Hazardous polycyclic aromatic hydrocarbons


In fact, we are no strangers to polycyclic aromatic hydrocarbons. I believe many people know that kebabs and fried foods contain carcinogens. Polycyclic aromatic hydrocarbons are a type of strong carcinogen.

Polycyclic aromatic hydrocarbons (PAHs for short) refer to hydrocarbons containing two or more benzene rings in their molecules. They are important environmental and food pollutants. So far, more than 200 PAHs have been discovered in humans, including naphthalene, anthracene, phenanthrene, and pyrene, and a considerable number of them are carcinogenic. Some PAHs also contain nitrogen, sulfur and cyclopentane.

Among the 94 compounds listed as carcinogenic to experimental animals by the International Center for Research on Cancer (IARC) in 1976, 15 were polycyclic aromatic hydrocarbons. Since benzopyrene was the first environmental chemical carcinogen discovered and is highly carcinogenic, people often use benzopyrene as a representative of polycyclic aromatic hydrocarbons.

The concentration of PAHs in industrial wastewater is as high as 1 mg/L. my country's drinking water hygiene standards stipulate that the content of benzopyrene in water should be less than 0.00001 mg/L. In the drinking water standards formulated by the World Health Organization, the maximum acceptable concentration of six representative polycyclic aromatic hydrocarbons is 0.00002 mg/L. The U.S. Environmental Protection Agency lists 16 types of polycyclic aromatic hydrocarbons, requiring their total amount to be no more than 0.0002 mg/L.

Polycyclic aromatic hydrocarbons exist in every corner of our lives. They are in the vegetables we eat, the water we drink, and the air we breathe. Any place where organic matter is processed, discarded, burned or used may produce polycyclic aromatic hydrocarbons, such as oil refineries, coking plants, rubber factories and thermal power plants. These factories that emit smoke and dust and even residents' cooking smoke contain polycyclic aromatic hydrocarbons.

Polycyclic aromatic hydrocarbons existing in the atmosphere provide the possibility for them to enter food directly. For example, polycyclic aromatic hydrocarbons can fall on the surface of vegetables, fruits, grains and grains stored in the open air. Food plants can also accumulate PAHs from soil and irrigation water contaminated with these substances. PAHs may contaminate water bodies, migrate to the human body through the food chain consisting of seaweed, crustaceans, molluscs and fish, and eventually accumulate in the human body.

Studies have shown that the content of benzopyrene in grains, fruits and vegetables grown in cities and near large factories is significantly higher than that in grains and vegetables in rural areas and remote mountainous areas. Vegetable oils made from grains from these contaminated areas and meat and dairy products from food animals fed grains from these areas have significantly higher levels of benzopyrene. However, levels of PAHs can be high even in soils far from industrial centers. Researchers have found that the content of polycyclic aromatic hydrocarbons in the soil in some places far away from human habitations can reach 100 to 200 micrograms/kg, which is mainly caused by the residue of rotten vegetables. Organic matter can also form polycyclic aromatic hydrocarbons under the action of soil microorganisms. Farmers in some areas of my country are accustomed to drying food on asphalt roads, which may cause direct contamination of food by polycyclic aromatic hydrocarbons.

Since crustaceans have poor degradability, they often accumulate considerable amounts of benzopyrene in their bodies. In addition, large amounts of polycyclic aromatic hydrocarbons are produced during food processing such as smoking and baking, which are more harmful to human health.

Many places implement landfill disposal of garbage, but this will produce garbage leachate. After being soaked in water, these garbage leachate can turn into organic wastewater containing a large amount of polycyclic aromatic hydrocarbons.

About hundreds of thousands of tons of polycyclic aromatic hydrocarbons are released into the atmosphere every year around the world. Most polycyclic aromatic hydrocarbons with five or more rings are concentrated in particulate matter or dispersed in atmospheric dust. In atmospheric dust, almost all polycyclic aromatic hydrocarbons are attached to inhalable particulate matter with a particle size of less than 7 microns, directly threatening people's health.

What harm do polycyclic aromatic hydrocarbons do to the human body?

First of all, polycyclic aromatic hydrocarbons can cause the body's immunosuppressive response, which is manifested as changes in serum immunological indicators. Animal experiments show that cooking fume condensation has a significant impact on the immune function of mice, and its impact on T lymphocytes is more significant.

Secondly, polycyclic aromatic hydrocarbons are potentially carcinogenic.

Surveys show that when the concentration of benzopyrene increases by 0.1 microgram per 100 cubic meters, the lung cancer mortality rate increases by 5%. Although PAHs in the environment are in trace amounts, they are difficult to degrade and easily accumulate in the environment, and then enter the human body through direct and indirect contact, ultimately causing damage to health. Residents in mountainous areas often keep fires on the spot to keep warm, and the indoor smoke is filled all day long, resulting in a higher incidence of nasopharyngeal cancer. People who eat foods cooked at high temperatures (such as grilled, fried) may increase the incidence of cancer in certain organs, especially the stomach and esophagus. For example, residents of Iceland like to eat smoked food, and their standardized mortality rate from gastric cancer is 125.5/100,000, which is significantly higher than other regions.

In fact, the carcinogenicity of polycyclic aromatic hydrocarbons has been studied for more than 200 years. As early as 1775, British doctor Porter confirmed that the high incidence of scrotal cancer among chimney sweeps was related to their frequent exposure to soot (coal tar). However, it was not until 1932 that the most important polycyclic aromatic hydrocarbon, benzopyrene, was isolated from coal tar and mineral oil, and was confirmed to be highly carcinogenic in animal experiments.

Since there are many types of PAHs, different types have different carcinogenic activities. Among them, benzopyrene is a strong carcinogen, which mainly causes tumors in epithelial tissues, such as skin cancer, lung cancer, gastric cancer, and digestive tract cancer. In 1973, research by Sabat and others showed that in addition to inducing gastric cancer and skin cancer, benzopyrene can also cause esophageal cancer, upper respiratory tract cancer and leukemia, and can cause fetal teratogenesis through the mother's body. Most of the benzopyrene that enters the human body with food can be absorbed by the human digestive tract, and then quickly spreads throughout the human body through blood circulation. Both human breast and adipose tissue can accumulate benzopyrene.

Part of the benzopyrene absorbed by the human body binds to proteins, causing the enzymes that control cell growth to mutate, causing cells to lose their ability to control growth and become cancerous. The other part is involved in metabolic decomposition and may eventually become a carcinogen - benzopyrenediol epoxide. This substance cannot be transformed and is extremely mutagenic. It can directly react with different components in cells (including DNA), causing gene mutations and leading to cancer. For various reasons, although the Food and Agriculture Organization of the United Nations and the World Health Organization have not set regulations on the allowable content of polycyclic aromatic hydrocarbons in food, some people estimate that the total amount of polycyclic aromatic hydrocarbons ingested by adults from food per year is 1 to 2 mg; if Cumulative intake of more than 80 mg may induce cancer. Therefore, it is recommended that the total daily intake per person should not exceed 10 micrograms.

In nature, there are elimination methods such as biodegradation, hydrolysis, and photolysis, which keep the content of PAHs in the environment at a low concentration level. However, in recent years, with the intensification of human production activities, the dynamic balance of PAHs in the environment has been destroyed, resulting in a large increase in PAHs in the environment, which has reached a point where control is indispensable. The prevention and control measures of PAHs generally have two aspects: one is to formulate specific emission standards to regulate and control the emission of PAHs, and the other is to use some methods to deal with PAHs that have caused pollution. Conventional methods for degrading polycyclic aromatic hydrocarbons include physical methods, chemical methods and biochemical treatment methods. However, these methods are currently unable to completely degrade polycyclic aromatic hydrocarbons, and the cost is also high. Therefore, it is very important to actively explore new high-tech methods to control polycyclic aromatic hydrocarbons pollution. necessary. Fortunately, scientists have proposed many effective methods, such as using microwave technology to treat polycyclic aromatic hydrocarbons. Although microwave elimination of polycyclic aromatic hydrocarbon pollutants is still in the laboratory research stage, this technology has the advantages of being efficient, fast, and not polluting the environment. I believe that as research continues to deepen, it will have broad application prospects in environmental protection.