Hesperian Health Guides
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Heavy metals such as lead, mercury, cadmium, and chromium, are harmful to people, animals and plants, even in very small amounts. Heavy metals are released into the environment by many industries, such as oil drilling and refining, mining, metal smelting, tanneries, and incineration.
Heavy metals are harmful when people breathe in or swallow dust or fumes, or get them on the skin or in their eyes and absorb them into the blood. Heavy metals may also collect in plants and animals and cause harm when people eat them.
Signs of heavy metal poisoning
Heavy metal poisoning usually does not happen from one large exposure, but from exposure to small amounts over time. Early signs include shaking, irritability, difficulty concentrating, tiredness, and weakness in the hands and feet. Other signs include:
Heavy metal poisoning can also cause damage to the kidneys and the reproductive system, and other serious long term health problems.
The next few pages discuss problems of mercury. Other heavy metals have similar problems. See problems from lead.
|Heavy metals travel through the air, into water, fish, soil, and plants, and into our bodies.|
Mercury is a heavy metal that can cause serious health problems when it is released into the environment by mining, especially gold mining, burning coal, building dams, or when products that contain mercury become waste. Mercury is highly toxic.
When mercury collects in rivers, lakes, and streams and combines with rotting plants, it can turn into a more toxic form called methyl mercury. Even a very small amount of mercury can poison all the fish in a pond or river. Methyl mercury in the environment is toxic for centuries.
Health problems from mercury
Breathing in or absorbing through the skin even a very small amount of mercury can cause damage to the nerves, kidneys, lungs, and brain, and birth defects. The health problems can take many years to show up.
Mild mercury poisoning causes tingling in the lips, tongue, fingers, and toes, and trembling in the hands and feet. In some cases, these signs do not appear until long after exposure.
Severe mercury poisoning causes headaches, memory loss, difficulty coordinating movement and vision, dizziness, metal taste in the mouth, muscle spasms, pain and stiffness in joints and muscles, rapid heartbeat, and a very weak or very strong pulse.
Exposure to mercury in men can lead to loss of ability to have sex, and sterility.
Exposure to mercury in women can lead to failure to have monthly bleeding and other problems in having babies.
In pregnant women, even small amounts of mercury can cause their babies to have developmental problems (see “Toxics at different stages of children’s growth”).
Mercury in fish
|Because larger fish and animals usually eat many smaller ones, the mercury builds up in their bodies.|
Methyl mercury collects in the bodies of fish, animals, and people. Fish that live in polluted water can be dangerous to eat, even though the water itself may not be harmful to bathe or swim in.
Small amounts of mercury can pass through the body without causing harm. If we stop eating food that contains mercury, our bodies begin to get rid of the mercury that has collected. But when we take in more mercury than our bodies can get rid of, mercury causes serious health problems.
Fish are good food, full of protein. Fish are sometimes called “brain food” because they have fats that are good for the brain. They are part of traditional diets for many people. But if they are caught in waters where mines drain or where mercury has been dumped, they may have unsafe amounts of mercury.
Fish and food safety
You cannot tell if a fish contains mercury by looking at it. Because mercury is stored in the flesh of the fish, there is no special way to clean or cook fish that will prevent mercury exposure. Some types of fish are likely to have less mercury in them, due to their feeding habits or life histories, and are safer for people to eat. If you live in a mine-drainage area,
It is more dangerous to eat:
- larger, older fish.
- bottom-feeding fish, such as catfish and carp.
- only fish as your main food.
- fish organs, especially the liver.
It is safer to eat:
- smaller, younger fish and fish that feed on insects.
- less fish. Meat, chicken, rice with lentils or beans, eggs, milk, and cheese are other good sources of protein.
- fish mixed with foods like rice or potatoes. This will not reduce the amount of mercury in the fish, but it will reduce the amount of fish you eat at your meal.
Treatment for heavy metal poisoning
Heavy metal poisoning is very difficult to treat. The main treatment is called chelation (pronounced kee-lay-shun). Chelation uses herbs and medicines to carry toxic metal out of the body. It is most effective for poisoning caused by sudden exposure to a large dose of metals (acute poisoning). Most exposure to heavy metals is from daily contact over a long period, so this treatment may not be useful.
Good nutrition can protect the body
When people do not have enough vitamins, calcium, iron, or protein in their diet they may suffer more severely from heavy metal poisoning. The body will use toxic heavy metals to fill in for the missing nutrients — leading to serious illness.
Foods that help the body resist heavy metal poisoning include: Beans, whole grains, meat, nuts, eggs, milk, red, yellow and green vegetables, dark leafy greens, coriander, cabbage, and fruits.
No foods will treat severe poisoning from heavy metals or other toxic chemicals. However, improving the diet helps in treating most illnesses, including illnesses caused by heavy metals. In areas where people are very poor and are exposed to heavy metals and other toxics, such as mining communities, the best approach may be a community nutrition program to ensure that everyone is well-fed, strong, and resistant to illness. (For a story about a nutrition program in a mining community, see “School and nutrition for child miners.”)