In the developing countries, especially India, the stone crushing industry plays an important role, which produces raw materials for various construction activities such as bridge, building, canal, highway road and railway track, etc. on the basis of the requirement. There are more than 12,000 stone crusher units in India, but keeping in mind the rapid urbanization and industrialization, this number is expected to more than double in the next decade. In India, the stone-crushing industry represents a financially significant sector because its annual turnover is more than Rs. 5000 million (more than 1 billion US dollars). It is estimated to provide direct employment to more than 500,000 people engaged in various activities like mining, crushing plants, transportation of mining stones and crushing products, etc. Most of the workers of stone crushers are related to rural and economically backward areas because there are limited employment opportunities. Stone crusher is an industry that is present in and around almost all major cities/towns of the country because construction activities run throughout the year. Since the cost of crushed stone products increases with the transportation of stones over long distances, therefore crushers need to be located near demand centers, like cities, bridges, canals, etc. Stone crushers also require electricity and a lot of manpower for their operation.

Crushers are always located near the source of raw materials such as stone mines, river beds, etc. Although stone crusher industries are a socio-economically backward area, this leads to a large amount of dust emissions, which causes respiratory diseases and creates health hazards for the surrounding population, along with the workers. Dust also adversely affects visibility, reduces the growth of vegetation and affects the aesthetics of the region.

In order to prevent/control these emissions, Central Pollution Control Board (CPCB) has already developed emission standards and guidelines in 1989, which were notified by the Ministry of Environment and Forests (MoEF) under the Environmental Protection Act (EPA) (1986), based on technical-economic viability for achieving standards.

In country like India, air pollution is an unavoidable harmful by-product of rapid industrialization and urbanization that is responsible for a variety of deleterious effects on both human and plant communities [1] . It has been a major environmental concern since the beginning of industrialization, resulting in a release of gaseous and particulate pollutants into the atmosphere. Industrialization has provided humanity with materials and social benefits. It has also brought in its wake up many unwanted substances and social problems. One of these problems is the degradation of our surrounding environment. Worldwide mining activity is one of the serious contributors to the environmental pollution and is considered one of the significant sources of air, soil and water pollution [2] - [4] . Pollutants released mix with the atmosphere and are transported at a long distance through the air from the mining area and leading to pollution in the surrounding undisturbed area [5] . The extraction of valuable minerals from an ore body, known as quarrying, often results in the degradation of ambient air quality due to the emission of dust particles in the range of 0 to 75 µm [6] . Vehicular movements, windstorms blowing over processed stockpiles, overburden, mine ore, and aggregate in transit contribute significantly to the degradation of ambient air quality in the mining areas [7] . The rapid growth of our global population and an associated increase in economic development are placing an ever-increasing stress on the availability of natural resources. Increased production has also resulted in a considerable amount of waste that has adverse effects on the surrounding flora, fauna as well as human beings. A key component associated with infrastructure development is the use of crushed rock (e.g. for road and building construction). During crushing and screening operations, the resulting dust is a primary air pollutant that can have a considerable effect on surrounding flora and fauna. The effects include a change in soil productivity and pH, decreased visibility in the neighboring areas, increased number of people with chronic respiratory illnesses and allergies, and degradation of natural habitats and resources, such as economic crops [8] - [11] . When the weather is dry, nations like India produce a lot of dust from their soil [12] . Dust deposition on plants increases due to activities viz., open-cast mining, loading and unloading of crushing stone, road traffic, poorly maintained roads, agriculture-related activities, construction and demolition activities, brick kilns industries and other industrial activities [13] . The dust deposited onto the foliar surfaces affects their morphological features as well as biochemical constituents [14] [15] . Air pollutants can negatively affect the biochemistry and physiology of plants, leading to a reduction in overall growth and development: These effects have been studied for many years [16] - [19] . As air currents flow through a tree canopy, some dust particles stick to the leaves, while others are deflected and deposited elsewhere. The fate of the particles depends on their size and other physical and chemical properties, wind speed, and the surface topography of the deposition zones. After deposition, the dust particles may remain on leaf surfaces until it rains or the leaf abscises and decomposes [20] [21] . Several factors contribute to the dust retention capacity of vegetation, including canopy structure, foliage density and morphology (roughness, leaf convection, presence of trichomes), and ambient meteorological conditions [21] - [25] . Dust accumulation affects plant physiological parameters by reducing photosynthetic rate and characteristics can also influence dust levels and thus leaf characteristics [26] [27] . Air pollution can damage canopy structure, reduce plant height and plant biomass, and have measurable effects on the internal biochemistry of affected plants. In addition to leaf surface characteristics, canopy morphology, structural configuration, leaf density, leaf inclination, and other factors that influence vegetation resistance to PM, a number of environmental factors such as precipitation, strong winds, dust storms, and human factors such as traffic flow and heating influence the effects of pollution/dust in the air [28] [29] . Fine dust increases leaf temperature up to 10 times more than coarse dust. Even at very low concentrations, fine dust particles can affect leaf function, while higher densities of coarse particles are required to have corresponding effects [30] . The features of the trees, like the canopy cover, leaf size, hardness, texture, etc., enhance the capacity of trees in lowering the pollutant level in the atmosphere [31] . Trees with large canopy cover restrict the pollutant’s downwind movements, and they also filter the air, which enhances environment quality [32] . Studies found that the vegetation to be used cannot be generalized and needs to be appropriately studied before its implementation, as, in open road conditions, tall trees had a more significant impact [33] . The process of green belt development requires proper management of plants and their growth. Then better management can be acquired by using naturally occurring and eco-friendly products. The air pollutants can also damage vegetation, by causing morphological changes, blocking the leaf pores making them less productive, and causing genetic modifications to the plants like stunt growths [34] . The tree species with maximum air pollutants and dust particles absorbing capacity with minimal impact on themselves can be chosen for plantation [27] [35] . The tolerance capacity of tree species can be well known depending on specific four biochemical and physiological parameters [36] . Plants help in combating the problem of air pollution, but in this process, they also get affected because of their continuous exposure to a particular environment. In the polluted environment, changes in plant morphological, physiological, and biochemical parameters (chlorophyll, carotenoid, and protein content) can be observed. Chlorophyll measurement has an imperative part in metabolism, and reduced chlorophyll concentration links directly with development of plants [37] . In addition, the severe effects may alter the biochemical and morphological characteristics of an exposed organism, resulting in the initiation of adaptive mechanisms to cope with the altered environment [38] . Several factors contribute to the dust retention capacity of vegetation, including canopy structure, foliage, density and morphology (roughness, leaf convection, presence of trichomes), and ambient meteorological conditions [21] - [25] . Serious environmental problems regarding quarry mining have been mainly observed under open-cast mining, which is common for the extraction of rock aggregate. The tones of overburden material that require extraction to reach the ore body contribute heavily to air quality degradation. The prevention and control of respirable dust have become a major focus of mine dust prevention in many countries, particularly respirable dust with a particle size of less than 5 µm. The reason why respirable dust is difficult to control is that most respirable dust is hydrophobic, which brings great difficulty to dust removal methods [39] . In this context, plants play an important role in monitoring and maintaining the ecological balance by actively participating in the recycling of nutrients and gases like carbon dioxide and oxygen and also provide a vast area for impingement, absorption, and accumulation of air pollutants to reduce the pollution level in the atmosphere [40] .

In the present study, we analyzed the specific physiological and biochemical responses of existing plant species in and around open cast mines towards air pollutants, which might be utilized to recognize those trees with high adaptability and mitigation capacity and purpose for greening around open cast mining areas. It includes fifty native tree species commonly found in the region of Bundelkhand of Uttar Pradesh in India. The species with high pollution tolerating capacity can be recommended for an effective greenbelt development along the roadside. The pollution-tolerant species can also be implemented in other regions with the similar climatic conditions. Generally, plants’ respond to dust accumulation varies among species, as deposition varies with foliage orientation, topography, phyllotaxy, epidermal and cuticular characteristics, presence of trichomes, canopy height, and architecture [26] [41] [42] . Plants are involved in biogeochemical cycles and play an important role in monitoring and maintaining ecological balance [43] .

Plants are having great role in the defense against to cope with air pollution and other adverse conditions of atmosphere. Dust, aerosols, and other airborne particles are scavenged by plant leaves. Leaf microstructure is characterized by groove area and trichomes which are significantly influenced dust deposition comparing to leaves with the smooth structure; foliar surface morphology has direct effects on the dust capture by leaves which is consistent with a degree of leaf roughness and the number of trichomes in the upper and lower epidermis of a leaf determined the dust retention capacity [44] . Generally, the load of pollution depends on the levels of emission sources, and micrometeorological factors. Plants exposed to pollution experience numerous morphological, physiological, biochemical and ultrastructural changes upon prolonged exposure [45] [46] . Leaves are most sensitive to air pollution as compared to other parts of plants [30] [47] . Dust deposition on the foliage of various plant species is affected by weather conditions, wind direction and plant leaves structures in addition to the sources of environmental contaminants [48] . In present investigation, there are 50 plant species have been selected from open cast mining sites as well from Bundelkhand university campus (as control). It has been observed that in present study on the basis of dust-holding capacity out of 50 species the following 10 species have been found maximum deposition of dust. Among these Tectona grandis (2.566 mg/cm²) having highest deposition of dust followed by Ficus hispida (2.39 mg/cm²), Calotropis procera (1.78 mg/cm²), Butea monosperma (0.964 mg/cm²), Ficus benghalensis (0.924 mg/cm²), Ficus infectoria (0.521 mg/cm²), Artocarpus heterophyllus (0.345 mg/cm²), Ipomoea purpurea (0.294 mg/cm²), Allianthus excelsa (0.224 mg/cm²) and Pongamia pinnata (0.188 mg/cm²) respectively. Lowest dust deposition has been observed in Pithecellobium dulce (0.016 mg/cm²). The variation of dust loading capacity of plant species from mining sites as well as well control site is depicted in Table 1 . Study indicated that the tolerance of plant species

is relatively to the levels of pollution which gives variation from one species to another species and ability to resist pollutants in the existing environment without showing external damage or loss. Contrary to control site, dust load is considered to be an important factor responsible for the decline in leaf performance at the contaminated site [26] . Reductions in the leaf area might be attributed to decreased leaf production, and/or higher rates of senescence caused by the impact of cement dust pollution stress on the photosynthesis capacity and cell elongation mechanism [49] [50] . When exposed to airborne pollutants, most plants experienced physiological changes before exhibiting visible damage to leaves [37] . The use of vegetation samples as bio-indicators of the degree of pollution through biochemical study in environmental monitoring is well established by several studies.

Many changes in plant physiology and growth, such as those caused by air pollution mainly the dust pollution originating from open cast mining, are biological compensatory responses to environmental stress. The main stress compensatory strategy in plants is to minimize damage from stress [70] . In fact, these changes help plants minimize stress and maximize use of internal and external resources [71] . The present study showed that the highest dust-capturing capacity was shown by T. grandis and it is followed by F. hispida, C. procera, B. monosperma and F. benghalensis respectively whereas the lowest is in C. accuminatus. The highest chlorophyll content was observed in T. grandis followed by F. hispida, C. procera, F. benghalensis and M. indica respectively whereas low chlorophyll content is in B. vulgaris. Chlorophyll measurement is an important tool to evaluate the effect of air pollutants on plants as it plays an important role in plant metabolisms and also reduction in chlorophyll content corresponds directly to plant growth [50] . Leaf chlorophyll content thus can provide valuable information about physiological status of plants. It also varies with the tolerance as well as sensitivity of the plant species. The change in the amount of carotenoid content depends on plant tolerance towards dust. The highest protein content was observed in T. grandis followed by F. hispida, C. accuminatus, D. sisoo and L. leucocephala respectively whereas low protein content is in A. indica. The change in the amount of protein content depends on plant resistance to chemical nature of dust. Tolerance is relatively proportional to the levels of pollution, which gives variation from one species to another species and capacity to resist pollutants in the mining environment without showing any external damage or loss. Characteristics features including species tolerance on the existing environment, biochemical changes, leaf shape, petiole length, leaf hairs, phyllotaxy and plant height are essential factors influencing dust deposition. On this background, above mentioned species having the highest content of chlorophyll, protein, carotenoid and dust-holding capacity may be recommended as the first-choice species for greenbelt design in an around open cast mining area to minimize the dust load of the neighboring environment.

The authors thankfully acknowledge the help of Managers and staff of respective mines during field surveys, identification of plant species and also support from local people. Special thanks to Director Jhansi and Head of ICAR-Central Agro-forestry Research Institute and Datia of ICAR-Central Soil and Water Research Institute for avail Laboratory facilities.