Heavy metals
Toxic elements (lead, mercury, cadmium, arsenic) that can contaminate food through the environment and accumulate in the body, mainly concerning certain specific foods.
Heavy metals (mercury, lead, cadmium, arsenic) are environmental contaminants found in soil, water and air (pollution, industry, natural sources). They can contaminate the food chain and accumulate in the body (which eliminates them poorly), with chronic toxicity (neurological, kidney, carcinogenic).
A fresh angle (bioaccumulation and the foods to watch): a key phenomenon, heavy metals concentrate as they move up the food chain (biomagnification). A large, old predatory fish accumulates the mercury of all the small fish it has eaten. Hence the targeted recommendations:
- Mercury in large predatory fish: tuna, swordfish, shark, marlin. The advice is to limit these fish, especially for pregnant women and young children (mercury affects the neurological development of the foetus). The paradox: fish is excellent (omega-3), but choosing small oily fish (sardine, mackerel, herring), rich in omega-3 AND low in mercury, is the optimal strategy.
- Cadmium: in some plant foods (cocoa, certain cereals, sunflower seeds) and offal, depending on the soil.
- Arsenic in rice: rice accumulates inorganic arsenic from soil and water more than other cereals. Rinsing rice and cooking it in a large volume of water (then draining) reduces the arsenic. Worth watching for heavy consumers and for infant feeding (rice cakes, rice drinks).
- Lead: historically found in water pipes, certain utensils and polluted soils.
Reducing your exposure:
- Vary your fish (small oily fish rather than large predators), and vary your food sources in general
- Rinse rice and cook it well (large volume of water)
- Be careful with poorly controlled supplements (some algae, clays and plants can be contaminated)
- Choose reliable origins
The benefit/risk paradox of fish: importantly, despite the mercury, the benefits of fish (omega-3, protein, iodine, selenium) far outweigh the risks for the general population, provided you vary your choices and favour small fish. Avoiding fish for fear of mercury would be counter-productive.
Sources of contamination: large fish (mercury), rice (arsenic), certain plant foods and offal (cadmium), polluted water and environments.