Chemistry of Environmental Pollution

1. What do you mean bye DO, BOD and COD? Explain. (5/3) (2018, 2019, 2020, 2021)
Ans: Dissolved Oxygen (DO): DO is a fundamental requirement for the maintenance of life of all
living organisms in water. A water body is said to be polluted when the DO level falls below a
certain minimal concentration necessary for sustaining a normal biota for that water. Dissolved
oxygen is required maximum by fish, then by vertebrates and least by bacteria.
Biological Oxygen Demand (BOD): BOD is the measure of the polluting organic matter present
in a gain sample of water. BOD can be defined as the amount of O2 used up during oxidation of
oxygen demanding waste when a sample of water is incubated for 5 days at 20° C with DO
measured before and after.
Chemical Oxygen Demand (COD) is an index of the organic content of water (oxygen demanding
substances in water) and is an important water quality parameter. It is more scientific than the
traditional empirical concept of BOD. The chemical oxygen demand is a measure of the oxygen
equivalent to that portion of organic matter present in the waste water sample that is susceptible to
oxidation by K2Cr2O7. This is an important and quickly measured parameter for stream, sewage
and industrial waste samples to determine their pollution strength.
2. What is environmental chemistry? Discuss the elements of environment. (5) (2018)
Ans: Environmental chemistry is the branch of chemistry that deals with the study of the
chemical processes occurring in the environment. It involves understanding how chemical
substances move through air, water, and soil, as well as how they affect ecosystems, human health
and the climate. Environmental chemistry also focuses on the study of pollutants, their sources,
their transformations in the environment and their potential impacts on living organisms.
i. Atmosphere (Air):
• The atmosphere is the layer of gases surrounding the Earth. It contains gases like nitrogen
(78%), oxygen (21%), carbon dioxide, water vapor and trace gases.
• Environmental chemistry focuses on air pollution (like greenhouse gases, ozone depletion,
smog) and how chemical reactions occur in the atmosphere.
ii. Hydrosphere (Water):
• This includes all forms of water on Earth, such as oceans, rivers, lakes, groundwater and
glaciers.
• Environmental chemists study water quality, pollutants (like industrial waste, oil spills,
heavy metals) and how chemicals dissolve, disperse and interact in aquatic systems.
iii. Lithosphere (Soil and Earth’s crust):
• The lithosphere is the Earth's solid outer shell, including the crust and upper mantle, which
contains rocks, soil and minerals.
• Soil chemistry involves studying the interaction of chemicals with minerals, organic matter
and microorganisms. It also examines soil contamination and its impact on food chains and
ecosystems.
iv. Biosphere (Living organisms):
• This refers to the global sum of all ecosystems, where living organisms interact with each
other and their physical environment.
• Environmental chemistry examines how chemicals (natural or man-made) affect plants,
animals and human health, including bioaccumulation and biomagnification in food chains.
3. Discuss different types of pollutant. (5) (2018)
Ans: Here’s a brief overview of different types of pollutants:
i. Based on origin:
• Primary pollutants: Released directly from a source (e.g., carbon monoxide, sulfur
dioxide).
• Secondary pollutants: Formed by chemical reactions in the environment (e.g., ozone, acid
rain).
ii. Based on state:
• Gaseous pollutants: Includes harmful gases like carbon dioxide, methane and sulfur
dioxide.
• Particulate matter (PM): Solid or liquid particles suspended in air (e.g., PM2.5, PM10).
• Aerosols: Fine particles or liquid droplets in the air.
iii. Based on nature:
• Organic pollutants: Carbon-based pollutants like pesticides, VOCs (volatile organic
compounds).
• Inorganic pollutants: Non-carbon-based substances like heavy metals (lead, mercury) and
acids.
iv. Based on medium:
• Air pollutants: Affect the atmosphere (e.g., carbon monoxide, ozone).
• Water pollutants: Contaminate water bodies (e.g., pathogens, heavy metals).
• Soil pollutants: Contaminate the land (e.g., pesticides, industrial waste).
v. Based on degradability:
• Biodegradable pollutants: Break down naturally (e.g., sewage, food waste).
• Non-biodegradable pollutants: Persist in the environment (e.g., plastics, heavy metals).
vi. Based on toxicity:
• Toxic pollutants: Harmful at low concentrations (e.g., lead, mercury).
• Non-toxic pollutants: Harmful mainly in large quantities (e.g., carbon dioxide, silt).
vii. Based on impact:
• Greenhouse gases: Contribute to global warming (e.g., carbon dioxide, methane).
• Ozone depleting substances: Break down the ozone layer (e.g., CFCs).
Each type has unique sources and impacts, requiring specific approaches to manage and mitigate
environmental harm.
4. Describe the characteristics of industrial wastes. (2.5) (2018)
Ans: Industrial wastes have the following key characteristics:
i. Physical characteristics:
• Can be solid, liquid or gaseous.
• Vary in volume, particle size and density.
ii. Chemical characteristics:
• May be toxic, corrosive, reactive or flammable.
• Can include heavy metals, acids and synthetic chemicals.
• Some are biodegradable, while others persist in the environment.
iii. Biological characteristics:
• May contain pathogens or harmful chemicals that bioaccumulate.
• Some wastes are biodegradable, while others are not.
 iv. Environmental impact:
• High potential for air, water and soil pollution.
• Can lead to eutrophication, long-term contamination and ecosystem harm.
v. Hazardousness:
• Some wastes are carcinogenic, mutagenic or teratogenic.
• Pose health risks like respiratory issues, cancer or skin diseases.
vi. Economic value:
• Certain wastes are recyclable or can be converted to energy.
vii. Source-specific:
• Vary based on the industry, such as mining, chemical production or manufacturing.
Effective management is essential to minimize environmental damage and health risks.
5. Describe the adverse effects of industrial pollutants in environment. (4/2.5) (2019, 2020)
Ans: Industrial pollutants have several adverse effects on the environment:
i. Air pollution: Emissions like sulfur dioxide, nitrogen oxides and particulate matter contribute
to smog, acid rain and respiratory problems in humans.
ii. Water pollution: Industrial waste discharged into water bodies contaminates rivers, lakes and
oceans, affecting aquatic ecosystems and making water unsafe for consumption.
iii. Soil contamination: Hazardous chemicals, heavy metals and toxic substances from industrial
activities degrade soil quality, harming plant growth and entering the food chain.
iv. Biodiversity loss: Pollution leads to habitat destruction, harming wildlife and reducing
biodiversity. Toxic substances can bioaccumulate, affecting entire ecosystems.
v. Global warming: Greenhouse gas emissions like carbon dioxide and methane from industries
contribute to climate change, causing extreme weather events and rising sea levels.
vi. Ozone depletion: Emissions of substances like chlorofluorocarbons (CFCs) deplete the ozone
layer, increasing harmful UV radiation exposure.
Industrial pollution significantly impacts air, water, soil and biodiversity, with long-term
environmental consequences.
6. Which parameters are examined to determine the purity of water? (2) (2019)
Ans: Determining the purity of water involves examining several parameters that assess its
physical, chemical and biological quality. Here are the key parameters typically analyzed:
i. Physical Parameters,
ii. Chemical Parameters,
iii. Biological Parameters,
iv. Microbiological Parameters.
These parameters collectively provide a comprehensive understanding of water quality and purity.
Regular monitoring and analysis are essential for ensuring safe drinking water and protecting
aquatic ecosystems.
7. What are the techniques used to purify industrial wastewater? (3) (2019)
Ans: Purifying industrial wastewater involves several techniques tailored to remove contaminants
effectively.
i. Physical treatment methods: It includes screening, which removes large solids and
sedimentation, where gravity causes suspended solids to settle. Filtration further purifies water
by passing it through various filter media, while floatation uses air bubbles to lift solids to the
surface for removal.
 ii. Chemical treatment methods: It involves coagulation and flocculation, where chemicals
agglomerate particles into larger flocs for easier removal. Neutralization adjusts the pH of
acidic or alkaline wastewater and oxidation employs oxidizing agents to break down organic
compounds. Precipitation forms solid particles from dissolved substances through chemical
reactions.
iii. Biological treatment methods: It utilizes microorganisms to degrade organic matter. The
activated sludge process aerates wastewater to promote microbial growth, while bioreactors
enhance microbial action. Constructed wetlands mimic natural processes, using plants and soil
for filtration.
iv. Advanced treatment methods: It includes membrane filtration, such as reverse osmosis,
which separates contaminants at a molecular level. Electrochemical treatment applies electrical
currents for contaminant removal and advanced oxidation processes (AOPs) use oxidants and
UV light to decompose persistent pollutants.
A combination of these techniques is often employed to achieve effective purification and meet
environmental standards.
8. What is water pollution? How are water pollutant classified? (3) (2021)
Ans: Water pollution occurs when harmful substances contaminate water bodies such as rivers,
lakes, oceans and groundwater. These pollutants degrade water quality, making it unsafe for
drinking, aquatic life and other uses. Pollution can originate from various sources, including
industrial waste, agricultural runoff, sewage discharge and plastic debris.
Water pollutants can be classified into several categories based on their sources, nature and impact
on the environment:
i. Organic pollutants: Pesticides, herbicides, detergents, oil and plastics.
ii. Inorganic pollutants: Heavy metals (lead, mercury, arsenic), salts and acids.
iii. Nutrient pollutants (Eutrophication): Nitrogen, phosphorus.
iv. Microbiological pollutants: Bacteria, viruses, protozoa and parasites.
v. Thermal pollution: Hot water discharged from cooling processes.
vi. Sediment pollution: Soil particles, sand, silt.
vii. Radioactive pollutants: Uranium, radon, thorium.
viii. Plastic and microplastic pollution: Large plastic debris, microplastics (tiny particles).
ix. Chemical pollutants: Toxic chemicals, pharmaceuticals, synthetic chemicals (e.g.,
polychlorinated biphenyls or PCBs).
9. Discuss the important characteristics of waste water. (4) (2021)
Ans: Here is a brief summary of the important characteristics of wastewater:
i. Physical characteristics:
• Color: Fresh wastewater is typically gray or light brown but darkens with decomposition.
• Odor: It starts with a musty smell and can become foul due to anaerobic decomposition.
• Temperature: Generally higher than natural water due to industrial/domestic discharges.
• Turbidity: Cloudiness caused by suspended solids.
• Solids: Includes total, suspended, dissolved, volatile and fixed solids.
ii. Chemical characteristics:
• pH: Measures acidity or alkalinity, typically between 6.5 and 8.5 for domestic wastewater.
• Biochemical Oxygen Demand (BOD): Oxygen needed by microbes to break down organic
matter, indicating organic pollution.
• Chemical Oxygen Demand (COD): Total oxygen needed to oxidize all organic/inorganic
matter.
• Dissolved Oxygen (DO): Essential for aquatic life; low levels indicate poor water quality.
 • Nutrients: Nitrogen and phosphorus contribute to nutrient pollution and eutrophication.
• Toxic substances: Includes heavy metals, chemicals and pesticides.
• Oil and grease: Interfere with water treatment and harm aquatic ecosystems.
iii. Biological characteristics:
• Microorganisms: Include bacteria, viruses, fungi and algae.
• Pathogens: Disease-causing organisms like bacteria and viruses.
• Coliform bacteria: Indicators of fecal contamination.
• Biomass: Organic matter that supports microbial activity during treatment.
These characteristics are essential for determining wastewater treatment requirements and its
impact on the environment.
10. Define pollutant and contaminant. List the harmful impact of As and Pb in human body.
(2+2) (2022)
Ans: Pollutant: A pollutant is a substance that when introduced into the environment, causes
harmful effects or poses risks to human health, ecosystems or the climate. Pollutants can be natural
or synthetic and can exist in various forms, including gases (like carbon monoxide), liquids (like
industrial wastewater) or solids (like heavy metals). They can originate from various sources, such
as industrial activities, agricultural practices, urban runoff and vehicle emissions. Pollutants are
typically regulated due to their potential to degrade air, water and soil quality.
Contaminant: A contaminant is any substance that alters the natural composition or quality of a
medium (such as air, water or soil) in a way that may cause adverse effects. Contaminants can
include pollutants but the term is broader and encompasses any unwanted or harmful substance,
regardless of its origin or concentration. For example, a natural substance like arsenic can be a
contaminant if it is present in excessive amounts in drinking water. Contaminants may not always
be toxic but can still indicate a deviation from the desired quality of a medium.
Arsenic (As) and lead (Pb) are toxic elements that can have serious harmful impacts on human
health. Below is a list of their harmful effects:
Harmful impacts of Arsenic (As):
i. Carcinogenic effects: Long-term exposure is linked to various cancers, including skin, bladder
and lung cancer.
ii. Skin lesions: Chronic arsenic exposure can cause skin changes, including hyperpigmentation
and keratosis.
iii. Neurological effects: Arsenic can lead to peripheral neuropathy, resulting in numbness,
tingling and weakness.
iv. Cardiovascular problems: Exposure is associated with an increased risk of cardiovascular
diseases, including hypertension and atherosclerosis.
v. Respiratory issues: Inhalation of arsenic can cause respiratory problems and lung damage.
vi. Diabetes risk: Some studies suggest a link between arsenic exposure and an increased risk of
developing type 2 diabetes.
vii. Reproductive effects: Arsenic exposure may affect reproductive health, leading to adverse
pregnancy outcomes and developmental issues in children.
Harmful impacts of Lead (Pb):
i. Neurological damage: Lead exposure is particularly harmful to the nervous system, causing
cognitive deficits, behavioral issues and developmental delays in children.
ii. Hematological effects: Lead can interfere with hemoglobin synthesis, leading to anemia.
iii. Kidney damage: Chronic lead exposure can cause kidney dysfunction and damage.
iv. Cardiovascular problems: Lead exposure is linked to hypertension and other cardiovascular
diseases.
 v. Reproductive issues: Lead can affect fertility and cause adverse effects on fetal development
during pregnancy.
vi. Immune system effects: Lead exposure may compromise the immune system, increasing
vulnerability to infections.
vii. Gastrointestinal symptoms: Lead poisoning can cause abdominal pain, constipation and
nausea.
Both arsenic and lead pose significant health risks, particularly with prolonged exposure. The
impacts can vary based on the level and duration of exposure, age and overall health of the
individual. Reducing exposure to these toxic elements is crucial for safeguarding health.
11. Interpret quality parameters of industrial waste water and standards for drinking water. (3)
(2022)
Ans: Here's a concise interpretation of the quality parameters for industrial wastewater and the
standards for drinking water:
i. Industrial wastewater quality parameters:
a. pH:
• Standard: 6.0 to 9.0.
• Importance: Indicates acidity or alkalinity.
b. Biochemical Oxygen Demand (BOD):
• Standard: < 30 mg/L.
• Importance: Measures organic matter decomposition demand.
c. Chemical Oxygen Demand (COD):
• Standard: < 250 mg/L.
• Importance: Indicates total oxygen needed for oxidation.
d. Total Suspended Solids (TSS):
• Standard: < 100 mg/L.
• Importance: Measures concentration of suspended particles.
e. Nutrients (Nitrates and Phosphates):
• Standard: Nitrates < 10 mg/L, Phosphates < 1 mg/L.
• Importance: Excess can cause eutrophication.
f. Heavy metals (e.g., Lead, Mercury):
• Standard: Varies; Lead < 0.05 mg/L.
• Importance: Toxic effects on health and the environment.
ii. Drinking water standards:
a. Microbiological contaminants:
• Standard: E. coli and total coliforms should be absent in any 100 mL sample.
b. pH:
• Standard: 6.5 to 8.5.
c. Lead:
• Standard: < 0.01 mg/L.
d. Nitrates (as NO3):
• Standard: < 10 mg/L.
e. Turbidity:
• Standard: < 1 NTU.
f. Total Dissolved Solids (TDS):
• Standard: < 500 mg/L.
These parameters are crucial for ensuring water safety, public health, and environmental protection.
12. What is threshold odor number (TON)? The threshold order number for a water sample of
40 ml, diluted to standard 200 ml mixture, in which odor is just barely detectable to the sense
of smell? (1+2) (2022)
Ans: Threshold odor number (TON) is defined as the number of parts of the sample that must
be diluted with a specified odor free water to render the odor just detectable to the sense of smell.
Given that, Volume of water sample, V = 40 ml
Threshold odor number represents the dilution ratio at which the odor is hardly detectable.
Therefore, Dilution factor, D = 200/40 = 5
To find TON, we need to determine the number of parts of odor free water that must be added to
the water sample to make the odor just detectable. Since the dilution factor is 5, we need to add 4
parts of odor free water to 1 part of the water sample to obtain the standard 200 ml mixture.
Therefore, the TON for the water sample is 5.
13. Define BOD, COD and DO with appropriate significance. What are the advantages of COD
determination over BOD determination? (3+2) (2022)
Ans: Biochemical Oxygen Demand (BOD) measures the amount of oxygen required by
microorganisms to decompose organic matter in water over a specified period (usually 5 days at
20°C). It serves as a crucial indicator of organic pollution, with higher BOD levels indicating
greater organic matter concentration, which can lead to oxygen depletion in aquatic environments.
BOD is essential for evaluating wastewater treatment efficiency and monitoring environmental
health.
Chemical Oxygen Demand (COD) quantifies the total oxygen required to chemically oxidize
both organic and inorganic substances in water using strong oxidizing agents. COD provides a
comprehensive assessment of water pollution, capturing both biodegradable and non-
biodegradable matter. It is instrumental in evaluating the effectiveness of wastewater treatment
processes and ensuring regulatory compliance, making it vital for environmental management.
Dissolved Oxygen (DO) represents the amount of oxygen dissolved in water, essential for the
survival of aquatic organisms. Adequate DO levels (typically above 5 mg/L) are critical for
maintaining healthy ecosystems. Low DO levels often indicate pollution or eutrophication, where
excessive nutrients lead to algal blooms. Monitoring DO is crucial in wastewater treatment
systems, particularly in aerobic processes, ensuring optimal conditions for microbial activity and
overall water quality.
Chemical Oxygen Demand (COD) determination offers several advantages over Biochemical
Oxygen Demand (BOD) determination. Firstly, COD tests provide faster results, typically within
2 to 3 hours, while BOD requires a 5-day incubation period. Secondly, COD measures both
biodegradable and non-biodegradable organic matter, giving a more comprehensive assessment of
total organic pollution. Additionally, COD is less variable and more stable, providing consistent
results. It can be applied to various water types, including industrial effluents, where microbial
activity may be unpredictable. These factors make COD a preferred method for rapid and accurate
water quality assessment.