Nitrate
The chemical compound ammonium nitrate, the nitrate of ammonia with chemical
formula NH4NO3, is commonly used in agriculture as a high-nitrogen
fertilizer. As a strong oxidizing agent, it has applications as
a component of explosives. In the latter use, it is mixed with a
hydrocarbon, usually Diesel fuel (oil). Because of the ready availability
in bulk of the raw materials, ammonium nitrate/fuel oil (ANFO) mixtures
have occasionally been used for terrorist bombs, for example by
the Provisional IRA and in the Oklahoma City bombing by Timothy
McVeigh and Terry Nichols.
The most common sources of nitrate are municipal and industrial
wastewaters, refuse dumps, animal feed lots, and septic systems.
Once nitrate is formed, its movement in soil and potential for contamination
of ground, water depend on several factors including the soil characteristics,
location and characteristics of the underground water formations
(aquifers), and climatic conditions. Potential for nitrate contamination
of drinking water also depends on the depth and construction of
wells.
Identifying the source of nitrates for an individual well is often
very difficult. Because nitrates move with the flow of groundwater,
the source may be located a considerable distance from the well.
In many cases, the time needed for nitrate to pass through the soil
into groundwater is difficult to predict due to many variables including
application rate, the soil type, and the depth to the water table.
Ammonium nitrate decomposes into gases including oxygen when heated
(non-explosive reaction); however, ammonium nitrate can be induced
to decompose explosively by detonation. Large stockpiles of the
material can be a major fire risk due to their supporting oxidation,
and may also detonate, as happened in the Texas City disaster of
1947, which led to major changes in the regulations for storage
and handling. A heavy explosion, with 561 casualties, occurred in
the city of Oppau (on the grounds of BASF near Ludwigshafen in Germany)
on September 21, 1921. Another one occurred, 80 years later, at
a plant in Toulouse, France, in September 21, 2001.
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