1,1,2,2-Tetrachloroethane is an industrial chemical which has been used as a metal degreaser, and in paint, paint removers, mothballs and pesticides. It damages the liver and nervous system, and may cause cancer.

1,2,3-Trichloropropane is a potent carcinogen that contaminates drinking water in agricultural regions where it was historically used as soil fumigant. Click here to read more about carcinogenic VOCs.

Arsenic is a potent carcinogen and common contaminant in drinking water. Arsenic causes thousands of cases of cancer each year in the U.S. Click here to read more about arsenic.

Bromochloromethane is a tap water disinfection byproduct; it is also used as an intermediate in chemical manufacturing and as a fire extinguishing agent. Disinfection byproducts in drinking water increase the risk of cancer.

Bromodichloromethane, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Bromodichloromethane and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Cadmium is a toxic metal found in food and drinking water. It has been linked to kidney toxicity, bone damage, cancer, and damage to developing fetuses.

Carbon tetrachloride, a volatile carcinogenic solvent, has been used in industrial chemical production and as a dry cleaning ingredient.

Chloroform, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Chloroform and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy.

Dibromochloromethane, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Dibromochloromethane and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Dichloroacetic acid, one of the group of five haloacetic acids regulated by federal standards, is formed when chlorine or other disinfectants are used to treat drinking water. Haloacetic acids and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Haloacetic acids are formed when disinfectants such as chlorine are added to tap water. The group of five haloacetic acids regulated by federal standards includes monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid.

Nitrate, a fertilizer chemical, frequently contaminates drinking water due to agricultural and urban runoff, and discharges from municipal wastewater treatment plants and septic tanks. Excessive nitrate in water can cause oxygen deprivation in infants and increase the risk of cancer. Click here to read more about nitrate.

Nitrate and nitrite enter water from fertilizer runoff, septic tanks and urban runoff. These contaminants can cause oxygen deprivation for infants and increase the risk of cancer. Nitrite is significantly more toxic than nitrate. Click here to read more about nitrate.

Radium is a radioactive element that causes bone cancer and other cancers. It can occur naturally in groundwater, and oil and gas extraction activities such as hydraulic fracturing can elevate concentrations.

Dry cleaning chemical tetrachloroethylene, or perc, can cause cancer. It pollutes soil and groundwater due to emissions from dry cleaning facilities, and automotive, metalworking and other industries.

Thalium is a naturally occurring metal released into the environment from metal smelting and coal burning. Exposure to too much thalium can cause hair loss, liver damage, reduced sperm motility and nervous system impairment.

Trihalomethanes are cancer-causing contaminants that form during water treatment with chlorine and other disinfectants. The total trihalomethanes group includes four chemicals: chloroform, bromodichloromethane, dibromochloromethane and bromoform.

Trichloroacetic acid, one of the group of five haloacetic acids regulated by federal standards, is formed when chlorine or other disinfectants are used to treat drinking water. Haloacetic acids and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Vinyl chloride is a known human carcinogen used for production of polyvinyl chloride (PVC) plastics. Discharges from plastics manufacturing can contaminate drinking water with vinyl chloride.

1,1,1,2-Tetrachloroethane is a synthetic chemical used in metal degreasing and as an intermediate in industrial chemical production.

1,1,1-Trichloroethane is a solvent and a degreasing agent used for manufacturing metal products and as ingredient in cleaners and aerosols. Exposure to 1,1,1-trichloroethane can harm the nervous system, liver and circulatory system.

1,1,2-Trichloroethane is a volatile neurotoxic solvent used for manufacturing products such as plastic wrap and carpet backing. It causes liver tumors in animal studies.

1,1-Dichloroethane is used in industrial chemical synthesis; in plastics, paint, varnish and finish removers; and as a pesticide. It can cause cancer.

1,1-Dichloroethylene is used for plastics production. It damages DNA and causes cancer in laboratory animal studies.

1,1-Dichloropropene is an industrial chemical.

1,2,3-Trichlorobenzene is a solvent and an intermediate for chemical manufacturing that was used historically as an insecticide for termite control. The National Toxicology Program lists it as a "reasonably anticipated" human carcinogen.

1,2,4-Trichlorobenzene is an industrial solvent that can harm the adrenal glands and may increase the risk of cancer.

1,2,4-Trimethylbenzene is a chemical intermediate, industrial solvent and component of gasoline, coal tar and petroleum products. In laboratory animal studies, it harms the adrenal glands.

1,2-Dichloroethane is a volatile carcinogenic chemical used to make plastic products such as polyvinyl chloride.

1,2-Dichloropropane is a volatile carcinogenic solvent discharged from chemical factories and landfills. It also contaminates farmland due to its former use as a soil fumigant.

1,3,5-trimethylbenzene is a neurotoxic, volatile chemical found in gasoline, and used as a solvent and paint thinner.

1,3-Dichloropropane is an industrial solvent uncommonly detected in drinking water.

2,2-Dichloropropane is an industrial chemical.

Antimony is a naturally occurring metal that enters tap water from plumbing fittings and also from industrial uses, such as production of metal alloys, batteries and plastics. Antimony causes organ damage and shortens lifespans in studies of laboratory animals.

Barium is a mineral present in rocks, soil and water. High concentrations of barium in drinking water increase the risk of cardiovascular disease and hypertension.

Benzene is a known human carcinogen. It also damages blood cells and the nervous system. Emissions from petroleum processing, hazardous waste landfills and underground storage tanks contaminate drinking water with benzene.

Beryllium is a toxic metal that is both naturally occurring and released into the environment from industrial pollution and incineration. Beryllium can damage lungs, bones and the digestive system.

Bromobenzene is an industrial chemical.

Bromoform, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Bromoform and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Bromomethane, or methyl bromide, is a pesticide fumigant that was banned because it depletes the ozone layer.

Chloroethane is a volatile solvent used in manufacturing, and as a refrigerant and aerosol propellant.

Chloromethane is an industrial solvent, aerosol propellant and a refrigerant. It also forms as a byproduct of water disinfection. The EPA classifies chloromethane as possibly carcinogenic to humans.

Chromium is a naturally occurring metal, but industrial uses can elevate its levels in water. One form, hexavalent chromium, causes cancer. Total chromium is not a good indicator of the amount of hexavalent chromium in drinking water.

1,2-Dichloroethylene, a neurotoxic solvent, exists in two different forms: trans-1,2-dichloroethylene and cis-1,2-dichloroethylene. A mixture of the two forms is used to manufacture other solvents and chemical products.

1,3-Dichloropropene is a volatile cancer-causing chemical primarily used as a nematocide to fumigate agricultural soils. It exists in two different forms: cis-1,3-dichloropropene and trans-1,3-dichloropropene.

Cyanide is a toxic chemical that causes central nervous system and thyroid toxicity. Water contamination is generally the result of metal mining and chemical industry waste, runoff from agriculture and road salts used for melting ice.

Dibromomethane is an industrial chemical and is also formed when disinfectants like chlorine are added to drinking water.

Dichlorodifluoromethane (Freon-12) is a refrigerant, solvent and aerosol propellant banned in 2000 under the Montreal Protocol because of its ozone-depleting properties. Freons can cause heart, nervous system and liver damage.

Methylene chloride is a common industrial solvent used for paint stripping, vapor degreasing, printing, electronics manufacturing and cleaning. It causes cancer and liver damage in animal studies.

Ethylbenzene, a component of petroleum, is a volatile cancer-causing chemical primarily used for production of plastics and rubber. Ethylbenzene is also released from gasoline fuel emissions.

Fluoride occurs naturally in surface and groundwater and is also added to drinking water by many water systems to prevent cavities and support oral health in people.

In 2015, the Department of Health and Human Services updated its recommendation of an optimal level of 0.7 parts per million, or ppm, added to drinking water based on the health benefits of tooth decay prevention. Studies have shown that fluoride added to community water systems at this level reduces dental cavities, especially in children.

And studies have conclusively shown that fluoride in toothpaste and mouthwash can also provide these benefits.

Hexachlorobutadiene is an industrial chemical and possible human carcinogen.

Isopropylbenzene, also called cumene, is an intermediate in industrial chemical production, and is also used as a thinner for paints and enamels. The National Toxicology Program classifies isopropylbenzene as a "reasonably anticipated" human carcinogen.

m-Dichlorobenzene is an industrial chemical.

Manganese is a naturally occurring element that is common in food and drinking water. Excessive manganese exposures may impair children's attention, memory and intellectual capacity. Click here to read more about manganese.

Mercury is a potent neurotoxin that also damages the kidneys and other internal organs. Mercury enters drinking water from industrial pollution, mining wastes and coal-fired power plants.

Monochloroacetic acid, one of the group of five haloacetic acids regulated by federal standards, is formed when chlorine or other disinfectants are used to treat drinking water. Haloacetic acids and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Monochlorobenzene is used as a solvent for pesticides, a degreasing agent and an intermediate for manufacturing other chemicals. It causes liver and kidney damage in studies of laboratory animals.

n-Butylbenzene is an industrial chemical.

n-Propylbenzene is a constituent of petroleum and coal, used for chemical manufacturing and in textile dyeing and printing.

Nitrite, closely related to the fertilizer chemical nitrate, comes from urban runoff and from fertilizer applied to agricultural lands to pollute drinking water. Nitrite is significantly more toxic than nitrate. Excessive nitrite in water can cause oxygen deprivation in infants and increase the risk of cancer.

o-Chlorotoluene, also called benzyl chloride, is a solvent and a chemical intermediate used for manufacturing industrial and consumer products.

o-Dichlorobenzene is used as a chemical intermediate for making agricultural herbicides. It is toxic to the liver, kidneys and the nervous system, and causes cancer in animal studies.

p-Chlorotoluene is an industrial chemical.

p-Dichlorobenzene is a carcinogenic insecticide used in mothballs, and added to deodorant blocks made for trash cans and toilets. Long-term exposure can cause liver damage and kidney problems.

p-Isopropyltoluene is a volatile solvent derived from coal distillation and petrochemical processing.

sec-Butylbenzene is an industrial chemical.

Selenium is an essential element in diets. But too much selenium can decrease thyroid hormone production and cause hair loss, skin lesions and brittle fingernails.

Silver occurs naturally in surface and groundwater and can be added to water as a biocide that inhibits growth of bacteria and algae. Increasingly, the use of antimicrobial nano-sized silver particles in consumer products contributes to silver in water sources used for drinking water.

Styrene is a volatile cancer-causing chemical used for manufacturing Styrofoam (polystyrene) and other plastics. Releases from industrial production sites and hazardous waste landfills cause styrene contamination in drinking water.

tert-Butylbenzene is an industrial chemical.

Toluene is a volatile solvent that harms the nervous and immune systems, damages the liver and may increase the risk of miscarriage and birth defects.

1,2-Dichloroethylene, a neurotoxic solvent, exists in two different forms: trans-1,2-dichloroethylene and cis-1,2-dichloroethylene. A mixture of the two forms is used to manufacture other solvents and chemical products.

1,3-Dichloropropene is a volatile cancer-causing chemical primarily used as a nematocide to fumigate agricultural soils. It exists in two different forms: cis-1,3-dichloropropene and trans-1,3-dichloropropene.

Trichloroethylene, an industrial solvent and common groundwater pollutant, damages the immune system, harms the developing fetus and causes cancer.

Trichlorofluoromethane (Freon 11) is a refrigerant, solvent and aerosol propellant banned in 2000 under the Montreal Protocol because of its ozone-depleting properties. Freons can cause heart, nervous system and liver damage.

Xylenes are solvents used in industrial and consumer products, such as cleaning agents and paint thinners. Xylenes cause nervous system damage and may harm developing fetuses.