Contaminant Level (MCL)
Styrene is an organic chemical used to make plastics (including the widely used polystyrene), paints, resins and coatings. According to Wikipedia, about 15 billion tons are produced every year. It arrives in drinking water through factory discharge and leaching from landfills.
According to the EPA, long term exposure to styrene can have harmful effects on the liver, kidney and circulatory systems:
Some people who drink water containing styrene well in excess of the maximum contaminant level [0.1 milligrams per Liter] for many years could have problems with their liver, kidney, or circulatory system.
The EPA recommends granular activated carbon (GAC) in combination with packed tower aeration (an air stripping technique).
(whole house & well units)