Scientists have taken a dive into mercury contamination in the lakes

The rule of thumb for eating fish from the Finger Lakes: No more than once a week or four times a month. Why? Mercury contamination.

How mercury pollution is getting into the lakes and the fish we eat was the subject of a presentation Tuesday at Finger Lakes Community College by researcher and assistant professor Roxanne Razavi. The Finger Lakes Mercury Project, involving Razavi and a team with Finger Lakes Institute and FLCC, conducted sampling, testing and analysis of fish from the lakes to learn more and build a framework for continued research.

What do we know from this project that began in 2015? The results are a mix of what we’d expect along with surprises.

Canandaigua Lake was key in the research, chosen as one of the lakes for sampling based on its status as one of the cleanest lakes — one whose nutrient levels are more in check than most other lakes in the region. Honeoye, too, was sampled as a lake at the other end of the spectrum, known for its higher nutrient levels.

But the obvious can be deceiving when it comes to mercury contamination.

“Lakes with lower nutrient levels are more at risk for higher contamination in the food web,” said Razavi, assistant professor in SUNY College of Environmental Science and Forestry. “So cleaner lakes can be at risk.”

But within a lake many different factors come into play. Mercury levels vary based on the type of fish, as well as its size and age. “Length and age matter,” she said.

Mercury levels also “vary be species, not by lake,” Razavi said.

Of concern: 25 percent of the fish in all the Finger Lakes have mercury levels above the amount deemed safe. Fish from Owasco Lake contain some of the highest levels. One type of fish to stay away from in any lake, if you plan to eat, is walleye.

“Walleye are hot,” said Razavi, who fielded questions through text and a Q&A session.

Razavi explained how older fish have more time to become contaminated. But since you can’t know the age of a fish when you catch it, “length is generally a good indicator of how much mercury is in that fish,” she said.

Referring to sampling from Canandaigua Lake, she named the smaller yellow perch and brown bullhead as safer, averaging well below concerning mercury levels.

Fish to avoid eating from Canandaigua Lake include largemouth, whose levels averaged higher than trout.

On the big question — how is mercury contamination landing in the lakes — Razavi took the audience through major points. While nature provides a source of mercury — related to volcanoes, rocks and oceans — the biggest source is from human activity. Globally, small-scale gold mining in areas of the world including Western Africa, Southeast Asia and South America provides the greatest source worldwide.

In the United States, the biggest source of mercury contamination is coal-fired power plants. Environmental regulations have helped reduce contamination in the U.S. since 2002, but coal-fired plants still remain the source of 50 percent of all mercury contamination nationwide, Razavi said.

Most mercury pollution is released into the air and then falls directly into water bodies or onto land, where it can be washed into waterways. When mercury gets into water, bacteria can change it into a form called methylmercury, which is absorbed by tiny aquatic organisms.

Research is looking at how climate change with more frequent severe weather, as well as invasive species and other factors, may influence mercury contamination.

The audience included representatives of event sponsor Canandaigua Lake Watershed Association, college students, anglers, business owners and others who nearly filled the lecture center.

One man, who said he owns a charter fishing fishing operation, asked if there is a way to prepare fish to avoid mercury contamination. Razavi said there is not. Mercury is distributed throughout a fish’s muscle tissue — the part you eat — rather than in the fat and skin. Trimming and skinning will not reduce the amount of mercury in a fish meal. The only way to reduce how much mercury you get from fish is to avoid certain species or eat less contaminated fish.

The state Department of Health recommends reducing exposures to mercury by avoiding or eating less largemouth and smallmouth bass, northern pike, pickerel, walleye, and larger yellow perch (for example, longer than 10 inches) because these fish tend to have higher mercury levels.

Razavi said ongoing research about mercury in fish may change eating guidelines. She also talked about the value of eating fish for its protein, essential nutrients and healthy fish oils that are low in saturated fat — coupled with the enjoyment and spiritual satisfaction from the sport of fishing and eating what you catch from your home lakes.