Polycyclic aromatic hydrocarbons refer to those containing two or morebenzene ringOfaromatic hydrocarbon，[1]It is called PAHs for short.They are mainly combined in two ways, one is non fused ring type, includingbiphenylAnd biphenyls and polyphenyl aliphatic hydrocarbons;The other is the fused ring type, that is, two carbon atoms are shared by two benzene rings.[2]
The sources of PAHs can be divided into natural sources and man-made sources.Natural sources mainly come from the biosynthesis process of terrestrial and aquatic plants and microorganisms. In addition, polycyclic aromatic hydrocarbons also exist in natural fires and volcanic eruptions in forests and grasslands, and in fossil fuels, lignin and sediment;Anthropogenic sources are mainly formed by incomplete combustion of various fossil fuels (such as coal, oil and natural gas), wood, paper and other hydrocarbons or pyrolysis under reducing conditions.[2]
PAHs are toxic, genotoxic, mutagenic and carcinogenic,[3]It can cause various hazards to human body, such as damage to respiratory system, circulatory system, nervous system, liver and kidney.[4]Identified as the main factors affecting human healthOrganic pollutants。[3]
Chinese name
Polycyclic aromatic hydrocarbons[2]
Foreign name
Polycyclic Aromatic Hydrocarbons[4]
Alias
Polycyclic aromatic hydrocarbon
Abbreviation
PAHs[4]
Source
Natural and man-made sources[2]
Classification
Biphenyls and biphenyls, polyphenyl aliphatic hydrocarbons and polycyclic aromatic hydrocarbons[1]
Hazards
Damage to respiratory system, circulatory system, nervous system, liver and kidney.[4]
Degradation method
Bioremediation and semiconductor photocatalytic degradation[3]
The sources of PAHs can also be divided into natural sources and anthropogenic sources.[2]
Natural source
Before the emergence of human beings, natural sources also existed in nature, mainly from the biosynthesis process of land, aquatic plants and microorganisms. In addition, natural fires and volcanic eruptions in forests and grasslands, as well as polycyclic aromatic hydrocarbons (PAHs) from fossil fuels, lignin and sediment, constituted the natural background value of PAH.Generally, the PAH background value of soil is 100~1000 μ g/kg.The background value of PAH in freshwater lakes is 0.01~0.025 μ g/L, that in groundwater is 0.001~0.01 μ g/L, and that in atmosphere is 0.1~0.5ng/mthree。[2]
Anthropogenic source
There are many pollution sources of polycyclic aromatic hydrocarbons (PAHs) caused by human factors, mainly from incomplete combustion of various mineral fuels (such as coal, oil and natural gas), wood, paper and other hydrocarbons or pyrolysis under reducing conditions. Simple hydrocarbons and aromatic hydrocarbons can form a large number of PAHs during high-temperature pyrolysis,It is particularly worth reminding that more than 150 kinds of polycyclic aromatic hydrocarbons have been detected in the smoke emitted by smokers so far.[2]
classification
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According to the different connection modes of benzene ring, polycyclic aromatic hydrocarbons are divided into biphenyls and biphenyls, polyphenyl aliphatic hydrocarbons andPolycyclic aromatic hydrocarbonClass.[1]
Biphenyls and Biphenyls
Compounds connected by σ bond between benzene rings are called biphenyls.Biphenyl derivatives and biphenyl compounds are named after biphenyl as the parent.The structure and properties are similar to those of monocyclic aromatic hydrocarbons.[1]
Polybenzoic aliphatic hydrocarbons Compounds formed by replacing hydrogen atoms in aliphatic hydrocarbons with several benzene rings.These compounds are named after phenyl as substituent and aliphatic hydrocarbon as parent.The structure and properties are similar to those of monocyclic aromatic hydrocarbons.[1]
Diphenylmethane
Picture Quoted From[1]。
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon refers to two or more benzene rings fused by sharing two adjacent carbon atoms.[1]
Polycyclic aromatic hydrocarbon
Naphthalene is the most abundant compound in coal tar. It contains about 10% in high temperature coal tar. The molecular formula of naphthalene is CtenHeightIt is fused by two benzene rings sharing two adjacent carbon atoms.Naphthalene is a white flake crystal with a melting point of 80 ℃ and a boiling point of 218 ℃. It is insoluble in water and soluble in hot organic solvents such as alcohol and ether.Volatile, easy to sublimate, with special smell.[1]
Picture Quoted From[1]。
Anthracene exists in coal tar, and the content is about 0.25%.The molecular formula of anthracene is CfourteenH10,It is fused by three benzene rings.Phenanthrene also exists in coal tar and interacts with anthraceneIsomer。[1]
Other polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbon
Aromatics mainly come from coal tar, in which condensed ring aromatics can be separated, such as indene, fluorene and acenaphthene, which are condensed aromatics of aliphatic ring and aromatic ring, and tetrabenzene and pyrene, which are high-grade condensed ring aromatics.In addition, the derivatives of anthracene and phenanthrene are polycyclic aromatic hydrocarbons with significant carcinogenic effects, called carcinogenic hydrocarbons for short.[1]
Polycyclic aromatic hydrocarbon
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Migration and transformation
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PAHs released into the atmosphere due to incomplete combustion of fuel are usually combined with various types of solid particles and aerosols.Therefore, the distribution, retention time, migration, transformation and sedimentation of PAHs in the atmosphere are subject to various conditions (such as particle size, atmospheric physical and meteorological conditions, etcWet deposition enters the soil, water and sediment, and enters the biosphere.[2]
Picture Quoted From[2]。
Migration and transformation
Toxicity and hazard
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With the increase of its ring number, the change of its chemical structure and the enhancement of its hydrophobicity, its electrochemical stability, durability, anti biodegradability and carcinogenicity will increase, and its volatility will also decrease with the increase of its molecular weight.Polycyclic aromatic hydrocarbons (PAHs) have bioaccumulation effects in many biological chains in nature, and their content in nature is quite amazing, so they are also recognized as the main impact on human healthOrganic pollutants。[3]PAHs damage the human respiratory system, circulatory system, nervous system, liver, kidney, etc.[4]
Respiratory system injury
PAHs and other harmful substances in the workplace are mostly attached to inhalable particles, entering the respiratory tract with respiratory movement and invading the body.Most of the workers exposed to PAHs have the phenomenon of throat redness, swelling and increased expectoration in varying degrees when they undergo occupational health examination.Some studies have found that benzo [a] pyrene can reducePulmonary surfactantAnd has a certain degree of influence on its stability;At the same time, PAHs can inhibit the growth of bronchi in vitroepithelial cellsThe anti apoptotic ability of mitochondria was weakened.In addition, in the case of early exposure to pyrene, the respiratory susceptibility of children with non allergic constitution increases.It was found that hydroxyphenanthrene and1-hydroxypyrene The accumulation of (1-hydroxypyrene, 1-OHP) is negatively correlated with the ratio of forced expiratory volume in the first second to vital capacity of coke oven workers, and the decline of lung function is more obvious with age.This indicates that occupational exposure to PAHs can cause the decline of lung function of workers. It is speculated that phenanthrene and pyrene may be the main substances that cause early lung injury in workers exposed to PAHs.[4]
Circulatory system damage
The decrease of heart rate variability (HRV) is a sign of cardiac autonomic nervous dysfunction and can be independently predictedCardiovascular diseaseIndicators of mortality.Research shows that the red blood cell count of workers exposed to PAHs in coking plantsNeutrophils、HematocritHorizontal andlymphocyteOliveTail distance and 1-OHPPhenylmercaptouric acidIt is suggested that the mixed exposure of PAHs and benzene may cause some changes in peripheral blood hemogram and lymphocyte DNA damage in coke oven workers.[4]
Nervous system injury
Since PAHs were concerned, previous studies have focused on the impact of PAHs on children's neural development, while there are few reports on the neurotoxicity of occupational populations.In terms of occupational exposure, PAHs and lead combined exposure can affect 16 genes and proteins, including 14 proteins and genes related to nervous system diseases. These genes and proteins damage the nervous system through ligand activation, apoptosis, oxidative stress and inflammatory mediators.[4]
Liver damage
The liver is rich in blood flow. It is the main metabolic organ of the human body and has a certain detoxification function for poisons.In some studies, 1-OHP was used as a biomarker of occupational exposure to PAHs to assess the liver function injury of coke oven workers. It was found that there was a correlation between liver biochemical indicators and heme binding protein. The level of heme binding protein was statistically significant among low, medium and high levels of PAHs exposure groups（P< 0. 05), and the expression is weakly related to the degree of exposure, suggesting that coke oven workers may have liver injury.Li Jichao and other researchers have shown that occupational exposure to PAHs is closely related to fatty liver, and with the increase of the level of harmful substances in the environment, the ratio also increases, suggesting that occupational exposure to PAHs can increase the risk of fatty liver among workers.[4]
Kidney damage
Blood uric acid and urine βtwo-Microglobulin(βtwo-Microglobulin，βtwo-MG) is an index reflecting renal function, which is of great significance in detecting early renal damage.A study found that the urine β of coke oven workerstwo-MG level is higher than that of control group（P< 0. 05), suggesting that the workers exposed to PAHs have kidney damage to some extent.[4]
Degradation method
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The removal of polycyclic aromatic hydrocarbons (PAHs) from the environment is considered to be the most important method to restore the polluted environment.Many physical and chemical treatment methods have been tried, including incineration, alkali catalytic dechlorination, ultraviolet oxidation, fixation, solvent extraction, etc., but these methods have disadvantages of high cost, complexity, and difficulty in regulation.In addition, these traditional environmental remediation technologies are difficult to completely remove these pollutants in many cases, but only transfer them from one environment to another or form another pollutant.[3]At present, bioremediation and semiconductor photocatalytic degradation technology are better methods to remove PAHs.[3][5]
Bioremediation
At present, microbial remediation has become an important technology for environmental remediation and removal of many pollutants, including polycyclic aromatic hydrocarbons.Compared with high molecular weight PAHs, low molecular weight PAHsrelative stabilityPoor, more soluble in water, so it is easier to beMicrobial degradation。After 3 billion years of evolution, bacteria have the ability to metabolize almost all compounds to obtain energy, and have been regarded as the ultimate natural scavenger.Because of its strong adaptability, bacteria have been widely used to reduce or repair the harm of polluted environment.At present, many kinds of PAHs degrading bacteria have been found, among which naphthalene and phenanthrene degrading bacteria are more widely studied.Bacteria usually degrade PAHs under aerobic conditions and metabolize them mainly through oxygenase, which mainly includes monooxygenase or dioxygenase.The first step of bacterial degradation of PAHs is to hydroxy the carbon atoms on the benzene ring through dioxygenase to form cis dihydroalcohol, form diol intermediates under the action of diol dehydrogenase, and lyse the diol intermediate estradiol through ortho cleavage or secondary cleavage via endogenous or exogenous dioxygenase to form intermediates (such as catechol), and finally transform intoTCARecycle intermediates.Fungi can metabolize PAHs into various oxidation products orcarbon dioxide。The degradation of PAHs by fungi is mainly through monooxygenase.However, the degradation of PAHs by fungi is only effective under specific strains and growth conditions.There are two main types of fungi that can degrade PAHs: lignin degrading bacteria（White rot fungus）And non lignin degrading bacteria.[3]
Semiconductor photocatalytic degradation
Semiconductor photocatalytic degradation method has the advantages of simple operation, can be carried out at room temperature and pressure, and can completely mineralize organic matter. It has good application prospects in the treatment of persistent organic pollutants such as PAHs.TiOtwoIt is highly activeSemiconductor photocatalystIt has been widely used in the research of PAHs degradation.Transfer TiO of dispersed phasetwoThe particles are suspended in the aqueous solution of pollutants, and the photocatalytic reaction is carried out by ultraviolet irradiation. Because of the large contact area between the catalyst particles and the reactants, the degradation efficiency is very high.Nitrogen atom modified TiOtwoIt has a high response in the visible light region, which is due to the introduction of N atoms, resulting in TiOtwoThe band gap of naphthalene becomes narrower. After 8 hours of visible light irradiation, naphthalene in N-TiOtwoThe degradation efficiency under catalysis is about 80%, and the degradation efficiency is greatly improved.[5]
