US research has found that perchlorate - a chemical used in rocket fuel and though to be linked to metabolic disruption in adults and mental retardation in children - is widely present in breast and cow's milk across the United States.
According to a New Scientist report, perchlorate is made naturally in the atmosphere, and subsequently finds its way into the water supply. The US Environmental Protection Agency last week set a safe level of perchlorate for drinking water, and although the quantities in tested milk are below this, scientists warn that perchlorate's affect on iodine uptake in humans - coupled to a general decrease in dietary iodine intake - may pose a risk to health.
Lead researcher Purnendu Dasgupta, a chemist at Texas Tech University, explains that "perchlorate knocks an iodine ion off a protein that transports the ion to the thyroid", leading to "iodine deficiency, which impairs thyroid development [which] is thought to be the main cause of mental retardation in young children".
Dasgupta adds that people are just not getting enough iodine; that "dietary levels have fallen to half those in the 1970s"; and that "pregnant women are taking in just half the iodine they should." He warns: "We have a potential problem with iodine nutrition - and perchlorate on top of it can make things worse."
Dasgupta's study took 36 breast milk samples from 18 states and 47 dairy milk samples from 11 states. Researchers discovered perchlorate in all but one dairy milk sample. The average level in breast milk was 10.5 micrograms per litre, and 2.0 micrograms per litre in dairy milk. The US Environmental Protection Agency safe level for drinking water is 24.5 micrograms per litre.
This limit was recommended by a US National Academy of Sciences study, although NAS adds that a safe perchlorate exposure for a baby should be 4 micrograms per litre. Given perchlorate's potential effect on iodine uptake, Dasgupta advises people to up their intake in the form of iodine-rich dried seaweed capsules. "I want people to be activists about good iodine nutrition," he concludes.
Other Texas Tech University scientists, meanwhile, are trying to work out why breast milk contains much greater levels of perchlorate than dairy milk. Developmental toxicologist Ernest Smith admits that the matter is "not clear", adding that just where the perchlorate is coming from is the "the million-dollar question". He speculates that lactating mums "could be getting the chemical from drinking store-bought milk and from eating food grown in perchlorate-tainted soil or irrigated with water containing the chemical".
It is fairly certain, however, that it cannot be coming from rocket fuel, since many of the states tested "are not known to host rocket launches", as Smith guardedly puts it. ®