Measuring Total Mercury Through Freeze-Thaw Cycles.

Total mercury (THg) analysis of fish tissue requires the samples to be frozen for long-term storage or analyzed immediately after the fish sample has been obtained. Such rigid field sampling protocols do not account for the logistical challenges that can occur if sampling is conducted in remote areas or collaboratively via community-based monitoring initiatives. Here we present a study that examines the loss of THg from Walleye tissue that has thawed for 3 and 5 days, mimicking potential thaw during transport from remote locations. THg concentrations were not significantly influenced (Kruskal-Wallace, p-value > 0.05) by the thaw and refreeze events. The mean THg concentration per day group was 0.67 ug/g, SD = 0.03, 0.65 ug/g, SD = 0.01, and 0.72 ug/g, SD = 0.01 for the control (no thaw), 3-day thaw and 5-day thaw, respectively. Results from this study suggest the analytical integrity of samples may be maintained if freeze-thaw situations arise when conducting community-based mercury monitoring programs.

Vitellogenin Induction in Mucus from Brook Trout (Salvelinus fontinalis).

Induction of vitellogenin (VTG) is widely used as a biomarker of exposure of male or immature fish to chemicals that are agonists of the estrogen receptor (i.e., xenoestrogens). Analysis of VTG in samples of epidermal mucosa collected from fish is a non-invasive method for evaluating whether wild fish are exposed to xenoestrogens. In this study, the mean levels of VTG in the mucus of immature brook trout (Salvelinus fontinalis) collected from the Credit River in Ontario, Canada downstream of aging residential septic systems and in an agricultural watershed were 0.67 ng per mg protein, which was significantly elevated relative to the mean VTG levels of 0.22 ng per mg protein in the mucus of immature brook trout collected from a less impacted site. To validate the mucus assay, immature brook trout were exposed in the laboratory to 17α-ethinylestradiol (EE2) at nominal concentrations of 10, 50 and 100 ng/L and VTG levels in mucus from these fish showed a concentration-dependent increase relative to fish from the control treatment. This study illustrates the utility of this non-lethal method for assessing whether wild fish have been exposed in situ to xenoestrogens. Exposures to xenoestrogens from non-point sources may be impacting brook trout populations in urban watersheds in southern Ontario.

Biological Responses in Brook Trout (Salvelinus fontinalis) Caged Downstream from Municipal Wastewater Treatment Plants in the Credit River, ON, Canada.

To determine whether discharges of contaminants from municipal wastewater treatment plants (WWTPs) may be contributing to the decline in populations of brook trout (Salvelinus fontinalis) in the watershed of the Credit River in ON, Canada, we caged juvenile brook trout upstream and downstream of the WWTPs of the small communities of Acton and Orangeville. Levels of vitellogenin were significantly elevated in liver tissue of trout caged downstream of both WWTPs, indicating exposure to estrogenic substances. Levels of thiobarbituric acid reactive substances indicative of oxidation of lipids were elevated in the gill tissue of brook trout caged downstream of the Orangeville WWTP, and levels of total glutathione were significantly lower in the gills of brook trout caged downstream of the Acton WWTP. Both biomarkers are indicative of oxidative stress, although many constituents of wastewater could be responsible for these responses. More work is needed to determine whether discharges of wastewater are contributing to the decline of brook trout in the Credit River and other cold-water streams in the Lake Ontario catchment basin.