اثرات فلزات آلاینده هوا بر سلامتی و بهزیستی گونه‌های گیاهی در شهرهای صنعتی (مقاله مروری)

Abstract
Metal particles polluting the air cause damage to living things and plants. Plants grown in a dusty environment show signs of damage. Plants are very efficient at trapping atmospheric particles. Depending on the dust load and duration and tolerance of plants to particles, damage and negative changes may occur in leaf surface, leaf structure and plant growth inhibition, reduction of leaf surface and therefore reduction of total biomass. Investigating the pattern of changes and adaptation of plant species for resistance and survival in the conditions of stress caused by environmental pollutants is useful and efficient in knowing the performance of species and effective exploitation of species, especially in industrial and urban environments. The elements available to plants in the environment are classified into two general categories: essential elements for survival and toxic and non-essential elements. Metals Ni, Co, Zn, MoMn, Fe, Cu are among the low consumption and essential elements for the survival of plants, and metals Al, Cd, Cr, Hg, Pb are toxic and non-essential elements. The presence of the lowest concentration of unnecessary elements in the environment around plants causes complications and the occurrence of biological reactions in order to deal with and adapt to stressful factors in the plant.

Introduction
Rapid urbanization and industrialization in many countries and regions of the world have led to the release of large amounts of suspended particles into the atmosphere. Atmospheric suspended particles can have very variable production sources and sizes. The concentration of metals in industrial urban environments is caused by natural (soil-generated) or human (man-made) sources, however, according to many studies of the sources of metal pollution in the dust of urban streets, it is mainly caused by human activities from such as car traffic and the erosion of pads and tires and the depreciation of car parts, the erosion of buildings, industries and the combustion of fossil fuels (Addo et al., 2012). Atmospheric dust is one of the important sources of heavy metals, especially in the environment. It is considered urban and industrial (boucko., 2010).
Metal pollutants usually do not disappear and self-sustainability mechanisms are evident in them, and therefore they can enter food chains and cause damage to ecosystems (Mahmoudi and Khademi, 2012). Air pollutants and airborne particles that include metal particles cause damage to living things and plants (Sawidis et al., 2011). Plants grown in a dusty environment show signs of damage (Kulshreshtha et al, 2009).
Plants are very efficient at trapping atmospheric particles. Depending on the dust load and duration and tolerance of plants to particles, damage and negative changes may occur in leaf surface, leaf structure and plant growth inhibition, reduction of leaf surface and therefore reduction of total biomass. Therefore, examining the pattern of changes and adaptation of plant species for resistance and survival in stress conditions caused by environmental pollutants is useful in knowing the species' performance and effective exploitation of these species, especially in industrial and urban environments. And it is efficient.
Vegetation is an important tool for removing nitrogen particles from the atmosphere. Studies show that leaves are the most sensitive part of a plant and can help absorb and stabilize dust in the environment. The sensitivity of leaves is based on the fact that most physiological activities are based on leaves. Therefore, leaves in different stages of development and growth can act as a good indicator for air pollutants.
In urban environments and industrial areas, trees have a purifying role against pollutants caused by industrialization. Plants are completely exposed to contamination due to lack of movement. Urban plants are constantly exposed to various types of air pollutants with high levels, which causes chronic damage to their physiological, morphological and anatomical characteristics. Air pollution is very effective in changing morphology, and pollutants not only affect the structure, but the change in the morphology of plants, while they can be effective in reducing air pollution to some extent, is affected by pollutants.
2- Elements in the air in industrial cities and their producing sources
Elements available to plants in the environment are classified into two general categories: essential elements for survival and toxic and unnecessary elements. Metals Ni, Co, Zn, MoMn, Fe, Cu are considered among the low consumption and essential elements for the survival of plants, and metals Al, Cd, Cr, Hg, Pb are toxic and unnecessary elements (Rosselli et al. , 2006). The presence of the lowest concentration of unnecessary elements in the environment around plants causes complications and the occurrence of biological reactions in order to deal with and adapt to stressful factors in the plant. On the other hand, plants use low consumption elements in a small but necessary amount.
However, the increase in the environmental dose of plant exposure to low consumption elements causes disruption and stress in the plant, and signs of resistance and adaptation will be observed in plants, and it also causes physiological, morphological and anatomical abnormalities in plants (Rubio). et al., 2012) some of the most important and abundant toxic elements in the air of industrial cities are presented below.
3-The effect of metallic pollutant particles on vegetation in urban and industrial environments
Pollutants discharged from cars mainly affect phenology, fruiting period, leaf and leaf surface senescence, wax characteristics, biomass production, seed germination, seedling growth, leaf physiology and biology (Iqbal et al. , 2015). The overall decrease in leaf area and leaf weight is caused by exhaust pollution (Tiwari et al., 2008). Kulshreshtha et al., 2009 reported that the particles from the exhaust of cars settled on the leaves and It reduces plant growth. The sensitivity of plants is different and it shows different reactions depending on the type of pollutant and its concentration. Particulate pollutants can cause many lethal effects in plants, such as stomatal blockage, reduced photosynthesis, leaf fall, and dead tissue (Younis et al., 2013).
Depending on the dust load and the duration and tolerance of plants to particles, there may be damage and negative changes in the leaf surface, leaf structure and inhibition of plant growth and as a result the reduction of the total biomass, causing stress due to contact with metals, leading to the appearance of similar symptoms Symptoms of drought stress such as increased leaf thickness. Several studies have shown that when plants are exposed to high concentrations of heavy metals, their fresh weight, dry weight and leaf length decrease (Souza and Rauser., 2003). In the presence of metals, the opening of stomata is affected (Doganlar et al., 2012).
Clogging of stomata reduces photosynthesis (Pourkhabbaz et al., 2010). Exposure of leaves to high traffic reduces leaf chlorophyll content and pollution stress in plants. Damage to photosynthesis occurs mainly due to the reduction of chlorophyll and the increase of lipid peroxidation. Almost every plant process is directly or indirectly affected by the water content of the plant, and water can be considered an essential factor in regulating plant growth. Therefore, in connection with the responses of plants to environmental stresses, special attention is paid to water relations from the cellular level to the whole plant. Heavy metals cause a decrease in relative water (Subbaro et al., 2000).
Studies show that reducing the transmission level is more effective than increasing the aperture resistance. Metals reduce plant growth and reduce photosynthesis. One of the most obvious effects of plant growth reduction is the reduction of the leaf area (Shariatamdari et al., 2011). Therefore, if the amount of photosynthesis per unit of leaf area does not change, the growth rate will decrease due to the decrease in the amount of photosynthesis in the whole plant (which is the result of the decrease in the area of photosynthesis leaf will decrease (Shariatamdari et al., 2011). Stomatal density is an important parameter of plant adaptation to the environment and it affects gas exchange and photosynthesis by creating physiological changes (Pompelli et al., 2010). Below are some of the effects of each metal.
Conclusion
Trees can be used for biomotoring to detect low concentrations of atmospheric pollutants. Although the difference between the load of metals obtained from soil and air sediments is hard and difficult and uncertain, but it is possible to study the cumulative effects of soil and air by using biological monitoring and examining the adaptations of plant organs and the qualitative changes of the environment. made it distinct and obvious.
Of course, compared to lower plants (mushrooms and lichen), trees have less potential for biological monitoring, but because their distribution is high in the city (Kardel et al, 2010. Norouzi and Khademi, 2015), they are very effective in biological monitoring and They are effective. Their biggest advantage is their long life and wide spatial distribution and the simplicity and low cost of their sampling, so they can be used for the temporal and spatial distribution of metals in the urban environment. Therefore, knowing the effects of metals on tree species and vegetation and investigating their changes has an effective role in managing air pollution in industrial areas