Environmental Toxin Collects in Breast Milk. healthfinder.gov.Dec 07, 2007.Perchlorate can then be passed on to nursing infants, rat study shows. Scientists have discovered the mechanism by which a chemical known as perchlorate can collect in breast milk and cause cognitive and motor deficits in newborns.Used since the 1940s to manufacture explosives and rocket fuel, the contaminant is still widely present in the water and food supply, experts say.And high concentrations of perchlorate in breast milk can be passed to an infant and affect it’s ability to manufacture essential thyroid hormone, the new study suggests. Perchlorate can also lessen the amount of iodide available to a mother to pass on to her infant, and a baby needs iodide to produce thyroid hormones [ See ]