Federal health researchers say a chemical that spilled into 300,000 people's water supply in January is toxic to pregnant rats in high doses.
The National Toxicology Program provided the update Friday on MCHM, a coal-cleaning agent.
Researchers found slight fetal weight changes for rats given daily doses 150 times stronger than what officials called safe for human drinking.
At 300 times the safe level, fetal weight decreased. At 600, some rats' fetal weight dropped, while miscarriages increased.
Others at 600 and 900 showed obvious clinical toxicity.
None showed increased external fetal birth defects.
The spill spurred a tap-water ban for days.
After declaring the water safe in January, federal officials advised pregnant women to find other water until chemicals dissipated.
They later said the water was fine for pregnant women.