Of particular concern at the time was the radioactive isotope iodine-131, with a half-life of about eight days. Iodine taken up by the human body is preferentially incorporated in the thyroid. As a result, consumption of iodine-131 can give an increased chance of later suffering cancer of the thyroid. In particular, children are especially at risk due to their thyroids not being fully developed. In the days following the disaster, tests were carried out on local milk samples, and the milk was found to be dangerously contaminated with iodine-131. It was thus decided that consumption of milk from the surrounding area should be stopped, and eventually restrictions were put in place on the consumption of milk from the 200 square-mile area surrounding the piles. Milk from about 500 km2 of nearby countryside was destroyed (diluted a thousandfold and dumped in the Irish Sea) for about a month. However, no one was evacuated from the surrounding area.