Mercury in Fish

Fish has always been recognized as a nutritious food that provides us with many health benefits. It is a good source of protein, vitamins and minerals and an excellent source of omega 3 fatty acids. Research has shown positive effects on health such as reducing the risk of cardiovascular disease, childhood asthma and prostate cancer. Researchers worldwide recommend that people consume at least 1-2 serves of fish/seafood a week.

Some people avoid consuming fish in their diet due to a concern that fish is high in mercury. Hopefully I can shed some light on this and provide you with amounts that are safe to consume.

So what is Mercury and where do we find it?

Mercury occurs naturally in the environment in air, water and food. It can be organic, inorganic, and metallic with the organic form being the most dangerous. Most people are exposed though food with the main source coming from fish. Micro-organisms transform the mercury into a toxic organic form called methyl-mercury. Aquatic organisms will then consume the mercury and also absorb it through their gills. All fish will contain some mercury with the amount depending on the habitat, age, size and feeding pattern of the fish. It is the predatory fish that are larger and at the top of the food chain that will tend to have higher levels of mercury. These fish also tend to live longer so they accumulate more methyl mercury through their life. Therefore it is the fish that are short lived and not predatory that we want to be including more in our diets.

Why the concern?

Just like fish our bodies accumulate mercury and we store it in fat tissue, brain and bones which our systems cannot cope with. Our bodies can remove mercury but it is a slow process which sometimes requires several months. This becomes even more difficult when amounts going into the body exceed what we are excreting.

The main concern is that exposure at toxic levels can result in neurological and renal damage. This causes a concern for unborn babies as their brain is developing at a rapid rate. This is why there are recommendations in place for pregnant women as the mercury consumed can be passed through the placenta to the developing baby. In Australia there have been no reported cases of mercury poisoning from seafood. There are also regulations in place to make sure that there is a limit on the mercury that can be present in fish sold.

Should we be limiting the amount we eat?

Most people consume only moderate amounts of fish therefore the nutritional benefits of consumption far outweigh the risk from the small amount of mercury present. It is still highly important for pregnant women and young children to also include fish in their diet. The main point would be (especially for pregnant women) to avoid consuming to much fish that is known to be high in mercury such as those listed below.

• Shark (flake in the fish and chip shops)
• Ray
• Swordfish/Broadbill
• Barramundi
• Gemfish
• Orange roughy
• Ling
• Southern bluefin tuna
• Marlin
• Catfish

Food Standards Australia New Zealand (FSANZ) has found it safe for all populations to eat 2-3 serves per week of most types of fish. They recommend limiting a few types of fish as mentioned above. FSANZ also have recommendations for pregnant women, women planning pregnancy and young children (see table below).

Some interesting points/tips

• Another high source of mercury in fish can come from waters polluted by manufacturing or mining.
  Cooking or food processing techniques such as canning or freezing will not reduce the mercury content in fish.
• Canned tuna would not be the safest choice of fish during pregnancy especially as you don’t really know what sort of tuna is in the can. A better choice would be salmon and canned salmon which can be consumed more frequently.
• There are no recommendations to restrict fish oil tablets as they are not a major source of mercury.

If you have any questions please send an email to bianca@thermomix.com.au

Useful Links

Mercury in Fish Brochure from FSANZ (PDF)
FSANZ updates advice on mercury in fish (Australia only)