Mercury in the Environment and Water Supply




Mercury Analysis (Univ. of Alberta)













Mercury in Fish

Because mercury occurs naturally in the environment, it is easily transported into the atmosphere and released into water and land. Once in the water, the mercury settles to the bottom, and can be transformed into methyl mercury by way of chemical changes due to bacteria found in the water. The methyl mercury can then be absorbed into fish by way of their gills or the organisms that they consume. This means that mercury levels in predator fish will usually be higher. Once in the fish’s body, the methyl mercury binds with the tissues of the fish, even the muscle tissue; cooking will not even reduce the amount of methyl mercury in the fish body.

Methyl mercury is found in fish everywhere, some types more than others. The usual amount of mercury found is at levels of anywhere between 0.01ppm to 0.5ppm, although in larger fish, such as swordfish or shark, and even some larger tuna, the levels can be elevated to regions of 1.0ppm, which is the FDA’s limit for human consumption For “commercially important species,” the most mercury that was found was less than 0.3ppm. To prevent fish that contains more than 1.0ppm of methyl mercury from being sold on the market, the FDA works with state regulators to monitor all commercial fish that are bought and sold locally, as well as monitoring imported fish by not allowing fish that exceed the FDA level of 1.0ppm into the states.

The danger of eating fish with mercury mostly affects women who are pregnant, and young children. The methyl mercury causes damage to the nervous system. Methyl mercury accumulates in fish such as Shark, Swordfish, King mackerel, marlin and Tilefish. Because these are larger fish, they tend to prey on other fish, and will contain all of the methyl mercury from every fish eaten. By consuming less of these, there is less chance of damage to the unborn child, or infant. The FDA goes on to report that fish in moderation (once per week) will not affect a person to the point of poisoning. Even so, in a 2001 consumer advisory report provided by the FDA and the EPA that women who are pregnant, of nursing age, and young children should limit their intake of fish, avoiding larger fish, and also avoid fish that are caught by family or friends from fresh water sources.

In recent studies done (August 29, 2003), it has been determined that mercury in fish is not as toxic as proposed. It was found that the type of mercury that is in fish that are consumed is not the most toxic type of mercury, and is far less harmful that methyl mercury chloride causes. In a study done in Seychelles Islands in Africa, it was found that there was no hard evidence that children born to mothers who consumed a lot of fish suffered from neurological problems when they were older. It was also found that fish do not contain methyl mercury chloride, but contain methyl mercury cysteine, or something that is similar by using an X-ray spectroscopy to obtain the spectra of the mercury in the fish. Although it was noted that the dangers of methyl mercury cysteine are not known, the zebra fish larva could hold up to twenty times more of the substance compared to that of methyl mercury chloride.