UGC NET Paper One
Unit 9: People, Development and Environment
Chapter 2: Environmental Issue: Water Pollution - Part 2
Major Metal Water Pollutants
Heavy metals pose significant health risks when they contaminate water sources.
1. Arsenic
- Toxic element found in water & food; linked to cancer, heart disease, and diabetes.
- Groundwater contamination is a major issue (especially in Eastern India).
2. Methylmercury
- Highly toxic form of mercury that accumulates in fish and shellfish.
- Methyl mercury in water can cause adverse human effects such as mental disturbance and impairment of speech, hearing, and vision. (Asked in Exam)
- Pregnant women & infants are most vulnerable.
3. Lead
- Enters water via old pipes and industrial pollution.
- Lead exposure can affect various parts of the human body, but it has the most significant and harmful impact on the brain. (Asked in Exam) Causes severe damage, especially in children.
4. Fluoride
- Added to water to prevent tooth decay, but excess fluoride harms bones & joints (skeletal fluorosis) and causes dental fluorosis (discolored teeth).
5. Nitrates
- Found in fertilizers; enters water through agricultural runoff.
- Nitrates are responsible for causing blue baby disease. (Asked in Exam)
- In agricultural regions, groundwater can have significant concentrations of Nitrate. (Asked in Exam)
Blue Baby Syndrome (Methemoglobinemia)
Definition: Oxygen deficiency turns a baby's skin blue.
Cause: Caused by nitrate-contaminated drinking water. Nitrites interfere with blood's oxygen transport.
Vulnerable Group: Most common in infants under six months.
Prevention: Requires nitrate-free drinking water.
Eutrophication and Nutrient Pollution
Nutrient Pollution
Occurs when excess nutrients, mainly Nitrogen and Phosphorus, are added to water bodies. Nitrogen-phosphorus is a pair of elements that is most important for the eutrophication process. (Asked in Exam)
Eutrophication Process
- Definition: When a water body gets enriched with nutrients, the process is called Eutrophication. (Asked in Exam)
- Impact: Eutrophication causes algae blooms, higher turbidity and odors, and makes it harder for aquatic life to thrive. (Asked in Exam)
- Human Impact: Cultural eutrophication is caused by increased nutrient input into the water body mainly due to human activities. (Asked in Exam) This accelerates the aging process of a water body.
Algae
Simple plant-like organisms. A Eutrophic lake is rich in nutrients and has high algal blooms. (Asked in Exam)
Real-life example: Green scum on a pond surface is likely an algal bloom.
Aquatic Weeds
- Aquatic weeds are fast growing weeds which can attain very high productivity when cultivated on nutrient rich wastewater such as domestic sewage. (Asked in Exam)
- Water hyacinth, salvinia, and duckweed are some examples of aquatic weeds. (Asked in Exam)
Trophic States of Water Bodies
The water body exhibits varying nutrient status at different levels, classified as eutrophic, mesotrophic, or oligotrophic. (Asked in Exam)
1. Oligotrophic Lakes
- When a water body is deficient in nutrients, it is known as Oligotrophic. (Asked in Exam)
- If a water body is healthy and supports no significant biological activity, then its condition is called Oligotrophic. (Asked in Exam)
- Characteristics: Low nutrients, high oxygen, clear water.
2. Mesotrophic Lakes
Moderate nutrients and balanced oxygen. A transition state.
3. Eutrophic Lakes
- Eutrophic water bodies are those that have high nutrient levels and high biological productivity. (Asked in Exam)
- Eutrophic lakes typically have high levels of nutrients, leading to high biomass production, especially algae and aquatic plants, which can make the water turbid and reduce clarity. (Asked in Exam)
4. Hypereutrophic Lakes
Excessive nutrients, frequent algal blooms, poor water quality.
5. Dystrophic Lakes
Acidic, high organic matter, dark-colored water (tea-like), low productivity.
Dissolved Oxygen (DO) and Oxygen Demand
Dissolved Oxygen (DO)
- A decrease in dissolved oxygen (DO) in water threatens aquatic life, mainly due to oxygen-demanding wastes. (Asked in Exam)
- Turbulent and rapidly flowing waters are typically well-oxygenated. (Asked in Exam)
- Low dissolved oxygen in water, caused by oxygen-demanding wastes, can harm aquatic life and lead to unpleasant taste and odor. (Asked in Exam)
Oxygen Demanding Wastes
- Oxygen demanding wastes decrease the oxygen level in water. (Asked in Exam)
- Oxygen-demanding wastes are substances that are oxidized in the receiving body of water. (Asked in Exam)
- Adding organic materials, such as sewage or paper pulp, to water stimulates activity and oxygen consumption by decomposers. (Asked in Exam)
Biochemical Oxygen Demand (BOD/CBOD/NBOD)
- CBOD: Carbonaceous Biological Oxygen Demand.
- NBOD: The full form of NBOD is Nitrogenous Biochemical Oxygen Demand. (Asked in Exam)
- Decomposition: As bacteria decompose oxygen-demanding wastes, they consume oxygen rather than release it. (Asked in Exam)
Waste Treatment: Aerobic vs. Anaerobic
Aerobic Digestion (Composting)
- Composting is aerobic degradation of organic materials under controlled conditions, yielding a marketable manure. (Asked in Exam)
- Both macro and micro-organisms play an important role in the composting process. (Asked in Exam)
- Aerobic digestion of sewage sludge requires lots of energy. (Asked in Exam)
- Aerobic digestion primarily produces carbon dioxide and water, not methane. (Asked in Exam)
- Note on Nutrients: While compost does contain important nutrients like nitrogen, phosphorus, and potassium, the concentrations of these nutrients in compost are generally lower than those found in commercial chemical fertilizers. (Asked in Exam)
Anaerobic Digestion
- Anaerobic digestion of sewage sludge is an efficient method for treating organic solids. This process produces methane as a byproduct. (Asked in Exam)
- Produces biogas (methane & CO₂) for energy.
Biological Contaminants and Pathogens
Bacteria, nutrients, and metals are the primary pollutants responsible for lowering the water quality in rivers and streams. (Asked in Exam)
Pathogens
Disease-causing organisms (viruses, bacteria, protozoa, helminths).
Viruses
Cause Hepatitis A, gastroenteritis.
Bacteria
E. coli causes diarrhea. Thrives in warm water.
Protozoa
Cause giardiasis & dysentery.
Helminths
Parasitic worms like schistosomes.
Diseases Caused by Polluted Water
Water-related diseases are classified based on how the water contributes to the transmission of the disease.
1. Water-borne Diseases (Ingested Polluted Water)
These diseases are caused by drinking water contaminated with human or animal excreta containing pathogens.
Cholera
- Caused by Vibrio cholerae. (Asked in Exam)
- Causes severe diarrhea & dehydration.
Typhoid Fever
- Caused by Bacteria (Salmonella typhi). (Asked in Exam)
2. Water-washed Diseases (Lack of Clean Water)
Trachoma
- Related to lack of water for personal hygiene. (Asked in Exam)
- Poor hygiene causes repeated eye infections which may lead to blindness.
3. Water-based Diseases (Contact with Polluted Water)
Schistosomiasis (Bilharzia)
- Results from contact with contaminated water. (Asked in Exam)
- Caused by parasitic worms (helminths), spread by Cercaria. (Asked in Exam)
4. Water-related Diseases (Insect Vectors)
Malaria
- Spread by mosquitoes that breed in water. (Asked in Exam)
- Caused by Plasmodium parasites.
Dengue
- Requires a mosquito vector for transmission. (Asked in Exam)
Chemical Contaminants in Water
Inorganic Chemicals: Salts
Salts are inorganic chemicals that can pollute water. (Asked in Exam)
Organic Chemicals: Pesticides
Pesticides are organic chemicals that can contaminate water. (Asked in Exam)
Radioactive Contaminants
Radioactive iodine can be a contaminant in water. (Asked in Exam)
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