Mercury in Alaska fish: Something else to worry about

REID BREWER and STEPHEN JEWETT

January 17, 2008 at 9:37AM AKST

For Alaska Newspapers

For the most part, most Alaska fish species have relatively low levels of mercury, but there are a few exceptions to consider.

In a recent University of Alaska study, 17 freshwater and 24 anadromous and marine fish species were examined for concentrations of methyl mercury, MeHg, the most toxic form to humans.

In total, 2,692 fish were analyzed to determine if levels of MeHg might prove harmful to Alaskans, who consume much more fish than the national average.

Intake of fish and fish oils has long been hypothesized to reduce and/or prevent cardiovascular disease, but recent epidemiological studies have shown that mercury may counteract the beneficial cardiovascular effects of n-3 fatty acids in fish.

Mercury is a naturally occurring element that has many uses, including acting as effective pesticides, fungicides and preservatives. Recent human-induced activities, such as erosion from mining and atmospheric deposition due to burning of fossil fuels, have caused unnaturally high concentrations of contaminants.

Among those contaminants is mercury, which can threaten the physical health of both fish species and the human populations that depend on them for subsistence.

Mercury tends to build up in higher trophic animals, such as fish, through a process called "biomagnification."

Bacteria, plankton and algae are mixed in and consume various nutrients and contaminants in the waters in which they live. Though mercury levels in plankton-eaters are relatively low, as higher-level trophic organisms consume masses of lower-level organisms, the dosage of nutrients and contaminants are then magnified in the tissues of these organisms.

Subsistence food provides people with the nutrients from fish as well as the contaminants that those fish may be carrying, such as mercury. Increasing exposure to even low concentrations of mercury in food is often associated with an increased risk of neurochemical or cardiovascular damage.

Of the species most commonly consumed in Alaska, salmon had exceptionally low mercury concentrations, Pacific halibut and sablefish had higher, but not dangerous, levels. And northern pike contained the highest concentration of mercury, often exceeding the state's guidelines for food consumption.

Mercury concentrations in freshwater fish can vary greatest from watershed to watershed.

Researchers also reported that mercury is not removed from fish tissue by common cooking methods and that cooking and drying subsistence foods, including fish, tends to remove water without removing mercury, thus increasing its concentration.

Based on federal Environmental Protection Agency guidelines, consumption limits for adults show that 16 chinook salmon meals or 31 sockeye salmon meals may be eaten per month, while one pike or six grayling meals may be eaten per month.

Because of children's body size, it is more hazardous for them to consume pike and grayling than it is for adults.

Nevertheless, the Alaska Department of Public Health strongly recommends that Alaskans continue consumption of fish from Alaskan waters as part of a balanced diet.

Reid Brewer of Unalaska is a marine biologist with the University of Alaska Fairbanks' Marine Advisory Program. He can be reached at reidbrewer@hotmail.com. Stephen Jewett is an associate and also is with UAF.

 

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