Mathematics
Polycyclic aromatic hydrocarbons (PAHs). Polycyclic aromatic hydrocarbons Undesirable consequences of the development of motorism

Polycyclic aromatic hydrocarbons (PAHs). Polycyclic aromatic hydrocarbons Undesirable consequences of the development of motorism

Polycyclic aromatic hydrocarbons- organic substances, the main elements of which - carbon and hydrogen - form benzene rings, unsubstituted or substituted, capable of polymerization.

These compounds are characterized by low solubility in water, high sorption capacity and stability in environmental components, especially soils.

The PAH group includes hundreds of chemicals. Currently, it is recommended abroad to monitor 16 substances from the PAH group in environmental objects: naphthalene, acenaphthylene, acenaphthene, fluorene, anthracene, phenanthrene, fluoranthene, benzo(a)anthracene, chrysene, pyrene, benzo(a)pyrene, dibenz(ah) )anthracene, benzo(g, h,i)perylene, benzo(a)fluoranthene, benzo(k)fluoranthene and indeno(1,2,3-cd)pyrene, and in Russia there is only one compound of this class - benzo(a) pyrene

PAHs enter the environment with waste from transport, energy, and, to a lesser extent, industry. These pollutants are formed during the combustion of gasoline, oil products, coal, gas, bitumen, wood (almost during the combustion of all types of combustible materials). They are contained in soot emissions from thermal power plants and any thermal units. Among industrial enterprises, aluminum smelters and carbon black production are in first place in terms of benzo(a)pyrene emissions.

Transport is the main source of PAH pollution. PAHs are contained in gas emissions from motor vehicles, aviation, and railway transport. Unsubstituted PAHs and nitroPAHs predominate in the exhaust gases of internal combustion engines.

PAHs are part of waste from coke plants, oil refineries and oil fields. They are formed during the production of resins by high-temperature processing of coal, shale, peat, and during oil cracking.

Anthropogenic sources emit more than 5000 tons of 3,4 benzo(a) pyrene. In 70-80% of cases, benz(a)pyrene ranks first among the substances associated with high urban pollution. PAHs enter the atmosphere in the form of soot particles (a product of incomplete combustion of fuel), in an adsorbed state on the surface of solid particles (oxides, metal salts, etc.). Gaseous PAHs in the atmosphere are sorbed by dust.

To characterize environmental pollution with PAHs, data on snow pollution are used. PAHs are usually concentrated in snow dust, and not in the soluble fraction. The accumulation of PAHs in the snow cover around thermal power plants and metallurgical plants has been established.

Levels of total PAH content in contaminated soils range from a few to hundreds and even thousands (2000-4000) µg/kg of soil. The Russian standard (MPC) for benzo(a)pyrene for soils is 20 μg/kg, surface water - 5 ng/l, air in populated areas (CA) - 1 ng/m 3.

One of the key processes that determines the fate of PAHs in the environment is sorption. The binding of pollutants by mineral, organomineral colloids and dissolved natural organic compounds creates the opportunity for aqueous migration of PAHs in the composition of solid phases, as well as emulsions.

The main reservoir of PAHs, as well as other pollutants in the ecosystem, is soil. Hydrophobic compounds are preferentially bound by soil organic matter. The presence of OH groups in PAHs allows the formation of additional bonds (hydrogen) with the organic and mineral soil matrix.

Aerotechnogenic input is mainly due to the pool of light PAHs in the soil. Heavy PAHs can be formed as a result of the transformation of organic matter in the process of pedogenesis, and benzo(a)pyrene can, under certain conditions (with an optimal combination of humidity, temperature, aeration, etc.) enhance the process of mineralization of soil organic matter and, accordingly, the pedogenic formation of heavy PAHs (Yakovleva et al., 2008).

The absorption of organic pollutants, including PAHs, by plant roots from the soil, according to the conceptual model of S. L. Simonich, R. A. Hites (1995), is presented as a function of the solubility of the substance in water, its content in the soil and the type of plant. The process of accumulation of persistent organic compounds by plants has general patterns; accumulation coefficients (the ratio of the content of a substance in the roots to its content in the soil) are a nonlinear function of their content in soils, which can be explained in the case of low concentrations by the sorption of the pollutant by the soil, and in the case of high concentrations by the inhibitory effect on plants. Calculations show (Voloshchuk, Gaponyuk, 1979) that in general the transfer of persistent organic pollutants from soil to plants is higher (35-70%) than to water (12-18%) and atmospheric air (18%).

Unlike most other persistent organic pollutants, which accumulate in the roots of plants grown in contaminated soils, PAHs are distributed more evenly throughout plant organs and even in many cases the concentration of pollutants in the leaves under similar conditions exceeds their concentration in the roots. Such a distribution may be evidence of the biophilicity of polyarenes for plants (some of their functional purposes), and even the synthesis of PAHs in the plants themselves cannot be ruled out (Vasilieva et al., 2008).

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Polycyclic aromatic hydrocarbons (PAHs) are among the most potent carcinogens. 0.1 mg of PAHs such as benzo(a)pyrene is sufficient to cause tumors in various animal species.

Currently, more than 200 representatives of this group are known, compounds formed, as a rule, during thermal exposure of food products. The most active carcinogens include: benzo(a)pyrene, dibenz(a,h)anthracene, dibenz(a,i)pyrene; moderately active - benz(h)fluoranthene; less active ones include benzo(e)pyrene, benzo(a)anthracene, dibenz(a,c)anthracene, chrysene, etc. The most famous representative of PAHs is benzo(a)pyrene.

The carcinogenic activity of real PAH combinations is 70-80% due to the presence of benzo(a)pyrene. Therefore, by the presence of benzo(a)pyrene in food products, one can judge the level of their contamination with PAHs and the degree of oncogenic danger to humans.

Every year, thousands of tons of benzo(a)pyrene of natural origin enter the biosphere, and even more from man-made sources (industrial enterprises, transport). PAHs are formed in nature and enter food chains primarily as a result of combustion at low temperatures of hydrocarbon raw materials, wood, polymers, food, etc. The development of uncontrolled processes of incomplete oxidation leads to the fact that in smoked products (meat, fish) the benzene content ( a) pyrene may exceed safe limits. In particular, PAHs are formed during the pyrolysis of fat that drips onto charcoal and enters the meat with smoke during smoking.

The conditions of thermal processing of food products have a great influence on the accumulation of benzo(a)pyrene. Up to 0.5 µg/kg of benzo(a)pyrene was found in a burnt bread crust, up to 0.75 µg/kg in a burnt biscuit, and over 50 µg/kg in home smoked products.

There is no benzo(a)pyrene in fresh beef and pork, the content

benzo(a)pyrene in cooked sausage is 0.2-0.5 mcg/kg, raw smoked sausage - 0-2, semi-smoked sausage - 0-7, fish - 0-2, smoked fish - 0.1-12.0 , sunflower oil - 1-30, refined sunflower oil - none, coconut oil - 15-45, vegetables - 1-25, dried fruits - 1-35 mcg/kg. The maximum permissible concentration of benzo(a)pyrene in air is 0.001 μg/m 3, in water - 0.005 μg/l, in soil - 0.2 mg/kg.

Polymer packaging materials can play a significant role in the contamination of food products with PAHs. Some food components are eluents, i.e. they extract PAHs from polymer packaging. For example, an effective PAH eluent is milk fat, which extracts up to 95% of benzo(a)pyrene from paraffin paper bags and cups.

All this indicates the need to comply with technological regulations and sanitary and hygienic requirements in the production of food products.

The most effective ways to reduce the content of PAHs in food products are to improve methods of technological and culinary processing of products, remove PAHs by refining vegetable oils, and use smoking liquids standardized for PAH content for the production of smoked meat products.

Methods for determining benzo(a)pyrene in food products

As noted above, benzo(a)pyrene is an indicator of the presence of carcinogenic PAHs in products. Having lipophilic properties, benzo(a)pyrene accumulates mainly in the fat fraction of food products. In order to extract benzo(a)pyrene from a sample, it is necessary to carry out alkaline saponification of the lipids of the analyzed product by exposing the sample to an alcoholic alkali solution. In this case, alkaline hydrolysis of fats occurs with the formation of glycerol and fatty acid salts, and an unsaponifiable lipid fraction containing benzo(a)pyrene remains.

Benz(a)pyrene is isolated from the unsaponifiable fraction of lipids by extraction with hexane. The resulting extract is purified from interfering impurities using column chromatography or solid-phase extraction. Identification and quantification of benzo(a)pyrene is carried out using spectrofluorimetry, thin layer or high performance liquid chromatography.

Soil contamination with one of the PAHs, benzo(a)pyrene, is an indicator of general environmental pollution due to increasing atmospheric air pollution.

Benz(a)pyrene accumulated in the soil can pass from the roots to the plants, that is, the plants become polluted not only with dust deposited from the air, but also through the soil. Its concentration in the soil of different countries varies from 0.5 to 1,000,000 μg/kg.

Depending on the pollution, different concentrations of benzo(a)pyrene were found in water: in ground water - 1-10 µg/l, in river and lake water 10-25 µg/l, in surface water - 25-100 µg/l.

PAHs are extremely stable in any environment, and if they are systematically formed, there is a danger of their accumulation in natural objects. Currently, 200 representatives of carcinogenic hydrocarbons, including their derivatives, belong to the largest group of known carcinogens, numbering more than 1000 compounds.

Based on carcinogenicity, polycyclic aromatic hydrocarbons are divided into main groups:
1 - most active carcinogens- benz(a)pyrene (bp), dibenz(a, h)anthracene, dibenz(a, i)pyrene;
2 - moderately active carcinogens- benz(h)fluoranthene;
3 - less active carcinogens- benzo(e)pyrene, benzo(a)anthrocene, dibenz(a, c)anthracene, chrysene, etc.

Benz(a)pyrene enters the human body not only from the external environment, but also with food products in which the existence of carcinogenic hydrocarbons has not been assumed until now. It is found in bread, vegetables, fruits, vegetable oils, as well as roasted coffee, smoked meats and charcoal-roasted meat products.

The conditions of thermal processing of food products have a great influence on the accumulation of BP. BP up to 0.5 μg/kg was found in a burnt bread crust, and up to 0.75 μg/kg in a burnt biscuit. Home smoked products may contain BP more than 50 µg/kg. The formation of carcinogenic hydrocarbons can be reduced by properly performed heat treatment.

Severe contamination of products with polycyclic aromatic hydrocarbons is observed when they are processed with smoke.

Fruits and vegetables contain benzo(a)pyrene on average 0.2-150 µg/kg of dry matter. Washing removes up to 20% of polycyclic aromatic hydrocarbons along with dust. A small portion of hydrocarbons can also be found inside the fruit. Apples from non-industrial areas contain 0.2-0.5 μg/kg of benzo(a)pyrene, and up to 10 μg/kg near busy roads.

Polymer packaging materials can play an important role in the contamination of food products with PAHs, especially if the products contain eluents (substances extracted in a solvent). For example, milk fat is an effective PAH eluent, which extracts up to 95% of BP from paraffin-paper bags or cups.

With food, an adult receives 0.006 mg of BP per year. In areas intensively polluted with PAHs, this dose increases by 3 or more times. It is assumed that for a person weighing 60 kg, the ADI of BP should be no more than 0.24 mcg. The maximum permissible concentration of BP in atmospheric air is 0.1 μg/100 m 3, in water bodies of water - 0.005 mg/l, in soil - 0.2 mg/kg.

When polycyclic hydrocarbons enter the body, under the action of enzymes, they form an epoxy compound that reacts with guanine, which interferes with DNA synthesis, causes disruption or leads to mutations that contribute to the development of cancer, including types of cancer such as carcinomas and sarcomas.

Considering that almost half of all malignant tumors in humans are localized in the gastrointestinal tract, the negative role of food products contaminated with carcinogens can hardly be overestimated. To minimize the content of carcinogens in food, the main efforts should be aimed at creating such technological methods for storing and processing food raw materials that would prevent the formation of carcinogens in food or eliminate contamination by them.

INTRODUCTION

Polycyclic aromatic hydrocarbons (PAHs) belong to the group of persistent organic pollutants. They have pronounced carcinogenic properties. One of the most dangerous representatives of PAHs is benzo(a)pyrene (BP).

Benz(a)pyrene was discovered in 1933, and later, in 1935, studies were conducted confirming its carcinogenicity. Today, benzo(a)pyrene is classified as a hazard class 1 carcinogen. It has mutagenic properties. Even a small concentration of BP has a negative effect on the human body. BP concentrations in the air exceeding the maximum permissible concentration (MPC) with prolonged exposure can cause lung cancer. Therefore, the problem of its detection and definition is acute. Based on its physicochemical properties, a number of similar methods for its determination have been developed, differing only in the stages of sample selection and preparation. The purpose of my work was to familiarize myself with the properties of PAHs and BP, to study methods for separating PAHs and methods for determining BP.

LITERATURE REVIEW

Polycyclic aromatic hydrocarbons (PAHs)

General information

PAHs are high-molecular organic compounds of the benzene series, numbering more than 200 representatives. They contain from 2 to 7 benzene rings. PAHs are widespread in nature and stable over time. They have carcinogenic and mutagenic activity. Due to their toxicity and carcinogenic properties, they are considered priority pollutants. The determination of PAHs is used in environmental and geochemical studies. The most toxic of them are 3, 4-benz(a)pyrene and 1, 12-benzperylene, which are especially often detected in environmental objects.

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Ministry of Agriculture of the Russian Federation

Federal State Educational Institution of Higher Professional Education State Agrarian University of the Northern Trans-Urals

Institute of Biotechnology and Veterinary Medicine

On the topic: Polycyclic aromatic hydrocarbons

Tyumen 2015

Introduction

Polyaromatic hydrocarbons (PAHs) are organic compounds characterized by the presence of two or more fused benzene rings in their chemical structure. In nature, PAHs are formed during the pyrolysis of cellulose and are found in layers of coal, brown coal and anthracite, as well as as a product of incomplete combustion during forest fires. The main sources of emission of technogenic PAHs into the natural environment are enterprises of the energy complex, road transport, chemical and oil refining industries. Almost all technogenic sources of PAHs are based on thermal processes associated with the combustion and processing of organic raw materials: petroleum products, coal, wood, garbage, food, tobacco, etc. Today we will learn about them in more detail.

polycyclic aromatic hydrocarbon toxicity

1. Effect of aromatic hydrocarbons on the environment

The presence of PAHs in the environment is a source of concern for organic chemists, biochemists, environmental chemists and geochemists. Because most low molecular weight PAHs are toxic to bacteria, they inhibit biodegradation, while others are carcinogenic. Additionally, for geochemists, understanding the presence of PAHs in geological samples leads to the identification of environmental sediment type, making PAHs potentially useful as biomarkers.

Polycyclic aromatic hydrocarbons (PAHs) are chemical compounds consisting of two or more interlocking benzene rings.

There are thousands of PAH compounds, each of which differs in the number and arrangement of aromatic rings, as well as the position of substituents.

PAHs are found in petroleum, coal, tar deposits, and also act as by-products of fuel combustion (whether it is fossil fuel or biomass-derived). As a pollutant they are of great concern because several compounds have been identified as carcinogenic, mutagenic and teratogenic.

Ecological and toxicological aspects of polycyclic aromatic hydrocarbons in the environment in relation to natural resources.

Environmental concerns have focused on PAHs, which have molecular weights ranging from 128.16 (naphthalene, 2-ring structure) to 300.36 (hexabenzobenzene, 7-ring structure). Unsubstituted PAH compounds with low molecular weight, containing 2-3 rings, show significant toxicity, and others have an adverse effect on some organisms, but are not carcinogenic; Higher molecular weight PAHs containing 4 to 7 rings are significantly less toxic, but many 4, 7 ring compounds are carcinogenic, mutagenic, or teratogenic to a wide range of organisms, including fish and other aquatic organisms, amphibians, birds, and mammals .(Edwards, 1983. Ismen, 1984.)

2. Sources of polycyclic aromatic hydrocarbons

PAHs are ubiquitous in nature. Thus, their presence has been proven in geological sediments, soil, air, on the surface of water samples, in plant and animal tissues. PAHs initially appeared as a result of natural processes such as forest fires, microbial synthesis and volcanic activity. (According to Battersby, S. 2004). They are also found in interstellar space, in comets, meteorites and they are also molecular markers at the basis of the earliest forms of life.

Human activities that result in significant releases of PAHs, which in turn lead to severe pollution in limited areas, include high temperature pyrolysis (>700 0 C) of organic materials, typical of some processes used in the production of iron and steel, in aluminum smelting furnaces, in metallurgical and coke plants, during oil refining, when generating energy using heating.

The aquatic environment can receive PAHs during accidental spills of oil and petroleum products from means of its storage and transportation, from sewage and from other sources.

The evidence showing that PAHs are the cause of cancerous and precancerous lesions is strong, and this class of substances is likely to be a major cause of the recent increase in cancer incidence in industrialized countries (Cook and Dennis 1984).

PAHs were the first substances known to be carcinogenic (Lee and Grant 1981).

Due to the carcinogenic characteristics of many PAHs and their increasing concentrations in the environment, until more definitive ecotoxicological data are available, it is advisable to reduce concentrations or completely neutralize them wherever possible (Eisler, R. 1987).

Rice. 1 Substances that have a significant level of toxicity, but are not carcinogenic

Rice. 2 Substances with a pronounced carcinogenic effect

3. Environmental impact of aromatic hydrocarbons

Polycyclic aromatic hydrocarbons, when released into the environment, usually become airborne. Some evaporate into the air from soil or groundwater and then adhere to microparticles suspended in the air.

Polycyclic aromatic hydrocarbons (PAHs) can break down over time when exposed to sunlight or by reacting with other chemicals in the air.

PAHs are poorly soluble in water; they stick to dust or dirt and sink to the bottom of lakes and rivers. Various groups of microorganisms in sediment and water can degrade some PAHs over time, with the higher the molecular weight, the slower the rate of degradation.

Polycyclic aromatic hydrocarbons move in the atmosphere in the form of microparticles suspended in the air. They are carried by air currents and settle in the form of dry or wet (rain, dew, etc.) deposits. Settled in lakes and rivers, they sink to the bottom. Some penetrate through the soil layer into groundwater.

The toxicity of polycyclic aromatic hydrocarbons to aquaculture and poultry ranges from moderate to high. Some cause damage and death to agricultural and ornamental grasses.

There is currently a paucity of data regarding acute and chronic toxicity to terrestrial animals. PAHs are moderately persistent in the environment and can bioaccumulate. The concentration of polycyclic aromatic hydrocarbons in fish and shellfish is sometimes significantly higher than in the environment of these organisms.

PAHs can also be directly genotoxic, meaning that the chemicals and their breakdown products can directly interact with genes and cause DNA damage. In a study of environmental pollutants in house dust conducted by the Silent Spring Institute, three PAHs (pyrene, benzo[a]anthracene and benzo[a]pyrene) were found in more than three-quarters of the homes surveyed.

4. Experience of PAHs for the environment

On the environmental hazard scale of 0 to 3, shown above in Figure 3, polycyclic aromatic hydrocarbons are rated 1.5. Level 3 poses a very high environmental hazard and Level 0 poses a low hazard. Factors taken into account include assessing the degree of toxicity or non-toxicity of a substance, measuring its ability to remain active in the environment and its ability to accumulate in living organisms. The release of the substance is not taken into account. This is reflected in the NPI level for a given substance. One of the substances whose environmental hazard is assessed as high is nitrogen oxide (3) and one of the substances whose hazard is assessed as low is carbon monoxide (0.8).

5. Toxicity of PAHs to humans

The toxicity of PAHs is highly dependent on the structure; even isomers can be either non-toxic or extremely toxic. Thus, highly carcinogenic PAHs can be small (less than 3 rings) or large (more than 4 rings). One PAH, benzo[a]pyrene, is the first carcinogen studied and is one of many carcinogens found in cigarettes. Seven PAHs were classified as probable human carcinogens: benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, crysen, dibenz[a,h]anthracene and indenopyrene.

PAHs known for their carcinogenic, mutagenic and teratogenic properties: benzo[a]anthracene and chrysene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzopyrylene, coronene, dibenzanthracene, indenopyrene and oval (Fetzer, D. K. (2000), Lach, A (2005)).

Due to the lack of representative mixtures of PAHs for research purposes, the effects of biological and non-biological modifiers on PAH toxicity and metabolism are not yet well understood.

The following safety criteria for total PAHs, carcinogenic PAHs and benzo(a)pyrene in drinking water and air and total PAHs and benzo(a)pyrene in food have been proposed: 0.01 to<0,2 мкг общих ПАУ/л, <0,002 мкг канцерогенных ПАУ/л и 0,0006 мкг бензо(а)пирена /л; воздух: < 0,01 мкг общих ПАУ/м 3 , <0,002 мкг канцерогенных ПАУ/м 3 и 0,0005 мкг бензо(а)пирена/м 3 ; пища: 1,6 до < 16,0 мкг общих ПАУ ежедневно и 0,16 до < 1,6 мкг бензо(а)пирена ежедневно.

6. Application of PAHs

Many PAHs are not used at all. But some are used in medicine, to make paints, plastics and pesticides. Mothballs, also known as mothballs, are used in the production of dyes, explosives, plastics, lubricants and moth repellents. Anthracene is used in paints, insecticides and wood preservatives.

Conclusion

From the above review it is obvious that, despite some usefulness of PAHs, their environmental and toxicological hazards are a matter of acute concern and their concentrations should be greatly reduced in the environment, and in the best case, they should be completely eliminated from it.

List of sources used

1. https://ru.wikipedia.org

2. Edwards N.T. 1983. Polycyclic aromatic hydrocarbons (PAHs) in the terrestrial environment—a review. Journal of Environmental Quality 12.427-441.

3. Isman, G. A., Davani, B., and Dodson, D. A. 1984. Hydrostatic testing of gas pipelines as a source of PAHs in the aquatic environment. International Journal of Environmental Chemical Analysis. 19:27-39.

4. http://jurnal.org/articles/2009/ekol2.html

5. Isler R (1987) Effects of polycyclic aromatic hydrocarbons on fish, wildlife and invertebrates: A synoptic review.

6. US Fish and Wildlife Service, Patuxent Wildlife Research Center. Laurel. EPA. 1980. Water quality in terms of polycyclic aromatic hydrocarbons. US Environmental Protection Agency. 440/5-80-069.193.

7.Fetzer D.K. (2000) Chemistry and analysis of heavy polycyclic aromatic hydrocarbons. NY. Willey.

8. Lee SD, Grant L. 1981. Health and environmental assessment of polycyclic aromatic hydrocarbons. Publishing house Patotex. Forest Souse Park, Illinois. 364 pp.

9. Lach A. (2005). Carcinogenic effect of polycyclic aromatic hydrocarbons. London: Imperial College Press, ISBN 1-86094-417-5.

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