Luckiamute Domestic Water Coop

What it means: 1,1,1-Trichloroethane (methyl chloroform) was a widely used industrial solvent for metal cleaning, electronic component degreasing, and aerosol propellants. Production was phased out under the Montreal Protocol due to ozone depletion; US manufacture essentially ended by 1996. Legacy groundwater contamination persists at former industrial sites and Superfund locations across the country.

Health effects: Chronic exposure to 1,1,1-trichloroethane affects the central nervous system (dizziness, incoordination) and can cause liver and cardiovascular effects at elevated doses. EPA has not classified it as a human carcinogen. It degrades in anoxic groundwater to 1,1-dichloroethylene and eventually vinyl chloride, which are more acutely toxic breakdown products.

Limit: 0.2 mg/L (200 ppb)

What it means: 1,1,2-Trichloroethane is a chlorinated solvent used as a chemical intermediate and industrial cleaning agent. It enters drinking water through industrial discharge and improper solvent disposal. It is less commonly detected than its isomer 1,1,1-trichloroethane but persists in groundwater and has been found at industrial contamination sites.

Health effects: Chronic exposure to 1,1,2-trichloroethane is associated with liver and kidney damage. EPA classifies it as a probable human carcinogen (Group B2) based on animal tumor data. Long-term exposure above the MCL is the primary concern; the general population near contaminated groundwater sources faces the greatest risk.

Limit: 0.005 mg/L (5 ppb)

What it means: 1,1-Dichloroethylene (1,1-DCE) is a chlorinated solvent used in the production of polyvinylidene chloride (PVDC) plastic wraps and coatings. It also occurs as a breakdown product of 1,1,1-trichloroethane and trichloroethylene in contaminated groundwater. Industrial discharge and solvent disposal are the primary pathways into drinking water sources.

Health effects: Chronic exposure to 1,1-dichloroethylene is associated with liver and kidney damage. EPA classifies it as a possible human carcinogen (Group C) based on animal data. Acute high-level exposure can cause central nervous system depression. Long-term exposure above the MCL is the primary concern for public water system violations.

Limit: 0.007 mg/L (7 ppb)

What it means: 1,2,4-Trichlorobenzene is an industrial solvent and chemical intermediate used in dye manufacturing, herbicide production, and as a dielectric fluid. It enters drinking water through discharge from industrial facilities and leaking underground storage tanks. It is moderately persistent in groundwater and has been detected in groundwater near industrial sites.

Health effects: Chronic exposure to 1,2,4-trichlorobenzene is associated with changes in adrenal gland function and liver and kidney effects in animal studies. EPA classifies it as a possible human carcinogen (Group C). Long-term exposure above the MCL is the primary concern for public water system violations.

Limit: 0.07 mg/L (70 ppb)

What it means: DBCP is a halogenated aliphatic soil fumigant used to control nematodes on crops including pineapple, grapes, and citrus. Its use was banned in the United States in 1979 after it was linked to male sterility in factory workers. DBCP is highly mobile in soil and extremely persistent in groundwater, and remains a significant contaminant in agricultural regions such as California's Central Valley.

Health effects: DBCP is classified by EPA as a probable human carcinogen (Group B2). It causes male reproductive toxicity — including reduced sperm count and sterility — at relatively low exposure levels. Chronic exposure is also associated with kidney damage. Men of reproductive age and developing fetuses are most at risk.

Limit: 0.0002 mg/L (0.2 ppb)

What it means: 1,2-Dichloroethane (ethylene dichloride) is a chlorinated solvent used as a chemical intermediate in vinyl chloride production and in other manufacturing processes. It is one of the highest-volume chlorinated compounds produced in the US. It enters drinking water through industrial discharge, leaking underground storage tanks, and improper disposal. It is moderately persistent in groundwater.

Health effects: Chronic exposure to 1,2-dichloroethane is associated with liver and kidney damage and neurological effects. EPA classifies it as a probable human carcinogen (Group B2) based on animal evidence of gastrointestinal and mammary gland tumors. Long-term exposure above the MCL is the primary concern; communities near chemical manufacturing facilities and Superfund sites face the greatest risk.

Limit: 0.005 mg/L (5 ppb)

What it means: 1,2-Dichloropropane (propylene dichloride) is a chlorinated solvent used as a chemical intermediate and industrial cleaning agent. It was historically used in fumigant mixtures for soil treatment but agricultural uses were canceled. It enters drinking water through industrial discharge, improper disposal, and leaching from contaminated soil. It is moderately persistent in groundwater.

Health effects: Chronic exposure to 1,2-dichloropropane is associated with liver and kidney damage. EPA classifies it as a probable human carcinogen (Group B2) based on animal evidence of liver and mammary gland tumors. Long-term exposure above the MCL is the primary concern; communities near Superfund sites and former agricultural fumigation areas face elevated exposure risk.

Limit: 0.005 mg/L (5 ppb)

What it means: Silvex (2,4,5-trichlorophenoxypropionic acid) was a chlorophenoxy herbicide used to control woody plants and broadleaf weeds on cropland, orchards, and roadsides. All uses were canceled in the United States in 1985 due to contamination with dioxin (TCDD) during manufacture. Legacy residues persist in agricultural soils and can leach into groundwater.

Health effects: Chronic exposure to Silvex is associated with liver damage. EPA classifies it as a possible human carcinogen (Group C). The dioxin contamination historically associated with its production added to concern about its carcinogenicity, though the MCL applies to Silvex itself. Long-term exposure above the MCL is the primary concern.

Limit: 0.05 mg/L (50 ppb)

What it means: 2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the most widely used herbicides in the world, applied to lawns, turf, pastures, and crops to control broadleaf weeds. It remains in active use in the United States. 2,4-D is water-soluble and can enter drinking water through agricultural and residential runoff and leaching into groundwater.

Health effects: Chronic exposure to 2,4-D is associated with kidney, liver, and adrenal gland damage in animal studies. IARC classifies it as possibly carcinogenic to humans (Group 2B); EPA's classification is not likely to be carcinogenic under current guidelines. Individuals with kidney or liver conditions may face greater risk from long-term exposure.

Limit: 0.07 mg/L (70 ppb)

What it means: Alachlor is a chloroacetanilide herbicide sold under the trade name Lasso, used primarily on corn and soybeans. It remains in limited use in the United States. Alachlor is moderately mobile in soil and can leach into groundwater and enter surface water through agricultural runoff, particularly in the Midwest.

Health effects: Chronic exposure to alachlor is associated with eye, liver, kidney, and spleen damage. EPA classifies it as a probable human carcinogen (Group B2) based on animal studies showing nasal tumors. Long-term exposure above the MCL is the primary concern; children may be more susceptible to carcinogenic effects.

Limit: 0.002 mg/L (2 ppb)

What it means: Atrazine is one of the most widely used herbicides in the United States, applied primarily to corn and sorghum fields. It is chemically stable and highly mobile in soil, making it one of the most frequently detected pesticides in US groundwater and surface water. Agricultural runoff after spring planting is the primary pathway into drinking water sources.

Health effects: Chronic exposure to atrazine is associated with endocrine disruption — particularly effects on reproductive hormones — and cardiovascular and adrenal effects in animal studies. EPA classifies atrazine as not likely to be a human carcinogen under current guidelines, though its endocrine-disrupting properties remain under research scrutiny. Fetuses and infants may be most sensitive to hormonal effects.

Limit: 0.003 mg/L (3 ppb)

What it means: Lindane (gamma-hexachlorocyclohexane, or gamma-BHC) is an organochlorine insecticide once used widely for crop protection, seed treatment, and head lice medication. Agricultural and pharmaceutical uses were canceled in the US by 2009. It is persistent in the environment and can leach from historically treated soils into groundwater.

Health effects: Lindane affects the central nervous system; acute high-dose exposure causes seizures, muscle spasms, and liver damage. Chronic exposure is associated with liver and kidney damage and immune system effects. EPA classifies lindane as a probable human carcinogen (Group B2). Children are particularly vulnerable to neurological effects.

Limit: 0.0002 mg/L (0.2 ppb)

What it means: Benzene is a fundamental aromatic hydrocarbon and component of crude oil, gasoline, and many industrial chemicals. It enters drinking water primarily through leaking underground fuel storage tanks, industrial discharge, and contaminated runoff. It is one of the most commonly detected VOCs at Superfund sites and underground storage tank cleanup sites across the United States.

Health effects: Benzene is classified by EPA as a known human carcinogen (Group A). Long-term exposure causes leukemia, particularly acute myeloid leukemia (AML), and other blood disorders including aplastic anemia. There is no established safe threshold. Children and individuals with compromised immune systems are most vulnerable to hematological effects.

Limit: 0.005 mg/L (5 ppb)

What it means: Benzo(a)pyrene (BaP) is a polycyclic aromatic hydrocarbon (PAH) formed during incomplete combustion of organic material. It enters drinking water primarily through leaching from coal tar linings in older water storage tanks and distribution pipes, as well as from contaminated soil and industrial runoff. It is one of the most studied PAHs due to its potent carcinogenicity.

Health effects: Benzo(a)pyrene is classified by EPA as a probable human carcinogen (Group B2) and is a well-established animal carcinogen. Long-term exposure is associated with increased cancer risk, particularly for reproductive organ cancers. It is also linked to immune system effects and developmental toxicity in animal studies.

Limit: 0.0002 mg/L (0.2 ppb)

What it means: Carbofuran is a systemic carbamate insecticide and nematicide used on crops including corn, rice, and soybeans. EPA regulatory action beginning in 2006 led to cancellation of most food uses by 2009 due to acute toxicity to birds and other wildlife. Carbofuran is water-soluble and mobile in soil and has been detected in groundwater near agricultural areas.

Health effects: Carbofuran is one of the most acutely toxic carbamate pesticides. It inhibits acetylcholinesterase, causing cholinergic toxicity at the nervous system. Short-term exposure above the MCL can cause nausea, headache, blurred vision, and in high doses respiratory failure. Children are most vulnerable to acute effects. EPA has not classified carbofuran as a human carcinogen.

Limit: 0.04 mg/L (40 ppb)

What it means: Carbon tetrachloride is a chlorinated solvent formerly used extensively as a cleaning and degreasing agent, fire extinguisher propellant, and grain fumigant. Its production was phased out under the Montreal Protocol. Legacy groundwater contamination is widespread at former industrial facilities, Superfund sites, and agricultural fumigation areas.

Health effects: Carbon tetrachloride is classified by EPA as a probable human carcinogen (Group B2). Chronic exposure causes liver and kidney damage and is associated with liver cancer in animal studies. Acute high-dose exposure causes severe hepatotoxicity — nausea, vomiting, jaundice, and acute liver failure. Communities near contaminated groundwater plumes and historical industrial sites face the greatest long-term risk.

Limit: 0.005 mg/L (5 ppb)

What it means: Chlordane is a broad-spectrum organochlorine insecticide used extensively for termite control and on crops including corn and citrus. All uses were banned in the United States in 1988. Chlordane is extremely persistent in soil and can leach slowly into groundwater over decades. Legacy contamination is most prevalent in areas with intensive historical use.

Health effects: Chronic chlordane exposure is associated with liver damage and increased cancer risk. EPA classifies it as a probable human carcinogen (Group B2). Animal studies show liver tumors at elevated doses. It bioaccumulates in fatty tissue and can be passed to infants through breast milk. Children and immunocompromised individuals are most vulnerable.

Limit: 0.002 mg/L (2 ppb)

What it means: Chlorobenzene is an aromatic solvent and chemical intermediate used in the production of DDT, nitrochlorobenzenes, and other industrial chemicals. It enters drinking water through discharge from chemical manufacturing facilities and leaching from contaminated industrial sites. It is moderately volatile and moderately persistent in groundwater.

Health effects: Chronic exposure to chlorobenzene is associated with liver and kidney effects in animal studies. EPA has not classified it as a human carcinogen based on available data. Short-term exposure at high levels can cause nervous system depression. Long-term exposure above the MCL is the primary concern for public water system violations.

Limit: 0.1 mg/L (100 ppb)

What it means: Radium-226 and Radium-228 are naturally occurring radioactive isotopes produced by the decay of uranium and thorium in bedrock. They dissolve into groundwater, particularly in deep aquifers with low oxygen and low pH. Granite bedrock and some deep sandstone and limestone aquifers present conditions where combined radium can reach detectable levels in drinking water.

Health effects: Radium is a bone-seeking radionuclide that accumulates in skeletal tissue after ingestion. Long-term exposure increases the risk of bone cancer and leukemia. There is no safe threshold for ionizing radiation — the MCL is set at a level balancing risk reduction with treatment feasibility. Children are particularly vulnerable due to higher rates of bone growth and calcium uptake.

Limit: 5 pCi/L (combined Ra-226 and Ra-228)

What it means: Dalapon is an organochlorine herbicide used to control grassy weeds in sugarcane, corn, and other crops, as well as along roadsides and waterways. It remains in agricultural use in the United States. It reaches water primarily through agricultural runoff and leaching.

Health effects: Long-term exposure to dalapon is associated with liver and kidney effects in animal studies. EPA has not classified it as a human carcinogen based on available data. The general population is the primary concern for chronic low-level exposure through drinking water.

Limit: 0.2 mg/L (200 ppb)

What it means: Di(2-ethylhexyl) adipate (DEHA) is a synthetic plasticizer used to make PVC and other plastics flexible. It enters drinking water through discharge from chemical factories and leaching from PVC plastic materials including some water distribution components. It is one of the less commonly detected regulated organic contaminants in US public water systems.

Health effects: Chronic exposure to DEHA is associated with reproductive effects and decreased body weight in animal studies. EPA classifies it as a possible human carcinogen (Group C). Long-term exposure above the MCL is the primary concern; the general population is at risk, with potential for greater sensitivity in developing fetuses and reproductive-age adults.

Limit: 0.4 mg/L (400 ppb)

What it means: Di(2-ethylhexyl) phthalate (DEHP) is the most widely used plasticizer in PVC products including pipes, flooring, medical tubing, and food packaging. It enters drinking water through discharge from rubber and chemical factories and leaching from PVC water distribution materials. It is one of the more commonly detected phthalates in US drinking water.

Health effects: Chronic exposure to DEHP is associated with reproductive and developmental toxicity — it acts as an endocrine disruptor and can interfere with hormone signaling. EPA classifies it as a probable human carcinogen (Group B2) based on animal liver tumor data. Developing fetuses, infants, and reproductive-age adults are most susceptible to its hormonal effects.

Limit: 0.006 mg/L (6 ppb)

What it means: Dichloromethane (DCM), also called methylene chloride, is a widely used industrial solvent employed in paint stripping, pharmaceutical manufacturing, and metal degreasing. It enters drinking water through industrial discharge and improper disposal. It is volatile and evaporates quickly from open water but can persist in groundwater.

Health effects: Chronic exposure to dichloromethane is associated with liver and kidney damage and neurological effects. EPA classifies it as a probable human carcinogen (Group B2); it is metabolized in the body to carbon monoxide and has been linked to cardiovascular stress. Workers in industrial settings and communities near manufacturing sites face the greatest risk.

Limit: 0.005 mg/L (5 ppb)

What it means: Dinoseb is a dinitrophenol herbicide and pesticide formerly used on crops including soybeans, cereals, and vegetables. Its US pesticide registrations were voluntarily canceled in 1986 after it was found to cause severe reproductive and developmental toxicity. It persists in soil and can leach into groundwater from historically treated agricultural fields.

Health effects: Dinoseb uncouples oxidative phosphorylation, disrupting cellular energy production. Chronic exposure causes reproductive toxicity: impaired sperm production in males and developmental harm, including birth defects, in developing fetuses. EPA has not established a formal carcinogenicity classification. Reproductive-age adults and pregnant women face the greatest risk.

Limit: 0.007 mg/L (7 ppb)

What it means: Diquat is a broad-spectrum contact herbicide used to control aquatic weeds, algae, and terrestrial vegetation. It remains in active use in the United States, applied directly to water bodies and irrigation canals. Diquat binds tightly to soil but can enter surface water directly during aquatic applications.

Health effects: Chronic exposure to diquat is associated with cataracts and kidney damage in animal studies. Acute high-level exposure causes gastrointestinal distress. EPA has not classified diquat as a human carcinogen. Individuals with kidney conditions may be at elevated risk from chronic exposure.

Limit: 0.02 mg/L (20 ppb)

What it means: Endothall is an aquatic and terrestrial herbicide used to control algae, weeds, and grass in irrigation canals, ponds, and lakes. It is still in use in the United States and is applied directly to water bodies for aquatic vegetation management. It degrades relatively quickly in aquatic environments but can appear in source water shortly after application.

Health effects: Short-term exposure above the MCL can cause gastrointestinal irritation and stomach cramps. Chronic exposure is associated with liver, kidney, and gastrointestinal damage in animal studies. EPA has not classified endothall as a human carcinogen. The general population is at risk from water system violations.

Limit: 0.1 mg/L (100 ppb)

What it means: Endrin was a cyclodiene organochlorine insecticide and rodenticide used primarily on field crops such as cotton, grains, and sugarcane. It was banned in the United States in 1991. Endrin is highly persistent in soil and binds strongly to sediment, meaning legacy contamination in groundwater and surface water can persist decades after use.

Health effects: Endrin is acutely toxic to the nervous system and can cause seizures, headache, dizziness, and liver damage at high doses. Chronic low-level exposure is associated with liver and nervous system effects. EPA classifies it as a possible human carcinogen (Group C). Children and the elderly are most vulnerable to acute neurological effects.

Limit: 0.002 mg/L (2 ppb)

What it means: Ethylbenzene is an aromatic hydrocarbon and BTEX compound used as a solvent and in the production of styrene. It is a natural component of petroleum and coal tar and enters drinking water through leaking underground fuel storage tanks, petroleum spills, and industrial discharge. It is moderately volatile and degrades relatively quickly under aerobic conditions.

Health effects: Chronic exposure to ethylbenzene is associated with liver and kidney effects. EPA classifies it as a possible human carcinogen (Group D — inadequate evidence) based on limited animal data. Short-term high-level exposure can cause eye and throat irritation and dizziness. Long-term exposure above the MCL is the primary concern for public water system violations.

Limit: 0.7 mg/L (700 ppb)

What it means: Ethylene dibromide (EDB) is a halogenated organic compound used as a soil and grain fumigant and as a lead scavenger in leaded gasoline. Its use as a pesticide was banned in the United States in 1984 following discovery of widespread groundwater contamination. EDB is highly persistent in groundwater and continues to be detected at legacy agricultural and fuel storage sites.

Health effects: EDB is classified by EPA as a probable human carcinogen (Group B2). It is acutely toxic at high doses, causing liver, kidney, and reproductive damage. Chronic low-level exposure is associated with increased cancer risk. Men of reproductive age face particular risk due to EDB's well-documented testicular toxicity.

Limit: 0.00005 mg/L (0.05 ppb)

What it means: Glyphosate is the most widely used herbicide in the United States, applied to crops, lawns, and roadsides. It is the active ingredient in Roundup and related products. It enters water through agricultural and urban runoff.

Health effects: Long-term exposure above the MCL is associated with kidney and reproductive damage in animal studies. EPA's current classification does not designate glyphosate as a human carcinogen, though IARC classifies it as probably carcinogenic (Group 2A). This classification remains a subject of active scientific and regulatory debate.

Limit: 0.7 mg/L (700 ppb)

What it means: Gross alpha particle activity is a screening measurement of all alpha-emitting radionuclides in water, excluding radon and uranium (which are regulated separately). If gross alpha exceeds 5 pCi/L, further analysis is required to identify specific radionuclides. Elevated gross alpha typically indicates water drawn from deep aquifers in contact with uranium- or thorium-bearing bedrock.

Health effects: Alpha-emitting radionuclides accumulate in bone and soft tissue, delivering sustained internal radiation doses that increase lifetime cancer risk. There is no established safe threshold for ionizing radiation. Individual contributors such as radium-226 and polonium-210 have their own MCLs; gross alpha serves as a cost-effective screening tool that triggers more specific radionuclide analysis when exceeded.

Limit: 15 pCi/L (excluding radon and uranium)

What it means: Heptachlor is a cyclodiene organochlorine insecticide used historically on soil insects and termites. Most uses were canceled in the United States by 1988. It is highly persistent in soil and can leach slowly into groundwater over decades. It is chemically related to chlordane and shares similar environmental fate characteristics.

Health effects: Chronic exposure to heptachlor is associated with liver damage and increased cancer risk. EPA classifies it as a probable human carcinogen (Group B2). Animal studies show liver tumors at elevated doses. The general population faces chronic risk from legacy soil contamination; children are most vulnerable to cumulative organochlorine exposure.

Limit: 0.0004 mg/L (0.4 ppb)

What it means: Heptachlor epoxide is the primary environmental metabolite of heptachlor, formed when heptachlor breaks down in soil, water, and biological tissue. Like its parent compound, it persists in the environment long after heptachlor use was discontinued. It is more toxic and more persistent than heptachlor itself and is detected independently in groundwater monitoring.

Health effects: Heptachlor epoxide is associated with liver damage and is classified by EPA as a probable human carcinogen (Group B2). It bioaccumulates in fatty tissue and can be transferred to infants through breast milk. Chronic low-level exposure is the primary concern in drinking water contexts.

Limit: 0.0002 mg/L (0.2 ppb)

What it means: Hexachlorobenzene (HCB) is a chlorinated aromatic compound formerly used as a fungicide on grain seeds and as an industrial chemical. All pesticide uses were canceled in the United States by 1984. It is also produced as a byproduct in the manufacture of certain chlorinated solvents and pesticides. HCB is highly persistent and bioaccumulates in fatty tissue and sediment.

Health effects: Chronic exposure to hexachlorobenzene is associated with liver damage, skin lesions, and neurological effects. EPA classifies it as a probable human carcinogen (Group B2). It can be transferred to infants through breast milk. Reproductive and developmental toxicity have been observed in animal studies.

Limit: 0.001 mg/L (1 ppb)

What it means: Hexachlorocyclopentadiene (HCCP) is a chlorinated cyclic compound used as a chemical intermediate in the manufacture of pesticides, flame retardants, and resins. It is not used directly as a pesticide. It enters drinking water through discharge from chemical manufacturing facilities. It is reactive and degrades relatively quickly in the environment.

Health effects: Chronic exposure to hexachlorocyclopentadiene is associated with kidney and stomach damage in animal studies. EPA has not classified it as a human carcinogen based on available data. Short-term high-level exposure may cause irritation of mucous membranes. Long-term exposure above the MCL is the primary concern for public water system violations.

Limit: 0.05 mg/L (50 ppb)

What it means: Methoxychlor was a broad-spectrum organochlorine insecticide used as a lower-toxicity alternative to DDT on livestock, pets, vegetables, and crops. Its EPA registration was voluntarily canceled in 2003. Though less persistent than DDT, it can leach into groundwater from historically treated agricultural soils.

Health effects: Chronic exposure to methoxychlor is associated with reproductive and endocrine disruption — it acts as an estrogen mimic and can interfere with hormone signaling. Liver and kidney effects have been observed in animal studies. Developing fetuses, infants, and individuals with hormonal conditions may be most susceptible.

Limit: 0.04 mg/L (40 ppb)

What it means: Nitrate (NO₃) is the most common chemical contaminant in US groundwater, entering from fertilizers, septic systems, and animal waste. It is odorless and tasteless — the only way to know if it's present is to test.

Health effects: Methemoglobinemia in infants under 6 months: gut bacteria convert nitrate to nitrite, which blocks oxygen transport in blood. Pregnant women should also take precautions. Chronic adult exposure at elevated levels may increase cancer risk.

Limit: 10 mg/L as nitrogen (NO₃-N)

What it means: Oxamyl is a carbamate insecticide and nematicide sold under the trade name Vydate, used on potatoes, apples, citrus, and other crops. It remains in agricultural use in the United States. Oxamyl is water-soluble and mobile in soil, making it prone to leaching into groundwater and entering surface water through runoff.

Health effects: Short-term exposure above the MCL can cause nervous system effects including headache, blurred vision, muscle weakness, and nausea, consistent with acetylcholinesterase inhibition by carbamate compounds. Chronic effects include nervous system damage. Children are most susceptible to acute neurological effects. EPA has not classified oxamyl as a human carcinogen.

Limit: 0.2 mg/L (200 ppb)

What it means: Pentachlorophenol (PCP) is a chlorinated phenol used as a wood preservative, primarily for utility poles, railroad ties, and fence posts. It remains in limited industrial use in the United States. PCP leaches from treated wood into surrounding soil and groundwater, and can enter surface water through runoff from treated wood storage sites.

Health effects: Chronic exposure to pentachlorophenol is associated with liver and kidney damage and immune system effects. EPA classifies it as a probable human carcinogen (Group B2). Acute high-level exposure can cause fever, profuse sweating, and cardiovascular collapse. Workers and communities near wood treatment facilities face the greatest exposure risk.

Limit: 0.001 mg/L (1 ppb)

What it means: Picloram is a systemic pyridine herbicide used to control broadleaf weeds and woody plants on rangeland, pasture, rights-of-way, and forestry sites. It remains in active use in the United States. Picloram is highly water-soluble and mobile in soil, persistent in the environment, and prone to leaching into groundwater and entering surface water through agricultural runoff.

Health effects: Chronic exposure to picloram is associated with liver damage in animal studies. EPA classifies it as a possible human carcinogen (Group C). The general population faces chronic risk from prolonged exposure above the MCL, particularly in agricultural regions where it is applied to rangeland and rights-of-way.

Limit: 0.5 mg/L (500 ppb)

What it means: PCBs are a family of synthetic chlorinated organic compounds formerly used as dielectric fluids in electrical transformers and capacitors, and as industrial lubricants and plasticizers. Their manufacture was banned in the United States in 1979. PCBs persist in sediment and soil for decades and enter water through runoff from contaminated sites and leaching from old electrical equipment.

Health effects: PCBs are classified by EPA as probable human carcinogens (Group B2). Long-term exposure is associated with liver damage, immune suppression, thyroid disruption, and reproductive and developmental effects. They bioaccumulate in fatty tissue. Developing fetuses and infants are most vulnerable to neurological and endocrine effects.

Limit: 0.0005 mg/L (0.5 ppb)

What it means: Simazine is a triazine herbicide used to control broadleaf weeds and grasses in orchards, vineyards, turf, and some crops. It remains in use in the United States and is chemically related to atrazine. Simazine is mobile in soil and readily leaches into groundwater, particularly in sandy soils.

Health effects: Chronic exposure to simazine is associated with potential cancer risk; EPA classifies it as a possible human carcinogen (Group C) based on animal studies. Blood and nervous system effects have also been observed in animal studies. Long-term exposure at levels above the MCL is the primary concern for public water system violations.

Limit: 0.004 mg/L (4 ppb)

What it means: Styrene is an aromatic hydrocarbon monomer used in the manufacture of polystyrene plastics, synthetic rubber, and resins. It enters drinking water through industrial discharge, leaching from plastic linings in water storage tanks, and contaminated runoff from manufacturing sites. It is moderately volatile and biodegrades under aerobic conditions.

Health effects: Chronic exposure to styrene is associated with liver, kidney, and nervous system effects. EPA classifies it as a possible human carcinogen (Group C) based on limited animal evidence. Short-term exposure can cause irritation of the eyes, nose, and throat. Long-term exposure above the MCL is the primary concern for public water system violations.

Limit: 0.1 mg/L (100 ppb)

What it means: Tetrachloroethylene (PCE), also called perchloroethylene, is a chlorinated solvent used extensively in dry cleaning and metal degreasing. It is one of the most frequently detected VOCs in US groundwater, found near dry cleaning facilities, industrial sites, and military bases. PCE is dense and sinks through soil into aquifers, where it persists for decades.

Health effects: PCE is classified by EPA as a probable human carcinogen (Group B2), with evidence linking it to bladder and non-Hodgkin lymphoma risk. Chronic exposure is also associated with liver and kidney damage and neurological effects. Communities near dry cleaning operations and contaminated military installations face the greatest long-term exposure risk.

Limit: 0.005 mg/L (5 ppb)

What it means: Toluene is an aromatic hydrocarbon solvent found in gasoline, paints, adhesives, and chemical manufacturing. It is a BTEX compound (benzene, toluene, ethylbenzene, xylene) and enters drinking water through leaking underground fuel storage tanks, petroleum spills, and industrial discharge. It is highly volatile but can persist in groundwater at contamination sites.

Health effects: Short-term exposure above the MCL can cause nervous system effects including headache, dizziness, and impaired coordination. Chronic exposure is associated with kidney and liver damage and neurological effects. EPA has not classified toluene as a human carcinogen. Developing fetuses may be particularly sensitive to its neurotoxic effects.

Limit: 1 mg/L (1,000 ppb)

What it means: Toxaphene was a complex mixture of chlorinated camphenes used extensively as an insecticide on cotton and other crops in the southern United States. It was banned in 1990. Toxaphene is persistent in soil and sediment and can enter surface water through runoff from historically treated agricultural land, particularly in the South.

Health effects: Chronic toxaphene exposure is associated with liver and kidney damage and effects on the immune and nervous systems. EPA classifies it as a probable human carcinogen (Group B2). Children and those with compromised liver or kidney function face greater risk from chronic exposure.

Limit: 0.003 mg/L (3 ppb)

What it means: Trichloroethylene (TCE) is a chlorinated solvent widely used for metal degreasing and as a chemical intermediate. It is one of the most common groundwater contaminants in the United States, found at hundreds of Superfund sites. TCE enters water through industrial discharge, improper solvent disposal, and leaking underground storage tanks. It is persistent in anoxic groundwater.

Health effects: TCE is classified by EPA as a known human carcinogen (Group A), associated primarily with kidney cancer and non-Hodgkin lymphoma. It is also linked to liver cancer and cervical cancer. Prenatal exposure is associated with cardiac defects. Workers at industrial facilities and residents near contaminated groundwater plumes face the greatest risk.

Limit: 0.005 mg/L (5 ppb)

What it means: Vinyl chloride is an industrial chemical used to manufacture polyvinyl chloride (PVC) plastic and related products. It enters drinking water primarily as a breakdown product of trichloroethylene and tetrachloroethylene in contaminated groundwater, and through discharge from PVC pipe manufacturing facilities. It is highly volatile but can persist in anoxic groundwater.

Health effects: Vinyl chloride is classified by EPA as a known human carcinogen (Group A). It is associated with a rare liver cancer called hepatic angiosarcoma, as well as liver and brain cancers. There is no safe threshold — any exposure carries some cancer risk. Workers in PVC manufacturing and communities near contaminated groundwater sites face the greatest risk.

Limit: 0.002 mg/L (2 ppb)

What it means: Xylenes are a group of three isomeric aromatic hydrocarbons (ortho-, meta-, and para-xylene) used as solvents and chemical intermediates in the production of plastics, synthetic fibers, and paints. They enter drinking water primarily through leaking underground fuel storage tanks and industrial spills, as they are components of gasoline and jet fuel.

Health effects: Short-term exposure above the MCL can cause nervous system effects including headache, dizziness, and impaired coordination. Chronic exposure is associated with liver and kidney damage. EPA has not classified total xylenes as human carcinogens. The general population is at risk; children may be more sensitive to neurological effects.

Limit: 10 mg/L (10,000 ppb)

What it means: cis-1,2-Dichloroethylene is a chlorinated solvent that occurs primarily as a breakdown product of trichloroethylene (TCE) and tetrachloroethylene (PCE) in contaminated groundwater. It is rarely used directly as an industrial chemical. Its presence in water typically indicates an upstream TCE or PCE contamination source undergoing natural attenuation.

Health effects: Chronic exposure to cis-1,2-dichloroethylene is associated with liver, nervous system, and immune system effects in animal studies. EPA has not classified it as a human carcinogen based on available data. Its detection in water often signals the presence of more acutely toxic parent compounds such as TCE or vinyl chloride.

Limit: 0.07 mg/L (70 ppb)

What it means: o-Dichlorobenzene (1,2-dichlorobenzene) is a chlorinated aromatic solvent used as a chemical intermediate, insecticide, and degreaser. It enters drinking water through industrial discharge and leaking underground storage infrastructure. It is moderately persistent in groundwater and has low but detectable volatility.

Health effects: Chronic exposure to o-dichlorobenzene is associated with liver, kidney, and blood effects in animal studies. EPA has not classified it as a human carcinogen based on current data. Long-term exposure above the MCL is the primary concern; the general population is at risk from contaminated groundwater sources.

Limit: 0.6 mg/L (600 ppb)

What it means: p-Dichlorobenzene (1,4-dichlorobenzene) is a chlorinated aromatic compound used as a moth repellent, toilet deodorizer, and chemical intermediate. It is one of the more commonly detected VOCs in US drinking water due to its widespread consumer and industrial use. It enters water through industrial discharge, landfill leachate, and volatilization from consumer products into indoor air that contacts water.

Health effects: Chronic exposure to p-dichlorobenzene is associated with liver and kidney damage. EPA classifies it as a possible human carcinogen (Group C) based on animal tumor data. Long-term exposure above the MCL is the primary concern. Individuals with pre-existing liver or kidney conditions may be at greater risk.

Limit: 0.075 mg/L (75 ppb)

What it means: trans-1,2-Dichloroethylene (trans-1,2-DCE) forms primarily as a breakdown product of trichloroethylene (TCE), tetrachloroethylene (PCE), and other chlorinated solvents in contaminated groundwater during natural attenuation. Like its cis isomer, it is rarely used directly as an industrial chemical; its presence signals upstream solvent contamination.

Health effects: Chronic exposure to trans-1,2-dichloroethylene is associated with central nervous system effects in animal studies. EPA has not classified it as a human carcinogen based on available data. Its primary public health significance is as a marker of more acutely toxic parent compounds — TCE, PCE, or vinyl chloride — that may also be present in the same groundwater.

Limit: 0.1 mg/L (100 ppb)