perchlorate and thyroid: Common water pollutant could harm babies - becomes actively concentrated in breast milk

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Common water pollutant could harm babies

Last Updated: 11:01pm GMT 03/12/2007

http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/12/03/scimilk103.xml

A chemical pollutant that is commonly found in water supplies could harm

nursing babies, even lead to mental impairment in extreme cases.

Perchlorate-an industrial pollutant linked to thyroid ailments-has been

found in US drinking water and a survey is currently under way to find

out its extent and impact in the UK.

Now it has been discovered that it becomes actively concentrated in

breast milk, according to a team at the Albert Einstein College of

Medicine, New York, and the s Hopkins School of Medicine, Baltimore.

Because it can interfere with the thyroid gland of the unborn child,

which secretes hormones that control a vast range of processes in the

body, perchlorate contamination of drinking water may pose a greater

health risk than previously realised, according to the study today in

the Proceedings of the National Academy of Sciences.

Perchlorate is known to interfere with the ability of the thyroid,

mammary glands and certain other tissues to absorb iodide from the

bloodstream. " Our study suggests that high levels of perchlorate may

pose a particular risk to infants, " says Prof Carrasco, senior

author of the study.

" Nursing mothers exposed to high levels of perchlorate in drinking water

may not only provide less iodide to their babies, but their milk may

actually pass on perchlorate, which could further deprive the infants'

thyroid glands of iodide. The thyroid requires iodide to synthesise the

hormones T3 and T4 that are essential for normal development of the

central nervous system. Babies who don't make enough of these thyroid

hormones may become mentally impaired. "

Iodide is relatively scarce in the diet, and tissues that need to

accumulate it-the breast and thyroid in particular-are equipped with a

cell-surface protein called NIS (sodium/iodide symporter) that actively

pulls iodide from the bloodstream and into the cells.

In the current study, Dr. Carrasco and her colleagues injected female

rats with perchlorate and then extracted the animals' breast milk and

tested it on cells that make NIS. The milk inhibited iodide transport in

the cells, indicating that perchlorate had become concentrated in the

milk. Thus cells that should be taking up iodide were taking up

perchlorate instead.

" We found that the same protein-NIS-that actively recruits iodide into

cells does the same thing for perchlorate, " says Prof Carrasco. " In

fact, NIS has a higher affinity for perchlorate than it does for iodide,

which certainly heightens the risk posed by this contaminant. "

Whereas several studies found no linkage between perchlorate exposure

and thyroid function, recent work suggests that long-term exposure, even

at lower doses, correlates with decreased manufacture of the hormone T3,

as would be expected to occur based on the new work. The team warns that

the perchlorate can be actively concentrated in breast milk. " This

effect would have potentially serious consequences for the child's

mental and physical development. "

Perchlorate has been detected in drinking water in a number of countries

including USA and Japan. But UK levels are not well understood and the

UK National Centre for Environmental Toxicology, run by the WRc Group,

has recently been awarded a contract with the Drinking Water

Inspectorate /Department for Environment, Food and Rural Affairs, Defra,

to survey its impact.

" Perchlorate has been detected in many drinking water sources in the

USA. It has been shown to inhibit thyroid function, but the

toxicological significance of the levels found in US drinking water is

not clear at present and no guideline values have been set by the World

Health Organization or a standard by the US Environmental Protection

Agency, " said Dr Rumsby, Principal Toxicologist, National Centre

for Environmental Toxicology.

" Perchlorate can occur naturally and in some industrial processes but

the main source is thought to be from the disposal of rocket fuel. It

seems unlikely that there will be significant contamination of UK

drinking water, but there has been no systematic monitoring to date. In

September 2007, WRc started a research project funded byDefra through

the Drinking Water Inspectorate to assess the risk to English and Welsh

drinking water sources based on usage and environmental behaviour. Some

targeted monitoring of raw and treated drinking water will then be

conducted to determine the levels of perchlorate. This monitoring is

scheduled to finish in February 2009. "

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