Why are environmentalists concerned about chlorine in potable water systems?

Environmentalists are particularly concerned about chlorine in potable water systems because it has the potential to react with naturally occurring organic matter, such as hydrocarbons, to form disinfection byproducts (DBPs). Some of these byproducts, notably certain trihalomethanes and haloacetic acids, have been linked to carcinogenic effects. This means that while chlorine is essential for disinfection and maintaining safe drinking water, its reaction with other substances can inadvertently create harmful compounds that pose serious health risks over prolonged exposure.

Other choices address important aspects of chlorine's impact on the water supply and public health but do not capture the primary environmental concern as critically as the formation of carcinogenic substances does. For instance, while corrosion of pipes or gastrointestinal issues might occur as side effects of chlorine use, the formation of carcinogenic byproducts represents a significant public health risk that is particularly alarming to environmental advocates focused on both immediate and long-term safety in water treatment practices.