Groth, E. 2010. Ranking the contributions of
commercial fish and shellfish varieties to mercury exposure in the
United States: Implications for risk communication. Environmental
Research
http://dx.doi.org/10.1016/j.envres.2009.12.006. Synopsis by
Jennifer F. Nyland
Experts send a mixed message to consumers when it comes to eating
fish: it's good for your heart health but beware of the
methylmercury. A new way of organizing and ranking the pollutant's
levels in fish and shellfish may help consumers navigate this
apparent contradiction, according to the study's author.
The reanalysis of the government-collected data could provide
consumers in the United States with an easier method to evaluate
dietary exposure to mercury through the fish they eat, making it
more likely they will choose the types and amounts of seafood that
are safest to eat. In particular, the calculation of a "mercury
input factor" weights both the amount of a particular fish sold and
its mercury content.
When sorted by market share, the news was good. Of the top five
selling fish and shellfish in the United States - shrimp, tuna,
salmon, pollock, and catfish - only tuna was ranked at the
above-average or higher mercury level.
Most human exposures to mercury are in the form of methylmercury and
from eating contaminated fish. Yet, consumer information on which
fish have high levels of mercury is sometimes difficult to find and
decipher - it can be confusing and contradictory. For instance, the
fish advisory on mercury issued by the Food and Drug Administration
and the US Environmental Protection Agency in 2004 is primarily
available through the Internet, which many people still cannot
access.
Methylmercury can interfere with brain development and is known to
affect learning and behavior at levels below those designated as
acceptable by federal agencies. Although everyone can be affected,
women of childbearing age and children are especially susceptible.
These groups are advised to choose seafood with low mercury levels
and limit amounts to other species to reduce their exposure to the
metal. Posing the biggest hazard are the older, predatory fish such
as tuna, swordfish and the angler-caught fish from local
contaminated waters.
Based on data gathered from the FDA and the National Marine
Fisheries Service, the 51 varieties of fish and shellfish that
makeup the seafood market in the United States were classified by
their mercury content and compared to pounds sold per year. They
were then sorted into categories based on mercury and market:
mercury levels, market share, consumption, mercury input factor and
mercury content.
The highest mercury levels were found in tilefish from the Gulf of
Mexico, followed by shark, swordfish, king mackerel and orange
roughy. The lowest levels were found in salmon, shrimp, sardines and
tilapia.
Consumers who eat fish with a low- or below-average mercury levels
are unlikely to be exposed at levels of concern set forth by federal
agencies, according the study's author. On the other hand, it may be
prudent to limit consumption of fish with above-average or higher
mercury levels.