Environmental Chemistry 

The environment is defined as the surrounding of any object or organism, including the biotic and abiotic factors. Every object or organism is made of the constitutive unit, which extends to chemistry to identify its composition. Thus, environmental chemistry is a chemical branch that studies the origin, transport, effects, reactions and fates of chemical species in the environment.

Table of Contents:

• Significance of Environmental Chemistry 
• Aspects of Environmental Chemistry
• Pollution 
• Environment Pollution
• Tropospheric Pollution
• Pollutants
• Gaseous Air Pollutants
• Smog
• Acid Rain
• Greenhouse Effect
• Stratospheric Pollution
• Water Pollution
• Soil Pollution 
• Industrial Waste
• Practice Problems
• Frequently Asked Questions

Significance of Environmental Chemistry 

Environmental chemistry holds applications in diverse areas such as: 

• To analyse and put forward innovative solutions for environmental challenges
• Understand the interaction between environmental components and organisms
• To solve the problems concerning environmental pollution 
• To understand and differentiate the presence of toxic and non-toxic components in the environment 
• Effect of Industrialisation on natural and man-made resources

Aspects of Environmental Chemistry

There are important sub-topics of environmental chemicals, such as

Pollution 

Pollution is defined as the introduction of any material (in any state of matter) or type of energy (radioactivity, heat, sound) into the environment. It is associated with negative effects on the environment. These may be of natural or man-made origin and hence are named accordingly, such as natural or man-made pollution. 

Causes of Pollution

Common causes are:

• Excessive industrialisation 
• Rapid urbanisation 
• Pesticide usage 
• Fast population growth 

Environment Pollution

The atmosphere part of the environment is divided into different layers:

• Troposphere: It is the lowest region and harbours life. 
• Stratosphere: Found above the troposphere, it has ozone that prevents UV rays from reaching the Earth. 
• Mesosphere: Continuing the atmosphere upward, it has lower temperature and density, making breathing difficult. 
• Thermosphere: It is the topmost layer of the atmosphere on Earth that absorbs X-rays and UV rays. 

Besides the atmosphere, there exist different other spheres as well. The hydrosphere refers to the aqueous or water-based part of Earth, the lithosphere is the solid rocky portion, and the biosphere is the biological envelope supporting life. 

Tropospheric Pollution

It is one of the most harmful forms of pollution as the pollutants here are directly inhaled and come in contact with the body. Different types of pollution here are discussed below. But first, let’s understand the term ‘pollutants’. 

Pollutants

These are undesirable materials causing harm to the environment. These can be organic, inorganic, biological or radioactive in nature. It is further categorised into different types, such as-

• Primary pollutants: These are the ones released directly into the environment from their source. Common examples include carbon monoxide, ammonia, sulphur dioxide, smoke, fumes and others. 
• Secondary pollutants: These originate from the reactions between primary pollutants and environmental particles such as sulphur trioxide, methane, nitrates, phenols, nitrogen dioxide and others. 
• Biodegradable pollutants: The pollutants that the micro-organism can degrade. The example includes kitchen waste. 
• Non-degradable pollutants: These are the pollutants that remain in the environment for a longer duration of time. Examples include lead compounds, mercuric salts, and pesticides. 
• Natural pollutants: These find their origin from natural activities such as volcanic eruptions, mines, floods, fires and forests. 
• Artificial pollutants: These are formulated through human-based activities such as industrial gases or liquids, sewage, automobile exhaust and others. 

Gaseous Air Pollutants

• Oxides of Sulphur: These are formed by the burning of fossil fuels like coal and petrol combustion, petrol refining and smelting. The common products include sulphur trioxide and sulphuric acid. These cause issues for humans by hindering the movement of air and lungs. It also harms the environment by causing chlorosis and dwarfing. The corrosive nature also impacts man-made monuments, textiles and other objects. 
• Oxides of Nitrogen: These develop on the reaction between lightning strikes and oxygen at higher altitudes. The fossil fuels burning at high temperatures, oxygen and nitrogen contribute to nitrogen dioxide and nitric oxide formation. Further reaction with water results in nitric acid formation. Chemical plants, explosives and fertiliser manufacturers also contribute to the levels. The higher concentration is responsible for damage to plant leaves and causing respiratory problems. 
• Oxides of Carbon: These originate from automobile exhaust and incomplete combustion of carbon found in wood, charcoal, motor vehicles and forest fires. The most common forms are carbon monoxide and carbon dioxide. The former is a lethal and poisonous gas that induces headache, visual impairments, coma and death. It also blocks the transport of oxygen. Carbon monoxide also has a higher affinity compared to carbon dioxide. 
• Other gaseous air pollutants include freon from industries manufacturing cooling equipment, chlorine and hydrogen chloride, cement and iron and steel industries, power generating stations, etc. 

Smog

It is the mixture of smoke and fog that harms children, plants, and adults. The smoke part comprises ash, carbon, oil and fog in the suspended droplet form. It is of two types, London or classical smog and Photochemical or Los Angeles smog. The classical smog comprises coal smoke and fog, mainly sulphur dioxide and trioxide. The photochemical smog has oxidised hydrocarbons and ozone in the presence of humidity. 

Acid Rain

It is defined as the precipitation consisting of acidic components in dry or wet form. These acidic components can be sulphuric or nitric acid, and precipitation can be as rain, dust, snow, hail, fog or any other form. The pH of rain lower than 5.6 is referred to as acid rain that impacts agriculture, plants, trees, monuments, water pipes, and animals. It also causes respiratory issues and produces salts with heavy metals. The contributors to acid rain are coal burning, furnaces, petrol and diesel burning, oil in power stations and other sources. 

Greenhouse Effect

Some of the gases present in the atmosphere are referred to as greenhouse gases. These include ozone, methane, chlorofluorocarbon compounds and water vapour. Their accumulation leads to the prevention of escaping Infrared rays which contributes to an increase in the atmosphere’s temperature leading to global warming. The consequences are evident in the rise in sea level due to the melting of glaciers and increased floods. It also leads to the development of several diseases. 

Stratospheric Pollution

It is the layer of the atmosphere housing the ozone layer. The gas protects the Earth from the ultraviolet rays of the sun that can cause skin cancer in humans. The chemical reaction between oxygen molecule and atom yields the ozone. Ozone depletion has been evident in the past due to the excessive use of pollutants like chlorofluorocarbons used in refrigerators and ACs. 

Water Pollution

The introduction of pollutants into the water bodies is water pollution. The consumption of water for numerous purposes, domestic, industrial and agricultural, causes the direct incorporation of contaminants into plants, humans and animals, causing damage to health. Water pollution is easily recognisable as the contaminated water loses its transparency and gains unpleasant odour and colour, bad taste and a murky oily appearance.

The sources of water pollution include domestic sewage, industrial waters, suspended particles, oil, atomic explosion, radioactive materials, clay and wastes from fertilisers. The source of water pollution is also recognised as point and nonpoint sources. The point sources refer to single and identifiable sources, and examples include pipes or ditches. The non-point sources are which gain contaminants from multiple sources. Examples include nutrient run-off from agricultural land. 

Effects of Water Pollution

• Loss of microorganisms in water due to oxygen depletion 
• Introduction of different pathogens into the human body, animals and plants that lead to lethal and non-lethal diseases like tuberculosis, dysentery, cholera, jaundice, diarrhoea and others. 
• Ecosystem imbalance
• Staining of fabrics, the bad taste of water and modification of its colour
• Organ system damage

Methods to Control Water Pollution

The different methods to control water pollution are: 

• Usage of aeration and trickling filters to recycle the wastewater. 
• Incorporating filtration and chlorination methods for the usage of chemicals 
• Using techniques like ion exchangers, electrodialysis, adsorption and reverse osmosis. 
• Using sewage water for irrigation and fish farms to leverage the nutrients. 
• Effectively treat the water before discharge 
• Grow water hyacinth for treating wastewater to absorb heavy metals. 
• Encourage and enhance the usage of precipitation and recycling to control water pollution.

Soil Pollution 

The presence of contaminants or foreign substances in the soil to such an extent that it deteriorates the soil productivity is soil or land pollution. It occurs due to discharge from agricultural lands where chemicals like fertilisers, insecticides, pesticides, and others are used. Domestic and industrial wastes, toxic metals, radioactive wastes, soil conditioners, hospital wastes, accidental oil spills, improper faecal matter disposal, heavy metals and pollutants lead to soil pollution. 

Effects of Soil Pollution

The directly affected elements from soil pollution are humans, plants and animals. The decrease in soil fertility, absorption of toxic materials from the soil, and consumption of the same is very easy through soil pollution. Moreover, the alteration in the ecosystem is also witnessed due to the same. Biomagnification also contributes to enhanced mortality and extinction rate. 

Methods to Prevent Soil Pollution

Soil pollution can be prevented through the following methods:

• Land farming
• Bioaugmentation and bioremediation
• Using plants for the extraction of heavy metals
• Aeration of contaminated soil
• Minimise the use of chemicals in agricultural lands

Industrial Waste

The waste generated and released from industries are referred to as industrial waste. It is classified into two types as

• Hazardous waste: It harms both human health and the environment. It comprises heavy metals and can be in the form of matter. 
• Non-hazardous waste: It does not harm any environmental components and does not need to be treated. The non-toxic waste is generated from industries like textiles, wood, cardboard and others. 

Practice Problems

Q1. What is the method to control air pollution?

a. Dissolving hydrogen chloride in water. 
b. Dissolving sulphur dioxide in alkaline solution
c. Adsorption of gases and liquid molecules over silica gel and activated charcoal
d. Use of precipitators, settling chambers and natural gas
e. All of these

Ans. e. All of these

All the measures must be taken by specific industries. 

Q2. What are the methods of industrial waste management?

a. Reuse-Reduce-Recycle
b. Waste collection 
c. Waste disposal
d. All of these

Ans. d. All of these

All of these are effective methods to control industrial waste from polluting other bodies. 

Q3. What is the permitted time level for the threshold limit value?

a. 40 hours a week
b. 10 hours a week
c. 60 hours a week
d. 2 hours a week

Ans. a. 40 hours a week

The threshold limit value is the measure of the permissible pollutant limit in the atmosphere that does not cause adverse effects if exposed to healthy work for 40 hours a week. 

Frequently Asked Questions

Q1. What are photochemical pollutants?
Answer: The pollutants that undergo chemical reactions on exposure to sunlight are photochemical pollutants. The nitrogen dioxide absorbs the blue wavelength and UV region of the sunlight to decompose into nitric oxide and atomic oxygen that contributes to ozone formaldehyde, peroxy acyl nitrates and acrolein. 

Q2. What are BOD and COD?
Answer: BOD or Biological Oxygen demand is the amount of free oxygen required to oxidise the organic matter by the aerobic method in a period of five days. COD or Chemical Oxygen Demand refers to the quantitative analysis of oxidisable impurities in sewage. COD values are generally higher than BOD. 

Q3. What is biomagnification?
Answer: The passage of toxic materials from lower to higher trophic levels and their accumulation in each is referred to as biomagnification. 

Q4. What is the difference between pollutant and contaminant?
Answer: The pollutants may be of human or natural origin, while contaminants are only of human origin. Contaminants are pollutants that cause harm to others.