The Food and Drug Administration proposed on Friday a limit for inorganic arsenic in infant rice cereal, saying that this common starter food is a leading source of exposure to the toxin.

Infants are particularly vulnerable to arsenic in rice because, relative to body weight, they eat about three times more rice than adults.

A growing body of research suggests that arsenic exposure is related not only to diminished intellectual function early in life, but also to adverse pregnancy outcomes, such as stillbirth.

The suggested limit is 100 parts per billion. “Data are still emerging on whether this level is sufficient, but it’s certainly a step in the right direction,” said Margaret R. Karagas, chairwoman of the epidemiology department at Geisel School of Medicine at Dartmouth.