What Are Polychlorinated Biphenyls?

English name: Polychlorinated biphenyls; Polychlorodiphenyls Alias: Chlorinated biphenyls; PCBs are labeled according to the number of chlorine atoms or the percentage content of chlorine. In China, PCBs are conventionally numbered according to the number of chlorines substituted on the biphenyls (regardless of the substitution position) Divided into trichlorobiphenyl (PCB3), tetrachlorobiphenyl (PCB4), pentachlorobiphenyl (PCB5), hexachlorobiphenyl (PCB6), heptachlorobiphenyl (PCB7), octachlorobiphenyl (PCB8), Nonachlorobiphenyl (PCB9), decachlorobiphenyl (PCB10). Polychlorinated biphenyls are carcinogens that easily accumulate in adipose tissue, cause diseases of the brain, skin, and internal organs, and affect the nervous, reproductive, and immune systems. ^[1]

On October 27, 2017, the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization initially compiled the reference. Polychlorinated biphenyls were included in the list of carcinogens. ^[2]

Chinese name: PCBs
English name: Polychorinated biphenyls; Polychlorodiphenyls
nickname: Chlorinated biphenyl
Chemical formula: C12H10-xClx
Molecular weight: PCB3: 266.5; PCB4: 299.5; PCB5: 328.4; PCB6: 375.7.
Melting point: PCB3: -19 -15 PCB4: -8 -5 PCB5: 8 12 PCB6: 29 33

Boiling point: 340 375
Water soluble: Insoluble in water, soluble in most organic solvents
Density: 1.44 (30 )
Exterior: Flowing oily liquid or white crystalline solid or amorphous resin
Flash point: 195 / open cup
Risk description: It is flammable in the presence of open flames and high heat, with the risk of cracking and explosion. It can liberate toxic gases.

Polychlorinated biphenyls

Polychlorinated biphenyls were first synthesized by German H. Schmitt and G. Schultz in 1881. The United States first started production in 1929. In the mid-1960s, the world's PCB production reached a peak, with an annual output of about 100,000 tons. It is estimated that PCBs produced and in use worldwide far exceed one million tons, of which 1/4 to 1/3 have entered the human environment, causing harm. ^[3]

Polychlorinated biphenyls are extremely difficult to dissolve in water, easily soluble in fats and organic solvents, and extremely difficult to decompose, so they can be abundantly enriched in biological fats. In 1968, a well-known public hazard caused by PCB contamination of rice bran oil: "oil disease". After 1973, countries began to reduce or stop production. The basic structure of PCB is: There are 10 hydrogen atoms on the biphenyl ring. According to the number of hydrogen atoms replaced by chlorine atoms, monochloride, dichloride ... decachloride are formed, each of which has several isomers. . Theoretically, there are 3 isomers of monochloride, 12 of dichloride and 21 of trichloride. There are 210 types of all isomers of PCB, and 102 types have been identified. Commercial PCB trade names: Kane chlor (KC) in Japan, Aroclor (AR) in the United States, Clophen in the Federal Republic of Germany, Phenochlor in France, Sovols in the Soviet Union, etc. Various products are labeled according to the number of chlorine atoms they contain: products commonly known as trichlorobiphenyls in China, KC-300 in Japan, and AR-1242 in the United States; Designated as KC-500 and US designated AR-1254. These products are mixtures, such as a considerable amount of trichloride and pentachloride, and a small amount of hexachloride. ^[4]

Physical and chemical properties of PCBs

Appearance and properties: flowing oily liquid or white crystalline solid or non-crystalline resin.

Melting point (° C): PCB3: -19 to -15 ° C; PCB4: -8 to -5 ° C; PCB5: 8 to 12 ° C; PCB6: 29 to 33 ° C.

Boiling point (° C): 340 to 375 ° C.

Relative density (water = 1): 1.44 (30 ° C).

Relative vapor density (air = 1):

Vapor pressure (kPa): PCB3: 0.133 × 10-3kPa; PCB4: 0.493 × 10-4kPa; PCB5: 0.799 × 10-4? KPa.

Flash point: 195 ° C / open cup.

Combustion heat (kJ / mol):

Stability and reactivity: stable.

Dangerous characteristics: Combustible in case of open flame and high heat. Reacts with oxidants. High heat releases toxic gases. In case of high heat, the internal pressure of the container will increase, and there is a danger of cracking and explosion.

Solubility: Insoluble in water, soluble in most organic solvents.

Incompatibility: Strong oxidants.

The pure compound of PCB is crystalline, and the mixture is oily liquid. Low chloride is liquid and has good fluidity. As the number of chlorine atoms increases, the viscosity increases correspondingly, and it is syrupy or even resinous. ^[1]

Use of PCBs

The physical and chemical properties of PCB are extremely stable, highly resistant to acids, alkalis and oxidation. It is non-corrosive to metals, has good electrical insulation and very good heat resistance (to be completely decomposed requires 1000 ° C to 1400 ° C), except for chlorine Non-combustible substances except compounds and dichlorides. PCB is widely used, can be used as insulating oil, heat carrier and lubricating oil, etc.It can also be used as many kinds of industrial products (such as various resins, rubbers, bonding agents, coatings, carbon paper, ceramic glaze, fire retardant, pesticide extender, Dye dispersant).

Emergency disposal of PCBs

Skin contact: Remove contaminated clothing and rinse with plenty of running water. Seek medical attention.

Eye contact: Raise eyelids and rinse with running water or saline. Seek medical attention.

Inhalation: Quickly leave the scene to fresh air. Keep your airways open. If breathing is difficult, give oxygen. If breathing stops, give artificial respiration immediately. Seek medical attention.

Ingestion: Drink plenty of warm water and induce vomiting. Stomach lavage and drainage. Seek medical attention.

Respiratory protection: When the concentration in the air exceeds the standard, you must wear a self-absorption filtering respirator (full face mask). Wear an air respirator for emergencies or evacuation.

Eye protection: Protection has been done in respiratory protection.

Body protection: Wear protective clothing.

Hand protection: Wear rubber gloves.

Other protection: No smoking, eating and drinking at the work site. After work, take a shower. Maintain good hygiene.

Emergency Response to Leakage: Evacuate personnel from the leaked contaminated area to a safe area and isolate them to strictly restrict access. Cut off the fire. It is recommended that emergency handlers wear self-contained breathing apparatus and wear protective clothing. Do not touch the spill directly. Cut off the source of the leak if possible. If it is a liquid, prevent it from flowing into restricted spaces such as sewers and flood drains. Absorb with sand. If there is a large amount of leakage, build a dyke or dig to contain it. Transfer to a tanker or special collector with a pump and recycle or transport it to a waste disposal site for disposal. If it is solid, collect it in a dry, clean, covered container with a clean shovel.

Hazardous combustion products: carbon monoxide, carbon dioxide, hydrogen chloride.

Fire extinguishing methods: Firefighters must wear filter respirators (full-face masks) or isolated respirators, wear full-body fire and gas protective clothing, and extinguish fires in the upwind direction. Move the container from the fire to the open space as much as possible. Spray water to keep the fire container cool until the fire is over. Containers in the fire area must be evacuated immediately if they have discolored or generate sound from a safety pressure relief device. Fire extinguishing agent: mist water, foam, dry powder, carbon dioxide, sand.

PCB Management Information

Operation management: closed operation, providing sufficient local exhaust. Prevent fumes or dust from leaking into the workplace air. Operators must be specially trained and strictly abide by the operating procedures. It is recommended that the operator wear a self-absorbent filter-type gas mask (full face mask), a rubber protective clothing, and rubber gloves. Away from fire and heat sources, smoking is strictly prohibited in the workplace. Use explosion-proof ventilation systems and equipment. Do not perform welding or cutting operations before removing liquids and vapors. Avoid generating steam or dust. Avoid contact with oxidants. Equipped with the corresponding variety and quantity of fire fighting equipment and leakage emergency treatment equipment. Empty containers may be harmful residues.

Storage management: Store in a cool, ventilated warehouse. Keep away from fire and heat sources. Protect from direct sunlight. Keep container tightly closed. It should be stored separately from oxidants and edible chemicals. Equipped with the appropriate variety and quantity of fire equipment. The storage area should be equipped with spill emergency treatment equipment and suitable containment materials.

Transportation management: Before transportation, check whether the packaging container is complete and sealed. During transportation, ensure that the container does not leak, collapse, fall, or damage. Mixed transportation with acids, oxidants, food and food additives is strictly prohibited. The transportation vehicle should be equipped with the corresponding variety and quantity of fire fighting equipment and leakage emergency treatment equipment during transportation. During transportation, it should be protected from direct sunlight, rain and high temperature. When transporting by road, follow the prescribed route and do not stop in residential areas and densely populated areas.

Management of PCB waste

The chemical properties of PCBs are very stable and difficult to decompose in nature. They belong to the category of persistent organic pollutants and are mostly used in power equipment, such as capacitors and transformers containing PCBs. The methods for processing PCBs can be summarized as follows: ^[4]

PCB burial

Polychlorinated biphenyls (PCBs) and PCB-contaminated pollutants are enclosed in specially designed structures or buried deep together with the structures. There are also ready-made caves or bomb shelters that are used to bury PCBs and their pollutants. (As temporary storage).

PCB removal by microorganisms

Japanese scholars have cultivated two yeasts from the soil: one is a strain of Rhodotorula and the other is ringworm. Experiments show that the former can decompose 40% of PCBs and the latter can decompose 30% of PCBs. A large number of cultures can be used to treat PCBs in industrial wastewater and soil. American scholars use gray oxygen bacteria to swallow PCBs, which has a significant effect.

PCB incineration

This method is considered to be the best treatment method at present, but it must be carried out in a dedicated high-efficiency incinerator that can completely decompose PCBs, and cannot be incinerated at will. Indiscriminate incineration of PCBs may produce substances such as polychlorinated dibenzodioxins (PCDD) and polychlorinated diphenylfurans (PCDF), which are more toxic than PCBs. In order to ensure the complete destruction of PCBs, incineration conditions must be strictly controlled. The U.S. Environmental Protection Agency stipulates that when PCBs are incinerated, the temperature should be higher than 1150 ° C, the residence time in the combustion chamber should be greater than 2 s, the oxygen excess should be greater than 3%, and the CO content in the tail gas must be less than 100 ppm. In addition, Canada, the United States, and Sweden have conducted tests on the destruction of PCBs in cement kilns. The results show that the cement kilns can meet the requirements for the destruction of PCBs.

PCB Chemistry

More than 10 methods have been used to treat PCBs by chemical methods, such as chlorolysis, hydrodechlorination, Sunohio, wet catalytic oxidation, sodium metal method, Goodyear method, metal sodium-polyethylene glycol method , Ozone method, etc. Some of them have practical devices or industrial test devices, and some have been successful in laboratory scale.

PCB physical method

Microwave plasma method, activated carbon adsorption method, radiation irradiation method and other methods have been put into practical use abroad.

Polychlorinated biphenyl plant rhizosphere repair method

This is an emerging field, using the interaction of plants and rhizosphere microorganisms to degrade PCBs, the effect is obvious!

PCB Toxicology Information

It has effects on skin, teeth, neurobehavior, immune function, liver, and has reproductive toxicity, teratogenicity and carcinogenicity ^[5] .

Acute toxicity: LD50: 1900 mg / kg (oral mouse); PCB3: LD504250 mg / kg (oral mouse); PCB4: LD5011000 mg / kg (oral mouse); PCB5: LD501295 mg / kg (large Rat orally); PCB6: LD501315 mg / kg (rat orally). The minimum lethal dose is 500 mg / kg (oral). When transdermal toxicity is applied to animal skin, the local epidermis thickens, hair follicles swell, and fatty degeneration and central atrophy appear in the liver.

Subacute and chronic toxicity: Subacute toxicity: a group of rats were fed PCB5 at 1 g / kg, and the animals died between 28 and 53 d (Tucker & Gabtree, 1970). Death from feeding with 2 g / kg of Phenochlor DP6 occurred between 12 and 26 days (Vos & Koeman, 1970). In the latter experiment, liver enlargement, spleen shrinkage, and progressive chemical hepatic porphyria were seen at necropsy. Aulerich et al. (1973) fed 30 mg / kg PCB-containing feed to adult mink (10 mg / kg PCB3, PCB4, and PCB6 each), and the mortality rate was 100% within 6 months.

Inhalation toxicity rats were exposed to 65% chlorine containing this product at an average concentration of 0.57 mg / m3, 16 h / d, and after 6 weeks, caused slight liver damage, so it was considered more harmful than naphthalene.

Chronic toxicity: Severe PCB poisoning can cause animals to develop symptoms such as diarrhea, blood tears, dyskinesias, progressive dehydration, and central nervous system depression, or even death. The most typical example of PCB harm to people is the rice bran oil incident in Japan in 1968. The victim consumed PCB contaminated rice bran oil (2000-3000 mg of PCB per kilogram of rice bran oil) and became poisoned. By the end of 1978, 28 prefectures in Japan (including Tokyo, Kyoto Prefecture, and Osaka Prefecture) had officially confirmed 1,684 patients as PCB poisoning patients, and more than 30 of them died before 1977. The toxicity of PCBs varies greatly depending on the species, sex, way of administration, the chemical structure of the PCB itself, and the impurities it contains. Humans are probably one of the most sensitive species.

Metabolism: PCBs are well absorbed through the gastrointestinal tract, lungs, and skin of mammals. After PCB enters the body, it is widely distributed in whole body tissues, with a higher content in fat and liver. The PCB in the mother can be transferred to the fetus through the placenta, and the PCB content in the liver and kidney of the fetus is often higher than that in the same tissue of the mother. The metabolic rate of PCB in the body decreases with the increase of chlorine atoms. PCBs in mammals are partly excreted in the form of phenolic metabolites. All hydroxyl metabolites are excreted from the feces through the gastrointestinal tract through the bile. Experiments also show that the higher the PCB chlorine content, the less likely this hydroxylation reaction will occur. A small amount of PCB can also be discharged in human milk, but all exist as the original compounds.

Poisoning mechanism: The liver is one of the main target organs of PCB poisoning. Many laboratory indicators of liver function and liver function are positive. For example, a number of liver enzyme activity indicators including SGPT are positive and are positively correlated with PCB content in the blood. In addition, the half-life of antipyrine in plasma was significantly shortened (indicating that liver mixed function oxidase activity was induced). The respiratory tract and skin of many patients with PCB poisoning are susceptible to infectious diseases, which indicates that the immune system of patients with poisoning may be suppressed.

Carcinogenicity : PCBs can cause carcinogenic reactions in rats and mice, and the organs that produce cancer are liver.

Mutagenicity : Pcakall et al. (1972) found that feeding turtle turtles with PCBs containing 10 mg / kg feed significantly increased the embryo's chromosomal aberrations.

Environmental hazards: serious harm to the environment, can cause pollution to water bodies and the atmosphere.

Ecotoxicological toxicity: aquatic toxicity: LD501 10 g / kg, fish, 96 h; 5 g / L, fish 45 d, death (PCB5); LC50 30 g / L, prawn, 7 d (PCB3); LC50 80 g / L, shrimp, 7 d (PCB5). Toxicity to poultry: 400 mg / kg, chicken, 20-24 d, death (PCB6); 254 mg / kg, Bengal finches, 56 d, LD50 (PCB5)

Biodegradability: During the process of the PCB in the environment passing through the biological food chain, low-chlorinated components gradually disappear due to selective biotransformation.

Non-biodegradability: The chemical properties of PCB are very stable, and it is impossible to degrade at a noticeable rate in the environment through hydrolysis or similar reactions. The decomposition in nature depends on the microbial enzymes in the soil and the ultraviolet rays in sunlight, but it is not efficient. Therefore, PCB residence time in the environment is quite long.

Residue and accumulation: PCB has a high residue in the environment. According to the (1987) Environmental Sanitation Benchmark (2) published by the IPCS, since 1930, the cumulative production of PCBs around the world has been about 1 million tons, and more than half of them have entered garbage dumps and landfills. Release is slow. Most of the rest enter the environment through the following ways: entering industrial rivers or coastal waters with industrial wastewater; seepage from non-closed systems or stacking in garbage dumps, due to the incineration of PCB-containing substances into the atmosphere. The final storage of PCBs entering the environment is mainly the sediments of rivers and coastal waters, and only a small part is transformed by biological and photolytic effects. PCB has a strong accumulation in the body, and is gradually enriched through the food chain. It is known that when 0.01 g / L PCB is contained in the water, the accumulation in the fish body can reach 200,000 times the concentration in the water, so the accumulation concentration in fish-eating birds and animals is high. The concentration of PCBs in some large fish in the sea and killers in the air, such as sharks, seals, and raptors, can be 10.7 to 10.8 times higher than in the surrounding environment. PCBs have been detected in penguins from Antarctica to seals in the Arctic, so PCB contamination has become a global problem. Once PCB3 enters the environment, it will exist in the environment for a long time, it is difficult to degrade, and it is difficult to recover the water and soil contaminated by PCB3.

Migration, transformation and degradation: The detectable concentration of PCB in the air ranges from 1 to 50 ng / m3. PCB content in unpolluted fresh water should be <0.1 ng / L; moderately polluted rivers and harbors are 50 ng / L; heavily polluted rivers are 500 ng / L. The concentration in living organisms depends on the degree of local PCB contamination. Human fat surveys in several countries have shown that, although some countries have reported high levels of PCBs, most samples have levels of 1 mg / kg or less. Occupational contacts have a much higher fat content, up to 700 mg / kg. Several national surveys have shown that the PCB concentration in blood is about 0.3 g / 100 ml, but the occupational contacts can reach 200 g / 100 ml. A survey of the population shows that the PCB content concentration in the majority of the population is about 0.02 mg / L. Although there are also records of up to 0.1 mg / L, the number is very small. According to IRPTC data (1982), it is estimated that the total daily intake of ordinary people from air, water and food is 5 to 100 g, which does not include unknown amounts from non-food sources. The PCB entering the air will be quickly adsorbed on the particles, and will settle at a certain speed according to the size of the particles or fall to the ground with rain. The PCB in the water body is mainly attached to the sediment. When the concentration in the water body is low, the concentration in the sediment can be tens or even hundreds of thousands of times higher than the water quality. PCBs are mainly adsorbed on the surface of the soil.

Polychlorinated Biphenyls Emergency Medical

Key points for PCB diagnosis

Patients with PCB poisoning have the following symptoms: acne rash, eyelid edema and increased eye secretion, skin, mucous membranes, nail pigmentation, jaundice, numbness of the limbs, gastrointestinal dysfunction, etc., which is called "oil disease". Workers who have been in contact with PCB for a long time often have acne rash, skin pigmentation, grayish black or light brown, which is obvious on the face and fingers. When systemic poisoning occurs, it shows lethargy, general weakness, loss of appetite, nausea, abdominal distension, abdominal pain, hepatomegaly, jaundice, ascites, edema, irregular menstruation, and decreased libido. Abnormal liver function and decreased plasma protein were seen during the test.

Processing principle:

Symptomatic treatment.

PCB prevention measures

When operating at high temperatures, ventilation and containment measures must be strengthened. If there is a possibility of splashing or leaking hot solution, you should wear a breathing mask; prevent skin contact, rinse with soap and water when the skin is contaminated. Perform physical examinations on occupational contacts on a regular basis, detect symptoms early, and perform disengagement or necessary detoxification treatment on patients; strictly prevent PCBs from entering the body from the respiratory and digestive tracts.

For suspicious carcinogens, thorough investigations and crowd surveys should be conducted to determine what protective measures need to be taken.

The main prevention of carcinogen PCB is to strengthen the control of carcinogen and reduce and avoid contact. For the large-scale environmental pollution that has been caused, effective measures must be taken in a timely manner to deal with it.