Short-chain perfluoroalkyl sulfonates and perfluoroalkyl carboxylates adversely affect rat livers and thyroid hormones just like their long-chain homologues do, the US National Toxicology Program says. But causing those effects requires higher doses of the short-chain versions of these environmentally persistent synthetic chemicals. That’s because the short-chain compounds generally have shorter half-lives in rodents than the longer-chain ones do, explains NTP Director Linda Birnbaum. These findings could have implications for establishing cleanup standards for drinking water and soil contaminated with these and other per- and polyfluoroalkyl substances. The perfluoroalkyl sulfonates are considered short chain if they have five or fewer carbons, while the carboxylates are considered short chain if they have seven or fewer carbons. NTP drew its conclusions on the basis of two 28-day studies in laboratory rats. One examined the effects of two short-chain chemicals—perfluorobutane sulfonic acid and perfluorohexane sulfonate potassium salt—along with those from long-chain perfluorooctane sulfonic acid. The other involved a short-chain compound, perfluorohexanoic acid, and long-chain perfluorooctanoic acid, perfluorononanoic acid, and perfluorodecanoic acid. Long-term toxicity and carcinogenicity bioassays and toxicokinetic studies with these compounds are ongoing, NTP says.