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Phone: 631-242-4249 | Toll-Free: 888-686-3454
Nitrate ions are present at varying concentrations (usually up to ≈ 20 mg/L) in ground and surface waters, as well as in municipal and industrial wastewaters. They are present almost exclusively in dissolved form in water samples. Nitrate levels of 15–50 mg/L indicate anthropogenic influences. They enter municipal wastewaters e.g. as the end product of nitrification.
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Nitrification is the bacterial oxidation of ammonia and other nitrogen-containing organic compounds. These emerge in large quantities as human and animal excretions or from decay processes of organic substances. Nitrates in surface and groundwaters can also originate from water-soluble components of artificial fertilizers.
Nitrate and the other nitrogen parameters ammonium and nitrite, are thus a measure for the contamination of a water body. It is important whether an increased nitrate content is linked to similarly increased ammonia and nitrite concentrations to evaluate the self-purification capacity of a water body.
If this is not the case, the self-purification capacity is sufficient for the mineralization of organic matter. The nitrate concentration is one of the most important chemical parameters to check the quality of drinking water. The EC guide value is 25 mg/L.
Detailed information about the nitrite and ammonium concentration as well as their relationships is essential for a proper assessment of drinking water. So-called reducing conditions are present if high ammonium and low nitrate levels are observed e.g. in a (ground)water polluted with nitrogen compounds. This nitrate reduction is effected among others by bacteria and fungi Streptomyces). Under oxygen-deficient conditions (O2 < 5 mg/L), nitrate (NO3–) is first reduced to nitrite (NO2– ), which is then degraded further e.g. to elemental nitrogen gas (N2). Other bacteria, by contrast, reduce nitrite (NO2– ) to ammonium (NH4+). The conditions are opposite in native, oxygen-rich groundwater. Here oxidation of ammonium (NH4+) and nitrite (NO2–) to nitrate (NO3–) by nitrogen bacteria (Nitrosomonas, Nitrococcus, Nitrobacter) takes place.
There is always pollution, if high nitrate concentrations cannot be attributed geologically to natural saltpeter deposits (especially in case of presence in groundwater).
Nitrate and nitrite are widely used as additives in the preparation of meat products (“curing”). On the one hand, the shelf life is extended by inhibition of putrefying bacteria. On the other hand, the heat- and storage-stable red curing color is formed (generation of the typical cured flavor), by the addition of nitric oxide (NO) to the muscle pigment myoglobin to form nitrogen oxide myoglobin.
The pollution of groundwater by nitrate is a serious deterioration of the environmental quality. Elevated nitrate levels have a negative impact on the ecology of the waters. They can also lead to a lower drinking water quality and thus to negative health effects. In the organism, nitrate can be converted, among other things, to nitrite, which inhibits Oxygen transport by the red blood pigment (hemoglobin).
Nitrate is primarily almost non-toxic (gastric inflammation usually occurs only at levels > 500 mg/L NO3–). The dangers from nitrates arise from the fact that they are partially converted to nitrites by bacteria in the body (Nitrite NO2– ). Tertiary conversion products of nitrate (in the human body, from amines and nitrite) can be N-nitroso compounds, which are classified as carcinogenic. Nitrate, depending on the dose, inhibits the iodide transport mechanisms of the human organism.
The notation of nitrate is NO3–, but often NO3-N is used instead. The difference is that in NO3-N only the mass of nitrogen is taken for account. The mass of oxygen in the nitrate is disregarded. The conversion factor is 4.43, which results from the large mass difference of nitrogen and nitrate.
Nitrate is a pollution indicator and one of the most important chemical parameters for the control of drinking water quality.
With regard to human nutrition, especially some strongly nitrate-containing vegetables such as spinach, soy beans, chard, beets or radishes are to be named.
The determination reacts analogously to DIN 38405-D9-2 and ISO 7890-1, the photometric determination as 4-nitro-2,6-dimethyl-phenol.
The reaction uses 2,6-dimethylphenol in a mixture of sulfuric acid and phosphoric acid. Direct nitration of dimethylphenol results in the formation of 4-nitro-2,6-dimethylphenol, depending on the nitrate content of the sample.
By adjusting the pH to 1-2 with sulfuric acid, the sample can be stored for up to 7 days (storage vessel: PE bottle). Ideally, storage and transport are carried out at 4 °C in the dark.
