No Surprise Here

Bay Journal, Mercury widespread in Chesapeake Bay headwaters fish. But we knew this already.

Nearly half of all gamefish in freshwater lakes, streams and rivers in the Chesapeake Bay watershed may be unsafe to eat because of high levels of mercury, a new study suggests.

In the first study to examine mercury across a spectrum of fish in the six-state region, scientists found that the pollutant remains prevalent in the environment in its most toxic form despite years of declining mercury emissions.

The totals vary widely by location, a possible indication that local conditions are raising or lowering the risk of contamination, according to the research conducted by three U.S. Geological Survey scientists.

“Our goal here was to really do a first cut of what we saw across the landscape,” said Collin Eagles-Smith, a USGS research ecologist. “Hopefully, that can be a springboard for future studies to get a better sense at why.”

The study centers on the type of mercury that is most toxic to humans: methylmercury. The neurotoxin is formed when inorganic mercury interacts with certain bacteria. It is particularly harmful to fetuses and children, potentially leading to intellectual deficits and problems with motor skills.

In the Chesapeake Bay watershed, mercury is the main trigger for fish-consumption advisories. Coal-fired power plants and trash incinerators are the largest sources of the pollutant in the region, scientists say. Once released into the air, mercury can travel great distances before getting deposited into waterways through rainfall or as a gas.

The Chesapeake watershed’s mercury levels — with 45% of all fish in the study exceeding the consumption standard — are similar to those found in many parts of the country, the authors say. The findings underscore the importance of checking for public health advisories before eating any wild-caught fish, said James Willacker, the study’s lead author.

Georgia used to work for the premier mercury biogeochemist from the Chesapeake Bay region, Dr. Cindy Gilmour, doing most of her mercury analysis in fish and a variety of other matrices. Mercury is, indeed, everywhere you look, if you have sensitive enough analytical techniques. And fish have so much it's not even particularly challenging.

In fact, many years ago, me and my fishing buddy Tom, who just happens to be Cindy's husband, helped catch a bunch of Striped Bass of varying sizes, from sub legal to 50 inches, and produced a data set that showed (not unexpectedly) that the concentrations of Hg were higher in larger fish, and that above about 30 inches, they usually had concentrations at which advisories would be recommended.

The techniques were well known, all that was necessary was for someone to go around and catch a few of each fish of edible size, from all the possible water ways, and analyze them. Oh, and somebody to pay for it. ICPMSs don't buy themselves.

The USGS researchers culled fish contamination records from two sources: a study conducted by the agency in the watershed from 2013–17 and state monitoring programs with reporting dating as far back as 1990.

Together, the collections contained measurements from nearly 8,000 fish caught in 600 locations.

The researchers found that the basin with the highest mercury concentrations was the Susquehanna. More than half of the basin’s freshwater areas ranked among the most toxic spots across the Chesapeake Bay watershed, which stretches from Virginia Beach, VA, to Cooperstown, NY.

Next was the Potomac, where 18% of waters landed in that tier. No water body outside of the Potomac and Susquehanna drainage areas fell into the most-polluted category. In contrast, at least half of the water bodies in the James, Rappahannock and York watersheds — all in Virginia — placed in the category with the lowest levels.

Eagles-Smith said it’s unclear why the watersheds in the northern end of the Chesapeake Bay basin have higher mercury levels in fish than those in the south. Regional air patterns would suggest the opposite — mercury tumbles from the atmosphere to the ground at higher rates in the South than in the North, according to the study.

Because methylmercury levels intensify with each step up food chain, the USGS scientists found the highest amounts in larger fish, including some of the region’s most prized sportfish.

 Ah, but where are the conditions better for the methylation of Hg, the step most necessary for its accumulation in fish?

Striped bass, a gamefish popular on restaurant menus, had the most mercury in its meat of the 32 fish tracked in the study, with a typical concentration of 0.31 parts per million. The U.S. Environmental Protection Agency has set a consumption limit for mercury of 0.3 parts per million.

“There are lots of people out there recreationally consuming that [fish],” said Betsy Nicholas, executive director of Waterkeepers Chesapeake. “These people don’t realize what they’re ingesting and how much of a detrimental impact that can have.”

Striped bass was followed, from more contaminated to less, by bowfin (0.2), walleye (0.19), largemouth bass (0.18) and flathead catfish (0.17), according to the report. The species with the least mercury included three types of trout and the creek chub.

“Trout are a great choice if you’re trying to avoid mercury exposure,” Eagles-Smith said.

Meh. If you're past reproductive age (or male) it takes a lot of Hg to be a real problem.



Wombat-socho has Rule 5 Sunday: Summer Musashi up and running as expected.