April 2011 / Vol. 7
Healthy, Sustainable Seafood: A Study of Mercury in Shrimp
by Sarah J. Nelson and Catherine Schmitt
Background
Mercury is a highly toxic element that can impair brain development in children, and affect cognition,
hearing, vision, and muscle coordination in adults. Many watersheds in the Northeast have relatively
high mercury concentrations for the US, because the region is downwind of major pollution sources.
Mercury is especially active in aquatic environments, so people are exposed to mercury primarily through the
consumption of fish. Shrimp, the most popular seafood in the United States, is often touted as a “low-mercury”
seafood choice, although available information is not specific to Maine’s native shrimp species.
This study intended to answer two questions:
Are shrimp truly a low-mercury food? Does it matter where the shrimp come from?
Marine Research in focus provides updates on marine research for coastal
communities. This fact sheet was produced by Maine Sea Grant with
programing support provided by University of Maine Cooperative Extension.
Methods
We purchased three types of frozen, headless shrimp from a Maine supermarket: Maine Northern shrimp
(Pandalus borealis), Louisiana brown shrimp (Farfantepenaeus aztecus), and Thailand tiger shrimp (Penaeus
monodon). After lab tests confirmed that shrimp had similar concentrations of mercury along the whole
length of the edible part1 of their bodies, a section of shrimp meat was analyzed in the University of Maine’s
Sawyer Environmental Chemistry Research Laboratory to determine total mercury concentration in each
individual shrimp.
Why Study Shrimp?
Shrimp is the number one type of seafood consumed in the United
States – over 1.2 billion pounds in 2009 (Fisheries Statistics Division
2010). While shrimp is promoted as a “low-mercury” seafood choice,
few2 studies have looked at mercury in commercially available shrimp.
The current safety level is based on only 24 samples from the 1990s3,
and the species is only identified for a few of those samples4, even
though several different species of
shrimp are available to consumers.
Most shrimp consumed in the
US is imported from farms in
Asia, but Maine has its own wild
shrimp fishery, for Pandalus
borealis or Northern shrimp. This
is a small but sustainable fishery
that employs fishermen in the
winter months. Maine shrimp
are typically available fresh from
December through April and
frozen year-round.
1. Some people do cook and/or consume shrimp whole with the shell, however we analyzed them headless and without shells, as most
consumers prepare them.
2. One study found that shrimp do accumulate mercury rapidly when they are in a high mercury environment (Palmer and Presley 1993);
another study in New Jersey (which did not say which species/origin shrimp they used) found low-mercury in shrimp and noted that bigger
shrimp tended to have less mercury (Burger et al. 2005). We are not aware of any studies that determined mercury in commercially available
Maine wild-caught shrimp.
3. http://www.fda.gov/Food/FoodSafety/Product-SpecificInformation/Seafood/FoodbornePathogensContaminants/Methylmercury/ucm115644.htm
4. http://www.fda.gov/Food/FoodSafety/Product-SpecificInformation/Seafood/FoodbornePathogensContaminants/Methylmercury/ucm191007.htm
Average and maximum mercury concentrations in shrimp and other seafood
This Study
All samples were very low in mercury, in agreement with the existing FDA data.
Mercury in commercially-available shrimp
Mercury in shrimp for all samples taken together (“All
Mercury in commercially-available shrimp
shrimp” bar) averaged 21 ppb, ww (parts per billion,
Maine
wet weight). The range of values in our study was 4 – 66
EPA
mercury
Maine
ppb, ww. Although there were statistically significant Gulf of Mexico
Maine
EPA
guideline
mercury
differences among the three types of shrimp we
mercury
Thai
Gulf of Mexico
Maine
guideline
guideline
studied, these differences are not meaningful for
mercury
Thai
All
shrimp
guideline
human consumption because the levels of mercury
All shrimp0
are so low. The differences among the types of shrimp
100
200
300
raise interesting research questions, such as, Does
0
100
200
300
shrimp size matter? What is the difference between
Total mercury, ppb ww
farm raised and wild shrimp?
Total mercury, ppb ww
Shrimp
Clam
Shrimp
Salmon (fresh/frozen)
Clam
Haddock
Salmon (fresh/frozen)
Crab
Haddock
Freshwater trout
Crab
Freshwater
Freshwaterperch
trout
Canned
lightperch
tuna
Freshwater
Lobster
Canned light
tuna
Bass (saltwater, striped,Lobster
black)
Bass (saltwater, striped,Halibut
black)
Canned albacore
tuna
Halibut
Swordfish
Canned albacore
tuna
Swordfish
FDA Data
Mercury in commonly-eaten seafood (FDA data)
Mercury in commonly-eaten seafood (FDA data)
EPA mercury
guideline
EPA mercury
guideline
Maine mercury
guideline
Maine mercury
guideline
Average
Average
Maximum
Maximum
0
0
300
300
600
600
1500
1800 3000
3300
Total
ppb ww 1500
900 mercury,
1200
Total mercury, ppb ww
900
1200
1800 3000
3300
The Maine Center for Disease Control and Prevention and the Environmental Protection Agency set limits
on the level of mercury in fish that is considered safe to eat. Maine’s guideline is stricter, to protect sensitive
populations like children and pregnant women. The average mercury concentration in shrimp in this study
(21 ppb) is 10 times lower than Maine’s fish tissue action level of 200 ppb. Even the one shrimp with the highest
mercury concentration (66 ppb) still had three times less mercury than Maine’s action level. By comparison,
EPA recently found that approximately half of the freshwater fish sampled from 76,559 lakes across the US had
mercury concentrations that exceeded the EPA’s recommended safety level of 300 ppb (US EPA 2009).
References
Burger J., A.H. Stern, M. Gochfeld. 2005. Mercury in commercial fish: optimizing individual choices to reduce risk. Environmental Health
Perspectives 113:266-271.
Fisheries Statistics Division. 2010. Fisheries of the United States 2009. Silver Spring, MD: National Marine Fisheries Service.
http://www.st.nmfs.noaa.gov/st1/fus/fus09/index.html
Palmer, S.J., B.J. Presley. 1993. Mercury bioaccumulation by shrimp (Penaeus aztecus) transplanted to Lavaca Bay, Texas. Marine Pollution Bulletin
26:564-566.
US EPA. 2009. The National Study of Chemical Residues in Lake Fish Tissue, EPA-823-R-09-006. Washington, DC: US Environmental Protection
Agency Office of Water.
Conclusion
Balancing safety, nutritional value, affordability, and environmental concerns when making food decisions is
challenging for many Maine families. This study provided more data to support the assertion that people who
are concerned about mercury should feel comfortable eating shrimp, including Maine shrimp. Shrimp are a lowfat, healthy protein source, and Maine shrimp are a local, affordable, and sustainably managed seafood choice.
Maine Safe Eating Guidelines
According to the Maine Department of Environmental Protection, mercury levels in Maine fish, loons, and
eagles are among the highest in North America. This has led the Maine Center for Disease Control and
Prevention to issue a statewide advisory recommending that pregnant women, women of childbearing age,
and young children limit their fish consumption based on the type of fish they consume. The advisories have
been in place since 1994 and remain in effect today because mercury levels in fish have not decreased.
Currently 49 states, including Maine, have fish consumption advisories due to mercury contamination.
http://www.maine.gov/dep/mercury/
The Maine Safe Eating Guidelines set fish consumption limits to protect everyone.
http://www.maine.gov/dhhs/eohp/fish
The Maine Family Fish Guide: Advice from the
Maine Center for Disease Control and Prevention
Healthy Fish for Pregnant Women and Families
Fish: 2 Meals a Week for Good Health
Eat 2 Meals a Week of Different Fish
for pregnant women, children, and adults
Buy
nd the Facts Fast
Cook Fish for Pregnant Women
Healthy
and Families:
Eat 2 Meals a Week of Different Fish
h to Eat and Fish to Avoid
ily-Friendly Fish: Eat 2 Meals a Week of Different Fish. . . . . . Page 3
h Mercury Fish to Limit or Avoid . . . . . . . . . . . . . . . . . . . . . . . . Page 4
Best Choices
Seafood High in Omega 3 Oils and Low in Mercury
Buy, Cook, Eat Fish Out
• Salmon – fresh and canned
Try budget friendly canned salmon. See recipe on page 10.
’t Buy Smelly Fish! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 5
l-Out Poster: Healthy Seafood 2 Meals A Week . . . . . . . . . . Page 6
for Dinner: Cook In or Eat Out . . . . . . . . . . . . . . . . . . . . . . . . Page 8
ish Sticks, Salmon, and Fish You Catch
to Eat Tuna, Fish Sticks, Farm-Raised Fish . . . . . . . . . . . . . . . . Page 9
mon: 3 Choices for Taste, Health, and Budget . . . . . . . . . . . . . Page 10
You Catch in Rivers, Lakes, or the Ocean . . . . . . . . . . . . . . . . Page 11
High Mercury
to Limit or Avoid
• SardinesFish
and Herring
Fresh Salmon
Smelt
Fish low in mercury
Light
Canned Tuna
Atlantic Mackerel
Clams and
Scallops
Haddock, Hake,
Cod and Pollock
Don’t Buy Smelly Fish!
• Smelt
Buy Fresh Fish
Advice for• Pregnant
and Nursing Women,
Atlantic Mackerel
• Buy fish in places you trust. Ask when the fish you plan to buy
Women Who
May Get Pregnant, and
• Mussels
came in. If Canned
it’s more than
a day or two old, choose
another kind.
Salmon
Sardines
Children Under Age 8
More Great Choices
• Check that fish has been properly iced or kept in a refrigerator.
Fish to Avoid: Pregnant and nursing women, women who may get
Other under
Seafood
Low NOT
in Mercury,
but Not as High Ask to smell it. It should smell fresh and mild, not strong or “fishy.”
pregnant, and children
age 8 should
eat these 4 fish.
They’re too high
mercury: 3 Fish Oils
ininOmega
• Ask for recipes.
•• Swordfish
Light Canned Tuna
•• Shark
Scallops and Clams
•• King
Mackerel
Shrimp
– fresh, frozen, canned, from Maine and away
Eat Out
•• Tilefish
Flounder
and Sole
more information:
eral information: http://www.maine.gov/dhhs/eohp/fish/
king fish: www.deliciousdecisions.org/cb/rec.html
Catch
der Main ingredients, check seafood, scroll to bottom and click submit)
These fish are high
in mercury
because
they
eatCod
other fish or live
• Haddock,
Hake,
Pollock,
and
a long time. Mercury
can damage
brain starting
formfrom
or grow.
• Imitation
Crab ora Lobster
(This istomade
various fish.)
health information about mercury in fish or omega 3Ifoils,
call Maine
CDC That’s
whysign
babies
in the womb,
nursing babies, and young children
you’re
pregnant,
this
means
caution
• Lobster – but do not eat tomalley, the green stuff inside the body
free in Maine: 1-866-292-3474
are at most risk.
ing fish: www.ocean.udel.edu/mas/seafood/handling.html
onal Health Program,
ntrol and Prevention, DHHS
Fish low in mercury and high in Omega 3 fish oils
Buy Frozen Fish
Mussels
Lobster
Flounder
and Sole
Imitation Crab
and Lobster
Shrimp
Don’t Eat These Fish!
If you are pregnant, nursing, may get pregnant or a child under 8
• Frozen seafood is just as healthy as fresh. Just make sure the packages
are sealed tight, not torn or crushed on the edges. Also don’t buy
packages covered in frost or ice crystals. This could mean the fish has
been stored a long time or thawed and refrozen.
• If you see the letters FAS, they mean Frozen At Sea.
When you buy FAS fish, it may still be frozen or it may be thawed.
It’s safe to buy either way.
Fish to Limit: Pregnant and nursing women and children under age
Questions?
8 may safely eat one meal per week of one of these fish. Choose
Why
are Omega
fishfish
oils
important?
Store Fish Safely
other fish listed
on page
3 for the32nd
meal
that week.Omega 3 fish oils are “brain
food” for babies in the womb and babies who are nursing. These oils also
•
Tuna
steak
In accordance with Federal laws, the Maine Department of
help protect adults from heart attack deaths. Fish is also a great source of • Best to cook and eat, or freeze, fresh fish (and thawed FAS fish)
Health and Human Services does not discriminate on the basis
within 2 days of purchase. You can safely keep fresh fish that you
•protein,
Whitezinc
canned
tuna
page
9)
of sex, age, color, national origin, or disability in admission or
and iron
and(see
is low
in saturated
fat.
access to or treatment or employment in its programs and
buy or catch in the freezer for up to 3 months. Mark the date on
• Halibut steak
activities. The Department’s Affirmative Action Coordinator has
Most farm raised fish are safe to eat. See page 9. For farm raised salmon, the package!
been designated to coordinate our efforts to comply with and
implement these Federal laws and can be contacted for further
see page 10.
information at: 221 State Street, Augusta, Maine 04333, (207)
• Fish that you buy frozen should go right into your freezer when
Advice for Everyone Else
287-2567, or Hearing Impaired call 1-800-606-0215.
you get home. Don’t let it thaw
3 until ready to cook.
Fish to Limit: Other adults and children over age 8 may safely eat
It can stay in the freezer for up to 3 months.
up to 2 meals per month of swordfish, shark, king mackerel, and
• If fish smells strong or feels slimy, throw it out. Don’t cook it
tilefish. These fish are high in mercury because they eat other fish or
or
eat
it.
live a long time. Too much mercury lowers the heart healthy benefits of
Omega 3 fish oils.
Swordfish • Shark • King Mackerel • Tilefish
Everyone else can eat 2 meals a month of these 4 fish
Call the Maine CDC
toll free in Maine: 1-866-292-3474
This brochure was produced with funding from the U.S.
Environmental Protection Agency Cooperative Agreement
#CR82628301-0
sta, ME 04333
Gov. John Elias Baldacci
Health Literacy Center,
Biddeford, Maine
partners who helped decide and test content, language,
y Children’s Task Force, York County Alliance for
nty Parents as Teachers, Maine Nutrition Network
Limits on Fish You Catch: See eating limits for sport caught
fish (fish from Maine rivers, lakes, ocean) on page 11.
4
5
Acknowledgements
Maine Sea Grant provided funding and support for this research. The Senator George J. Mitchell Center at the University of Maine provided
support to S.J. Nelson for participation in this work. M. Lagerklint and C. Devoy at the Sawyer Environmental Chemistry Research Laboratory at
the University of Maine analyzed samples. K. Johnson of Husson University and staff from the Maine Center for Disease Control and Prevention
provided constructive comments and information about Maine’s human health guidelines.
Funding provided by:
Maine Sea Grant supports marine science research and outreach activities. Based at the University of Maine, our coastwide
program works in partnership with marine industries, scientists, government agencies, private organizations, and a
wide range of marine resource users. For more information on the activities of the Maine Sea Grant College Program at
the University of Maine, please call 207.581.1435 or visit our website at www.seagrant.umaine.edu.
Edited by Catherine Schmitt, Maine Sea Grant; Design by Kathlyn Tenga-González, Maine Sea Grant. Photos—Cover, shrimp: NOAA; seafood: Kathlyn Tenga-González. Page 2: Ken La Valley.
In complying with the letter and spirit of applicable laws and pursuing its own goals of diversity, the University of Maine shall not discriminate on the grounds of
race, color, religion, sex, sexual orientation, including transgender status or gender expression, national origin, citizenship status, age, disability, or veteran’s status in
employment, education, and all other areas of the University System. The University provides reasonable accommodations to qualified individuals with disabilities
upon request. Questions and complaints about discrimination in any area of the University should be directed to the Director of Equal Opportunity, the University
of Maine, 5754 North Stevens Hall, Room 101, Orono, ME 04469-5754, telephone (207) 581-1226, TTY (207) 581-9484.
MSG-E-10-16
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