Naperville

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: 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: 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: 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: 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: 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: 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: 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)