Recently, the relevant reports on 9 nitrosamines detected in drinking water in China have aroused people's concern about various phenomena of exposure to nitrosamines in life. What are nitrosamines? What about the daily contact? Undoubtedly, it is a matter of great concern to people.
Nitrosamines are a class of organic compounds with the structure of - N - N=O, which have been discovered for more than 100 years. In 1937, Freund reported for the first time two cases of occupational exposure to N-nitrosodimethylamine (NDMA) in the nitrosamine family, and the patient showed toxic liver damage. In 1956, British scientists Magee and Barnes found that NDMA had a strong carcinogenic activity on experimental animals, and since then nitrosamines have attracted widespread attention. At present, researchers have found nearly 300 kinds of nitrosamines, and it has been confirmed that 90% of nitrosamines can induce tumors in different organs of animals. The pollutant risk information integration system managed by the US Environmental Protection Agency classifies nitrosamines as B2 carcinogens, that is, substances with insufficient evidence of carcinogenicity to humans and sufficient evidence of carcinogenicity to experimental animals.
Nitrosamines are easily formed by the reaction of secondary amine and nitrite, and the above reactions can be successfully completed under natural conditions and in the process of laboratory research, as well as in human and other animals. Therefore, nitrosamines are widely distributed in nature, and can be found in soil, water, air, tobacco, bacon, pickles, beer, plastics and other substances.
In our daily life, nitrosamines are widely contacted. First, nitrite and nitrate, the precursors of nitrosamines, are widespread in the human living environment. The survival of human beings and even all kinds of animals can not be separated from the photosynthesis of plants. Plants need to absorb nitrate as their nutrient if they want to synthesize protein in the growth process. Nitrate is reduced to nitrogen in plants, and forms amino acids and nucleic acids with organic acids synthesized through photosynthesis to form plants; When photosynthesis is insufficient, there will be excessive nitrate in the plant body. The nitrate content in Chinese cabbage, spinach, celery, rape and lettuce can reach 600mg/kg-4000mg/kg. Nitrate has low toxicity, but during processing and storage, nitrate in vegetables will be converted into nitrite, which will react with amine, the decomposition product of protein, to generate nitrosamine under appropriate conditions.
When curing meat, fish or making sausage and ham, Nitrite is often used as a coloring agent and preservative. During the curing process of meat products, protein will degrade to produce amino acids and amine compounds, which are precursors of nitrosamines. The nitrogen oxides produced by nitrite in meat will be at the appropriate pH with secondary amine Nitrosamine compounds are formed under the condition. The common nitrosamines in meat products mainly include N-dimethylnitrosamine, N-diethylnitrosamine and N-pyrrolidine nitrosamine.
In recent years, researchers have found traces of nitrosamines and their precursors in rubber products such as baby pacifiers, baby pacifiers, balloons, latex gloves, and rubber bands of dental appliances. Nitrosamines in baby pacifiers, baby pacifiers and other children's products mainly come from the vulcanization process of rubber. Rubber products are usually molded through the high-temperature vulcanization process, which requires the use of a vulcanization catalyst. During the vulcanization process, secondary amines will be generated, and under certain conditions, stable nitrosamines will be generated with nitrogen oxides in the air or additives. Due to the characteristics of rubber material, it is difficult to remove nitrosamines through washing and soaking. For example, the presence of nitrosamines can still be detected after the nipple is boiled for 10 minutes. In June 2009, the EU officially issued the New Toy Safety Directive, which stipulates that the use of nitrosamines is strictly prohibited for toys used by infants under 3 years of age and toys put into the mouth by children. If it is unavoidable during production, the total migration of nitrosamines should not be more than 0.05mg/kg.
Because there are many kinds of nitrogen-containing substances in cosmetics raw materials, many nitrosamines can be detected in cosmetics. Some nitrosamines in cosmetics come from production raw materials, and some are formed by nitrosation of precursors during production and placement. Relevant studies have shown that nitrosamines can be formed by the reaction of nitrosamines and amines under the catalysis of formaldehyde in neutral or alkaline environment; Some preservatives in cosmetics may release formaldehyde, which can catalyze the formation of nitrosamines.
Water is the source of life, and the safety of drinking water directly affects human health. Due to the shortage of water resources and pollution of water sources, in order to ensure the safety of drinking water, it is necessary to take coagulation, sedimentation, filtration, disinfection and other treatment measures for the water sources. The purpose of disinfection is to kill pathogenic bacteria and viruses. However, while preventing the occurrence and spread of diseases, disinfectants will react with some natural organic substances and organic pollutants in the water body to generate disinfection by-products harmful to human health. In 1989, nitrosamines were first detected in drinking water in Ontario, Canada. In order to control and eliminate the formation of nitrosamines disinfection by-products in drinking water, many studies analyzed the formation process of nitrosamines in drinking water, including precursors and formation mechanism, as well as the influencing factors in the formation process, such as disinfectants, water pH, etc. So far, The researchers believe that the nitrosamines by-products formed during the disinfection of drinking water are related to factors such as chloramine disinfection, the use of amino polymer coagulants, the use of amino resin, pesticides, herbicides and other factors that pollute water bodies.
Medical research results show that the carcinogenic effect of nitrosamines on animals is certain, and so far no animal has been found to be resistant to the carcinogenic effect of nitrosamines. It has been reported that nitrosamines can cause tumors in all organs of animals, Among them, digestive system tumors are the most serious, and the place with the highest carcinogenic rate is the liver, Esophagus and pharynx take second place. However, the research on the direct carcinogenic effect of nitrosamines on human beings is still lack of exact evidence. At present, the research reports on the carcinogenic effect of nitrosamines on human beings are mostly the results of epidemiology. Some researchers found that northern Iran, central Brittany in France and Linxian County in Henan Province in China, The incidence of esophageal cancer is high. Investigators found that the content of nitrosamines and their precursors in some foods in high incidence areas of esophageal cancer was significantly higher than that in low incidence areas. Researchers found in Linxian County, Henan Province, China that Fusarium shenzhu and Geotrichum candidum, which pollute local food, not only can reduce nitrate to nitrite, but also can increase the content of amine in moldy food, which can promote the synthesis of nitrosamines.
To prevent the potential harm of nitrosamine compounds to human health, two measures can be taken: one is to reduce the intake of nitrosamines and their precursors nitrate and nitrite; The second is to block the synthesis of nitrosamines in vivo and in vitro.
Meat products are an important part of people's diet. The use of nitrite and nitrate in the production of meat products can produce attractive color and flavor, and can also effectively inhibit the growth of pathogenic bacteria. However, nitrite and amine in meat products can generate nitrosamines under certain conditions, so the amount of nitrate and nitrite must be strictly limited. Our country stipulates that the consumption of sodium nitrate in meat products should be less than 0.5 g/kg, and that of sodium nitrite should be less than 0.15 g/kg; The residual amount is calculated by sodium nitrite and shall not exceed 0.03-0.05g/kg. Considering that the nitrate content in cured and smoked meat products is usually high, proper control should be taken in daily diet selection.
Relevant research shows that vitamin C can reduce the content of nitrosamines in food, block the synthesis of nitrosamines in the body, prevent cancer in experimental animals, and prevent the harm of nitrosamines to human body. Vitamin E and some components in natural fruit juice can also block the synthesis of nitrosamines in vivo. Therefore, people should pay attention to the intake of foods rich in vitamin C and vitamin E and food diversification in the choice of diet to prevent the harm of nitrosamines to human body. Because some research results have proved that some natural ingredients in plants have a stronger scavenging effect on nitrite than simple vitamin C, which provides a theoretical basis for reducing nitrite residues in meat products and guides people's healthy diet from the perspective of nutrition.
In recent years, some researchers have irradiated meat products and compared them with non irradiated products. It is found that irradiated foods can effectively reduce the content of nitrosamines in them. At present, the research on irradiation treatment of meat products is still in the exploratory stage. Considering the particularity of irradiation technology, there are still many problems to be solved when it is applied to the production and processing of meat products. Therefore, the use of irradiation treatment to reduce the nitrosamines generated in meat products cannot be actually applied to the production and consumption fields for the time being.
