Metal contaminants are found naturally in the environment, however, excessive levels can be increased through industrial activity or pollution. You will see that certain species of fish can accumulate more than others and it is usually predatory fish.
Mercury is the metal that presents the most concern with regards to seafood consumption and health so lets talk about it.
What is Mercury?
- Elemental mercury- liquid at room temperature (known as “quicksilver”), can vaporize with heat or contact with air
- Inorganic mercury- salts
- Organic mercury compounds- Alkyl mercurial ex: methymercury (This form is ingested by fish)-bacteria puts the methyl group (CH3) on mercury.
Uses of Mercury
- Mirror and Felt hat industries 19th century-lead to occupational exposure
A fictional character in Lewis Carroll’s Alice’s Adventures in Wonderland, famous phrase “mad as a hatter” This phrase is from neurological toxicity from mercury poisoning in the felt hat industry. Hence the felt hat he wears. (Trivia)
- Medical devices like thermometers (we are trying to phase these out)
- Compact fluorescent light bulbs
- Liquid elemental mercury can help concentrate gold from crushed ore or sediment (big pollutant), mining
- Amalgam tooth fillings, medicinal applications, hair dyes, Chinese traditional medicine applications (also phasing out), vaccines (use to have thimerosal-mercury containing)
- Wood preservation, outdoor painting, electroplating, coal combustion, power plants
Remember there are many forms of mercury. Our main focus is pollution of ex: methylmercury which finds its way into bodies of water and accumulates in fish tissue.
So what happens if I eat a lot of methylmercury?
- It’s absorbed from our intestinal tract into our bloodstream. Its lipophilic (meaning its fatty like in configuration), thus it can cross the blood brain barrier and deposit in the brain.
So then what…
- Accumulation in the brain (CAUSES CELL DEATH): Cause numbness around mouth, malaise, visual field deficits, deafness, coordination issues (not reversible)
- Acrodynia: syndrome reported in small kids (google it to learn more)
- Kidney disease-subtle abnormalities noted (reversible)
- This mercury substance does cross the placenta and will effect a developing fetus (talk to your doctor about this)- Definitely need to be aware of how much and what type of fish you are eating
Prevention is key! Limit dietary exposure.
So you are probably reading this thinking ok this sounds interesting but come on does this really happen I have never heard of anyone getting mercury toxicity.
- Study on Iraqi farmers, had outbreak in their seed grain 1971-2. From eating bread, many kids were effected.
- Japan: 1953-9. Minamata Bay fish contaminated with methylmercury.
All these folks had neurological issues as described above. Some with very detrimental consequences.
From studies like these guidelines have been made to stay far away from the “toxic zone”
Click below to see a table of fish and mercury content
- Natural Resources Defense Council: fish with 0.3 to 0.49 mg/kg (o.3-0.49 ppm) may be safely consumed three times per month. Fish with >0.5 mg/kg (>0.5 ppm) should be avoided.
3 Safety Tips (FDA)
By following these 3 recommendations for selecting and eating fish or shellfish, women and young children will receive the benefits of eating fish and shellfish and be confident that they have reduced their exposure to the harmful effects of mercury.
- Do not eat shark, swordfish, king mackerel or tilefish because they contain high levels of mercury.
- 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, albacore (“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 albacore 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.
- Mercury is a natural occurring metal used in various industries
- Organic (methylmercury) “pollution” can accumulate in our waterways and end up in fish and shellfish and cause health hazards (Neurological effects)
- Certain types of fish have higher levels of methylmercury, such as shark, swordfish, king mackerel, and tilefish
- Children and Pregnant woman should be extremely cognizant to what type of fish they are eating and how often
- Fish is GOOD FOR You, just be aware as to how often you are eating it and how much mercury you are consuming! If you have any questions ask your doctor.
Thanks for taking the time to read this. If you have any questions as always, please feel free to contact me.