The heavy metals, which include copper (Cu), zinc (Zn), lead (Pb), mercury (Hg), nickel (Ni), cobalt (Co), and chromium (Cr), are common trace constituents in the earth crust. Their concentrations in the ambient environment have increased dramatically since the Industrial Revolution, as have lead and copper since Roman times. Many of these metals play an essential role in human physiology. For example, the enzymes that synthesize DNA and RNA contain zinc ions, and cobalt is an integral part of coenzyme B 12 and
|Contaminant||MCL or TT 1 (mg/L) 2||Potential Health Effects from Ingestion of Water||Sources of Contaminant in Drinking Water|
|Maximum Contaminant Level (MCL) –The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards.|
|Treatment Technique –A required process intended to reduce the level of a contaminant in drinking water.|
|2 Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts per million.|
|3 Lead and copper are regulated by a treatment technique that requires systems to control the corrosiveness of their water. If more than 10 percent of tap water samples exceed the action level, water systems must take additional steps. For copper, the action level is 1.3 mg/L, and for lead is 0.015 mg/L.|
|SOURCE: U.S. Envionmental Protection Agency. Ground Water and Drinking Water. Available from http://www.epa.gov/safewater/mcl.html#/mcls|
|Cadmium||0.005||Kidney damage||Corrosion of galvanized pipes; erosion of natural deposits; discharge from metal refineries; runoff from waste batteries and paints|
|Chromium (total)||0.1||Allergic dermatitis||Discharge from steel and pulp mills; erosion of natural deposits|
|Copper||TT 3 ; Action level = 1.3||Short term exposure: Gastrointestinal distress||Corrosion of household plumbing systems; erosion of natural deposits|
|Long term exposure: Liver or kidney damage|
|People with Wilson's Disease should consult their personal doctor if the amount of copper in their water exceeds the action level|
|Lead||TT 3 ; Action level = 0.015||Infants and children: Delays in physical or mental development; children could show slight deficits in attention span and learning abilities||Corrosion of household plumbing systems; erosion of natural deposits|
|Adults: Kidney problems; high blood pressure|
|Mercury (inorganic)||0.002||Kidney damage||Erosion of natural deposits; discharge from refineries and factories; runoff from landfills and croplands|
vitamin B 12 . It is possible to be deficient in these metals, or to have an optimal or a damaging or lethal intake. However, nonessential elements such as chromium, lead, and mercury have little or no beneficial role in the human body, and the daily intake of these metals is often toxic or lethal. Many heavy metals cause nervous-system damage, with resulting learning disorders in children. Ingestion of mercury can cause the severe breakdown of the nervous system, and metals such as lead and nickel can cause autoimmune reactions. Chromium occurs in a relatively harmless form and a much more dangerous, oxidized hexavalent form. Several studies have shown that chromium (VI) compounds can increase the risk of lung cancer and that ingesting large amounts of chromium (VI) can cause stomach upsets and ulcers, convulsions, kidney and liver damage, and even death, according to the Agency for Toxic Substances and Disease Registry. The dangers of hexa-valent chromium in drinking water were popularized in the movie Erin Brockovich. Many fish are very sensitive to heavy-metal pollution. For example, trout cannot live in waters that contain more than about five parts per billion of copper. Heavy-metal contamination is very widespread, especially lead and mercury.
Most heavy-metal contamination stems from high-temperature combustion sources, such as coal-fired power plants and solid-waste incinerators. Local metal sources may include metal-plating industries and other metal industries. The use of leaded gasoline has led to global lead pollution even in the most pristine environments, from arctic ice fields to alpine glaciers. The metal fluxes from point sources have been strictly regulated, and the introduction of unleaded gasoline has taken a major lead source away. Several sites with severe heavy-metal pollution have become Superfund sites, most of them still under study for decontamination. Site decontamination can be done with large-scale soil removal and metal stripping, or through more gradual methods, like phytoremediation. Nonetheless, even today metals are delivered from the atmosphere to the landscape. In the United States, drinking water is monitored for heavy metals to ensure that their concentration falls below the safe limit or maximum contaminant level (MCL) set by the Environmental Protection Agency. Many urban estuaries like Boston Harbor, San Francisco Bay, and Long Island Sound are severely contaminated with heavy metals. These sedimentary basins will remain polluted for decades, and a small percentage of the sediment-bound metals is released back into the water and occasionally transformed into more dangerous forms.
U.S. Department of Labor, Occupational Safety and Health Administration. "Safety and Health Topics: Toxic Metals." Available from http://www.osha-slc.gov/SLTC/metalsheavy .
Johan C. Varekamp