Nitrate is an inorganic compound composed of one atom of nitrogen (N) and three atoms of oxygen (O); the chemical symbol for nitrate is NO3. Nitrate is not normally dangerous for the health unless it is reduced to nitrite (NO2).
Nitrate is one of the most frequent groundwater pollutants in rural areas. It needs to be regulated in drinking water basically because excess levels can cause methaemoglobinaemia, or "blue baby" disease. Although nitrate levels that affect babies are not dangerous for older children and adults, they do indicate the possible presence of other more serious residential or agricultural pollutants, such as bacteria or pesticides.
The origin of nitrate in groundwater is primarily from fertilizers, septic systems, and manure storage or spreading operations. Fertilizer nitrogen not taken up by plants, volatilized, or carried away by surface runoff ends up in the groundwater in the form of nitrate. This makes the nitrogen unavailable to the plants, and can also raise the concentration in groundwater above the admissible levels for drinking water quality. Nitrogen from manure can be similarly lost from fields, barnyards, or storage locations. Septic systems remove only half of the nitrogen in wastewater, leaving the other half to leach to groundwater, this way raising groundwater nitrate concentrations.
Nitrate in drinking water is measured either in terms of the amount of nitrogen present or in terms of both nitrogen and oxygen. The federal standard for nitrate in drinking water is 10 mg/l nitrate-N, or 50 mg/l nitrate-NO3, when the oxygen is measured as well as the nitrogen. Unless otherwise specified, nitrate levels usually refer only to the amount of nitrogen present, and the usual standard, therefore, is 10 mg/l.
Short-term exposure to drinking water with a nitrate level above the health standard is a potential health problem especially for babies. Babies drink large quantities of water considering their body weight, especially if water is used to mix powdered or concentrated recipes or juices. Also, their digestive systems are inmature, and thus more likely to allow the reduction of nitrate to nitrite. The nitrite in the digestive tract of babies can cause methaenoglobinaemia.
Nitrate occurs naturally in many vegetables, such as lettuce and spinach, and is produced by microbes in the human gut, with the result that only a small part of the nitrate in the body comes from drinking water.
The intake of nitrate from vegetables is unlikely to cause health problems because very little of this nitrate is converted to nitrite. Meat products account for less than 10 percent of nitrate in the diet, but 60 to 90 percent of the nitrite consumed. This is basically because sodium nitrite is added to foods such as hot dogs, bacon, or ham. Fruits, grains, and dairy products contribute almost no nitrate or nitrite to people's diets.
Definition: Clinical condition arising from the excessive conversion of haemoglobin to methaemoglobin, which is incapable of binding and carrying oxygen. Methaemoglobin is formed when iron in the haemoglobin molecule is oxidised from Fe2+ to Fe3+.
Toxicology: Methaemoglobin occurs when haemoglobin is oxidised at a rate exceeding the normal enzymatic capacity to reduce the haemoglobin. Many agents may be responsible for this oxidation. The most frequently found are:
Ground or surface water contaminated with nitrates
Methaemoglobinaemia could also be developed due to non-toxic causes, as congenital enzyme deficiencies.
A typically greyish cyanosis can be observed when the level of methaemoglobin exceeds 1.5 g/dL, which is about 10% of the total haemoglobin in a normal individual. At this level, the patient may not notice any symptoms yet.
The symptoms of methaemoglobinaemia are usually those related to impaired oxygen delivery (headache, weakness, tachycardia and breathlessness) and develop gradually as concentrations of methaemoglobin rise above 20%.
Concentrations higher than 50% result in severe hypoxaemia and central nervous system depression.
Concentrations higher than 70% may cause death.
For individuals that suffer from anaemia, cardiac failure or pulmonary disease the symptoms of hypoxia may appear at lower percentage levels of methaemoglobin.
An easy solution to eliminate the nitrites in the water is to oxidize them to nitrates (as we said before, nitrates are much less toxic than nitrites). This can be done by injecting ozone in the water. Ozone is a very oxidizing chemical that would oxidize all the nitrites into nitrates, thus eliminating the toxicity caused by nitrites.