Widely distributed in low concentrations in water; also occurs as a result of contamination through its manufacture; byproduct of smelting.

0.05 mg/l MCL

Causes death through heart failure; chronic exposure may cause neurological difficulties and cancer, particularly of the skin. Elevated levels may cause histological/morphological changes in animal tissues; changes in physiology, biochemistry, behavior or reproduction of aquatic organisms.

May enter water from rock weathering, soil runoff, mining.

.006 mg/l MCL

In animals, causes decreased lifespan, weight.

Can enter waters from mining operations or when corrosive water leaches it from asbestos cement pipes; natural deposits; manufacture of cement products, paper, paint, and plastics.

7 million fibers per liter longer than 10 millimicrons

Known human carcinogen when inhaled. Basis for water quality standard based on non-cancerous tumors in rats.

Food is more likely source than water; byproduct of coal burning, diesel fuels; also naturally occurring.

2 mg/l MCL

Blocks nerves and affects heart and blood vessels.

Major source is through fossil fuel combustion.

0.004 mg/l MCL

Likely human carcinogen; can damage bones, lungs, and cause weight loss.

Natural in zinc ores; may be inhaled through cigarette smoke; byproduct of mining, smelting; corrosion of galvanized pipe; sewage sludge.

0.005 mg/l MCL

Causes damage to kidneys, digestive tract upsets; brittle bones; linked to lung cancer. Elevated levels may cause histological/morphological changes in tissues; changes in physiology, biochemistry, behavior or reproduction of aquatic organisms.

Naturally occurring but quite rare; improper waste disposal or runoff; waste incineration; mining sites; industrial discharge, chrome plating.

0.1 mg/l MCL

Causes kidney, liver, nervous and circulatory damage; also respiratory disorders, dermatitis, and digestive problems and lung cancer. Elevated levels may cause histological/morphological changes in tissues; changes in physiology, biochemistry, behavior or reproduction of aquatic organisms.

More frequent in surface water than groundwater; can be dissolved from plumbing; water chlorination increases concentration.

1.3 mg/l (Action Level)

Necessary to human health but too high levels can irritate the gastrointestinal tract.

Short lived and not common in U.S. atmosphere and water supplies.

0.2 mg/l MCL

High levels can cause brain, spleen, liver damage. Low doses do not accumulate.

Natural in most waters; occurs in most foods; added to public water supplies but occasionally in greater amounts than is safe for children's teeth.

4 mg/l MCL

Excessive fluorides (2mg/l is the SMCL) may produce fluorosis (mottling) of teeth. Optimum concentrations from .7 to 1.2 mg/l are recommended; also could cause a crippling skeletal disease-fluorosis.

Gasoline, paints and ceramic products; caulking, and pipe solder. Acidic water causes lead to corrode and dissolve into water systems, if present in lead containing pipes, solders, or fixtures.

15 ug/l (Action Level) in drinking water

Affects almost every organ and system; most sensitive is central nervous system; can damage kidneys and immune system; hypertension; deficits in learning abilities. Elevated levels may cause histological/morphological changes in tissues; changes in physiology, biochemistry, behavior or reproduction of aquatic organisms.

Occurs naturally in coal and mineral ores; used in fungicides; preservatives in cans of water based paints, battery cells, thermometers, fluorescent lamps, industrial waste discharge.

.002 mg/l MCL

Exposed generally via ingestion of food and water. Toxic to developing fetuses. Can cause mental retardation, blindness, death. Highly toxic to fish; LC 50 ranges from .0044 to 0.42 mg/l. Elevated levels may cause histological/morphological changes in tissues; changes in physiology, biochemistry, behavior or reproduction of aquatic organisms.

Rarely found in water supplies but may occur due to human activities such as mining, smelting.

0.1 mg/l MCL

Believed essential to humans in low levels but higher levels may cause kidney, heart, liver damage and dermatitis.

Municipal and industrial wastewater; refuse dumps; animal feed lots; septic systems; leachate from manured or fertilized land; power plants; auto exhaust.

10 mg/l MCL

Toxicity is due to the reduction of nitrate to nitrite which can form methemoglobinemia ("blue baby" syndrome) in infants; possible carcinogen if converted to N-nitrosamine. In presence of sufficient P, nitrate can stimulate growth of plants, bacteria, and fungi, which may become injurious to designated uses of water.

Naturally occurs in atmosphere; found in fertilizers, animal wastes, and septic systems.

1 mg/l MCL

May result in death by suffocation in infants; causes breath shortness.

Very little is found in drinking water supplies; primary source is weathering rocks and soil; water solubility varies. Used in pigments/dyes; manufacture of glass, paints; fungicides; feed additives.

.05 mg/l MCL

In humans, too much can cause hair and fingernail loss, and damage to kidneys, liver, and nervous and circulatory systems. Too little can cause adverse health effects.

Occasionally occurs in contaminated groundwater; rare occurrence in tap water. Used in manufacturing and as rodent poison.

.002 mg/l MCL

Affects gastrointestinal tract and nervous system, and damages liver, kidneys, and brain; also causes hairlessness.