Rethinking sources of perchlorate.

Although best known as a pollutant linked to its use in rocket fuel, perchlorate also made its way into U.S. agricultural soils from Chilean nitrate fertilizers that came into use in the early 1900s. But the chemical, which disrupts thyroid function, also occurs naturally in the environment, notably in South America's Atacama Desert. Scientists now know that perchlorate hot spots are not limited to known contamination or natural sources. In an Environmental Science & Technology article published online 6 June 2007, Texas Tech and USGS researchers report that a substantial reservoir of natural perchlorate exists in unsaturated zones (between the land surface and the water table) of the U.S. Southwest, and that this reservoir is large enough to affect drinking water, groundwater, and crops when irrigation or precipitation flushes the chemical from the soil. The authors write that this may help explain increasing reports of perchlorate in dry-region agricultural products.