From the smokestacks of power plants to the discharges from wastewater treatment plants, and other places, mercury in the form of the compound methylmercury exists in the enviroment, and it can settle to the seafloor and be taken up by tiny organisms that live or feed on bottom sediments.
From there mercury or other toxic contaminants that settle on the seafloor poses a threat to the ecosystem. According to NOAA’s Ocean Explorer website:
… these compounds aren’t digested, they accumulate within the animals that ingest them, and become more and more concentrated as they pass along the food chain as animals eat and then are eaten in turn. This is biomagnification, and it means that higher-level predators-fish, birds, and marine mammals-build up greater and more dangerous amounts of toxic materials than animals lower on the food chain.
Human exposure to methylmercury occurs mostly from consuming fish and shellfish and “almost all people have at least small amounts of methylmercury in their bodies, reflecting the widespread presence of methylmercury in the environment,” according to EPA’s Health Effects of Exposures to Mercury. For most people, blood mercury levels are below levels associated with possible health effects, but the EPA website includes this warning: “Methylmercury … is a powerful neurotoxin, and people exposed to high levels may experience adverse health effects. If you are concerned about your exposure to methylmercury, you should consult your physician.”
In 2002, Peg Van Patten, who was then the Communications Director for Connecticut Sea Grant, profiled Dr. Johan “Joop” Varekamp in Wrack Lines magazine on his research connecting mercury contamination in the Sound with an industrial city’s hat making past. Varekamp, who was then a professor in the Earth and Environmental Sciences Department at Wesleyan University, was able to trace through sediment core samples that the source of mercury deposits found in the Housatonic River at the mouth of Long Island Sound was from Danbury, a city located off the banks of the Still River, an upstream tributary of the Housatonic. In the 19th century and 20th centuries Danbury was known as the Hat City where fur hats were manufactured using mercury to toughen the fur hat fibers. Varekamp also wrote about the legacy contaminant in the fall 2012 issue of Long Island Sound Study’s Sound Update newsletter (see page 3).