U NC-SG-B P-12-02
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North Carolina - north CAROLINA sea grant nc state university box 8605 raleigh, nc 27695-8605
Purchasing Seafood
Answering Questions of Mercury in North Carolina-Caught Species
Results from N.C. Fishery Resource Grant Projects
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or seafood consumers, deciding which of the many
products available to purchase can be confusing. Providing
selection criteria is difficult because seafood consumption
guidelines can vary based on the individual. Adding to the
confusion, recommendations are available from the U.S.
Food and Drug Administration (FDA), the U.S. Environmental
Protection Agency (EPA), and nongovernmental groups. The FDA
and EPA provide information on contaminants in seafood, most
notably mercury content. Nongovernmental organizations, which
often provide recommendations in the form of seafood cards
or digital applications, also include factors associated with the
status of the fish stock and how the fish is harvested.
Mercury and Methylmercury
Mercury is a heavy metal that occurs naturally in the
environment but is released into the air through natural causes
and industrial pollution. It can enter various water bodies where
it is converted by bacteria to methylmercury, a form that is
toxic to humans, and readily available to aquatic organisms.
Methylmercury can accumulate in fish tissues that are
eventually consumed by humans.
In fact, the primary source of human exposure to mercury
is through seafood (Grandjean et al., 1995). That is why
mercury is a major consideration in seafood consumption
recommendations. In particular, the nervous systems of fetuses
and young children are very sensitive to mercury exposure. As
a result, mercury consumption recommendations vary with the
intended audience.
Federal Guidelines
EPA provides recommendations on seafood consumption
based on methylmercury content. The action level established
by EPA is 0.3 parts per million (also reported as 0.3 milligrams
per kilogram), a level by which species are considered to
have high methylmercury. However, the actual consumption
recommendations vary based on the individual and the average
number of seafood meals consumed per week. A seafood meal
is defined as 6 ounces of a given species.
EPA considers two groups of consumers in their
recommendations. The general public are males 15 years and
older, and women older than 44 years. Higher-risk individuals
are women of childbearing age and children less than 15
years of age. Table 1 shows the maximum number of meals
for each group at various methylmercury levels. While figures
are provided for those in the higher risk group, it is generally
recommended that pregnant or nursing mothers, and young
children limit or avoid consuming fish with mercury levels
greater than 0.3 ppm.
Table 1. Maximum seafood consumption limits for consumer group
and methylmercury level, based on data from U.S. EPA document EPA
828-B-00-008.
Group
Methylmercury
level (ppm)
Maximum number
of meals per week
Maximum amount
of seafood per
week (oz)
Higher risk 1
0.1
3.0
18
0.2
15
9
0.3
10
6
0.5
0.5
3
10
0.3
2
2.0
0.2
1
General public 2
0.1
9.4
56
0.2
4.7
28
0.3
3.1
19
0.5
19
11
10
0.9
5
2.0
0.5
3
1. Women of childbearing age and children less than 15 years of age.
2. Males 15 years and older, and women older than 44 years.
Insufficient Data and New Research
The data on methylmercury content in seafood that is used
for consumption advisories in North Carolina is obtained from
both in- and out-of-state sources, and often does not accurately
reflect what is caught locally. In addition, dated samples further
complicate establishing effective guidelines.
In 2010, the N.C. Fishery Resource Grant Program,
administered by North Carolina Sea Grant, funded two separate
methylmercury studies. Derek Aday, Sally Petre and Dana
Sackett from North Carolina State University, and fisherman
Dale Britt conducted project 10-ST-02. Duke University
researchers Dan Rittschof, Amy Freitag and Nari Sohn, and
