Air Pollution: Metal Culprits In Metro Cities

Air pollution is a serious global health threat that is responsible for 6.7 million premature deaths annually. It is caused by various factors, including vehicle emissions, industrial emissions, and household activities. Among the metals, lead is a significant pollutant released from vehicles, especially in big cities. Copper, chromium, and cadmium are also harmful pollutants found in the air. Particulate matter (PM), including PM2.5 and PM10, is another major concern, with sources such as traffic, transportation, industrial activities, and power plants. Studies have investigated air pollution in metro cities like Delhi, Kolkata, London, Toronto, Montreal, and Vancouver, revealing the impact of commuting and industrial sources on particulate matter exposure. Climate change and wildfires further contribute to particle pollution, emphasizing the urgency of addressing air quality issues.

Lead is a harmful pollutant released from vehicles

Lead is a toxic metal and air pollutant that has been widely used in products, including motor vehicle gasoline, paints, and batteries. Lead is released into the environment through various human activities, and one significant source of lead pollution is vehicles that use leaded gasoline.

Lead is a harmful pollutant that poses serious health risks to humans, especially children and pregnant people. Once lead enters the body, it is distributed to various organs, including the brain, kidneys, liver, and bones, and can cause adverse health effects. Children are particularly vulnerable to lead poisoning, which can cause permanent brain damage, reduced intelligence, behavioural problems, and learning deficits. Lead exposure during pregnancy can also harm fetal development and increase the risk of preterm birth.

In addition to vehicles, lead pollution is also released into the air through industrial activities such as ore and metal processing, lead smelting, and waste incineration. Lead particles emitted into the air can be inhaled or ingested, leading to lead exposure. Lead is persistent in the environment and can contaminate soils, especially in urban areas, where it can be resuspended into the air and contribute to air pollution.

The effects of lead exposure are widespread and serious. Lead is a neurotoxin that can cause neurological damage, behavioural changes, and intellectual disabilities. It can also affect the cardiovascular system, kidney function, the immune system, and reproductive health. There is no known safe level of lead exposure, and even low levels of lead in the blood have been associated with negative health outcomes.

To mitigate the harmful effects of lead pollution, governments and regulatory bodies have taken steps to reduce lead emissions. For example, the US Environmental Protection Agency (EPA) has successfully reduced lead levels in the air by 98% between 1980 and 2014 through the removal of lead from motor vehicle gasoline. Similar regulations have been implemented in other countries, leading to a phase-out of lead in gasoline and a subsequent decline in lead emissions from the transportation sector.

Copper pollutants are found in water

Metal air pollutants are a growing concern in metropolitan cities. While there is no definitive answer to which metal is the main air pollutant, lead, copper, iron, and zinc are all common contributors to air pollution in metro areas.

Copper, for example, is a significant pollutant in aquatic systems, including surface waters and groundwater. Copper pollution in water can arise from both natural and anthropogenic sources. Natural sources include geological deposits, volcanic activity, and the weathering and erosion of copper-bearing rocks. On the other hand, anthropogenic sources of copper pollution are diverse and include mining activities, agriculture, metal and electrical manufacturing, sludge from publicly-owned treatment works, and pesticide use.

One of the primary anthropogenic sources of copper pollution in water is the use of copper in plumbing systems. Older homes, in particular, are more likely to have copper piping, and copper can leach into drinking water if the water is corrosive. Corrosive water can dissolve copper in plumbing parts, leading to pinhole leaks, pitting, and blue-green stains on plumbing fixtures. Additionally, carbonated or acidic beverages that come into contact with copper tubing or containers can also contribute to copper contamination in water.

The presence of copper in drinking water is a health concern, especially for individuals with Wilson's disease and infants under one year old. While most healthy people can effectively process copper, excessive copper intake can lead to adverse effects such as headaches, vomiting, diarrhoea, stomach cramps, nausea, liver damage, and kidney disease. High levels of copper can also damage red blood cells and impair their ability to carry oxygen, potentially affecting male fertility.

To mitigate the risks associated with copper in drinking water, it is recommended to use cold water for drinking and cooking, as this can help maintain lower copper levels. In cases where copper levels are a concern, arranging for water testing through a certified laboratory is advisable. If copper levels exceed the recommended threshold of 1,300 µg/L, home water treatment options may need to be considered to ensure the safety of drinking water.

Chromium is a result of coal and oil combustion

Chromium is a metal that is released into the atmosphere as a result of coal and oil combustion. It is a hazardous trace element (HTE) that can cause potential health problems, public disease risks, and environmental deterioration. Chromium emissions from coal combustion have been studied in China, Australia, and Switzerland, with varying concentrations depending on geographical and temporal factors.

In China, coal resources are diverse, and the combustion of high-chromium coals has been linked to adverse effects. The concentration of chromium in coal varies across different regions, with South China having higher levels than North China. The combustion of coal in power plants contributes significantly to the release of hazardous trace elements, including chromium, into the environment.

Studies in Australia have focused on chromium speciation analysis in coals and ash by-products. They found that the more toxic hexavalent chromium (Cr6+) was present in the vapour phase during Oxy-fuel combustion, which produced higher levels of toxic chromium species compared to air combustion.

Additionally, chromium emissions from coal and oil combustion in China were estimated to be approximately 1.92×10⁵ tons in the atmosphere. The metal fabrication industry and the leather tanning sector were identified as the dominant sources of chromium emissions, with significant contributions to the total emissions.

The impact of chromium emissions on human health and the environment is a growing concern. Commuter exposure to particulate air pollution in metro systems has been studied in Toronto, Montreal, and Vancouver, Canada. These studies found that time spent in the metro contributed significantly to daily exposure to metallic elements, including chromium.

In summary, chromium is a metal that is released into the atmosphere as a byproduct of coal and oil combustion. Its presence in the environment, particularly in metropolitan areas, poses potential risks to human health and ecological systems. Studies have been conducted in various regions to understand the sources, concentrations, and impacts of chromium emissions, with a focus on coal-fired power plants and industrial activities.

Cadmium enters the air through the ground

Lead, copper, iron, zinc, magnesium, and sodium are some of the metals that are considered air pollutants in metro cities. While it is difficult to pinpoint one metal as the main pollutant, particulate matter in the air, which includes various metallic elements, is a significant concern in metropolitan areas. One of the metals that contribute to this pollution is cadmium.

Cadmium is a chemical element and a natural component of the Earth's crust. However, human activities can increase its presence in the environment, particularly in the air, water, and soil. Mining and smelting are significant contributors to the release of cadmium into the atmosphere. When released through these processes, cadmium compounds can be associated with respirable-sized airborne particles and can be carried over long distances before being deposited onto the ground by rain or other forms of precipitation.

Once on the ground, cadmium can contaminate the soil and subsequently enter the food chain. This was observed in Japan, where zinc mining operations contaminated local water supplies with cadmium. Local farmers used this water for irrigation, leading to the uptake of cadmium into their rice crops.

In addition to mining and smelting, other human activities that introduce cadmium into the environment include combustion processes, such as burning coal and household waste, as well as industrial processes. Cadmium can also be released during metal refining and iron and steel production. These activities contribute to the presence of cadmium in the air and its eventual deposition onto the ground, where it can persist and impact the surrounding ecosystem.

To summarize, cadmium enters the air through human activities such as mining, smelting, combustion, and industrial processes. Once released, it can be transported over long distances and eventually deposited onto the ground, where it poses risks to the environment and human health, particularly through the contamination of soil and the subsequent uptake by plants and entry into the food chain.

Particulate matter (PM) is inhalable particles

Particulate matter (PM) is a mixture of solid particles and liquid droplets found in the air. These particles vary in size, shape, and chemical composition, and can be emitted directly from sources such as construction sites, unpaved roads, fields, smokestacks, or fires. Most particles, however, form in the atmosphere as a result of complex reactions between chemicals. PM is not a single pollutant but a complex mixture of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. These particles can contain inorganic ions, metallic compounds, elemental carbon, organic compounds, and compounds from the earth's crust.

PM is classified into two main categories based on particle size: PM10 and PM2.5. PM10, or inhalable coarse particles, have diameters between 2.5 and 10 micrometers. They are large enough to be inhaled and can deposit in the upper airways, including the nose, throat, and bronchi. Exposure to PM10 is associated with adverse health effects, particularly for those with respiratory conditions such as asthma, bronchitis, and rhinosinusitis. Several studies suggest a link between long-term exposure to PM10 and respiratory mortality.

PM2.5, on the other hand, refers to fine particles with diameters of 2.5 micrometers or less. These particles are so small that they can penetrate deep into the lungs, reaching the bronchioles and alveoli. They pose the greatest risk to health and are the main cause of reduced visibility (haze) in some regions. Short-term exposures to PM2.5 have been linked to premature mortality, increased hospital admissions for heart and lung issues, acute and chronic bronchitis, asthma attacks, and restricted activity days. Long-term exposure is associated with reduced lung function growth in children and an increased risk of lung cancer.

The sources of particulate matter vary. In the case of railway systems, the friction between steel wheels and tracks releases particles of iron, copper, zinc, manganese, chromium, nickel, vanadium, and lead into the air. Ambient levels of PM2.5 and its elemental components can be significantly higher in metro environments compared to outdoors, as seen in studies conducted in Toronto, Montreal, and Vancouver. Additionally, indoor spaces can be affected by outdoor sources, with particles entering through doors, windows, and building structures. Indoor activities, such as smoking tobacco, cooking, and burning incense, also contribute to particulate matter levels.

The health effects of particulate matter exposure are widespread and concerning. In addition to respiratory issues and lung cancer, PM exposure has been linked to cardiovascular diseases, nervous system disorders, and metabolic conditions. The World Health Organization (WHO) provides guidelines to limit exposure to PM, and air quality alerts, such as the Air Quality Index (AQI), can help individuals protect themselves when PM levels are harmful.

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