Caution: Mercury Levels in Tuna and Other Fish
From the Editors of E/The Environmental Magazine
Dear EarthTalk: I always thought eating fish was healthy, but now I’m concerned about mercury in tuna and other fish. Are there any fish that are still safe to eat? -- Brit Brundage, Fairfield, CT
You should be concerned about contaminants in certain fish, including some kinds of tuna. The non-profit Environmental Defense Fund (EDF) recommends minimizing consumption of albacore (white) tuna, a large fish that accumulates moderate amounts of mercury in its fatty tissue. But other kinds of (smaller) tuna, such as skipjack (usually canned as “light”), which accumulates a third the amount of mercury as albacore, are OK to eat in moderation, though consumption by those under age seven should be limited.
To further complicate the issue, some canned light tuna may contain yellowfin tuna, which has mercury levels similar to those of albacore; these products are sometimes but not always labeled as “gourmet” or “tonno”—and their consumption should be limited, even by adults.
Mercury, a known “neurotoxin” (a poison that affects the nervous system), is particularly insidious because it is widespread in our oceans, primarily due to emissions from coal-burning power plants. These smokestacks deposit mercury into waterways, which carry it to the ocean where bacteria convert it into methylmercury. Fish then ingest it with their food and from water passing over their gills.
Generally speaking, bigger, older and large predatory fish (such as sharks, swordfish, tilefish, king mackerel and some tuna) near the top of marine food chains are more likely to have high levels of mercury than fish lower in the marine food chain. People exposed to high levels or frequent doses of mercury can suffer nervous system disorders, impaired mental development and other health problems.
An April 2003 study, published in Environmental Health Perspectives, found that 89 percent of study subjects, chosen because they ate a significant amount of fish, had blood mercury levels above the U.S. Environmental Protection Agency’s (EPA’s) safety threshold of five micrograms per liter. Even though there are health benefits to eating fish (including the intake of healthy omega-3 fatty acids), the EPA advises that young children, pregnant women, nursing mothers and women of childbearing age limit their intake of high-mercury fish to one serving per week at most, while limiting their overall intake of any fish or shellfish to no more than two to three servings, or 12 ounces total, per week.
Mercury isn’t the only harsh pollutant lurking in the ocean. Industrial chemicals like PCBs and pesticides like DDT are awash in marine food chains around the world. According to EDF, it can take five years or more for women of childbearing age to rid their bodies of PCBs, and 12-18 months to appreciably reduce their mercury levels. EDF adds that moms who eat toxic fish before becoming pregnant may have children who are slower to develop and learn because fetuses are exposed to stored toxins through the placenta.
To learn more, visit the EPA’s Fish Advisories website. It includes links to individual state advisories, which have details on what fish should or shouldn’t be eaten from nearby lakes or coastal areas. Catfish, Pollock, salmon, shrimp and canned light tuna are currently on the EPA’s safe list, as they feed toward the bottom of the food chain and thus have less opportunity to accumulate mercury and other contaminants.
Photo: Mark H. Anbinder, courtesy Flickr
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