W1045: Agrochemical Impacts on Human and Environmental Health: Mechanisms and Mitigation (From W045)

Non-Technical Summary: Perchlorate is now found commonly in many agricultural waters, as well as in a variety of foods, including vetables and milk. This substance is know to interfere with iodine metabolism and cause thyroid function problems. The purpose of this project is to determine whether perchlorate is formed as a natural product, through oxidation of chloride by sunlight and a variety of soil surfaces and/or nitrate. This research can potentially have a major impact on management of waters in arid regions. It has demonstrated that a contaminant of considerable concern, perchlorate, is naturally produced in sunlight. Suggestions have been made to limit perchlorate in drinking water to 4-6 ppb, which is well within the concentrations that may be observed from runoff from soils that are irradiated by sunlight. It may also account for perchlorate found in a variety of irrigated vegetables. <P> Approach: In recent years, perchlorate has been observed in surface and groundwater at many sites in the southwestern United States. Some of these occurrences have clearly been associated with industrial discharge of perchlorate, including a manufacturing facility of rocket propellant oxidizer, ammonium perchlorate. However, the widespread occurrence of perchlorate, particularly over large areas of Texas, has suggested an alternative perchlorate source. One of these is nitrate fertilizer, which has historically been mined in the Atacamba Desert of Chile. It is known to have up to percentage levels of perchlorate for several decades, since some of these fertilizers were know to have causes chlorosis in plants, one of the symptoms of perchlorate toxicity. However, even this additional source cannot explain the wide distribution of perchlorate. Sunlit soil surfaces in the desert southwest are known to generate potent oxidants, including hydroxyl radical. This oxidant is sufficiently reactive to oxidize effectively all organic compounds and several inorganic compounds, including chloride. We have developed experimental evidence that shows that perchlorate is formed by irradiation of constituents commonly found in soils, including nitrate and the common semiconductor photocatalyst, titanium dioxide. Thus, an additional source of perchlorate may be from photooxidation of chloride. No evidence of this transformation has previously been available. Experiments will be conducted to evaluate the following questions. (1) Is perchlorate indeed formed through nitrate photooxidatipn of chloride and titanium dioxide photocatalyzed oxidation. (2) Can this result be confirmed using sunlight and arid lands soils? (3) Is there sufficient nitrate and/or other photooxidative catalysts on surface soils in the Southwest to produce perchlorate? (4) Is perchlorate found in arid lands soil surfaces in the southwest? We have extensive experience conducting soil photolysis experiments for pesticides during the previous 20 years. We will utilize a variety of fluorescent solar simulators, as well as sunlight to examine the production of perchlorate,. These experiments will determine the conditions necessary to form perchlorate and quantitate how much perchlorate will be generated under a variety of environmental conditions.