The influence of legacy contamination on the transport and bioaccumulation of mercury within the Mobile River Basin.

Past industrial use and subsequent release of mercury (Hg) into the environment have resulted in severe cases of legacy contamination that still influence contemporary Hg levels in biota. While the bioaccumulation of legacy Hg is commonly assessed via concentration measurements within fish tissue, this practice becomes difficult in regions of high productivity and methylmercury (MeHg) production, like the Mobile River Basin, Alabama in the southeastern United States. This study applied Hg stable isotope tracers to distinguish legacy Hg from regional deposition sources in sediments, waters, and fish within the Mobile River. Sediments and waters displayed differences in δ202Hg between industrial and background sites, which corresponded to drastic differences in Hg concentration. Sites that were affected by legacy Hg, as defined by δ202Hg, produced largemouth bass with lower MeHg content (59-70%) than those captured in the main rivers (>85%). Direct measurements of Hg isotopes and mathematical estimates of MeHg isotope pools in fish displayed similar distinctions between legacy and watershed sources as observed in other matrices. These results indicate that legacy Hg can accumulate directly into fish tissue as the inorganic species and may also be available for methylation within contaminated zones decades after the initial release.

Developmental effects of a municipal wastewater effluent on two generations of the fathead minnow, Pimephales promelas.

Municipal wastewater effluents have been shown to contain a variety of anthropogenic compounds, many of which are known to display estrogenic properties. While multiple laboratory studies have shown the effects of such compounds on an individual basis at elevated concentrations, little research has attempted to characterize the effects of exposure to environmentally relevant mixtures of estrogenic compounds. The current study examined the effects of long-term exposure to graded concentrations (0, 50, 100%) of wastewater effluent on the fathead minnow, Pimephales promelas. The F1 generation was cultured in control water to test for transgenerational effects from parental exposure to wastewater effluent. Total estrogenic activity in the wastewater was determined to be approximately 1.7ng/L 17beta-estradiol equivalents. Survival, growth, and reproduction in the parent generation were not affected by exposure to the wastewater treatments. An increase in the gonadosomatic index and a reduction in the expression of secondary sex characteristics in male fathead minnows exposed to 100% wastewater in the parent generation were observed. Conversely, the expression of secondary sex characteristics was greater in males from the F1 generation of wastewater-exposed parents. Additionally, a positive relationship between parental exposure to wastewater and the onset of reproductive activity in the F1 generation was observed. Results of this study suggest that exposure to wastewater effluent did not pose a significant threat to the successful growth, development, and reproduction of the fathead minnow. Early onset of reproductive activity observed in the F1 generation of wastewater-exposed parents in subsequent generations should be studied further.

The developmental effects of a municipal wastewater effluent on the northern leopard frog, Rana pipiens.

Wastewater effluents are complex mixtures containing a variety of anthropogenic compounds, many of which are known endocrine disruptors. In order to characterize the developmental and behavioral effects of such a complex mixture, northern leopard frogs, Rana pipiens, were exposed to a range of concentrations (0%, 10%, 50%, 100%) of municipal wastewater effluent from the egg stage through metamorphosis. The estrogenic activity of the effluent was quantified by the calculation of an estradiol (E2) equivalency (EEQ) factor and was determined to be equivalent to 1.724+/-2.103ng/L E2. Individuals from the 50% and 100% wastewater treatments took significantly longer to reach metamorphosis than individuals in the 0% and 10% treatments. An increased incidence of male testicular oocytes was observed in the 50% and 100% treatments when compared to the control treatment. Morphological changes in the thyroid glands of 100% wastewater-treated individuals were also noted. No effects of wastewater exposure on growth, sex ratio, swim speed, startle response, or female gonadal development were observed. These results suggest that municipal wastewater effluent can alter the timing of the metamorphic process and impact male sexual development in R. pipiens.

Biochemical and behavioral effects of diazinon exposure in hybrid striped bass.

The effects of environmental stimuli on biochemical processes may influence behavior. Environmental contaminants that alter behavior can have major impacts on populations as well as community structures by changing species' interactions. One important behavior is the ability to capture prey. We hypothesized that sublethal exposure to diazinon, an organophosphate pesticide, may lead to feeding behavior abnormalities in hybrid striped bass (Morone saxatilis x M. chrysops) through inhibition of brain acetylcholinesterase (AChE) activity. This can potentially reduce the organism's survival by affecting its ability to find and capture food. To test this hypothesis, bass were exposed to diazinon for 6 d, followed by a 6-d recovery period in clean water. Brain AChE activity and the ability of bass to capture prey fathead minnows (Pimephales promelas) were measured every third day. Exposed fish exhibited a concentration- and duration-dependent decrease in ability to capture prey. While bass in all diazinon treatment groups had significantly inhibited brain AChE activity, only the medium and high treatment groups showed a dose- and time-dependent increase in time to capture prey. Acetylcholinesterase activity also decreased in an exposure duration- and concentration-dependent manner. The AChE levels in exposed fish did not recover to control levels during the 6-d recovery period. These results suggest that sublethal exposure to AChE-inhibiting substances may decrease the ecological fitness of hybrid striped bass by reducing their ability to capture prey.