Contents of this article
- 1. Nitrosamines are not chemical carcinogens
Nitrosamines are not chemical carcinogens
A large number of experiments show that nitrosamine compounds (NOC) are strong carcinogens. There are more than 100 kinds of nitrosamines, 41 of which can cause tumors in animals, and more than a dozen kinds of nitrosamines can cause esophageal cancer in animals. Starting from esophageal epithelial hyperplasia and gene mutations, esophageal cancer is mainly the result of the direct action of nitrosamines. The changes in tumor suppressor genes caused by nitrosamines are similar to the changes in human primary esophageal cancer. Nitrosamines can cause the loss or mutation of multiple tumor suppressor genes of p53, Rb, APC and MCC in the same esophageal tissue (Du Bailian, 1994; Guo Yongjun, 1994). After nearly two decades of research, the cause of esophageal cancer is concentrated on the chemical carcinogenesis of nitrosamines. Judging from various data, the role of nitrite seems to play a key role in the onset of esophageal cancer (Cao Wei et al., 1996; Guo Yongjun, 1994; Feng Qirui, 1986; Henan Cancer Prevention and Treatment Research Team, 1976).
Some researchers have paid sufficient attention to nitrosamines and their precursors nitrite and nitrate in the environment and conducted investigations (Lu Shixin et al., 1988; Wang Lidong, 1994; Mirvish et al., 1993; Cheng K K, 1996 ; Park Hechun, 1996), found that nitrates and nitrites in the human body mainly come from food, local grains, vegetables and water, while nitrosamines taken directly from the environment are very trace. Both nitrate and nitrite are the precursors of nitrosamines, so more nitrosamines in the human body are synthesized in the body from exogenous nitrates or nitrites (Henan Geological Bureau Hydrogeology Team et al., 1978; Cheng K K, 1996; Yang Wenwen et al., 1992). The total nitrogen content, nitrate nitrogen (
) and ammonium nitrogen (
) contents in the soil in this area basically follow the pattern of gradual decline from mountainous areas to hills to plains (Table 4-15). Research by agronomists has also found that nitrate (
) taken in by plants from the soil is first reduced to nitrite (
) by nitrate reductase, and then reduced to
by nitrite reductase. Since the activity of nitrite reductase is much higher than that of nitrate reductase, nitrate nitrogen (
) and ammonium nitrogen (
) mainly exist in the plant (Chen Zhende, 1993). The detection rate of nitrosamines in grains in high-incidence areas is 23.3% to 33.3% (Henan Cancer Prevention and Control Research Team, 1976), and the detection rate of nitrates is (6.3±2.9) to (17.1±4.2) μg/g (Feng Qirui, 1986; Henan Geology Bureau Hydrogeology Team et al., 1978), while the detection rate of nitrosamines in grain in low-incidence areas is only 0-1.2% (Henan Cancer Prevention and Control Research Team, 1976). The nitrate + nitrite content of sweet potatoes in Ci County is 120.35 μg/g, while that in the plain low-incidence area of Tang County is only 73.07 μg/g. Ci County is significantly higher than Tang County. The nitrate and nitrite of vegetables in high-incidence areas are 0.828-2.002mg.kg and 0.029-0.067mg/kg respectively (Wei Huijuan et al., 1986). The sauerkraut and pickles that local residents like to eat also contain a lot of nitrates. This study also found that the nitrate ions contained in drinking water in Ci County are much higher than those in Linzhang and Wei counties, which is directly proportional to the incidence of esophageal cancer. The three nitrogen contents (nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen) of the water from 87 wells in nine townships of Cixian County exceeded the national standards by 20.6%, 50.5%, and 33.3% respectively. The nitrite content was the same as that of these nine townships in 1983~ There was a positive correlation between the mortality rate of esophageal cancer in 1989 (Zhang Xiulan et al., 1996).
The consistent relationship between esophageal cancer and the geological and ecological environment is related to the distribution of total nitrogen, nitrate nitrogen, and ammonia nitrogen in the environment. In Table 4-16, the total nitrogen, nitrate nitrogen, and ammonia nitrogen contents are not much different among soils in mountainous areas, hills, piedmont and alluvial plains, but they are different in the same geological and ecological environment: on the one hand, it may be due to the large number of samples. less; on the other hand, it is related to the diversification of nitrogen sources in the soil. Nitrogen in soil can come from the decomposition of organic matter, atmospheric precipitation, dustfall, groundwater and surface water, organic fertilizers and chemical fertilizers. However, according to the current research level, it is difficult to determine which source of nitrogen is the main source in various geological and ecological environments.
In addition, some literature also records that the nitrogen oxide content of drinking water in mountainous areas (Lin County), hills and flood plains (Anyang) and flood plains (Fan County) is 16.4, 18.1 and 3.2 mg/L respectively (China Institute of Oncology, Academy of Medical Sciences, 1980), the nitrate of dry well water in Cixian mountainous area is 5 mg/L, and the well water of hills and piedmont flood plains is 10-240 mg/L. The nitrate content increases with the increase of well depth. This is because of nitrate ions. (
) It is easy to migrate to depth with the aqueous solution. In areas of extremely thick flood sediments, the groundwater table is getting deeper and deeper, and the nitrogen oxide content is getting higher and higher. The nitrogen content in the ecological environment can be roughly arranged in mountainous areas > hills > plain areas, which is generally consistent with the distribution of esophageal cancer incidence rates.
Table 4-l6 Nitrogen content in soil
Data source: According to the measurement by the Geophysical and Geochemical Exploration Institute of the Ministry of Geology and Mineral Resources.
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