For sixty-one years, chemical companies in Ashland, MA dumped their chemical waste into the ground near the Sudbury River. Rain washed the chemicals, including the toxic chemical mercury, into the river. The mercury was carried downstream and dangerous amounts of it still is found in the water and the riverbed. The federal Environmental Protection Agency has published a plan to help restore the river’s water quality, but some local residents want to stop the agency from carrying it out.
THE CHEMISTRY BEHIND THE NEWS:
Mercury is a chemical element which is represented by the symbol Hg. In its elemental form it is a metal. It is unusual as it is a liquid at room temperature. Because it is a liquid, mercury evaporates fairly easily to form mercury vapor, which has the chemical symbol Hg(g). Although both are harmful, mercury vapor is more toxic than the liquid metal because the vapor is absorbed easily through the lungs. In the body, elemental mercury reacts with enzymes that contain the element selenium, deactivating them and leading to brain and nerve damage.
In the presence of oxygen or sulfur, mercury is oxidized to the mercury(II) ion, Hg2+. This ion is known to cause kidney damage.
Although these two forms of mercury are toxic, the mercury in the Sudbury river exists in an even more toxic form called methyl mercury. The chemical formula for methyl mercury is [HgCH3]+. Methyl is the chemical name for the CH3 part of the molecule. Methyl mercury is formed from elemental mercury when it is buried in places with low oxygen and large amounts of decaying organic material, such as riverbeds and lake bottoms. Bacteria that live in these environments have enzymes that add the methyl group to the mercury atom.
In living organisms, methyl mercury binds tightly to the amino acid cysteine, which is found in proteins. That means that it is absorbed very easily when it is ingested. It also hangs around in the body for a long time. If a human being eats a fish contaminated with methyl mercury, half of the methyl mercury will still be in their body after 50 days. This means that methyl mercury can build up in the bodies of animals like fish and people that keep eating contaminated food over a long period of time.
The EPA has determined that the amount of methyl mercury that is in the Sudbury River is dangerous to those people who eat fish they catch in the river. The methyl mercury may also be damaging the wildlife such as birds, fish, turtles, and mammals that live in the river. Therefore, they are proposing to place a layer of sand over the contaminated river bottom to keep the mercury from spreading into the water.
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