Monster Seminar JAM - The Contamination of Freshwater Fishes with Pesticides and Mercury
Dr. David W. Schindler
Department of Biological Sciences, University of Alberta
Freshwater fishes of temperate and arctic regions have been found to contain high levels of toxic pollutants such as DDT, HCH, toxaphene, PCBs and other Persistent Organic Pollutants, (POPS) and mercury. In some lakes, concentrations are high enough to potentially affect the health of humans and other fish-eating predators.
Several studies have shown that these pollutants are transported long distances in the atmosphere. Atmospheric trajectories suggest that Eurasia may be an important source area for western Canada, although there are also regional sources of some contaminants. Semi-volatile POPs appear to migrate from warmer to colder regions as the result of cold condensation. Although the concentrations of POPs in rain and snow are only a few parts per trillion, biomagnification in long aquatic food chains of polar regions causes POPs to reach concentrations in predators that are as much as a million times higher than in precipitation.
In contrast, the high concentrations of POPs in fish from subalpine Bow Lake in Banff National Park could not be explained by biomagnification. Instead, cooler temperatures and greater precipitation at high altitude caused increased deposition of POPs. Melting of glacial strata that had been contaminated with POPs the mid 20th century also deliver large quantities of POPs to lakes. For the more volatile pollutants, cold lake surfaces also act as condensers, allowing direct inputs from gaseous sources.
Forest fires cause increased delivery of mercury and nutrients from burned catchments to freshwaters. The pulse of nutrients causes increased aquatic production, which results in increased recruitment of young of the year fish. The resulting increase in piscivory caused increased mercury in fishes, requiring consumption advisories to be needed for some species. The increased inputs of mercury also contributed, to the mercury burden, but to a lesser degree.
Date and Time:
November 10, 2005,
11:00 am - 12:30 pm