According to a new study published today in the Proceedings of the National Academy of Sciences 40 years of less mercury consumption, less emissions, and less pollution in the Great Lakes region have not caused any comparable declines World led amount of mercury that accumulates in big game fish.
Researchers, including those at the University of Wisconsin-Madison, say it's mainly due to aquatic invasive species in Lake Michigan – mostly quaga and zebra mussels – that have upset the food web and forced fish, atypical, with mercury to search for enriched food sources.
Mercury or methylmercury, as found in fish, is a neurotoxin that can damage the nervous system when consumed by humans or animals. The study has implications for health officials and natural resource managers who need the best possible science to make their decisions, says senior author Ryan Lepak, a postdoctoral fellow at the UW-Madison Aquatic Sciences Center (ASC).
"Our work highlights that mercury concentrations in fish can not be predicted by emissions inventories alone, and other factors such as changes to the food web are needed to get a complete picture," says Lepak, a US Environmental Protection Agency Toxicology and Ecology Division is based in Duluth, Minnesota. "All five Great Lakes have recommendations on fish consumption because mercury poses a disproportionate risk to the health of children and pregnant women."
Lepak and co-author James Hurley, ASC director, were interested in the reasons for the increased rates of mercury concentrations in larger fish, such as lake trout, despite measures that have largely reduced mercury emissions into the waters of the Great Lakes.
To understand the history of mercury in Great Lakes fishes and determine the sources of contaminants, the research team conducted a combination of mercury, nitrogen and carbon isotope analyzes, which Lepak calls a "fingerprint", on samples of lake trout which were archived from 1978 to 2012.
Over the same period, Lepak also studied archived sediment samples from the lake to compare the trends of mercury sources with sediments and fish.
The study years covered the period in which hospitals and municipalities stopped burning waste, which spared the Great Lakes from additional mercury pollution. The researchers expected that the decline would reduce the accumulation of methylmercury in fish.
However, Hurley said that the unique fingerprinting technique from the 1980's onwards showed measurable changes in mercury concentrations in the lake's archival fish and sediment samples, although the sediment record revealed a reduced mercury loading.
Hurley notes that this despite the fact that after about 1990, mercury emissions and uses were significantly reduced and led to a reduction in mercury exposure in the Great Lakes.
Analysis shows that the cause of this is invasive trichosite Shells, zebras, and quaggs exploded in Lake Michigan in the 1990s, and trillions of shells have been estimated to cause significant shifts in the feeding habits of lake trout.
Dreissenides have filtered and consumed wild phytoplankton, and had cleared Lake Michigan's waters, fish had to look deeper for food waters in the offshore zone of the lake and at the bottom of the lake in coastal waters.The food that the fish finds here provides less energy but is enriched with mercury. 19659005] "People like to do sport fishing for lake trout the bigger the fish, the more mercury has accumulated in fillets of this species, "explains Lepak. "Unfortunately, when people decide to serve fish for dinner, people have to take into account the pollutant content."
The mercury content in fish varies with the water content in lakes
Ryan F. Lepak el al., "Changes in the source of mercury and changes in the food web are altering the contamination signatures of Lake Michigan predators", PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1907484116
Invasive Species Short Benefits Mercury Reduction in the Great Lakes (2019, 4 November)
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