Heavy Metals in Fish

Eating certain kinds of fish has become a major health concern due to the amount of heavy metals and other contaminants found in water. Seafood is a healthy source of iodine, essential fats and easily digested protein and is often considered a healthy addition to any diet.  There are ways to safely eat fish, it’s just a matter of how often and what kinds you choose.

What is a heavy metal?

There is no firm definition of what a heavy metal is, however some definitions are based on density. Copper, nickel, cadmium, iron, lead, mercury and zinc usually fit into this category. When considering heavy metals in the ocean and the effect on human health, lead, mercury and cadmium give the most cause for concern.

Heavy metals in the ocean     

Heavy metals accumulate in the ocean due to increased industrial activity and disposing of waste products into waterways. Overall there is an increase of heavy metals in our atmosphere which subsequently leads to an increase in ocean metal concentration. Believe it or not, heavy metals are a natural component of the earth’s crust and weathering and erosion cause metals to wash from the land into the water.

Levels of heavy metals, especially mercury, accumulate in fish as they feed. It is also absorbed through their gills as they swim. Mercury in the water is converted by microorganisms to methylmercury which is the most dangerous form.

Who is at risk?

Every person who consumes seafood is at some risk. Mercury is a known neuro toxin that can bioaccumulate in humans causing:

• numb or tingling fingers, lips and toes
• developmental delays in children
• muscle and joint pain
• increased risk of heart attack.

Pregnant women are at greater risk as their unborn baby’s nervous system is the most vulnerable to the effects of mercury. Mercury exposure may slow a child’s development in the early years, affecting attention, memory and developmental milestones such as walking and talking. Even women who are planning to conceive in the next six months, infants and young children should also limit their exposure to heavy metals in fish.

Fish with the highest levels of mercury

Generally speaking, the larger and older the fish, the higher the level of heavy metal contamination. Other factors include species of fish and its location, diet and habitat. Fish that are at the top of the ocean food chain tend to contain more mercury.

Examples of fish to avoid:

• Swordfish
• King mackerel and tilefish
• Shark
• Barramundi
• Gemfish
• Orange roughy (deep sea perch)
• Ling
• Southern bluefin tuna

A guide to choosing the safest fish

Choose fresh, wild-caught fish from Australian and New Zealand waters. Imported fish, especially from Thailand, usually have much higher levels of contamination as fish are either farmed or caught in heavily polluted waters.

Here are some safer seafood options.

• Shellfish, including prawns, lobsters and oysters
• Salmon
• Tinned tuna (chunk light, skipjack)
• Snapper
• Whiting
• Anchovies
• Perch
• Cod
• Calamari

If catching and eating your own fish, don’t fish in polluted waters. Bottom feeder species, such as catfish, may ingest more pollutants.

Limiting your exposure

Avoid fish with higher levels of mercury and limit your seafood intake of safer fish to 2-3 serves per week to reduce heavy metal exposure. One serve of fish equates to 150g for adults and 75g for children.

Eliminating heavy metals

Another component to address is supporting your body so that it can safely eliminate heavy metals to prevent storage in tissues.

To reduce your heavy metal burden, eat a diet high in fresh fruits and vegetables to supply your body with an abundance of antioxidants and fibre that support the bodies natural detoxification processes.

Coriander, zinc, selenium, milk thistle, vitamin C and chlorella are used in natural therapies to chelate heavy metals or support the health of our important detoxification organs such as the liver and kidneys.

Reasons to eat fish

Australia’s leading health research body, the National Health and Medical Research Council (NHMRC), suggests that Australians should eat more fish. Seafood, particularly fish, is considered an important part of any diet and if eaten within guidelines provides a source of calories and a range of important vitamins, minerals and other nutrients. It is rich in omega-3 essential fatty acids which encourages healthy heart, eyes, brain, joint and skin function. Regular consumption of fish can reduce the risk of various diseases and disorders including asthma, dementia, diabetes and inflammatory conditions. It is also high in iodine, B12, zinc and vitamins A and D (depending on species).

The future of our oceans

Due to increased awareness, changes in legislation and much research, the future is looking brighter. A major review of data collected in the last four years confirms that today’s oceans contain far lower levels of mercury, DDT and other toxic substances in the last four decades. They found a significant drop in mercury concentrations—from about 50% for mercury to more than 90% for polychlorinated biphenyls, or PCBs.

Things to remember

• Avoid fish that contain higher amounts of mercury
• Safely consume seafood with lower levels of heavy metals 2-3 times per week
• These guidelines are particularly important for pregnant women, women planning to conceive within the next 6 months and children under the age of 6
• Fish is highly nutritious and should be an important component of one’s diet

References

1. http://www.foodstandards.gov.au/consumer/chemicals/mercury/Pages/default.aspx
2. https://www.betterhealth.vic.gov.au/health/healthyliving/mercury-in-fish
3. https://www.betterhealth.vic.gov.au/health/healthyliving/fish
4. http://www.latimes.com/science/la-me-fish-toxins-20160208-story.html
5. Starling P, Charlton K, McMahon AT, Lucas C. Fish intake during pregnancy and foetal neurodevelopment—a systematic review of the evidence. Nutrients. 2015 Mar 18;7(3):2001-14 https://www.ncbi.nlm.nih.gov/pubmed/25793632
6. Mozaffarian D, Rimm EB. Fish intake, contaminants, and human health: evaluating the risks and the benefits. JAMA. 2006 Oct 18;296(15):1885-99 https://www.ncbi.nlm.nih.gov/pubmed/17047219
7. Balshaw S, Edwards J, Daughtry B, Ross K. Mercury in seafood: mechanisms of accumulation and consequences for consumer health. Rev Environ Health. 2007 Apr-Jun;22(2):91-113 https://www.ncbi.nlm.nih.gov/pubmed/17894202