Perchlorate levels in samples of sodium nitrate fertilizer derived from Chilean caliche

Abstract

Paleogeochemical deposits in northern Chile are a rich source of naturally occurring sodium nitrate (Chile saltpeter). These ores are mined to isolate NaNO3 (16-0-0) for use as fertilizer. Coincidentally, these very same deposits are a natural source of perchlorate anion (ClO4-). At sufficiently high concentrations, perchlorate interferes with iodide uptake in the thyroid gland and has been used medicinally for this purpose. In 1997, perchlorate contamination was discovered in a number of US water supplies, including Lake Mead and the Colorado River. Subsequently, the Environmental Protection Agency added this species to the Contaminant Candidate List for drinking water and will begin assessing occurrence via the Unregulated Contaminants Monitoring Rule in 2001. Effective risk assessment requires characterizing possible sources, including fertilizer. Samples were analyzed by ion chromatography and confirmed by complexation electrospray ionization mass spectrometry. Within a lot, distribution of perchlorate is nearly homogeneous, presumably due to the manufacturing process. Two different lots we analyzed differed by 15%, containing an average of either 1.5 or 1.8 mg g-1. Inadequate sample size can lead to incorrect estimations; 100-g samples gave sufficiently consistent and reproducible results. At present, information on natural attenuation, plant uptake, use/application, and dilution is too limited to evaluate the significance of these findings, and further research is needed in these areas.

Perchlorate exposure from food crops produced in the lower Colorado River region

“…The range for green beans (Phaseolus vulgaris) includes one very high value that was re-analyzed and verified. This very high value was collected from an organic farm in the Imperial Valley of California, and we suspect the grower used Chilean nitrate, a known source of perchlorate (Urbansky et al, 2001). Previous work has shown generally higher perchlorate concentrations in organic compared to conventionally produced leafy vegetables (Sanchez et al, 2005a).…”

Widespread Presence of Naturally Occurring Perchlorate in High Plains of Texas and New Mexico

“…Records of Chilean fertilizer use in Texas were not identified; however, for comparison the amount of Chilean nitrate used from 1923 to 1998 in California, which has roughly the same area of improved farmland as the study area, was 4.77 × 10 8 kg (36). Assuming a measured concentration of 0.1% ClO4 -in the fertilizer (37), and taking the calculated mass of ClO4 -in the saturated zone of the Ogallala, a conservative estimate of 1.60 × 10 9 kg of the Chilean nitrate fertilizer is required if considered as the sole source of ClO4 -in the Ogallala aquifer. This value would require 10% of the entire Chilean nitrate imported into United States from 1938 to 1968 to have been applied over the Ogallala aquifer portion of the study area alone.…”

Perchlorate Exposure of the US Population, 2001–2002

“…Perchlorate can also form naturally in the atmosphere leading to trace levels in precipitation and is concentrated geologically in some locations such as regions of west Texas and northern Chile (Urbansky et al, 2001). A combination of human activities and natural sources has led to the widespread presence of perchlorate in the environment.…”

“…As of November 2005, perchlorate was detected at least once in 4.1% of community drinking water systems from 26 different states and two territories, with levels ranging from the method detection limit of 4 mg/l to a maximum at 420 mg/l (EPA, 2005b). Perchlorate exposure from the diet is likely, due to the contamination of vegetable crops irrigated with perchlorate-containing water (Yu et al, 2004) or fertilized with Chilean nitrate (Urbansky et al, 2001). Milk can also contain perchlorate, possibly from perchlorate contamination of forage crops (Kirk et al, 2003;Capuco et al, 2005).…”