PLANT ADAPTATION TO ANTHROPOGENIC FACTORS - 2017

3. ENVIRONMENTAL POLLUTION BY INDUSTRIAL CHEMICAL WASTE

3.2. Components of Atmospheric Pollution

Pollutants entering the atmosphere typically take the form of gases and aerosols. The former include true gases and vapors characterized by molecular dispersion, while the latter consist of Solid and liquid particles. The physical state of an atmospheric pollutant determines its physicochemical properties, dispersion in the atmosphere, and phytotoxicity. Gases and vapors, for instance, readily react chemically with other substances, with vapors additionally capable of condensing and settling. While gaseous substances easily penetrate internal plant Tissues, dust particles settle on their surfaces. Only dissolved substances can enter leaves alongside the flow of Water (Fig. 6).

Class="center">

Fig. 6 - Components of atmospheric pollution

Aerosols can be solid or liquid. They are defined as fine solid or liquid-droplet particles suspended in air acting as the dispersion medium (dispersants). Collections of solid particles manifest as smoke, whereas liquid ones appear as fog or clouds. Aerosol particle sizes vary across a broad spectrum—from hundredths of a micron to tens and hundreds of microns. Particles smaller than 5 µm can remain suspended in the air for extended periods, whereas those exceeding 10 µm settle rapidly.

Particularly high levels of atmospheric air pollution by aerosols occur in major cities and near industrial facilities that emit large volumes of dust particles, which are then carried downwind.

Solid aerosol particles exhibit diverse chemical compositions. The solid fraction of air pollutants most frequently contains silicon, calcium, and carbon compounds (unburned coal particles), along with tarry substances, and less commonly metal oxides such as iron, aluminum, magnesium, zinc, manganese, copper, and others.

The primary sources of solid and liquid particle emissions into the atmosphere include brown coal-fired thermal power plants, metallurgical enterprises, beneficiation (sintering) plants, cement and carbon black works, chemical facilities producing dusts, and transportation, among others. A single blast furnace department emits over 190 tons of dust particles daily. Metals vaporizing during smelting and escaping into the open atmosphere exist in a suspended state as extremely fine dust composed of iron, manganese, copper, zinc, lead, silver, antimony, bismuth, cadmium, selenium, and tellurium oxides, among others. For every ton of cement produced, a plant loses 240 kg of product as dust.

Solid Suspensions in the atmosphere also form through the chemical interaction of gaseous substances released into it. For instance, ammonia reacts readily with chlorine or hydrogen chloride, yielding ammonium chloride. Crystals of ammonium salts and metal oxides are highly dispersed; they remain suspended in the air for long periods and are carried by air currents over vast distances, sometimes spanning thousands of kilometers.

Carbon black plants discharge several hundred kilograms of soot particles ranging from 0.033 to 0.04 mm in size into the atmosphere every day. With ventilation stack heights of 20–25 m, the soot content in the ground-layer air on the windward side of a plant measures 0.9–10.7 mg/m³ at 0.2 km, 0.5–1.6 mg/m³ at 0.5 km, 0.37–1.1 mg/m³ at 1 km, and 0.03–0.1 mg/m³ at 2 km. In winter, when vertical air mixing decreases, the concentration of soot particles in the air rises.

Liquid aerosol particles are generated during the Condensation of vapors of acids, bases, phenols, resins, and other substances, as well as through Chemical Reactions between pollutants and water vapor or droplets present in the atmosphere during fog or rain. For example, in moisture-saturated air, sulfurous, sulfuric, hydrochloric, hydrofluoric, and other acids form from their corresponding anhydrides released into the atmosphere in gaseous form.

Aerosols emitted by industrial enterprises and motor vehicles gradually settle onto the land surface and contaminate the soil. Consequently, elevated concentrations of sulfur, chlorine, fluorides, and heavy metals (such as iron, zinc, and copper) accumulate in the soil. This leads to a substantial degradation of soil health and its salinization (sulfate or chloride). Such conditions suppress soil microflora activity and diminish soil fertility.

Agroindustrial enterprises represent another source of soil pollution. Specifically, the unjustified use of mineral fertilizers, pesticides, insecticides, herbicides, and other toxic chemicals causes them to accumulate in the soil, creating unfavorable conditions for Plant Growth and leading to the bioaccumulation of toxic substances within plants.

Industry and agriculture also serve as sources of massive water body pollution by hazardous substances. Industrial wastewater contains significant concentrations of toxic compounds. All substances introduced by human activity or deposited into the soil from the atmosphere can be leached by precipitation into groundwater and subsequently enter aquatic ecosystems.

Operating industrial plants typically discharge a mixture of gases, vapors, and solid particles comprising substances involved in or generated by the production process.

Most industrial waste is forcibly released into the atmosphere through stacks, aspiration systems, and ventilation units, where the bulk of it is captured. Fugitive emissions escape from industrial systems that have lost their airtight integrity (through windows, doors, and aeration devices), as well as from extraction, loading, and raw material transport sites in open-pit mining, and from the spontaneous combustion of sulfur-bearing rocks in waste heaps. Fuel combustion furnaces and metal smelting/remelting furnaces rank among The most significant sources of atmospheric air pollution.

Emissions from industrial plants and transportation comprise around a hundred identified substances alongside a substantial fraction of yet-unidentified ones. The most prevalent air-polluting gases include sulfur dioxide and sulfur trioxide, fluorine and chlorine compounds, nitrogen oxides, carbon disulfide, hydrogen sulfide, ammonia, unsaturated Hydrocarbons, and carbon monoxide, among others.

Solid particles entering the atmosphere most commonly consist of unburned coal particles, ash, metal sulfates and sulfides (iron, copper, zinc, lead), silica, chlorides, and calcium and sodium compounds, among others.

In addition to incoming acid vapors, phenols, and other substances, liquid aerosols contain compounds formed through the interaction of gases and solid particles with water vapor (Fig. 7).

Fig. 7 - Components of atmospheric pollution

Acidic and Alkaline Gases

Sulfur dioxide (SO₂) is generated during the Processing and combustion of organic matter (hard and brown coal, petroleum and petroleum products, wood), the roasting and smelting of sulfur-bearing ores, and the production and application of sulfuric acid. Sulfur dioxide is emitted in large quantities by thermal power plants, ferrous and non-ferrous metallurgy enterprises, by-product coke plants, cement and ammonia works, and Cellulose synthetic fiber and sugar factories, among others.

A thermal power plant that Burns 4,500 tons of coal containing 3% sulfur per day releases 270 tons of sulfur dioxide into the atmosphere. Meanwhile, smelting copper from 2,250 tons of ore concentrate with a 30% sulfur content emits 1,360 tons of sulfur dioxide. Pig iron smelting generates a large volume of blast furnace gas, about 10% of which escapes into the atmosphere. According to statistics, smelting 1 ton of pig iron is accompanied by the emission of an average of 22.4 kg of sulfur dioxide into the atmosphere. Enormous amounts of sulfur compounds enter the air from iron ore processing plants; during the smelting of copper, zinc, nickel, and other metals; and during coal coking.

The spontaneous combustion of sulfur compounds present in waste rock from coal mines is accompanied by the release of sulfur dioxide. The amount of SO₂ entering the air depends on the COMPOSITION OF THE mine waste heaps and can reach 0.2-5.0 mg/m³ in the direction of smoke dispersion, causing plant damage within a radius of up to 200-300 m from the heap. The highest concentration of sulfur dioxide is observed at a distance of up to 300 m from the waste heaps.

In large cities and industrial regions of Europe and North America, the average annual concentration of sulfur dioxide is 0.8-4.0×10^-3 mg/m³. In northern regions, even weaker sources of atmospheric pollution than metallurgical plants create higher concentrations of sulfur and nitrogen dioxides in the surface air layer. This is caused by frequently recurring heavy cloud cover, which reduces vertical air mixing.

Sulfur dioxide is capable of reacting with water vapor droplets present in the air, fog, or rain to form sulfurous acid.

The solubility of sulfur dioxide in water was studied by Terraglio and Manganelli. According to their findings, the dissolution rate of SO₂ in water depends on its concentration in the ambient air. Specifically, when the SO₂ content in the air was 0.81 mg/m³, 4.53 µg/ml of it was detected in the solution; at 2.54 mg/m³, it was 8.88 µg/ml; at 5.54 mg/m³, 12.83 µg/ml; and at 8.73 mg/m³, 16.75 µg/ml. At the same time, the acidity of the solution decreased. This sharp drop in acidity is caused by the dissociation of the resulting sulfurous acid, as well as The formation of hydrogen (H⁺) and bisulfite (SO₃^2-) ions. Sulfite solutions were found to contain over 98.5% bisulfite ions and only 1.5% sulfurous acid compounds.

Sulfurous acid is an unstable compound that dissociates with the release of sulfur dioxide.

In the presence of atmospheric oxidants (such as ozone) and moisture, a portion of the sulfur dioxide is easily converted into sulfur trioxide, sharply increasing their combined phytotoxicity. The ratio of sulfuric acid aerosols to sulfur dioxide was 3.2% in clear weather and 15.7% in misty weather. When sulfur dioxide enters the atmosphere, it is accompanied by about 2% sulfur trioxide, but over time, the proportion of the latter rises to 16%.

Sulfur trioxide is highly hygroscopic and, upon combining with water vapor, forms a sulfuric acid aerosol that remains suspended in the air as a fog. Sulfuric acid has strong oxidizing properties and actively binds water. The simultaneous presence of sulfur dioxide and sulfur trioxide in the ambient air results in high toxicity to plants.

Hydrogen sulfide (H₂S) enters the atmosphere along with other pollutants in relatively small quantities compared to sulfur dioxide. It is constantly present in the emissions of coking plants and is released during The production of synthetic fibers and sugar, in coal mines, oil fields, oil refineries, and elsewhere. Hydrogen sulfide has strong reducing properties and is toxic to plants.

Nitrogen compounds are emitted by facilities producing mineral fertilizers, nitric acid and nitrates, aniline Dyes, nitro compounds, viscose rayon, celluloid, and photographic film, as well as by motor vehicle exhaust.

Among the mixture of nitrogen oxides (NO, NO₂, N₂O₃, N₂O₅) emitted into the air as a yellow-brown smoke ("fox tail"), NO₂ and N₂O₅ predominate. This is because nitric oxide (NO) is unstable and is oxidized by atmospheric oxygen to nitrogen dioxide. Nitrogen dioxide, in turn, can be oxidized to nitrogen pentoxide in the aforementioned sequence.

Nitrogen oxides (NO₂, N₂O₃, N₂O₅) readily dissolve in atmospheric moisture, forming aerosols of nitric (HNO₃) and unstable nitrous (HNO₂) acids. The ease with which one nitrogen oxide converts into another makes it difficult to account for the content of each individually in the air; therefore, their total concentration is typically expressed as a sum. A high percentage of nitrogen oxides in the atmosphere is also generated in cities with heavy traffic.

Ammonia (NH₃) is released into the atmosphere in small amounts during the production of ammonium fertilizers, urea, and nitric acid, as well as by sugar refineries, tanneries, and other industrial plants. In the air, ammonia reacts with carbon dioxide to form (NH₄)₂CO₃, or with water to turn into NH₄OH. In the presence of more reactive anions in the air, ammonia interacts with them to form ammonium salts (sulfates, fluorides, etc.). These circulate in the air as fine crystals and settle slowly.

Ammonia exhibits reducing properties with weakly expressed toxicity.

Fluorine compounds are among the most harmful to plants. Fluorine readily reacts with almost all elements. Therefore, it enters the free atmosphere not in its pure form, but combined with other substances as a gas or dust particles (HF, NH₄F, H₂SiF₆, NaF, etc.). Sources of air pollution by fluorine compounds include aluminum and cryolite plants, facilities manufacturing phosphates and phosphate fertilizers, enamel and ceramic works, etc. A certain amount of fluorine compounds is emitted from furnace combustion of coal and from fluxes used in pig iron smelting. Gaseous and water-soluble fluorine compounds penetrate plants through leaves and roots.

Some plant species are capable of accumulating high doses of fluorine, which, upon systematic ingestion by animals, can cause fluorosis. Fluorine compounds are highly toxic to plants. Complete defoliation and death of tree foliage are frequently observed near enameled cookware plants that emit hydrogen fluoride and silicon tetrafluoride into the atmosphere. The destructive effect of fluorine on plants is exacerbated by high air humidity and precipitation.

Chlorine compounds are highly reactive oxidizing agents. Chlorine is almost never found in its free state in nature or industrial emissions. Atmospheric pollution by chlorine compounds originates from titanium-magnesium plants; chemical plants producing insecticides, herbicides, Hydrochloric acid, organic dyes, cement, superphosphate, acetic acid, Hydrolysis alcohol, bleaching powder, and soda; as well as from electroplating and other sources. Numerous sources of chlorine compound emissions account for the presence of the latter in the ambient air of most modern cities. The concentration of chlorine in cities averages 2.6-9.5×10^-8%. Hydrogen chloride and its Other Compounds are required by plants only in limited amounts. When absorbed in high doses, chlorine causes profound Structural and functional disorders that often lead to plant death.

Carbon monoxide is released everywhere during the incomplete combustion of carbon-containing substances (coal, petroleum products, natural gas). For example, CO content reaches up to 30% in blast furnace gas, 1 to 13.7% (averaging 6.3%) in vehicle exhaust, and 13 to 15% in cupola furnace emissions. Carbon monoxide is a reducing agent. It negatively affects plants at relatively high concentrations exceeding 1%.

Oxidants

Ozone (O₃) is arguably the most important air pollutant detrimental to plants worldwide. The ozone layer is remarkably thin. If this gas were concentrated at the Earth's surface, it would form a layer only 2-4 mm thick (minimum at the equator, maximum near the poles). This very layer reliably protects us by almost completely absorbing dangerous ultraviolet radiation. Without the ozone layer, life would survive only in the depths of water (deeper than 10 m) and in soil layers impenetrable to solar radiation.

Exposure to high concentrations damages the foliage of plant organisms, while a further increase in concentration over a short period can cause significant plant injury, manifesting in particular as necrosis, with discoloration ranging from metallic gray to brown. Exposure to low concentrations over a prolonged period can produce a cumulative effect. Signs of chronic damage include bronze coloration of leaves, chlorosis (discoloration), and premature Aging (Figs. 6, 7). Ozone exposure alters the permeability of plant tissues to water, glucose, and ions, and inhibits Photosynthesis by reducing both electron transport system activity and chlorophyll content. Ozone's effect on Plant Respiration can be either stimulatory or inhibitory. The damaging concentration varies widely among species: for sensitive plant species, it may be 0.05-0.1 ppm over 2-4 hours, whereas for tolerant species, it is 0.4 ppm. Conifers are highly sensitive to ozone (Fig. 8).

Fig. 8 - Impact of industrial enterprises on the environment

Peroxyacetyl nitrate (PAN), along with ozone, is one of the most toxic oxidants for plants. PAN is a compound formed from hydrocarbons (HCs) and nitrogen oxides (NO_x) under METABOLISM/18.html">The Influence of sunlight. Ethanol that enters the air also serves as a source for the formation of atmospheric acetaldehyde and peroxyacetyl nitrate, which contributes to the accumulation of NO_x in the atmosphere. This compound causes tissue damage in plants. Similar to ozone, PAN reacts with various exhaust gases in the presence of sunlight. Due to the continuous input of industrial pollutants into urban air, PAN exerts a negative impact on All living organisms.

Organic compounds

Ethylene (H₂C-CH₂) is a gas that dissolves well in water and has a distinct odor. Ethylene is present in vehicle exhaust, is produced as a byproduct of incomplete coal and gas combustion, and is a byproduct of polyethylene manufacturing. It causes damage similar to the effects induced by PAN and ozone in urban environments. The Effect of ethylene on plant growth was first discovered in 1901 by D. M. Neljubow. He was investigating the causes of leaf shedding when exposed to so-called illuminating gas, among the ingredients of which ethylene was the most active. D. M. Neljubow established that at very low concentrations, this gas caused a triple response in plants: it inhibited stem elongation, promoted stem thickening, and altered horizontal orientation. Somewhat later, it was demonstrated that ethylene accelerates fruit ripening. In 1934, R. Gane proved that plants themselves are capable of synthesizing ethylene. At very low concentrations, on the order of 0.001–0.1 µL/L, it can inhibit and alter plant growth patterns, and accelerate fruit ripening. It has been established that its precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), moves throughout the plant and participates in signal Transduction. Ethylene itself, when released into the atmosphere, can provide signaling between plants. Local centers of ethylene synthesis have not been found; it appears in any plant Organism.

The good solubility of ethylene in water allows it to be transported in aqueous solution within the plant. As a gas, ethylene differs from other phytohormones by its volatility; for this reason, ethylene from one plant can affect processes in a neighboring plant. The classic effect of ethylene action is observed in fruit and vegetable storage facilities or during long maritime transport—overripe fruits enhance the ripening of neighboring less ripe fruits.

An important Physiological Effect of ethylene is also considered to be The stimulation of leaf abscission: it affects the enlargement of the Separation layer located at the Base of the leaf petiole. L. I. Musatenko and T. P. Mamenko believe that the plant hormone ethylene, despite its simple two-carbon Structure, is an effective modulator of Plant GROWTH AND DEVELOPMENT. It controls many important physiological processes in the plant organism and mediates the expression of 7% of the plant genome. Ethylene is involved in critical aspects of the plant life cycle, governing seed germination, ROOT Hair development, root modulation, flower blooming, leaf abscission, and fruit ripening. The production of ethylene by plants is regulated by internal signals during growth and development, as well as in response to external biotic and abiotic stimuli such as wounding, Hypoxia, ozone, freezing, drought, and others. Scientists are extensively studying ethylene-insensitive mutant plants, as well as mutants with ethylene-sensitive phenotypes, including etr 1, etr 2, etr 3, ein 5/ain 1, ein 4, ein 6, and eir 1. Mutants capable of ethylene overproduction (eto 1, eto 2, eto 3), constitutive activation of ethylene signaling pathways (ctr 1), or lacking apical dominance (hls 1) have also been identified. The availability of these mutants makes it possible to use them for isolating genes responsible for the perception and transduction of the ethylene signal in plants, and helps partially decipher the molecular pathways through which the signal travels to trigger or suppress specific physiological programs.

Ethylene is not only an important regulator of numerous physiological processes in higher plants, but it also Functions as a mediator of plant responses to biotic and abiotic stress factors. It plays a significant role in plant Disease resistance; however, depending on the pathogen type and plant species, the functions of ethylene may vary. Most commonly, ethylene suppresses symptom development during necrotrophic pathogen infection, but increases Cell mortality caused by Other types of pathogenic infections by participating in programmed cell death. Upon pathogen infection, avirulent signals are recognized due to the presence of a specific plant resistance (R) Gene. This avr/R interaction is referred to as gene-for-gene resistance and often triggers a defense mechanism involving a cell death program at the infection sites (known as the hypersensitive response). The Transcription factor Pti 4 has been identified—a protein structurally similar in Amino Acid Sequence to EREBP_S that can specifically bind to the GCC-box cis-element present in the promoter of many ethylene-regulated pathogen-responsive (PR) genes. Pti 4 expression in tomato leaves is rapidly induced by ethylene, which drives the expression of GCC-box-containing PR genes. These results indicate that the ethylene response is a component of gene-for-gene resistance in plants.

When the hypersensitive response is activated, a prolonged response known as systemic acquired Immunity (systemic acquired resistance, or SAR) is triggered, providing immunity against subsequent infection by a wide range of pathogens. In many cases, SAR is characterized by an increase in endogenous salicylic acid (SA) content and the expression of PR genes, leading to enhanced resistance to a broad spectrum of virulent pathogens. However, some pathogens can induce defensive plant resistance through the activation of ethylene and jasmonic acid (JA) in signal transduction pathways. Although SA-dependent and JA/ethylene-dependent pathways are involved in establishing plant stress-defense reactions and resistance to various pathogens, significant crosstalk is observed between these two pathways in SAR. The term "cross-talk" is used here to denote the interaction between two separate, linear signal transduction pathways simultaneously activated in the same Cells. Thus, the components of both signaling pathways are expressed in the same cells and exhibit interaction under normal physiological conditions. Ethylene signal transduction pathways can interact with JA pathways for the co-regulated expression of defense PR genes, such as PDF 1.2, involved in plant disease resistance. Furthermore, there is an interaction between JA/ethylene- and SA-dependent pathways. During necrotrophic pathogen infection, symptom development is accelerated and cell mortality caused by other types of pathogenic infections is increased, participating in programmed cell death.

It is hypothesized that the abiotic stress-induced response shares partial similarities with pathogen-defense pathways, and the interaction between SA, JA, and ethylene modulates the response to reactive oxygen species. It has been revealed that the stimulation of ethylene Biosynthesis under stress factors such as ozone, UV radiation, and wounding involves the Generation of reactive oxygen species, which include superoxide anions, hydroxyl radicals, and hydrogen peroxide, causing damage to cellular Organelles As a result of Lipid Peroxidation. In addition, reactive oxygen species, particularly hydrogen peroxide, function as signaling molecules. Specifically, an excess of hydrogen peroxide and other reactive oxygen species in tissues can stimulate ACO or induce the de novo formation of its isoforms. Therefore, it is believed that the elevation of ethylene biosynthesis under stress conditions depends on the rapid conversion of ACC to ethylene, and The activity of ACO, which catalyzes the final step of ethylene biosynthesis. However, the primary regulatory process of ethylene biosynthesis is the expression of ACC synthase (ACS).