Nitrate (NO3-) and nitrite (NO2-) are chemical roots of nitric acid (HNO3) and nitrous acid (HNO2) respectively. They exist in the aquatic environment, the living organisms and artificial products, as pollutants, which can cause food poisoning, cancers or even death. It's important to detect and eliminate such chemicals with the efficient methods. Currently, several detection methods have already been in use but all are not entirely harmless. For example, granular Cd grains are recommended for the NO3- determination for fruits and vegetables because they are easy to make and recover, and can be used repeatedly. However, Cd cannot be recycled easily, and may cause additional pollution. So the goal of our project is to provide an efficient and a more environment friendly method of detecting nitrates/nitrites and we strive to design biosensors to avoid the disadvantages of traditional methods.
Specific details of the pollution of the Nitrites and Nitrates:
Nitrate (NO3-) and nitrite (NO2-) are Chemical roots of nitric acid (HNO3) and nitrous acid (HNO2). They exist in nature, especially in the gaseous water, surface water and groundwater, as well as plants and animals and food within, as environmental pollutants.
There exist a lot of pollution sources of nitrate and nitrite in the environment, such as:
1. Artificial fertilizers: ammonium nitrate, calcium nitrate, potassium nitrate, sodium nitrate and urea;
2. Sewage, garbage and human and animal feces: according to tests, 1 liters of domestic sewage in the natural degradation process can produce 110 mg of nitrate; 1 kg of garbage and fecal compost under natural conditions can produce 492 mg of nitrate leaching decomposition;
3. Large amounts of ammonia which food, fuel or oil refining factories emit in waste: after nature biological, chemical conversion cause the formation of nitrate into the environment;
4. Cars, trains, ships, aircraft, boilers, civil furnace combustion of petroleum fuels, coal, natural gas: can produce large amounts of nitrogen oxides. Average burning one ton of coal, of 1 kiloliter oil and 10,000 cubic meters of natural gas can produce nitrogen dioxide gas, respectively 9.13 and 63 kg. These nitrogen dioxide gas can be formed after precipitation leaching nitrate descend to the ground and waters ;
5. Food preservation and preservation: nitrate and nitrite are widely used in corrosion protection and preservation of meat and fish, so that the meat is red and aroma. Adding sodium nitrate per kilogram of meat in food (usually sodium nitrite) 5 mg or less, within a certain time will percept a good flesh color ; added 20 mg or more, and may exhibit the needed stability in the commercial color; added 50 mg of a special smell.
These chemical fertilizers in irrigation, sewage, garbage and fecal, industrial nitrogenous waste, fuel combustion, emissions containing nitrogen gas and other pollutions, after precipitation leaching and decomposition in natural conditions, will form nitrate into the river, the lake and into the ground, resulting in nitrate pollution of surface water and groundwater. Infiltration such as sewage, sewage irrigation and unrestrained use of fertilizers sharp increase in groundwater nitrate content can be from a few mg / l to 400 mg / l or more (the national life of the nitrate content of drinking water health standards less than 88.6 mg / l to nitrogen of less than 20 mg / l); indiscriminate use of fertilizers, irrigation, nitrate pollution of water irrigation cause crops absorb large amounts of nitrates, such as over-fertilization spinach production per kilogram dry weight containing nitrite 3600 mg of salt. Moreover, pickled sauerkraut, vegetables after the lon g-distance transport and long-term storage, as well as overnight cooked vegetables are all unhealthy. Because not only a large number of nitrate content increased, but also in the role of nitrate-reducing bacteria, nitrates are reduced to nitrites.
Large amounts of nitrate and nitrite contain in drinking water, vegetables, grain, fish, meat, sauerkraut, overnight cooking, allow direct poisoning by human consumption. Nitrate in the human body can also be reduced to nitrite. Nitrite reacts in human blood; cause the formation of methemoglobin, so that the blood loss of oxygen functionality makes oxygen poisoning. The symptoms caused by it such as dizziness on light, palpitations, vomiting, lips cyanosis, severe cases, unconsciousness, convulsions, shortness of breath, can be life threatening if not rescued in time. Moreover, nitrite may react with secondary amines and from nitrosamines in the environment both in and out human bodies, which will become carcinogenic, teratogenic and mutagenic substances if reaches a certain dose, this will totally do great harm to human health.
In order to prevent the hazard of nitrate and nitrite, in addition to achieve scientific and rational application of fertilizer, prohibit the use of sewage irrigation ,implement the manure treatment of sewage and garbage and other environmental protection measures to protect surface and ground water sources from nitrate and nitrite nitrate pollution, human should also keep a minimum to eat pickled, smoked, wax system of meat, canned food, stains sauerkraut, and salted vegetables; does not buy foods that were kept too long, lethargic or tertian; finish the food right after buying them; does not eat overnight cooked vegetables or keep tertian boiled vegetables; and remember not to confuse the industrial nitrite with normal salt for eating.
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