Heavy metal contamination along the roadside is a matter of concern nowadays, especially in industrial areas of developing countries. The non-degradable nature of heavy metals makes them injurious to all living beings. Soil, dust and plants are the main media for the entry of these metals into our food chain. Heavy metal contamination along the roadside is a matter of concern nowadays, especially in industrial areas of developing countries. The non-degradable nature of heavy metals makes them injurious to all living beings. Soil, dust and plants are the main media for the entry of these metals into our food chain. Leaves of roadside plants are a reservoir for noxious emissions through vehicles. Roadside surroundings like auto repair shops, brake lining wears and industries are a big source of heavy metals. The contamination of soil and water over the years by toxic heavy metals has become a major concern for soil, water and air. Heavy industries (coal combustion, power plants, metallurgical industries, chemical plants, and auto repair shops) are metal contamination sources. Due to the overflow of hazardous wastes such as toxic liquids and gases, which can pollute drinking water, reduce soil quality, and release toxins in the air, industries have become very important in terms of environmental degradation. Metal contamination causes variation in plant growth and physiology of roadside plants. Metal contamination has a mutagenic, genotoxic and cytotoxic impact on a living organism. Vehicular emissions as a major source of heavy metal pollution have negative effects on the ecosystem.
Plants growing on metal-contaminated sites exhibited metabolic changes, reduced growth, reduced biomass production, and reduced metal accumulation. Various physiological and biochemical processes of plants are affected by Roadside metals. Symptoms of heavy metal toxicity were investigated as softness in tissues, vomiting, nausea, diarrhea and some reproductive problem, kidney, and liver ailments in living organisms. Sometimes it led to chronic diseases after long-term exposure. Contamination gets into the human body or animals through contaminated plants. Therefore, heavy metal impacts on the food chain are prevalent because every single living organism depends on others for food.
Developed countries have established threshold levels to control contamination but, there are no standards for streets or roadside dust contamination through heavy metal. Although in Pakistan there are some flexible standards so provided by APA Pakistan there are hard and fast rules to follow to these standards therefore proper rules and regulations adopted to tangle this problem. Roadside automobile emissions and industrialization are the main sources of surface and groundwater contamination. It gets grave importance worldwide, which is harmful to humans and other living organisms. Urbanization and industrialization have led to an increase in roadside environmental degradation through metal pollution. Waste material in solid, liquid and gaseous form causes biological, chemical, and physical alteration in pure air which badly affects the living organism. Urbanization and industrialization are directly related to environmental degradation.
Roadside metal contamination is increasing day by day, so it has become a nuisance at a global level. Roadside pollution is the main problem in developing countries because of unplanned urbanization and industrialization. Low budget, the least resources and technology have become sources of roadside metal contamination in developing countries. Vehicular emissions affect plant growth and development, which is an alarming situation for the ecosystem. Toxic substances released from automobiles enter the water, soil, and air that adversely affect the plant, animal, and human health. Copper and nickel released from vehicles negatively impact living organisms which impacts on anatomy, physiology and morphology of plants. Some metals like Mn, Ni and Cu are essential nutrients for plants at the lower levels but cause toxicity when these elements exceed permissible limit They play essential roles in metabolic activities, especially in hemoglobin formation but when their concentration crosses the permissible limit. The permissible limit of copper set by FAO (1984) for edible plants is 3.00 µg g–1 or less, permissible limit of manganese set by FAO (1984) for edible plants is 2 µg g–1, the permissible limit set by FAO (1984) for nickel in edible plants is 1.63 µg g–1. The natural process of plants (Photosynthesis) has been affected by the toxicity of heavy metals. Manganese toxicity cause neurological, respiratory and digestion problems in adults. Metal-contaminated Road dust causes chemical changes in the soil and affects the nutritional value of plants. Metal stressed plants have a great chance of pest attack that causes inhibition of plant growth and development. Metal contaminated dust particles stuck on leaves and cause altered stomatal action, decreased water potential, inhibition of respiration, and altered metabolism. Some particulate contaminants are absorbed in the soil and increase the soil pH. Heavy metals toxicity causes the shedding of leaves in plants. In severe cases, the death of tissues in plant leaves (chlorosis) has been observed.
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