Milk is a big source of mercury, which has been linked to cancer and brain damage.
The latest study finds a link in milk.
The study, published in the journal Environmental Health Perspectives, looked at a group of 3,000 infants who were born in the United States and then raised in Sweden.
Mercury levels were found in the milk of 2.5% of infants, and in milk from 1.7% of babies.
Milk from cows who are not pregnant is less likely to be contaminated by mercury, the researchers said.
“There is a possibility that there are some very low concentrations of mercury in milk produced in a non-procreative milking environment,” the researchers wrote.
Milkers who drank less milk and drank more milk from dairy cows who were not pregnant were more likely to have mercury in their milk.
However, there were no differences in the levels of mercury found in other milk sources, such as cow’s milk and cow’s meat.
Milky water also had lower levels of contaminants than milk from cows that were not born pregnant.
The authors said the results did not mean there was a causal relationship between mercury levels in milk and other sources of mercury.
The researchers said that the findings showed that “the risk of mercury exposure to infants is increased if mothers are breastfeeding”.
“This finding is consistent with our previous studies that have demonstrated that mothers’ milk is a more likely source of environmental mercury exposure,” they wrote.
The Australian Institute of Health and Welfare, a leading nutrition research body, has recommended that all babies are milk-free by the age of four, unless they are breastfed.
It said that there was “clear evidence” that milk consumption can raise the risk of certain childhood illnesses, such a mercury poisoning in babies.
The AAP said it supported the AAPs advice, but added that “there is a clear need for milk to be milk-safe”.