Columbia University researchers are linking the risk of developing schizophrenia to the amount of lead a baby was exposed to in the womb.

The BBC reports that people whose mothers took in high amounts of the heavy metal in exhaust fumes were twice as likely to develop the mental illness in adulthood. The research is based on blood samples taken from pregnant American women in the 1960s, when lead was a common additive in gasoline.

"It's the first time that any environmental toxin has been related to the later risk of schizophrenia," the lead researcher, Dr. Ezra Susser, told the BBC. "It's a preliminary finding, but an intriguing one. We think that people will now look at a variety of environmental toxins which can disrupt brain development, and see whether they are also related to the risk of schizophrenia."

Susser, who delivered his findings at the annual meeting of the Association for the Advancement of Science in Seattle, speculates that lead interferes with the growth of nerve cells in a key developmental period in the womb.