaries at dietary MeHg concentrations of 6.55 and 12.88 mug/g (dry weight). PCBs in the form of the commercial mixture Aroclor 1242 had no measurable effect on fathead minnow reproduction.Wastewater effluent contains estrogenic compounds, often in complex mixtures, that are associated with reproductive abnormalities in wild fish populations. I exposed the sentinel invertebrate Ceriodaphnia dubia to the natural estrogen 17beta-estradiol (E2), a synthetic estrogen, ethinylestradiol (EE2), and a synthetic progestin, medroxyprogestone. These compounds had no significant effect on reproduction and survival during the chronic exposure of C. dubia, even at 106 times the concentrations that reproductive effects are demonstrated in many fish species. C. dubia is used for monitoring the toxicity of wastewater effluent, but they appear to be insensitive to synthetic and natural vertebrate hormones.I exposed reproducing pairs of medaka to mixtures of the environmental estrogens Nonylphenol (NP), EE2, and E2, as well as treatments of equivalent estrogenicity to the mixtures that were composed of E2 alone. Relative estrogenicity was a good model for predicting some, but not all, reproductive responses. Reproducing medaka exposed to mixtures of estrogenic compounds and equipotent treatments of estradiol alone had very similar responses in terms of mortality and reproduction. However, mixtures of NP, E2, and EE2 elicited a smaller vitellogenic response than equipotent concentrations of E2 alone.Several of the persistent and pseudopersistent pollutants studied alter fish reproduction at environmentally relevant concentrations. However, the link between adverse reproductive effects found in the lab and population level effects in wild fish remains to be established.