Zinc

Zinc is a bluish-white shiny metal and one of the most common elements found in the earth's crust. It is found in air, soil, water, and in all foods. Zinc is also found in toxic coal waste, and sewage sludge.

Uses
Zinc is used commercially as a coating to prevent rust, in dry cell batteries, and in alloys like brass and bronze. Today, pennies in the United States are made from a zinc and copper alloy. Zinc is combined with other elements to make zinc compounds, which are then used to make paint, rubber, dyes, wood preservatives, and ointments.

In the Environment
While some zinc is released into the environment via natural processes, most comes from human activities, including mining, steel production, coal burning, and burning of waste. Once in the environment, zinc attaches to soil, sediments, and dust particles in the air. Rain and snow remove zinc from the air. Most zinc in the soil stays in the soil and does not dissolve in water. However, some zinc compounds can move into the groundwater and into waterways. Zinc can build up in fish and other organisms, but cannot build up in plants.

Hazardous waste sites often contain zinc chloride, zinc oxide, zinc sulfate, and zinc sulfide.

In Sewage Sludge
In sewage sludge applied to land, the U.S. EPA limits zinc to a concentration of 7,500 parts per million. In the Targeted National Sewage Sludge Survey, a 2009 test of 84 samples of sewage sludge from around the U.S., the EPA found zinc in every sample in concentrations ranging from 216 to 8,550 parts per million.

Human Exposure
Humans are exposed to zinc via food, water, and dietary supplements. Beverages stored in metal containers or water that flows through pipes coated with zinc are also be a source of zinc exposure. Occupational exposure also occurs in the following industries: construction, painting, automobile mechanics, mining, smelting, and welding; manufacture of brass, bronze, or other zinc-containing alloys; manufacture of galvanized metals; and manufacture of machine parts, rubber, paint, linoleum, oilcloths, batteries, some kind of glass, ceramics, and dyes.

Health Effects
Zinc is an essential element in the human diet. Both too little zinc and too much zinc can be harmful. Harmful effects typically begin at levels 10 to 15 times higher than the amount required for good health. In the short term, large doses can cause stomach cramps, nausea, and vomiting. Over a longer period of time, high doses of zinc can cause anemia and decrease the levels of good cholesterol (HDLs). Rats fed very large doses of zinc became infertile.

Breathing in large amounts of zinc dust or fumes can cause a short-term disease called "metal fume fever." Low levels of zinc acetate and zinc chloride may also cause skin irritation if applied to skin.

Related SourceWatch articles

 * Biosolids
 * Sewage sludge
 * Food Rights Network
 * Heavy metals and coal

External resources

 * Dietary Supplement Fact Sheet: Zinc, National Institutes of Health