Dioxin Contamination of Food and Its Prevention

作者：admin  点击次数：17  发布时间：2025-04-19

Chlorinated dibenzo-p-dioxins (PCDDs) and chlorinated dibenzofurans (PCDFs) are generally referred to as dioxins (PCDD/Fs), while polychlorinated biphenyls (PCBs) and chlorinated diphenyl ethers have similar physical and chemical properties and toxicity to dioxins, and are also called dioxin analogs. Here we mainly introduce dioxins.
(I) Physical and chemical properties
PCDD/Fs are colorless needle-shaped crystals with poor water solubility and are easily soluble in organic solvents and fats. Therefore, they can accumulate in the adipose tissue of animals and can be enriched through the food chain; they can still exist stably in strong acids, strong bases and oxidants, and are also very stable to heat. They will only begin to be degraded when the temperature exceeds 800°C, and will only be destroyed in large quantities at temperatures above 1000°C; their average half-life is about 9 years, and they can exist in the environment for a long time; PCDD/Fg can be photodegraded under the action of ultraviolet rays.
(II) Toxicity and carcinogenicity
1. General toxicity
Most PCDD/Fs have strong acute toxicity. For example, the oral LD ​​of tetrachlorodibenzo-p-dioxin (TCDD) to guinea pigs is only 1 mg/kg body weight, but different species of animals have great differences in sensitivity to it. For example, the oral LD ​​of hamsters and guinea pigs can differ by 5,000 times. Its acute poisoning is mainly manifested by extreme weight loss, accompanied by a sharp decrease in muscle and adipose tissue (hence the name waste syndrome). Its mechanism may be to reduce food intake by affecting the hypothalamus and pituitary gland. In addition, skin contact or systemic exposure to large amounts of dioxins can cause chloracne, which is manifested as excessive keratinization and pigmentation of the skin.
2. Hepatotoxicity
Dioxins have different degrees of liver damage to animals, mainly manifested as hepatocyte degeneration and necrosis, increased intraplasmic lipid droplets and smooth endoplasmic reticulum, increased activity of microsomal enzymes and transaminases, and monocyte infiltration. Different species of animals have different sensitivities to its hepatotoxicity. Hamsters and guinea pigs are less sensitive, while rats and rabbits have extremely severe liver damage, which can lead to death.
3. Immunotoxicity
Dioxins have a strong inhibitory effect on both humoral immunity and cellular immunity. At non-lethal doses, they can cause severe atrophy of the thymus of experimental animals, inhibit the production of antibodies, and reduce the body's resistance.
4. Reproductive toxicity
Dioxins are environmental endocrine disruptors and have obvious anti-hormone effects. The mechanism may be that these substances induce the activity of estradiol metabolizing enzymes, thereby increasing its catabolism and causing a decrease in the concentration of estradiol in the blood, which in turn causes changes in the sexual cycle and reproductive dysfunction. A large number of studies have shown that TCDD can reduce the uterine weight and estrogen receptor levels of mice and rats, leading to a decrease in pregnancy rate, a decrease in the number of litters, and even infertility. In recent years, some studies have also shown that TCDD also has a significant anti-androgenic effect, which can cause changes in testicular morphology, a decrease in sperm count, a decrease in male reproductive function, and a significant decrease in serum testosterone levels in male animals. Other studies have shown that humans may be more sensitive to the anti-androgenic effects of TCDD than mice.
5. Developmental toxicity and teratogenicity
TCDD is teratogenic to many animals, especially mice, and can cause fetal rupture and hydronephrosis. Rats are more sensitive to the developmental toxicity of TCDD. Pregnant mice given 0.064pg/kg body weight of TCDD (one-time exposure) at 15 days after implantation can cause abnormal testicular development and sexual behavior in male animals after birth. Examination 120 days after birth still shows that the weight of the testicles and epididymis is significantly lighter than that of the control animals, and the number of sperm is also significantly reduced.
6. Carcinogenicity
TCDD is extremely carcinogenic to many animals, especially rodents. The lowest liver cancer-causing dose for rats and mice is 10ng/kg body weight. Epidemiological studies have shown that exposure to PCDD/Fs is related to the occurrence of certain tumors in humans. In 1997, the International Agency for Research on Cancer (IARC) identified TCDD as a Class I carcinogen that is carcinogenic to humans. However, no significant mutagenic effects have been found for PCDD/Fs, so it is believed that such compounds may be non-genotoxic carcinogens, whose main effect occurs in the promotion stage of tumors, and are a class of strong carcinogens.
(III) Sources of dioxins in the environment and food
Dioxins can be formed from a variety of precursors through Ullmann reaction and Smiles rearrangement. The direct precursors of PCDD/Fs include polyaminobiphenyls, 2,4,5-trichlorophenol, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), pentachlorophenol and its sodium salt, etc.
1. Dioxins in the environment Dioxins and their analogues are widely present in the atmosphere and floating dust, water bodies and sediments, and soil in the environment. PCDD/Fs are by-products produced during the incineration of garbage, destruction of organic chemicals, and industrial production. If chlorine is present, wood, cotton, coal, and gasoline containing carbon, oxygen, and hydrogen will produce PCDD/F; when burned at 200~650℃, while copper, iron, zinc, aluminum, chromium, and manganese have catalytic effects. The incineration of garbage and medical waste, especially incomplete combustion or combustion at lower temperatures and the presence of PVC plastics, is the main source of PCDD/Fs in the environment. The synthesis of pesticides such as chlorophenol, sodium pentachlorophenol, mycophenol, hexachlorobenzene, and chlorinated diphenyl ethers is accompanied by the production of PCDD/F;. In the chlor-alkali chemical industry, organic chlorination industry, dye chemical industry, pesticide chemical industry, pulp and paper industry, and metal smelting industries, PCDD/F; may exist in the final product and waste gas, wastewater, and waste residue. 2. Sources of PCDD/Fs in food
Dioxins and their analogues in food mainly come from environmental pollution. Expanded polystyrene, PVC plastics, and paper products as food packaging materials can migrate dioxins and their analogues into food.
(IV) Preventive measures
1. Control PCDD/Fs pollution in the environment
Controlling PCDD/Fs pollution in the environment is a fundamental measure to prevent dioxins from contaminating food and causing harm to the human body. For example, reduce the use of pesticides and other compounds containing PCDD/Fs; strictly control