ABCNEWS.com : Infant Formula Ingredient Studied in Rats
Breast milk contains 4-6 micrograms per liter (mcg/L) of manganese, while milk-based infant formula contains about 30-50 mcg/L and soy formula contains 200-300 mcg/L. Manganese is a mineral that helps the cells to obtain energy and it is essential for life, but can be toxic at very high levels.

"Very little is actually known about the association between manganese and ADHD specifically," said Dr. James Perrin, a professor of pediatrics at Harvard Medical School and co-chairman of the American Academy of Pediatrics subcommittee on attention-deficit/hyperactivity disorder (ADHD). "It's too soon to worry."