A new study by two UConn researchers has found that mercury contamination levels in the meat of largemouth bass caught in Connecticut lakes were significantly lower in 2005-2006 than levels documented a decade earlier.

But the study’s results are tempered by the findings that although mercury contamination in fishes is lower than previously, it is still present at levels that merit a continuation of the statewide fish consumption advisory.

“Formal inference about any trend of mercury contamination in fish tissue through time will require more data to create a proper time-series,” says Jason Vokoun, an assistant professor of natural resources and the environment in the College of Agriculture and Natural Resources, and co-author of the new study.

“Qualitatively, there was a smaller proportion of individual fish sampled with mercury concentration values above thresholds that are used to determine risk to human health,” he says.

“However, these higher-contamination fish were still widespread and occurred in all five regions of the state.”

The study by Vokoun and Christopher Perkins, laboratory co-director at UConn’s Center for Environmental Sciences and Engineering, is the second statewide assessment of mercury levels in fishes from Connecticut lakes and the first to directly compare the mid-90s to the present.

Currently, the state Department of Public Health advises young women who are or may become pregnant, nursing mothers, and children under age six to limit eating freshwater fish to one meal per month because of the risk of mercury contamination.

Research shows that exposure to mercury is particularly destructive for the developing nervous system and can lead to behavioral or learning problems.

State officials have cautioned other members of the public to limit consumption of all locally caught freshwater fish to one meal per week, except for trout raised in hatcheries and released in stocking programs into ponds, streams, rivers, and lakes around the state.

There are many health benefits to eating fish, however, Vokoun notes.

Connecticut and U.S. health officials believe the elevated levels of mercury in freshwater fishes in the Northeast are largely the result of mercury released from coal-burning power plants – many of them far away. Once in the air, the toxic metal can travel vast distances before entering soil and water.

Once mercury settles into watersheds and enters the water, it is transformed by water-borne bacteria and then can enter algae, which are eaten by plankton, which are eaten by little fishes, which in turn are eaten by bigger fishes such as largemouth bass.

At each step in the food chain, the mercury accumulates and becomes more concentrated.

Mercury is a naturally occurring metal, but becomes toxic to human and animal consumers when highly concentrated in fish flesh.

Because of mercury’s toxicity, both federal and state public officials have agreed to efforts to reduce manmade mercury emissions in power plants.

The federal Clean Air Act has imposed stricter standards on coal-burning plants and smokestack “scrubbers” have been placed in many facilities in the upper Midwest that send mercury towards Connecticut.

“Our study suggests these efforts may be starting to pay off,” says Vokoun.

“Other researchers in upstate New York and Massachusetts have recently reported declines as well. We hope to continue to monitor at least every 10 years, and perhaps more frequently if mercury levels continue to fall and the removal of a statewide consumption advisory seems possible.”

For the study, lakes were chosen from every region of the state, and fish were collected by boat electrofishing (a sampling technique that generates an electric field in the water to stun fish so they can be easily netted). Additional fish were donated by anglers.

Fish were euthanized and the fillets (the muscle meat) removed, blended together, and analyzed for mercury contamination levels.

The study also experimented with a new non-lethal biopsy method to determine mercury levels in the fish. Some states have already transitioned to the biopsy method as a research technique.

“Our study validated the biopsy method for Connecticut,” says Vokoun.

“Future studies can now conduct this type of non-lethal monitoring without taking fish from the wild.”