Unsafe at Low Levels: Adopt a Federal MCL for 1,2,3-Trichloropropane in United States’ Drinking Water

1,2,3-trichloropropane (TCP) is a toxic, man-made chemical used widely in agricultural and other contexts from the 1940s to the 1980s. TCP has settled into the groundwater supplies nearly everywhere it was used. In 2009, the Environmental Protection Agency (EPA) included TCP on the Third Contaminant Candidate list (CCL3) and listed the safe oral reference dose (RfD) for TCP at 0.004 milligrams per kilogram per day. Since then, we have learned that the scope of the TCP contamination problem is greater than first understood. At least 13 states and one territory have contaminated wells. Animal studies show that TCP is a potent carcinogen, and toxicology studies suggest that TCP is unsafe at levels at and above its 5 ppt detection limit. Three states, California, Hawaii, and New Jersey have adopted enforceable maximum contaminant levels of TCP in groundwater. As other states become aware of contamination levels, it is likely that some of them will also regulate TCP, but that could take many years. Federal legislation could mandate EPA advisories sooner than state legislation. The EPA has used the detection limit as the maximum for at least one other chemical, 1,2-Dibromo-3-chloropropane (DBCP), a common co-contaminant of TCP. We recommend that the EPA adopt TCP’s lowest detection level, 5 ppt, as the federal maximum contaminant level