Fertilizer's Perchlorate Legacy

Groundwater contaminated with perchlorate (ClO₄ ^–) from fertilizer appears to be a consequence of the U.S.’s agricultural history, according to an environmental monitoring study by John Karl Böhlke of the U.S. Geological Survey and colleagues (Environ. Sci. Technol., DOI: 10.1021/es9006433). Synthetic perchlorate, used as an oxidizer in rocket propellants, has found its way from manufacturing and test sites into some localized drinking-water supplies and agricultural products such as lettuce and milk. But a potentially more widespread perchlorate source is the trace amount of naturally occurring perchlorate in Chilean saltpeter (NaNO₃) used to make fertilizer, mostly prior to 1950. The principal concern with perchlorate is that it can disrupt thyroid function by interfering with the uptake of iodine. The researchers used mass spectrometry to measure ³⁷Cl/³⁵Cl, ¹⁸O/¹⁶O, and ¹⁷O/¹⁶O ratios of perchlorate in groundwater samples from Long Island, N.Y. The distinctive isotopic ratios attributable to synthetic and natural perchlorate, along with geochemical and chronological data, helped the team pinpoint the sources and ages of the contaminant in the study area, which includes a fireworks disposal pit and current and former farms. The method should help local authorities determine the sources of perchlorate contamination in order to establish what drinking-water treatment steps might be necessary.