Mercury and cyanotoxins in Lake Champlain pose health concerns to humans and the ecosystem. Mercury poisoning through the consumption of contaminated fish has been well documented for more than half a decade, typically with top predators posing the greatest threat. And while the most common route of cyanotoxin intoxication is exposure through drinking water and recreational contact, research has shown cyanotoxin levels in fish can reach concentrations that pose health risks, if consumed. The aim of this study was two-fold, 1) to reassess fish mercury throughout the lake to determine which species at what size pose a health concern, identify areas that are disproportionally impacted by mercury and assess long-term changes, along with 2) determining if cyanotoxins are present in fish, and if so, do concentrations in fish correlate with presence in water samples.
More than 600 fish of five species (smallmouth bass, walleye, lake trout, yellow perch and white perch) from the seven segments of Lake Champlain (South Lake, South Main Lake, Main Lake, North Main Lake, Malletts Bay, Northeast Arm and Missisquoi Bay) were analyzed for total mercury. While all fish species had specimens exceed the US EPA mercury advisory limit of 300 ppb, walleye and smallmouth bass had 38% (28/74) and 17% (27/157) of their specimens, respectively, exceed the USFDA action limit of 1000 ppb. Fish length and location were significant factors explaining mercury variability for the five species tested, however, no consistent trend was observed for location among species. Because these species include cold, cool and warm-water fish feeding from benthic and pelagic food webs along with different growth rates and efficiencies, utilizing fish mercury concentrations to determine lake segments that are disproportionately affected by mercury was inconclusive.
Assessing long-term mercury trends in fish shows a significant decrease in lake trout, walleye and yellow perch from their initial mercury surveys (1987-1990). Smallmouth bass and white perch did not show a significant decrease from their initial surveys in the mid-1990s. An unexpected finding was the increase in smallmouth bass and yellow perch mercury concentrations since the 2011 study. Similar findings have been documented in the Great Lakes region and Ontario with proposed explanations including enhanced deposition from Asia, invasive species and climate change. These along with impacts of Hurricane Irene in 2011 are plausible explanations for the increase in Lake Champlain fish mercury but require additional research.
Cyanotoxins (microcystins, anatoxin-a and cylindrospermopsin) were measured in water samples collected throughout the summer and fish samples during low and high bloom periods from the Main Lake and Missisquoi Bay. Analysis utilized HPLC coupled with tandem mass spectrometry able to detect microcystin metabolites, a technical advancement over ELISA that can react with non-microcystin metabolites leading to spuriously high values. However, all water and fish measurements were below the detection level agreeing with VT DEC data showing no microcystin or anatoxin in water samples during this time period. Although correlations of cyanotoxin concentrations between water and fish could not be compared due to non-detectable levels, the study validated the method used for microcystin detection and demonstrated microcystin, anatoxin and cylindrospermopsin did not bioaccumulate in fish as cyanotoxins were present in 2015.