Suchergebnisse

Paleogeochemical deposits in northern Chile are a rich source of naturally occurring sodium nitrate. These caliche ores are mined and processed to isolate NaNO3 (16-0-0) for use in fertilizers. Coincidentally, these very same deposits are a natural soure of perchlorate anion (ClO4-). At sufficiently high concentrations, perchlorate interferes with iodide uptake in the thyroid gland and has been usewd medicinally for this purpose. In 1997 perchlorate contamination was discovered in a number of U.S. water supplies, including Lake Mead and the Colorado River. Subsequently, the Environmental Protection Agency (EPA) added this species to the Contaminant Candidate List (CCL) for drinking water and will begin assessing occurrence via the Unregulated Contaminants Monitoring Rule (UCMR). While much og the contamination has been associated with waste discharges from military activities, defense contractors, or aerospace industries, efforts are underway to discern whether fertilizers can contribute significantly. In order to assess and manage risks properly, it is necessary to know the concentrtion and distribution of perchlorate that can be gfound in any source likely to be encountered, such as Chile saltpeter. Additionally, perchlorate may have an ecological impact in some localities, especially on aquatic life or groundwater. In this work, the homogeneity of perchlorate distribution was investigated. Perchlorate concentration was quantitated by ion chromatography in samples taken from two manufacturing lots of commercial sodium nitrate fertilizer derived from Chilean caliche. Identification was confirmed by complexation electrospray ionization mass spectrometry. Perchlorate concentration was 1.5 mg g-1 for one lot and 1.8 mg g-1 for the other. Within a lot, perchlorate distribution is nearly homogeneous, presumably due to the manufaacturing process. Inadequate sample size can lead to incorrect estimations; 100-g samples gave sufficiently consistent.