High levels of toxic metals like lead and arsenic in breast milk may impair growth in infants, according to an alarming study. 

Breast milk is the best source of nutrition for infants under six months of age. However, tt can also be a potential route of exposure to toxic metals and other contaminants that may impair neurological development and immune function, said the researchers from the University of Arizona in the US.

The team focussed on Mayan women in Guatemala's Lake Atitlán watershed region, and found concentrations of arsenic and lead that exceeded World Health Organization safety standards in breast milk in mothers.