What is Methylmercury? How does it get into fish?• Essentially mercury, which is extremely toxic to the nervous system, kidneys, liver, and others.• Sources - Both man-made & natural: Industrial air & water pollution, but also as a by-product of forest fires, volcanoes, and the natural weathering of mercury-containing rock.• Methylmercury then leaks into the air or rivers, getting carried to the ocean over land or by air.• Plankton & fish both eat and absorb MeHg in the ocean (referred to as “bio-accumulation”).• Smaller fish are consumed by larger fish in the food chain. Larger fish also have longer lives, thus larger (potential) amounts of MeHg.
What is Methylmercury? How does it get into the body?• Human ingestion of fish with MeHg, leads to contamination of blood.• During digestion, MeHg is complexed with other proteins, mimicking an essential amino acid Methionine.• MeHg is thus transported freely across the mother’s blood-brain barrier, and to the child through the placenta.• The body can remove methylmercury, but it may take over a year for levels to drop significantly. (MeHg has a half-life of 50 days)
Methylmercury: Pathology• MeHg prevents the fetal nerve sheaths from forming , by inhibiting the formation of myelin.• Because of it’s long dwelling time in the body, toxicity is usually indicated by the peak level of mercury, and not the duration of exposure.• Treatment: Chelation therapy – ingestion of compounds that bind to heavy metals in the body.
Case Study # 1• Minimata, Japan: Caused by Chisso Corp.’s release of industrial wastewater into Minimata bay & Shiranui Sea, 1932-1968.• Outbreak ensued with patients c/o neurological impairment of unknown etiology. (Signs/Symptoms: ataxia, numbness, fatigue, vision/hearing/speech impairment – insanity, paralysis, coma, death)• As of 2001, 2,265 people have been officially recognized with the condition; 1,784 have died, over 86 million USD has been awarded to 10,000 victims for financial compensation.
Case Study # 2• Between 1962 – 1970 Dryden Chemicals in Ontario, Canada dumped 20,000 lbs of MeHg into the Wabigoon- English River system.• In 1970, the Canadian government officially banned fishing in the river due to toxins.• Two Native American societies downstream experienced adverse health affects, were tested (by a specialist from the Minimata contamination), and found to have significantly high methyl-mercury levels.• Canada’s government, plus the companies involved, paid 16.67 million in compensation.
Parasites• Parasitism is a factor in all food, but greater in uncooked fish, such as sushi.• Women are at a greater risk during pregnancy due to hormonal changes that suppress the immune system.• Listeriosis – Bacteria found in groundwater, soil, plants, animals; easily destroyed by cooking. – 14-fold increase in the incidence of infection for pregnant women; pregnant women make up 27 % of all cases. Results: Listeriosis bacteria infects the mother’s nervous system and/or placenta, leading to health problems after birth for the child. – S/S: GI problems (< 3 D.) , fever, chills, headache. Muscle & back aches > 11 D.• Toxoplasmosis – 1.5 mil. People infected with this every year; most asymptomatic & resolve by immune system. – S/S: (> 10 D.) Low-grade fever w/ rash, muscle aches, headaches, possible lymphadenopathy.
Parasites (cont’d)• Salmanellosis – Bacteria spread through GI contents or waste of animals. – Greatest risk = Salmonella Typhi; although rare, can cause miscarriage, stillbirth or premature labor. – S/S: (< 12 - 36 H.): Headache, N/V/D, abd. pain, chills, fever.• Campylobacteriosis – Bacteria found in GI of animals (mostly poultry), and untreated water. – If transmitted to the placenta, can cause miscarriage, stillbirth & premature labor. – S/S: (< 2 – 5 D.) Fever, N/V/D, stomach cramps, muscle pain.• Although most parasites can be treated relatively easily with antibiotics, taking them during pregnancy may cause adverse affects to the developing fetus.
The Bottom Line: Prevention• Bacterial Prevention - FDA Recommendations: – Wash hands frequently. – Ensure cooking & food preparation utensils are cleaned thoroughly & not cross-contaminating. – Thoroughly rinse fruits and vegetables before consuming. – Cook meats to over 165˚ F. – Avoid raw fish, unpasteurized milk & under-cooked dairy products (soft cheeses), cold hotdogs & deli meats.• Methlymercury Toxicity Prevention: – Since no amount of cooking can eliminate MeHg, avoid large fishes: salmon steak, tile fish, shark, king mackerel, and limited consumption of albacore tuna. – Additionally, avoid freshwater fish from local waters, as there may be concentrated levels of industrial pollution. – Limit albacore tuna consumption to < 6 0z per week, and < 12 oz of other fish & shellfish per week.
Discussion Questions1. Do the benefits of seafood consumption outweigh the potential risks?2. What is your favorite type of seafood?3. Has this presentation caused you to consider avoiding seafood consumption is general?