A chemical preservative found in cosmetic products obstructs brain development in tadpoles even in very low concentrations, according to a new study.

Brown University researchers said that scientists, regulators and manufacturers were already aware that the cosmetic chemical, biocide methylisothiazolinone or MIT, is harmful to people and animals in high concentrations.  However, the cosmetic industry considers the ingredient safe at concentrations less than 100 parts per million.

Brown researchers sought to confirm the industry standard and performed a series of experiments to explore the effects of 10-day exposure to concentrations as low as 1.5 parts per million on developing tadpoles.

"The lower concentrations we studied didn't kill the animals or cause any big deformities or affect the behavior you'd see just by looking at them," said Carlos Aizenman, associate professor of neuroscience and the study's senior author in a statement released Tuesday. "But then we decided to do a series of functional tests and we found that exposure to this compound during a period of development that's critical for the fine wiring of the nervous system disrupted this period of fine tuning."

Researchers exposed tadpoles to two different concentrations at 1.5 ppm and 7.6 ppm and found abnormalities in both behavior and in basic brain development.

Tadpoles exposed to any chemical concentrations were less likely to avoid light patterns that unexposed tadpoles avoided, and tadpoles exposed to 7.6 ppm concentrations were significantly more likely to succumb to seizures that unexposed or lower concentration exposed tadpoles could hold off. 

Researchers noted that seizure susceptibility had nothing to do with epilepsy but was instead a measure of more general neural development in their experiments. 

Researchers conducted electrophysiological analysis on a part of the brain responsible for processing visual information and found that the chemical seemed to have stunted a key part of brain development, the process by which tadpoles prune and refine neural connections, for each tadpole.

"The neural circuits act like the neural circuits of a much more immature tadpole," Aizenman explained. "This is consistent with the previous findings in cell cultures."

Consumers should be aware of the ingredients in products that they use, researchers said. 

More studies should be conducted to study neurodevelopmental effects of even lower concentrations of products because the results of the study clearly showed that exposure to MIT resulted in a “non-obvious but real deficit in neural function,” researchers said.

The study will be published in the journal Neuroscience.