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Geochemical associations of nitrate and perchlorate in the Mojave Desert, USA.
Perchlorate is an environmental contaminant found in soils and groundwater that adversely affects human health by interfering with iodide uptake in the human thyroid gland. Naturally formed perchlorate co-occurs with nitrate in arid environments worldwide, but the relationship is not fully understood in the desert soils of the southwestern US. Our project focused on natural sources of perchlorate and nitrate in Death Valley, California. We documented the first significant correlation between nitrate and perchlorate in the Mojave Desert, California and the highest concentration of naturally formed perchlorate in the southwestern United States. Nitrate oxygen isotopes were used to determine that the Mojave Desert nitrates were composed of a mixture of atmospherically derived and biologically fixed nitrogen. Comparatively, nitrate salts in the dry deserts of Chile and Antarctica originate primarily from the atmosphere. The relationship between nitrate and perchlorate in the Mojave Desert was weaker than relationships observed for the Atacama Desert, suggesting distinctive nitrate and perchlorate deposition and/or preservation mechanisms. We examined soil chemical, morphologic, and geologic data sets to develop a “bottom-up” salt accumulation hypothesis, where nitrate, perchlorate, and other soluble salts are being redistributed into the overlying soil through the weathering of salt-rich geologic strata. Link to associated publication: The geochemical associations of nitrate and naturally formed perchlorate in the Mojave Desert, California, USA. |
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