Study reveals new mercury risks for fish and birds
LEE KARNEY, U.S. FISH AND WILDLIFE SERVICE
search biologist with the USGS es901400c), the coauthors perMercury’s toxicity to humans has Patuxent Wildlife Research Cenformed a time-series study of been recognized for more than ter, because “often, monitoring of mercury levels in two small fish two centuries. The 19th-century mercury and fish has been done species in the San Francisco Bay phrase “mad as a hatter” alluded independently of what might eat estuary: longjaw mudsuckers (Gilto the strange behaviors somethe fish. This paper does a nice lichthys mirabilis) and threespine times seen in hatmakers who had job of combining the fish monisticklebacks (Gasterosteus aculeabeen poisoned by inhaling the toring with the effects the mertus), representing benthic and pemercury vapors from curing felt. cury-contaminated fish Lewis Carroll immortalized might have on wildlife.” the phenomenon by having “I’m impressed that it was his character Alice attend a a very big, very thorough “mad tea party” in Wonderstudy, with big sample land with the Hatter, who sizes,” Heinz adds, with “lots confused the conversation of fish sampled, lots of birds. with nonsense verse and I think we can put a lot of non sequiturs. credence in their findings.” But mercury poisoning is The next step is to learn no joke: high concentrations more about why the merof the heavy metal can cury levels in small fish vary cause neurological injury to so much over such short wildlife as well as humans and impair or even prevent The Forster’s tern feeds on small fish such as threespine time periods. “Is it a fundamental process, or could one reproduction. Once present, sticklebacks and longjaw mudsuckers. High levels of mercury persists in the envi- mercury in those fish coincided with peaks in the lake have one reason it goes reproductive cycle of the terns. up and down” and another ronment and readily binds have a different reason? asks Heito proteins as animals take it in lagic food webs, respectively. After nz. “The authors hypothesize, but with their food. Mercury can sampling several hundred fish I don’t think anyone fully underbuild up (bioaccumulate) in the from three different sites over five stands this variation. They recogtissues of animals all along the continuous months, along with nize that more research needs to food chain, becoming more confish collected around hundreds of be done in this area.” centrated in predators at higher bird nests, Eagles-Smith and AckA. Russell Flegal, a professor of levels. Watery habitats such as erman found that mercury levels environmental toxicology at the lakes, rivers, open ocean, estuarin the fish fluctuated significantly University of California Santa ies, and wetlandsswhere bioin a very short period of time, inCruz, agrees with Heinz’s assessgeochemical processes convert creasing by 40% from March to ment of the newly published reinorganic mercury to its more May, then decreasing 40% from search, calling it “an extremely toxic, organic methylmercury May to July. thorough preliminary study, with (CH3Hg+) formsare particularly at Eagles-Smith and Ackerman also rigorous sampling.. ., very rigordemonstrate that the period of risk from mercury contamination. ous chemical analysis, and very highest mercury levels in the prey Although this phenomenon has rigorous statistical analyses.” fish coincided with peaks in the become better understood in reFlegal, whose work involves exreproductive cycle of breeding Forcent decades, many open quesamining the biogeochemical cyster’s terns (Sterna forsteri), the tions remain. cling of mercury through the most abundant nesting fish eater in Researchers Collin Eagles-Smith environment and how it is taken the region. The terns, which chow and Joshua Ackerman of the U.S. up by aquatic organisms, says the down on threespine sticklebacks Geological Survey (USGS) have findings have implications for asfor 25% of their diet and longjaw taken solid steps toward answering sessing risks to both wildlife and mudsuckers for 36%, began buildtwo of the remaining questions: public health. “This was a study ing 68% of their nests for the seahow widely mercury levels can vary with birds, but you [can] consider son during the period of peak in prey species over a short period the birds as a proxy for humans mercury levels in their prey fish. of time and how these variations that also eat fish,” Flegal notes. They hatched 31% of their chicks can intersect with key periods in a “These little fish would be eaten during the same time span. predator’s breeding cycle. by bigger fish, and some of the These findings are useful and In recently published research fish in San Francisco Bay exceed valuable, says Gary Heinz, a rein ES&T (2009, DOI 10.1021/ 9048 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / December 15, 2009
10.1021/es903304s
2009 American Chemical Society
Published on Web 11/11/2009
state and federal criteria for human health consumption. So it’s directly analogous to that.” The contamination in San Francisco Bay includes a “legacy of mercury from mining operations” of about 150 years ago, Flegal notes. “The largest mercury mine in North America drains into San Francisco Bay in its southern reach,” he says. “In the northern reach of San Francisco Bay, the mercury mined in the southern reach was used for gold mining in the Sierras.” On top of this are the contemporary sources of mercury, he says, including industrial operations in the greater San Francisco Bay area, atmospheric pollution from fossil fuel combustion within the U.S., and contaminants that blow across the Pacific Ocean from coal-fired power plants in China and India. Given the myriad sources of mercury contaminating the bay,
says Flegal, the new study “just shows that what was previously considered extremely difficult to manage is even more difficult to manage. Much, much more data is needed on short-term temporal variations.” The most important question the study raises, according to Linda Campbell of Queen’s University in Ontario, “is whether it is important to incorporate temporal monitoring in programs” that track the distribution of mercury in the environment. “For example, the Ontario Ministry of the Environment has a 30-plus-year database of sportfish contaminants from 1500 sites, which my laboratory is using to map spatial trends in different decades,” says Campbell, who specializes in aquatic ecosystem health, including the dynamics of mercury and other contaminants in the food web. “But we are not
able to look for seasonal trends within that database, as amazing as it is.” Campbell believes that the next steps in this line of research will include clarifying the reasons that the mercury levels oscillated so quickly. “I found it interesting that the authors were not able to elucidate, in their words, the reasons for the peak in the small-fish mercury concentrations,” she says. “But [they] did outline possible factors, including methylation of mercury and [how] the age structure and growth rate [of the fish] may have coincided, resulting in this peak.” “I would think the authors will need to monitor mercury in the small fish species year-round,” suggests Campbell, “as well as the methylation rates in the surrounding wetlands.” —EMILY GERTZ
December 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 9049
