Frequent Questions

1. What disinfection byproducts does EPA regulate, how are they formed, and what are their health effects in drinking water at levels above the maximum contaminant level?

Disinfection Byproduct (Chemical Abstract Service Registry Number)How is it formed?Health Effects
Total Trihalomethanes
Bromodichloromethane (75-27-4) Trihalomethanes occur when naturally-occurring organic and inorganic materials in the water react with the disinfectants, chlorine and chloramine. Some people who drink water containing total trihalomethanes in excess of the MCL over many years could experience liver, kidney, or central nervous system problems and increased risk of cancer.
Bromoform (75-25-2)
Dibromochloromethane (124-48-1)

Chloroform (67-66-3)

Haloacetic acids:
Dichloroacetic acid (79-43-6) Haloacetic acids occur when naturally-occurring organic and inorganic materials in the water react with the disinfectants, chlorine and chloramine. Some people who drink water containing haloacetic acids in excess of the MCL over many years may have an increased risk of getting cancer.
Trichloroacetic acid (76-03-9)
Chloroacetic acid (79-11-8)
Bromoacetic acid(79-08-3)

Dibromoacetic acid (631-64-1)

Bromate (15541-45-4) Bromate occurs when bromide in the water reacts with the disinfectant, ozone. Some people who drink water containing bromate in excess of the MCL over many years may have an increased risk of getting cancer.
Chlorite (7758-19-2) Chlorite occurs when chlorine dioxide breaks down. Some infants and young children who drink water containing chlorite in excess of the MCL could experience nervous system effects. Similar effects may occur in fetuses of pregnant women who drink water containing chlorite in excess of the MCL. Some people may experience anemia.

This health effects language is not intended to catalog all possible health effects for disinfection byproducts. Rather, it is intended to inform consumers of some of the possible health effects associated with disinfection byproducts in drinking water when the rule was finalized.

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