The first shipment of saltpeter to Europe arrived in England from Peru in 1820 or 1825, right after that country's independence from Spain, but did not find any buyers and was dumped at sea in order to avoid customs toll.[6][7] With time, however, the mining of South American saltpeter became a profitable business (in 1859, England alone consumed 47,000 metric tons).[7]Chile fought theWar of the Pacific (1879–1884) against the alliesPeru andBolivia and took over their richest deposits of saltpeter. In 1919,Ralph Walter Graystone Wyckoff determined itscrystal structure usingX-ray crystallography.
Advertisement for sodium nitrate fertilizer from Chile on a wall of a village in the Algarve area of PortugalMines of Chile, green is sodium nitrate area
The largest accumulations of naturally occurring sodium nitrate are found inChile andPeru, wherenitrate salts are bound within mineral deposits calledcaliche ore.[8] Nitrates accumulate on land through marine-fog precipitation and sea-spray oxidation/desiccation followed by gravitational settling of airborne NaNO3, KNO3, NaCl, Na2SO4, and I, in the hot-dry desert atmosphere.[9] El Niño/La Niña extreme aridity/torrential rain cycles favor nitrates accumulation through both aridity and water solution/remobilization/transportation onto slopes and into basins; capillary solution movement forms layers of nitrates; pure nitrate forms rare veins. For more than a century, the world supply of the compound was mined almost exclusively from theAtacama desert in northern Chile until, at the turn of the 20th century, German chemistsFritz Haber andCarl Bosch developed a process for producingammonia from the atmosphere on an industrial scale (seeHaber process). With the onset ofWorld War I, Germany began converting ammonia from this process into a syntheticChilean saltpeter, which was as practical as the natural compound in production ofgunpowder and other munitions. By the 1940s, this conversion process resulted in a dramatic decline in demand for sodium nitrate procured from natural sources.
Most sodium nitrate is used in fertilizers, where it supplies a water-soluble form of nitrogen. Its use, which is mainly outside of high-income countries, is attractive since it does not alter thepH of the soil. Another major use is as a complement toammonium nitrate in explosives. Molten sodium nitrate and its solutions with potassium nitrate have goodthermal stability (up to 600 °C) and highheat capacities. These properties are suitable for thermallyannealing metals and forstoring thermal energy in solar applications.[10]
Sodium nitrate is also afood additive used as a preservative and color fixative in cured meats and poultry; it is listed under itsINS number 251 orE number E251. It is approved for use in the EU,[11] US[12] and Australia and New Zealand.[13] Sodium nitrate should not be confused withsodium nitrite, which is also a common food additive and preservative used, for example, in deli meats.
Sodium nitrate has also been investigated as aphase-change material for thermal energy recovery, owing to its relatively high melting enthalpy of 178 J/g.[14][15] Examples of the applications of sodium nitrate used for thermal energy storage includesolar thermal power technologies and direct steam generatingparabolic troughs.[14]
Studies have shown a link between increased levels of nitrates and increased deaths from certain diseases includingAlzheimer's disease,diabetes mellitus,stomach cancer, andParkinson's disease: possibly through the damaging effect ofnitrosamines on DNA; however, little has been done to control for other possible causes in the epidemiological results.[17] Nitrosamines, formed in cured meats containing sodium nitrate and nitrite, have been linked togastric cancer andesophageal cancer.[18] Sodium nitrate and nitrite are associated with a higher risk ofcolorectal cancer.[19]
Substantial evidence in recent decades, facilitated by an increased understanding of pathological processes and science, exists in support of the theory that processed meat increases the risk ofcolon cancer and that this is due to the nitrate content. A small amount of the nitrate added to meat as a preservative breaks down into nitrite, in addition to any nitrite that may also be added. The nitrite then reacts with protein-rich foods (such as meat) to producecarcinogenic NOCs (nitroso compounds). NOCs can be formed either when meat is cured or in the body as meat is digested.[20]
However, several things complicate the otherwise straightforward understanding that "nitrates in food raise the risk of cancer". Processed meats have no fiber, vitamins, or phytochemical antioxidants[citation needed], are high in sodium, may contain high fat, and are often fried or cooked at a temperature sufficient to degrade protein into nitrosamines. Nitrates are key intermediates and effectors in the primary vasculature signaling which is necessary for all mammals to survive.[21]
