4. Soil pollution

SOIL POLLUTION—SOURCES OF SOIL POLLUTION

Pesticides: It can be classified as:
(i) Insecticide: The most common insecticides are chlorinated hydrocarbons like DDT, BHC etc.
As they are not much soluble in water, they stay in the soil for long time. They are ‘ absorbed by the soil and contaminate root crops like radish, carrot etc.
(ii) Herbicides: These are the compounds used to control weeds, namely, sodium chlorate (NaCl0₃) and sodium arsenite (Na₃As0₃) are commonly used herbicides but arsenic compounds, being toxic are no longer preferred.
Fungicides: Organo-mercury compounds are the most common fungicides. Its dissociation in soil produces mercury which is highly toxic and harmful for the crops. i Industrial Waste: It has seen that most of the industrial wastes are thrown into water or dumped into the soil. These industrial wastes contain huge amounts of toxic chemicals which are mostly non-bidegradable. For example, metal processing industries, mining cement, glass industries, petroleum industry etc., fertilizer industry produce gypsum.
The disposal of non-biodegradable industrial solid waste is not done by suitable methods i and cause many serious problems.

INDUSTRIAL WASTE

The waste materials generated by industries or industrial processes, is called industrial waste. It includes chemicals, trash, oils, solvents, dirt and gravel, many harmful gases etc. These are dumped in seas, rivers or land without adequate treatment. Thus, become a large source of environmental pollution. 

Types of industrial wastes 

Industrial waste can be divided into following two types

• Biodegradable industrial waste
• Non – biodegradable industrial waste 

Biodegradable wastes – Those waste materials which can be decomposed into simpler unharmful substances by the action of microorganisms are called biodegradable wastes. Some industries such as the paper industry, food industry, sugar industry, wool industry etc. mostly produce biodegradable industrial wastes. Management of these wastes can be done at low cost and easily. 

Non-biodegradable wastes – Non-biodegradable waste cannot be further decomposed via the action of the microorganisms. Such waste is the major source of toxins in the landfills. Chemicals, metals, plastics, paints, rubber etc. are examples of non-biodegradable wastes. These materials can remain as landfills for thousands of years without any damage. Toxins from metals and plastics get soaked into the earth and pollute the soil and water sources. Cleaning materials such detergent, phenols etc. producing industries, coal industries, dying industries etc. produce a large amount of non-biodegradable industrial waste. These types of wastes are difficult to manage and very toxic in nature. 

Effects of Industrial Waste 

Industrial waste is very harmful for us and our environment. Few impacts are stated below –

• Liquid industrial waste which is thrown into the sea is at an alarmingly dangerous level for marine ecosystems. 
• Industries release many harmful gases such as carbon dioxide, sulfur dioxide, nitrogen oxides etc. which cause air pollution. 
• In industrial wastewater nitrates and phosphates are there which often cause eutrophication. 
• Generally, air around industries is highly polluted and causes skin, eyes, throat, nose and lungs diseases.
• Industries use large quantities of water and also release a huge quantity of wastewater which contain many harmful chemicals and heavy metals. This wastewater pollutes natural sources of water and ultimately our health and environment. 
• It is one of the main causes of global warming. 
• Industrial wastewater destroys useful bacteria and other microorganisms present in soil. 
• Some industries cause sound pollution as well. 
• Industrial wastes and industries are destroying natural habitat of many species and responsible for wildlife extinction. 

Proper disposal and treatment is the only solution of prevention from effects of industrial wastes. 

Management of Industrial Waste  

Management of industrial solid waste is not the responsibility of local bodies or governments. Industries which are generating these solid wastes should manage such wastes by themselves. They need to take authorization from the pollution control board as well. Different procedures and methods are used to manage industrial waste. Although some basic steps involved in all processes are the same. Those basic steps are as follows –

• Analysis or Segregation 
• Collection 
• Transportation 
• Recovery 
• Recycling 
• Disposal 

Analysis or Segregation – Industrial waste is segregated or analyzed, and some biodegradable wastes or recyclable material are kept separately. Industries should segregate waste materials in different categories such as biodegradable, non-biodegradable, hazardous waste etc. 

Collection and Transportation – Industrial waste must be collected and transported to waste management plants. 

Recovery – In waste management plants recovery should be done. It means useful materials should be recovered from industrial wastes during treatment in waste management plants. 

Recycling and Disposal – If during recovery we get any useful materials then recycling should be done and disposal should be done of waste and harmful materials. 

STRATEGIES TO CONTROL ENVIRONMENTAL POLLUTION

Environmental pollution is also a major global concern due to the harmful effects of pollution on a person’s health and on the environment as well. Some of the strategies that are to be followed to lessen environmental pollution include the following:

• Stop smoking or at least follow “No Smoking” regulations at public places.
• Do not use open fires for waste disposal.
• Instead of plastic, use eco-friendly or biodegradable products, because plastic-like products are highly toxic in nature.
• Maintain proper waste disposal, especially for toxic wastes, and plan some strategies to reduce waste.
• Do not litter in public places, and some anti-litter campaigns should be run to educate the public.

GREEN CHEMISTRY

Green Chemistry is a way of thinking and is about utilising the knowledge and principles of
chemistry that would control the increasing environmental pollution.
Green chemistry in day-to-day life:
(i) Dry-Cleaning of clothes and laundary: Replacement of halogenated solvent like (CCl₄) by liquid C0₂ which is less harmful to groundwater.  Hydrogen peroxide (H₂0₂) is used for the purpose      of bleaching clothes.
(ii) Bleaching of Paper: In place of chlorine H₂0₂ is used for the bleaching of paper,
(iii) Synthesis of Chemicals: Ethahal (CH₃CHO) is prepared by step oxidation of ethene. Such as,

Definition of green chemistry

Green chemistry is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. Green chemistry applies across the life cycle of a chemical product, including its design, manufacture, use, and ultimate disposal.

Green chemistry:

• Prevents pollution at the molecular level
• Is a philosophy that applies to all areas of chemistry, not a single discipline of chemistry
• Applies innovative scientific solutions to real-world environmental problems
• Results in source reduction because it prevents the generation of pollution
• Reduces the negative impacts of chemical products and processes on human health and the environment
• Lessens and sometimes eliminates hazard from existing products and processes
• Designs chemical products and processes to reduce their intrinsic hazards

How green chemistry differs from cleaning up pollution

Green chemistry reduces pollution at its source by minimizing or eliminating the hazards of chemical feedstocks, reagents, solvents, and products.

This is unlike cleaning up pollution (also called remediation), which involves treating waste streams (end-of-the-pipe treatment) or cleanup of environmental spills and other releases. Remediation may include separating hazardous chemicals from other materials, then treating them so they are no longer hazardous or concentrating them for safe disposal. Most remediation activities do not involve green chemistry. Remediation removes hazardous materials from the environment; on the other hand, green chemistry keeps the hazardous materials out of the environment in the first place.

If a technology reduces or eliminates the hazardous chemicals used to clean up environmental contaminants, this technology would qualify as a green chemistry technology. One example is replacing a hazardous sorbent [chemical] used to capture mercury from the air for safe disposal with an effective, but non-hazardous sorbent. Using the non-hazardous sorbent means that the hazardous sorbent is never manufactured and so the remediation technology meets the definition of green chemistry.

Green chemistry's 12 principles

These principles demonstrate the breadth of the concept of green chemistry:

1. Prevent waste: Design chemical syntheses to prevent waste. Leave no waste to treat or clean up.

2. Maximize atom economy: Design syntheses so that the final product contains the maximum proportion of the starting materials. Waste few or no atoms.

3. Design less hazardous chemical syntheses: Design syntheses to use and generate substances with little or no toxicity to either humans or the environment.

4. Design safer chemicals and products: Design chemical products that are fully effective yet have little or no toxicity.

5. Use safer solvents and reaction conditions: Avoid using solvents, separation agents, or other auxiliary chemicals. If you must use these chemicals, use safer ones.

6. Increase energy efficiency: Run chemical reactions at room temperature and pressure whenever possible.

7. Use renewable feedstocks: Use starting materials (also known as feedstocks) that are renewable rather than depletable. The source of renewable feedstocks is often agricultural products or the wastes of other processes; the source of depletable feedstocks is often fossil fuels (petroleum, natural gas, or coal) or mining operations.

8. Avoid chemical derivatives: Avoid using blocking or protecting groups or any temporary modifications if possible. Derivatives use additional reagents and generate waste.

9. Use catalysts, not stoichiometric reagents: Minimize waste by using catalytic reactions. Catalysts are effective in small amounts and can carry out a single reaction many times. They are preferable to stoichiometric reagents, which are used in excess and carry out a reaction only once.

10. Design chemicals and products to degrade after use: Design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment.

11. Analyse in real time to prevent pollution: Include in-process, real-time monitoring and control during syntheses to minimize or eliminate the formation of byproducts.

12. Minimize the potential for accidents: Design chemicals and their physical forms (solid, liquid, or gas) to minimize the potential for chemical accidents including explosions, fires, and releases to the environment.

Green chemistry's roots in the Pollution Prevention Act of 1990

To stop creating pollution in the first place became America's official policy in 1990 with the Federal Pollution Prevention Act .

The law defines source reduction as any practice that:

• Reduces the amount of any hazardous substance, pollutant, or contaminant entering any waste stream or otherwise released into the environment (including fugitive emissions) prior to recycling, treatment, or disposal.
• Reduces the hazards to public health and the environment associated with the release of such substances, pollutants, or contaminants.

The term "source reduction" includes:

• Modifications to equipment or technology
• Modifications to process or procedures
• Modifications, reformulation or redesign of products
• Substitution of raw materials
• Improvements in housekeeping, maintenance, training, or inventory control

Section 2 of the Pollution Prevention Act establishes a pollution prevention hierarchy, saying:

• The Congress hereby declares it to be the national policy of the United States that pollution should be prevented or reduced at the source whenever feasible;
• Pollution that cannot be prevented should be recycled in an environmentally safe manner, whenever feasible;
• Pollution that cannot be prevented or recycled should be treated in an environmentally safe manner whenever feasible; an
• Disposal or other release into the environment should be employed only as a last resort and should be conducted in an environmentally safe manner.

Green chemistry aims to design and produce cost-competitive chemical products and processes that attain the highest level of the pollution-prevention hierarchy by reducing pollution at its source.

For those who are creating and using green chemistry, the hierarchy looks like this:

1. Source Reduction and Prevention of Chemical Hazards
   • Designing chemical products to be less hazardous to human health and the environment*
   • Making chemical products from feedstocks, reagents, and solvents that are less hazardous to human health and the environment*
   • Designing syntheses and other processes with reduced or even no chemical waste
   • Designing syntheses and other processes that use less energy or less water
   • Using feedstocks derived from annually renewable resources or from abundant waste
   • Designing chemical products for reuse or recycling
   • Reusing or recycling chemicals
2. Treating chemicals to render them less hazardous before disposal
3. Disposing of untreated chemicals safely and only if other options are not feasible

*Chemicals that are less hazardous to human health and the environment are:

• Less toxic to organisms
• Less damaging to ecosystems
• Not persistent or bio accumulative in organisms or the environment
• Inherently safer to handle and use because they are not flammable or explosive

• Environmental pollution: It is the effect of undesirable changes in the surroundings that have harmful effects on plants, animals, and human beings.
• Troposphere: The lowest region of atmosphere which extends up to the height of 10 km from sea level in which man and other living organism exists.
• Stratosphere: It is above troposhere between 10 to 50 km above the sea level.
• Acid rain: It is caused by the presence of oxides of sulphur and nitrogen and C0₂ in the atmosphere. The pH of the rain drops below 5.6, and it becomes acidic.
• Greenhouse gases: Some gases like carbon dioxide, methane, ozone, water vapours, CFCs have the capacity to trap some of the heat radiations from the earth or from the sun. This leads to global warming.
• Eutrophication: When phosphate ion increases in water it increases the growth of algae which consume the dissolved oxygen in water consequently aquatic life is adversely affected. This results in loss of biodiversity and the phenomenon is known as Eutrophication.
• COD (Chemical Oxygen Demand): It is calculated as the amount of oxygen required to oxidise the polluting substances. It is measured by treating the given sample of water with an oxidising agent, generally K₂Cr₂0₇in the presence of dil. H₂S0₄.