Polycyclic aromatic hydrocarbons (abbreviated as PAHs) are persistent organic pollutants. They have pronounced carcinogenic characteristics. In total, over 200 representatives are listed in this group. The most dangerous of them is benzapyrene. It is often found in the study of environmental objects.
About benzapyrene
The discovery of this component occurred in 1933. Two years later, through careful research, its carcinogenicity was proven.
Today benzapyrene is ranked in the first class of danger. He has mutagenic characteristics. And even its modest concentration adversely affects the human body. With its significant proportions in the air (above normal) and long exposure, lung cancer occurs.
For this reason, its detection is especially relevant. Based on the properties of the substance, methods were created for its calculation. They differ only in the stages of sampling and sample formation.
PAC Category Analysis
It includes elements whose chemical structure contains at least three benzene rings. The simplest polycyclic aromatic hydrocarbons are anthracene and phenanthrene. They do not mutate and do not differ in toxic qualities. Pyrene and benzperylene are similar in structure to them.
What polycyclic aromatic hydrocarbons PAHs are carcinogens? Cholatrene, dibenzpyrene and perylene are qualified as especially toxic (in addition to benzapyrene). They pose the greatest threat to human health.
Conditions for generating
The formation of PAHs occurs during the combustion of the following products:
- oil category;
- coal;
- wood;
- garbage waste;
- tobacco products;
- food.
The lower the temperature in the incinerator, the greater the amount of these substances. In relatively modest proportions, benzapyrene is found in asphalt.
Together with other combustion products, polycyclic aromatic hydrocarbons penetrate the air. At room temperature data, all of these components have a solid crystalline form. They melt at 200 ° C
When hot gases, including PAHs, are cooled, these elements accumulate in the emission section. For example, at a distance of 2-5 km from a coal thermal power station, the surface layer of the soil is saturated with such pollutants. But a greater percentage of them rush through the air at considerable distances.
The best adsorbent for polycyclic aromatic hydrocarbons PAHs is carbon black. Approximately 10 14 molecules of these substances can concentrate on one square centimeter of its surface.
Sources and Contributions
Here statistics take into account mainly benzapyrene emissions. The indicator t / year is given. For example, the United States obtained such data.
|
A source |
Parameter (t / year) |
|
Coal burning |
600 |
|
Coke making |
200 |
|
Forest fires |
150 |
|
Burning wood |
70 |
|
Cigarette smoke |
0.05 |
The last value is the smallest and at first glance it may seem insignificant. However, with local proportions, quite significant indicators are obtained. They are listed in the table below.
|
Air |
Indicator (ng / m 3) |
|
In the village |
0.1-1.0 |
|
In the city |
0.2-20 |
|
In a room full of tobacco smoke |
100 |
In drinking water, the carcinogen is concentrated in a volume of 0.3-2.0 ng / L.
Polycyclic aromatic hydrocarbons, when in the atmosphere, are particularly stable. They are gradually converted into other products, interacting with ozone and nitrogen dioxide. In the first case, polynuclear quinones appear. In the second - nitrobenzapyrenes.
PAH detection in the air
The following methods are used for this:
- Gas chromatography (GC).
- High Performance Liquid Chromatography (HPLC)
First, the main 16 components of the PAH group are separated. For this, special columns are used. Method 1 uses capillary devices. In the second case - highly effective.
To develop the effectiveness of the result, preliminary screening is carried out among other compounds available in the samples. For this, LC with reduced pressure is used in one of two systems:
- Liquid is a solid.
- Fluid is a fluid.
Any suitable adsorption, for example silica gel, is used here. Sensitivity detectors are also used to increase the objectivity of the results.
The first method is supplemented by:
- Flame ionization device. Function - quantitative measurements after determining the compound by other unrelated methods.
- Mass spectrometer. Gives quantitative data, but often they are limited due to the coincidence of the masses of substances with different structures
The second technique is supplemented by such detectors:
- Fluorimetric. Determines the trace amounts of PAHs, but does not provide data on their structure.
- Spectrophotometric. Objectively identifies compounds and their structure.
When selecting analytical equipment intended for screening, determining and quantifying the study of such elements, certain criteria should be taken into account:
- The degree of calculated content in the analyzed samples.
- The number of related impurities and substances.
- Methodology for the implementation of measuring operations.
- The potential of serial technology.
From the standpoint of separation technology, it is more advantageous to use capillary GC. The number of compounds, which in theory is divided into a temporary unit in this technique, is 5–10 times greater when compared with the HPLC method. However, there is no clear advantage here. Since some compounds are effectively divided precisely by liquid chromatography. For example, this is pyrene dibenzo (a, h) anthracene
Soil detection
In it, PAHs are due to emissions. Their presence is provided by the plant or other source that caused pollution. The following methods are used to detect and analyze polycyclic aromatic hydrocarbons here:
- Chromatographic separation. Separates PAHs from other compounds.
- Fluorimetry. Details analyzes these substances in the soil.
As a rule, samples are taken from sites close to any enterprises. These are peaty and podzolic soils.
Water research
Detecting PAHs in water bodies and wastewater is quite difficult. A high performance liquid chromatograph is used. He has:
- Gradient elution mechanism.
- UV sensor on a diode array.
- Fluorescent indicator.
Dilute solutions of polycyclic aromatic hydrocarbons in water are recovered using methylene chloride. They are purified on a column using silica gel. Excess impurities are removed. The result is an extract. It is dried and dissolved in a composition of water and acetonitrile. Further analysis is carried out using an indicator with a diode matrix.
Food situation
Benzapyrene can enter food that is cooked. This representative of polycyclic aromatic hydrocarbons in foods may be contained in different proportions. They are shown in the following table.
|
Product |
Proportion (mcg / kg) |
|
Burnt bread crust |
0.5 |
|
Dark crust sponge cake |
0.75 |
|
Homemade smoked meat |
more than 50 |
|
Boiled sausage |
0.26 - 0.5 |
|
Roasted veal |
0.18 - 0.63 |
|
Fruits and vegetables |
0.2-150 |
|
Smoked fish |
11.2 |
|
Vegetable oil |
0.9 - 30 |
|
Potatoes |
1 - 16 |
|
Apples from sections near roads |
ten |
|
Non-industrial zone apples |
0.2-0.5 |
Today, a carcinogen is found in many common products: bread, milk, butter, potatoes, etc. If the products are processed correctly, the concentration of harmful substances can be reduced. Vegetables and fruits should be washed thoroughly. This eliminates about 20% of PAHs.
They can appear due to the reaction of eluents (elements formed in the solvent) with polymer packaging. For example, milk fat forms about 95% benzapirene from paraffin-paper containers or cups.
