MERCURY in Fish and Shellfish

  

Why is it important to eat fish and shellfish?

Fish and shellfish are an important part of a well-balanced healthy diet. They contain high-quality protein and other essential nutrients, are low in saturated fat and contain omega-3 fatty acids.  Deep sea fishes like mackerel, herring, tuna, halibut, salmon, cod fish, whale, dolphin and seal blubber are rich in omega-3 fatty acids yielding 1 gram in about 3.5 ounces of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), ideal for making fish oil supplements.  Note that our body does not produce its own omega-3 fatty acids or make omega-3 fatty acids from omega-6 fatty acids.  DHA and EPA represent about 97% and 93% of all omega-3 fatty acids in the brain and eyes respectively.

 

Healthful benefits

 

+  Omega-3 intake is of great help in improving the blood circulatory system. It is commonly used to lower blood pressure or high cholesterol and for prevention of heart disease or stroke.  Clinical studies showed its effectiveness when taken in the recommended dosage.

 

+  Fish oil is occasionally used after heart transplant surgery to prevent high blood pressure and kidney damage that can be caused by the surgery itself or by drugs used to reduce the chances of the body rejecting the new organ.  In some instances,  it is also used after coronary artery bypass surgery to help keep the blood vessel that has been rerouted from closing up and reduces inflammation.  Of course, it should not be combined with other blood thinning drugs to avoid over-diluting problem.

 

+  As a brain food, those with nervous disorders like depression, psychosis, attention deficit-hyperactivity disorder (ADHD), Alzheimer’s disease can find improvement if fish oil is taken on a prolonged period.

 

+  Vision problems like dry eyes, glaucoma and age-related macular degeneration (AMD) do gain much benefits.

 

+  Women can take fish oil to prevent painful periods, breast pain and complications associated with pregnancy such as miscarriage, high blood pressure late in pregnancy and early delivery.

 

+  Sufferers of diabetes, asthma, developmental coordination disorders, movement disorders, dyslexia, obesity, kidney disease, weak bones (osteoporosis), certain diseases related to pain and swelling such as psoriasis, and preventing weight loss caused by some cancer drugs should include this fatty acid in the diet.

 

Mercury poisoning

 

Mercury poisoning is a disease caused by exposure to mercury or its compounds.  It is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses.

 

The consumption of fish and shellfish is by far the most significant source of ingestion-related mercury exposure in humans and animals, although plants and livestock also contain mercury taken in from soil, water and atmosphere, and ingesting other mercury-containing organisms.  Exposure to mercury can occur from breathing contaminated air, eating foods with mercury residues during processing, exposure to mercury vapour in mercury amalgam dental treatments, and from improper use or disposal of mercury and mercury-containing objects like batteries and fluorescent lamps.

 

Mercury is a highly reactive toxic agent that can cause damages to the central nervous system, endocrine system, kidneys and other organs, and adversely affects the mouth, gums and teeth.  Prolonged or heavy exposure to mercury vapour can result in brain, lung damage and ultimately death.

 

Mercury and its compounds are particularly toxic to fetuses and infants. Women who have been exposed to mercury in pregnancy can give birth to children with serious birth defects.

The most vulnerable groups are fetuses and infants. Women who have been exposed to mercury in pregnancy can give birth to children with serious birth defects. Kids can have severe neurological consequences, preventing nerve sheaths from forming properly, inhibiting the formation of myelin. There is some evidence that mercury poisoning may affect fertility in men, resulting in low sperm count.

 

Signs and symptoms

 

Symptoms typically include sensory impairment (vision, hearing, speech), disturbed sensation and a lack of coordination. The type and degree of symptoms exhibited depend upon the individual toxin, the dose, and the method and duration of exposure.

 

Mild symptoms of mercury poisoning include itching, burning or pain, skin discoloration (pink cheeks, fingertips and toes), swelling and shedding of skin.  Other symptoms may include profuse sweating, faster heart-beat, increased salivation and hypertension.

 

In affected children, bodily symptoms are - red cheeks, nose and lips, loss of hair, teeth and nails, transient rashes, muscle weakness, and increased sensitivity to light.  More serious symptoms may include kidney dysfunction or neuropsychiatric symptoms such as emotional instability, memory impairment or insomnia.

 

How much mercury is found in fish and shellfish?

 

As explained most marines have traces of mercury in their bodies.  For most of us eating fish and shellfish do not pose a health hazard.  However, the vulnerable ones like old people, sick people, children and pregnant mothers should exercise caution in selecting the fish intake.

The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) are advising this group of people to avoid some types of fish and eat fish and shellfish that are low in mercury.

 

Recommendations are as follows:

• Do not eat shark, swordfish, king mackerel or tilefish as they contain high levels of mercury.  Also are whale and dolphin meat harvested in Japan found to contain mercury exceeding 20 times the acceptable national standards.

• Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury.

• Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock and catfish.

• Another commonly eaten fish – white tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of white tuna per week.

• Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don’t consume any other fish during that week.

Same recommendation applied to children only to serve smaller portions.

Frequently Asked Questions :

• “What is mercury and methylmercury?”
  Mercury occurs naturally in the environment and can also be released into the air through industrial pollution.  After dropping from the air, it can accumulate in streams and oceans and turns into methylmercury in the water.  This is a harmful substance to an unborn baby and young child.  All marines taken from the waters are contaminated, the extent of which depends on the water condition and how much toxin is ingested.

• “I’m a woman who could have children but I’m not pregnant – so why should I be concerned about methylmercury?”
  By eating certain types of fish high in methylmercury regularly, it can accumulate in your blood stream over time. Though our body can remove it naturally, the process is very gradual.  So way before pregnancy, it may be present in your body.  This being the reason why women who are expecting in the near future should avoid eating certain types of fish high in mercury content.

• “Which ones has more methylmercury?”
  Larger fish like swordfish, shark, king mackerel and tilefish that have lived longer tend to chalk up high levels of methylmercury given more time to accumulate it and thus pose the greatest risk. Other types of fish and shellfish may be eaten in the amounts recommended by FDA and EPA.

• “I don’t see the fish (for list see below) I eat in the advisory. What should I do?”
  If you want more information about the levels in the various types of fish you eat, see the FDA food safety  EPA website.

• “What about fish sticks and fast food sandwiches?”
  Fish sticks and “fast-food” sandwiches are commonly made from fish that are low in mercury.

• “The advice about canned tuna is in the advisory, but what’s the advice about tuna steaks?”
  As tuna steak generally contains higher levels of mercury than canned light tuna, you may eat up to 6 ounces (one average meal) of tuna steak per week.

• “What if I eat more than the recommended amount of fish and shellfish in a week?”
  One week’s consumption of fish does not change the level of methylmercury in the body much at all. If you eat a lot of fish one week, you can cut back for the next week or two. Just make sure you average the recommended amount per week.

• Is mercury the only contaminant to watch? Many fish and seafood products contain potentially high levels of lead, PCBs and other contaminants as well.

http://www.fda.gov/Food/FoodSafety/Product-SpecificInformation/Seafood/FoodbornePathogensContaminants/Methylmercury/ucm115662.htm

In summary…

A well-balanced diet that includes a variety of fish and shellfish can contribute to a healthy body for adults and children in their proper growth and development due to the many nutritional benefits.  So do not stop eating but eat wisely!

 

Mercury Levels in Commercial Fish and Shellfish (1990-2010)

 

Table 1. Fish and Shellfish With Highest Levels of Mercury
SPECIES	MERCURY CONCENTRATION (PPM)					NO. OF SAMPLES	Source of data
	MEAN	MEDIAN	STDEV	MIN	MAX
MACKEREL KING	0.730	N/A	N/A	0.230	1.670	213	GULF OF MEXICO REPORT 2000
SHARK	0.979	0.811	0.626	ND	4.540	356	FDA 1990-2007
SWORDFISH	0.995	0.870	0.539	ND	3.220	636	FDA 1990-2010
TILEFISH (Gulf of Mexico)	1.450	N/A	N/A	0.650	3.730	60	NMFS REPORT 1978

Table 2. Fish and Shellfish With Lower Levels of Mercury
SPECIES	MERCURY CONCENTRATION (PPM)					NO. OF SAMPLES	SOURCE OF DATA
	MEAN	MEDIAN	STDEV	MIN	MAX
ANCHOVIES	0.017	0.014	0.015	ND	0.049	14	FDA 2007-2010
BUTTERFISH	0.058	N/A	N/A	ND	0.36	89	NMFS REPORT 1978
CATFISH	0.025	0.005	0.057	ND	0.314	57	FDA 1991-2010
CLAM *	0.009	0.002	0.011	ND	0.028	15	FDA 1991-2010
COD	0.111	0.066	0.152	ND	0.989	115	FDA 1991-2010
CRAB 1	0.065	0.050	0.096	ND	0.610	93	FDA 1991-2009
CRAWFISH	0.033	0.035	0.012	ND	0.051	46	FDA 1991 -2007
CROAKER ATLANTIC (Atlantic)	0.065	0.061	0.050	ND	0.193	57	FDA 2002 – 2009
FLATFISH 2*	0.056	0.050	0.045	ND	0.218	71	FDA 1991-2009
HADDOCK (Atlantic)	0.055	0.049	0.033	ND	0.197	50	FDA 1991-2009
HAKE	0.079	0.067	0.064	ND	0.378	49	FDA 1994-2009
HERRING	0.084	0.048	0.128	ND	0.560	26	FDA 2006-2009
JACKSMELT	0.081	0.050	0.103	0.011	0.500	23	FDA 1997-2007
LOBSTER (Spiny)	0.093	0.062	0.097	ND	0.270	13	FDA 1991-2005
MACKEREL ATLANTIC (N.Atlantic)	0.050	N/A	N/A	0.020	0.160	80	NMFS REPORT 1978
MACKEREL CHUB (Pacific)	0.088	N/A	N/A	0.030	0.190	30	NMFS REPORT 1978
MULLET	0.050	0.014	0.078	ND	0.270	20	FDA 1991-2008
OYSTER	0.012	ND	0.035	ND	0.250	61	FDA 1991-2009
PERCH OCEAN *	0.121	0.102	0.125	ND	0.578	31	FDA 1991-2010
POLLOCK	0.031	0.003	0.089	ND	0.780	95	FDA 1991-2008
SALMON (CANNED) *	0.008	ND	0.017	ND	0.086	34	FDA 1992-2009
SALMON (FRESH/FROZEN) *	0.022	0.015	0.034	ND	0.190	94	FDA 1991-2009
SARDINE	0.013	0.010	0.015	ND	0.083	90	FDA 2002-2010
SCALLOP	0.003	ND	0.007	ND	0.033	39	FDA 1991-2009
SHAD AMERICAN	0.045	0.039	0.045	0.013	0.186	13	FDA 2007-2010
SHRIMP *	0.009	0.001	0.013	ND	0.050	40	FDA 1991-2009
SQUID	0.023	0.016	0.022	ND	0.070	42	FDA 2005-2010
TILAPIA *	0.013	0.004	0.023	ND	0.084	32	FDA 1991-2008
TROUT (FRESHWATER)	0.071	0.025	0.141	ND	0.678	35	FDA 1991 -2008
TUNA (CANNED, LIGHT)	0.128	0.078	0.135	ND	0.889	551	FDA 1991-2010
WHITEFISH	0.089	0.067	0.084	ND	0.317	37	FDA 1991-2008
WHITING	0.051	0.052	0.030	ND	0.096	13	FDA 1991-2008

Table 3. Mercury Levels of Other Fish and Shellfish
SPECIES	MERCURY CONCENTRATION (PPM)					NO. OF SAMPLES	SOURCE OF DATA
	MEAN	MEDIAN	STDEV	MIN	MAX
BASS (SALTWATER, BLACK, STRIPED)3	0.152	0.084	0.201	ND	0.960	82	FDA 1991-2010
BASS CHILEAN	0.354	0.303	0.299	ND	2.180	74	FDA 1994-2010
BLUEFISH	0.368	0.305	0.221	0.089	1.452	94	FDA 1991-2009
BUFFALOFISH	0.137	0.120	0.094	0.032	0.430	17	FDA 1992-2008
CARP	0.110	0.134	0.099	ND	0.271	14	FDA 1992 – 2007
CROAKER WHITE (Pacific)	0.287	0.280	0.069	0.180	0.410	15	FDA 1997
GROUPER (ALL SPECIES)	0.448	0.399	0.278	0.006	1.205	53	FDA 1991-2005
HALIBUT	0.241	0.188	0.225	ND	1.520	101	FDA 1992-2009
LOBSTER (NORTHERN / AMERICAN)	0.107	0.086	0.076	ND	0.230	9	FDA 2005-2007
LOBSTER (Species Unknown)	0.166	0.143	0.099	ND	0.451	71	FDA 1991-2008
MACKEREL SPANISH (Gulf of Mexico)	0.454	N/A	N/A	0.07	1.56	66	NMFS REPORT 1978
MACKEREL SPANISH (S. Atlantic)	0.182	N/A	N/A	0.05	0.73	43	NMFS REPORT 1978
MARLIN *	0.485	0.390	0.237	0.100	0.920	16	FDA 1992-1996
MONKFISH	0.181	0.139	0.075	0.106	0.289	9	FDA 2006-2008
ORANGE ROUGHY	0.571	0.562	0.183	0.265	1.120	81	FDA 1991-2009
PERCH (Freshwater)	0.150	0.146	0.112	ND	0.325	19	FDA 1991-2007
SABLEFISH	0.361	0.265	0.241	0.090	1.052	26	FDA 2004 – 2009
SCORPIONFISH	0.233	0.181	0.139	0.098	0.456	6	FDA 2007 – 2008
SHEEPSHEAD	0.093	0.088	0.059	ND	0.170	6	FDA 2007 – 2009
SKATE	0.137	N/A	N/A	0.04	0.36	56	NMFS REPORT 1978
SNAPPER	0.166	0.113	0.244	ND	1.366	67	FDA 1991-2007
TILEFISH (Atlantic)	0.144	0.099	0.122	0.042	0.533	32	FDA 2002-04
TUNA (CANNED, ALBACORE)	0.350	0.338	0.128	ND	0.853	451	FDA 1991-2010
TUNA(FRESH/FROZEN, ALL)	0.391	0.340	0.266	0.000	1.816	420	FDA 1991 – 2010
TUNA (FRESH/FROZEN, ALBACORE)	0.358	0.360	0.138	ND	0.820	43	FDA 1992-2008
TUNA (FRESH/FROZEN, BIGEYE)	0.689	0.560	0.341	0.128	1.816	21	FDA 1991 – 2005
TUNA (FRESH/FROZEN, SKIPJACK)	0.144	0.150	0.119	0.022	0.260	3	FDA 1993 – 2007
TUNA (FRESH/FROZEN, YELLOWFIN)	0.354	0.311	0.231	0.000	1.478	231	FDA 1991-2010
TUNA (FRESH/FROZEN, Species Unknown)	0.415	0.339	0.308	0.000	1.300	120	FDA 1991-2010
WEAKFISH (SEA TROUT)	0.235	0.157	0.216	0.000	0.744	46	FDA 1991-2005

Source of data:

FDA 1990-2010 , “National Marine Fisheries Service Survey of Trace Elements in the Fishery Resource” Report 1978, “The Occurrence of Mercury in the Fishery Resources of the Gulf of Mexico” Report 2000

**Mercury was measured as Total Mercury except for species (*) when only Methylmercury was analyzed.  ND-mercury concentration below detection level (Level of Detection (LOD)=0.01ppm)

The following species have been removed from the tables:  

• Bass (freshwater), Pickerel – not commercial

Includes: Blue, King, Snow,Flounder, Plaice, Sole, Sea bass/ Striped Bass/ Rockfish

NOTE:  On February 8, 2006, technical changes were made to the data that was posted on January 19, 2006. The changes corrected data or more properly characterized the species of fish or shellfish sampled.

 

Source:  http://www.fda.gov/Food/FoodSafety/Product-SpecificInformation/Seafood/FoodbornePathogensContaminants/Methylmercury/ucm115644.ht