Introduction

Pollution is the introduction of harmful materials into the environment.

These harmful materials are called pollutants. Pollutants can be natural, such

as volcanic ash. They can also be created by human activity, such as trash or

runoff produced by factories. Pollutants damage the quality of air, water, and

land.

Figure 1. Pollution Environments

Source: https://track2training.com/2021/11/09/environmental-pollution-2/

Pollution is a global problem. It poses a serious threat to the balance

and sustainability of our world. It not only disturbs natural cycles and

habitats, but it also leads to climate change, biodiversity loss, and a variety of

health problems. This paper focuses on the following type of pollution

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environments: solid environment; noise pollution; and toxic and hazardous

waste treatment.

Solid environment pollution is a pressing environmental concern that

arises from the introduction of particulate matter and solid pollutants into our

surroundings, posing significant threats to ecosystems, human health, and

overall environmental quality. Solid pollutants take physical form,

manifesting as particulate matter that can range from fine dust to larger

debris. This form of pollution affects air, water, and soil, with diverse sources

contributing to its proliferation.

Noise pollution refers to the presence of excessive, disruptive, or unwanted

sound in the environment that can have detrimental effects on human health,

wildlife, and the overall well-being of ecosystems. Sound becomes pollution

when it interferes with normal activities such as sleeping, conversation, or

disrupts the natural soundscape. Common sources of noise pollution include

traffic, industrial activities, construction sites, airports, loud music, and

various mechanical equipment.

Toxic and hazardous waste treatment refers to the processes and methods

used to manage and mitigate the environmental and health risks associated

with waste materials that pose threats to human health, ecosystems, and the

environment due to their toxic or hazardous nature. Proper treatment is

2
essential to prevent the release of these harmful substances into the air, water,

or soil.

Discussion

1. Solid Environment

Solid Waste is often named garbage or trash. It is described as discarded

material or garbage that is produced as a result of human or animal activities.

Figure 2. Solid Waste

Source: https://evreka.co/blog/solid-waste-let-the-garbage-do-the-job/

Solid waste production is one of the detrimental results of

industrialization. The rate of waste being produced by human beings is

growing all over the world. In 2016, it was revealed that cities around the

world produced 2.01 billion tons of solid waste which equated to 0.74

3
kilograms per person per day. Therefore, solid waste has been a problem for

as long as people have lived in villages and residential areas.

Type of Solid Waste

There are two main categories of waste, the biodegradable and

nonbiodegradable waste.

Biodegradable substances are commonly found in everyday life, such

as food waste, tree leaves, and grass clippings. Plant materials are typically

biodegradable.

Biodegradable wastes are waste materials that decompose and degrade

by either or both abiotic factors like air, water, sunlight, temperature, UV

radiation, and biotic species like animals and microorganisms, fungi.

Figure 3. Biodegradable Waste

Source: https://www.geeksforgeeks.org/biodegradable-and-non-
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 biodegradable/

Non-biodegradable substances are those that cannot be broken down easily

by biotic or abiotic means and needs stronger chemical treatment to dispose

of. Hence, they are present for many long years causing varieties of pollution.

Plastic, for example, is synthesized with specific qualities of strength,

and life suited to the purpose of use. As intended they have a long life to be

destroyed and pose a serious threat to the biotic species apart from the

nauseating sight. They pollute the air, water, and soil which are essential for

humans and other animals living.

Figure 4. Non-Biodegradable Waste

Source: https://www.geeksforgeeks.org/biodegradable-and-non-

biodegradable/
Non-biodegradable wastes waste that cannot be degraded waste that

cannot be degraded by living organisms, posing a serious threat to the

5
environment and surroundings. They are a serious threat to the atmosphere

also. Refrigerant glasses for example are highly atmospheric pollution to the

extent of destroying the protecting ozone layer of our earth from UV light.

Sources of Solid Waste

Solid wastes are generated from various sources and include items that

are discarded by households, businesses, institutions, and industries. The

sources of solid waste can be broadly categorized into residential,

commercial, industrial, and institutional sources. Here is an overview of each:

1. Residential Sources

Household Waste: This includes everyday items discarded by individuals

and families. Common household waste includes food scraps, packaging

materials, old clothing, furniture, appliances, and other items that are no

longer needed.

2. Commercial Sources

Retail Businesses: Waste generated by stores, shops, and commercial

establishments, including packaging materials, expired products, and

unsold merchandise.

Restaurants and Food Services: Food waste, packaging, and disposable

items from restaurants and food establishments contribute to solid waste.

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 Office Buildings: Waste generated in offices, such as paper, cardboard,

electronic waste (e-waste), and other office supplies.

3. Industrial Sources

Manufacturing Facilities: Industries generate a significant amount of solid

waste, including production residues, packaging materials, and byproducts

from manufacturing processes.

Construction and Demolition: Building and construction activities

produce debris, concrete, wood, and other materials that contribute to

solid waste.

4. Institutional Sources

Schools and Educational Institutions: Educational facilities generate solid

waste, including paper, textbooks, and other materials used in classrooms.

Hospitals and Healthcare Facilities: Medical waste from healthcare

institutions is a specialized category of solid waste that requires careful

handling and disposal.

Government Offices: Municipal and government offices produce solid

waste from administrative activities.

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Common Effects of Solid Waste

Any type of solid waste if left untreated can lead to disastrous effects

on the environment. The following shows the effects of solid waste on the

environment, humans and animals.

Effects on the Environment: Huge piles of waste at open dumping sites

can cause environmental pollution. Methane is produced from the waste pile

that is a greenhouse gas. The emission of greenhouse gasses leads to global

warming and ultimately climate change.

Effects on Humans: Accumulated solid waste often results in disease

outbreaks. Solid waste is a source of vector-borne diseases as many vectors

such as mosquitoes and vermin find solid waste dumps as a breeding ground.

Humans living near open dumping sites suffer skin diseases, respiratory

problems, etc. Depending upon the type of waste, humans can also get cancer

and other serious illnesses.

Effects on Animals: Solid waste such as plastic causes suffocation

among animals and hence is responsible for biodiversity loss. Solid waste

dumping also leads to animals dying or relocating because the land is

rendered unfit for their survival.

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Solid Waste Management

The term solid waste management mainly refers to the complete

process of collecting, treating and disposing of solid wastes.

In the waste management process, the wastes are collected from

different sources and are disposed of. This process includes collection,

transportation, treatment, analysis and disposal of waste. It needs to be

monitored so that strict regulations and guidelines are followed.

Figure 5: Solid Waste Management

Source: https://byjus.com/biology/solid-waste-management/

Many people may not be aware of this but there are many benefits to

solid waste management to our health and for our environment. One of the

many benefits of proper solid waste management is that it improves the

overall air and water quality in the country, which essentially keeps us

9
healthy due to the presence of less harmful particles in the air we breathe and

the water we drink.

Proper solid waste management also protects citizens from biohazards

and physical harm, nurtures community health, promotes sanitation, and

provides opportunities to earn from recycling. The following are the most

common waste management methods:

3Rs. It is a “reduce, reuse, and recycle” method. Reduce means using

products that produce less waste, reuse means using products again and

recycle means using the discarded products as a resource. Waste generated in

high quantities can be minimized by using the 3Rs method.

Landfill. Landfill is a land area, which is specially designed for the

disposal of solid waste. Sanitary landfills allow proper disposal of waste.

Composting. This method consists of the decomposition of

biodegradable waste.

Incineration. In this method, waste is reduced in size by burning at

high temperatures. The residues are then subjected to landfill sites.

Waste to Energy. WtoE a method by which energy is produced as a

result of incineration.

Pyrolysis. Pyrolysis involves the thermal breakdown of organic waste

for industrial purposes.

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 2. Noise Pollution

The term "noise pollution" refers to unwanted or disturbing sound that

has an adverse effect on the health and well-being of humans and other

organisms (National Geographic, 2023). Machinery, amplified music, noisy

vehicles, and other things can cause noise pollution.

Figure 6. Noise Pollution

Source: https://cpd.org.bd/noise-pollution-killer-disguise/

Key components of noise pollution include:

1. Intensity (Loudness): The volume or loudness of a sound is measured in

decibels (dB). Prolonged exposure to high-intensity noise, especially at

levels exceeding 85 dB, can lead to hearing damage or loss.

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2. Duration: The length of time a person or community is exposed to noise is

crucial. Chronic exposure to noise over extended periods can have

cumulative and more severe health impacts.

3. Frequency: Different frequencies of sound can have varying effects on

human health. Low-frequency noise, such as that generated by heavy

machinery, may have different physiological impacts compared to

highfrequency noise, such as loud music.

Causes of Noise Pollution

Cities today have become the epicenters of noise pollution. Drivers

honking horns, road workers drilling roads, aircrafts flying overhead, all of

these are sources of noise pollution.

Figure 7: Sources of Noise Pollution

Source: https://sigmaearth.com/sources-of-noise-pollution/

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 Although it is invisible, noise can cause severe damage to humans.

Noise pollution also causes significant damage to wildlife. It affects the

breeding cycles of wild species. Some experts say that noise pollution is

causing accelerated extinction rates of some species.

There are many sources of noise pollution. However, the main sources

of noise pollution are:

1. Road traffic: The honking of a bus produces noise at 100 dB, and a car

produces 90 dB. A motorbike generates a noise level of 95 dB.

2. Air traffic: One single aircraft produces noise between 100-200 dB.

Imagine the noise from tens of airplanes flying over cities every day.

3. Construction sites: The drills used in the construction or maintenance

of roads and pavements generate noise of 110 dB.

4. Nightlife and events: Open or rooftop bars and restaurants produce

more than 100 dB of noise. Apart from bars, events such as weddings and

dances also produce noise at a similar level. Rock concerts create noise at

around 120 dB.

5. Animals such as cats and dogs: When barking or howling, dogs

generate a noise level between 60 to 80 dB.

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Measurements of Noise

The standard used for measuring noise is the decibel (dB). Decibels

indicate how much air vibrations make up a sound. The lowest sound that

humans can hear on a decibel scale is 0 dB. The level at which sound

becomes painful to hear is 80 dB.

A Sound Level Meter (SLM) is the most commonly used instrument to

measure noise. The basic structure of an SLM consists of a display screen,

electronic circuits, and a microphone. The microphone detects the vibrations

in the air produced from a sound. The circuits convert the detection of air

pressure into electrical signals. These signals then travel to the display screen,

where the expression of noise level is in decibels.

Figure 8: Sound Level Meter (SLM)

Source: https://en.wikipedia.org/wiki/Sound_level_meter

14
Characteristics of Noise

There are two characteristics of sound or noise essential to determine

and evaluate the noise level. They are: Frequency and Amplitude.

The frequency of sound is the number of cycles in a sound wave generated

per second. It is expressed with the unit Hertz (Hz). Noise that is below 250

Hz is called low-frequency noise. Noise that is higher than 2000 Hz is called

high-frequency noise. Noise falling between 250-2000 Hz is called

midfrequency noise.

The amplitude of the sound is the measurement of the height of a sound

wave from a median position. Unit of Amplitude is decibels (dB). The

decibel scale is logarithmic. Small increments in decibel levels on a

logarithmic scale correspond to huge increments in sound energy.

Figure 9: Characteristics of Noise

Source: https://sigmaearth.com/sources-of-noise-pollution/

15
Effects of Noise Pollution

Constant exposure to loud noise can damage human health in several

ways. Noise pollution impacts millions of people every day, and some do not

even realize it. Children and the elderly are the populations most affected by

noise pollution. A study on children living near busy streets and airports

found that they suffer from stress. Apart from stress, they also suffer from

memory impairments, poor reading skills, and decreased attention levels.

Excess levels of noise even affect animals. Studies have found that a

caterpillar’s dorsal vessels (their heart) beat faster when exposed to loud

noises. Noise pollution even causes hatchling failure in birds. Animals such

as bats use their sound to navigate, attract mates, escape predators, and find

food. Noise pollution interferes with their ability to perform these tasks,

decreasing their chance of survival.

Apart from land animals, noise pollution even affects animals in the

ocean. Dolphins and whales depend on the reflection of sounds to find food,

navigate, and find mates. Noise pollution caused by ships, oil rigs, sonar

submarines, and underwater seismic studies does not allow them to perform

their basic tasks effectively. Noise pollution in the ocean also damages the

ears of marine animals, causing grave injuries. Whales get stranded on

beaches and die due to noise interference with their ability to echolocate.

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Auditory Effects

Noise-induced hearing loss is the single most common effect of noise

pollution on humans. Single exposure to high-intensity sound or long-term

exposure to sound levels higher than 85 dB can induce hearing loss. Exposure

to such sounds damages the cochlea, a part of the inner ear responsible for

hearing. Large sounds damage the hair cells in the cochlea. These cells

cannot regenerate. Therefore, we can preserve our hearing ability only by

preventing exposure to noise.

Non-Auditory Effects

Apart from hearing, noise pollution can damage human health in

several ways. Some of the main non-auditory effects of noise pollution are:

1. Psychological effects. Noise can cause anxiety, depression, fatigue,

and stress in humans and animals.

2. Sleep disorders. It is almost impossible to sleep when the surrounding

noise exceeds 45 dB. Loud noise can have latent effects on our behavior,

causing aggressive behavior and irritability.

3. Memory. A high level of noise is harmful to memory. It reduces our

ability to focus and makes it difficult to study in the case of children.

4. Physical effects. Noise pollution causes respiratory agitation, racing

pulse, high blood pressure, and headaches. When exposed to loud sources of

17
noise pollution for an extended period of time, it can cause gastritis, colitis,

and even heart attacks.

Solution to Reduce Noise Pollution

Awareness of noise pollution is essential to beat this invisible enemy.

For example: avoid very noisy leisure activities, opt for alternative means of

transport such as bicycles or electric vehicles over taking the car, do your

housework at recommended times, insulate homes with noise-absorbing

materials, etc. Educating the younger generation is also an essential aspect of

environmental education.

Governments can also take measures to ensure correct noise

management and reduce noise pollution. For example: protecting certain

areas from noise, establishing regulations that include preventive and

corrective measures — mandatory separation between residential zones and

sources of noise like airports, fines for exceeding noise limits, etc. —,

installing noise insulation in new buildings, creating pedestrian areas where

traffic is only allowed to enter to offload goods at certain times, replacing

traditional asphalt with more efficient options that can reduce traffic noise by

up to 3 dB, among others.

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 3. Toxic and Hazardous Waste Treatment

Toxic and hazardous waste are materials that pose significant risks to

human health, the environment, and other living organisms due to their

chemical, physical, or biological properties. These wastes are produced by a

variety of industrial, commercial, and domestic activities and contain

substances that, if not handled and disposed of properly, can cause harm.

Toxic or hazardous waste is typically classified based on the potential harm it

poses, and such waste is subject to stringent regulations and guidelines to

ensure safe management.

Figure 10: Toxic and Hazardous Waste

Source: https://www.junkgator.com/blog/how-to-dispose-of-toxic-waste-

safely/

Hazardous-waste characteristics

Hazardous wastes are classified on the basis of their biological,

chemical, and physical properties. Hazardous waste is generally at least one

of these:
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 Ignitability. Ignitability is the property used to classify wastes as

hazardous if they could catch fire during transport, storage, or disposal.

Ignitable wastes burn at relatively low temperatures, posing an immediate fire

risk. Examples of ignitable wastes include waste oils and used solvents.

Wastes is considered ignitable when they exhibit any of the following

characteristics: Liquid, other than an aqueous solution containing less than

24% alcohol by volume, with a flashpoint less than 140°F (60°C) as

determined by flashpoint testing.

Corrosivity. Corrosive substances have the ability to eat through containers

which can cause leakage of harmful materials. Corrosive wastes include

strong acidic or alkaline substances. They destroy solid material and living

tissue upon contact, by chemical reaction.

A corrosive liquid has a pH of less than or equal to 2 or greater than or

equal to 12.5, or has the ability to corrode steel. Some examples of corrosive

materials include hydrochloric acid and nitric acid.

Reactivity. Reactive wastes are wastes that readily explode or undergo

violent reactions. A waste is considered reactive if it: explodes or reacts

violently when exposed to water or under normal handling conditions. creates

toxic fumes or gases when exposed to water or under common handling

conditions.

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 Toxicity. Toxic wastes are poisons, even in very small or trace

amounts. They may have acute effects, causing death or violent illness, or

they may have chronic effects, slowly causing irreparable harm. Some are

carcinogenic, causing cancer after many years of exposure. Others are

mutagenic, causing major biological changes in the offspring of exposed

humans and wildlife.

Figure 11. Household Hazardous Waste

Source: https://www.falmouthma.gov/695/Household-Hazardous-Waste-

Collection

It has been observed that as population grows, as cities get more

industrialized and developed, etc., so does garbage production. The

management of toxic and hazardous waste is crucial for both the environment

and public health.

21
 To reduce the dangers brought on by these pollutants, sophisticated

treatment, containment, and disposal techniques are frequently used. Here

are some common methods for treating toxic and hazardous waste:

Chemical Treatment

Waste is subjected to chemical treatment in order to lessen its hazard

by employing particular chemicals such as acids, bases, oxidizers, reducers,

etc. Examples of this are stated below.

1. Chemical Neutralization. Some hazardous wastes can be neutralized

using chemical reactions to transform them into less harmful substances.

Acids can be neutralized with bases, and vice versa.

2. Chemical Oxidation. Chemical oxidation methods involve the use of

strong oxidizing agents to break down and detoxify hazardous chemicals in

the waste.

3. Ion Exchange. Ion exchange resins are used to remove specific ions or

heavy metals from liquid hazardous waste streams.

Another example of this are Absorption, Chemical precipitation,

Chemical reduction, Wet oxidation, Dehalogenation, and Chemical fixation

and solidification.

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Physical Treatment

Physical treatment describes the physical techniques used to separate

hazardous waste from non-hazardous stuff.

1. Solidification: This is accomplished by encapsulating the trash in

plastic, asphalt, or concrete. A solid mass of material that is resistant to

leaching is created through encapsulation. In order to create a solid, cement-

like product, waste can also be combined with lime, fly ash, and water.

2. Physical Separation: Techniques like filtration, sedimentation, and

centrifugation are used to separate solid particles from liquid waste.

Thermal Treatment

The process of thermal treatment involves heating the trash to disinfect

it. Thermal treatment's main goal is to turn trash into a stable and usable final

product and lessen the amount that needs to be disposed of in landfills.

1. Incineration: Incineration is a thermal treatment process that involves

burning hazardous waste at high temperatures. This method is effective for

destroying organic compounds, pathogens, and some hazardous chemicals.

However, it may not be suitable for all types of waste and can produce air

emissions that need to be controlled and treated.

23
2. Thermal Desorption: This method involves heating contaminated soil

or solid waste to vaporize and separate volatile contaminants from less

volatile materials. The contaminants can then be collected and treated

separately.

3. Incineration with Energy Recovery: Some hazardous waste

incineration facilities use the heat generated during the process to produce

steam and generate electricity, making it a more sustainable treatment option.

Biological Treatment

Biological treatment involves the use of microorganisms to break down

organic hazardous waste. This can include methods such as bioremediation

and composting. Microorganisms can metabolize or degrade certain toxic

chemicals, reducing their toxicity.

1. Anaerobic Systems: Anaerobic treatment differs from conventional

aerobic treatment in that no aeration is applied. The absence of oxygen leads

to controlled anaerobic conversions of organic pollutants to carbon dioxide

and methane.

2. Composting: Composting is a biological treatment method used for

organic waste materials which uses microorganisms to decompose organic

24
matter into stable, nutrient-rich compost. This process can reduce the volume

of organic waste and produce a useful product.

Conclusion

Environmental pollution is not a new phenomenon, yet it remains the

world’s greatest problem facing humanity, and the leading environmental

causes of morbidity and mortality. Man’s activities through urbanization,

industrialization, mining, and exploration are at the forefront of global

environmental pollution.

Around the world, people and governments are making efforts to

combat pollution. Reducing pollution requires environmental, political, and

economic leadership. Developed nations must work to reduce and recycle

their materials, while developing nations must work to strengthen their

economies without destroying the environment. Developed and developing

countries must work together toward the common goal of protecting the

environment for future use.

Both developed and developing nations share the burden of pollution

together, though awareness and stricter laws in developed countries have

contributed to a larger extent in protecting their environment. Despite the

global attention towards pollution, the impact is still being felt due to its

severe long-term consequences.

25
Post Test

Test 1. Identification.

1. _________ is the introduction of harmful materials into the

environment that poses a threat to the balance and sustainability of our

world.

2. _________ is described as discarded material or garbage that is

produced as a result of human or animal activities.

3. _________ is a process of actions and activities that are employed to

manage waste that is being produced from various sources.

4. _________ is defined as an unwanted or disturbing sound that has an

adverse effect on the health and well-being of humans and other

organisms.

5. _________ refers to materials that are harmful to our environment due

to its chemical, physical, radiological, and biological properties.

Test II. Enumeration.

1. Give the 2 main categories of Solid Waste. ( 2 points )

26
 2. What are the main sources/causes of Noise Pollution? ( 4 points )

3. A hazardous waste is generally at least one of these. (4 points )

Test III. True or False.

1. Waste is subjected to physical treatment in order to lessen its hazard by

employing particular chemicals such as acids, bases, oxidizers, reducers,

etc.

2. The process of thermal treatment involves heating the trash to disinfect it.

3. Physical treatment describes the physical techniques used to separate

hazardous waste from non-hazardous stuff.

4. Biological treatment involves the use of microorganisms to break down

organic hazardous waste.

5. Composting is a chemical treatment method used for organic waste

materials which uses microorganisms to decompose organic matter into

stable, nutrient-rich compost.

27
Answer Key

Test I. Identification

1. Pollution

2. Solid Waste

3. Solid Waste Management

4. Noise Pollution

5. Toxic and hazardous Waste

Test II. Enumeration

1. Biodegradable & Non-Biodegradable

2. Traffic Noise, Aircraft Noise, Construction Site, Catering and nightlife,

Animals

3. Ignitable, Corrosive, Reactive, Toxic

Test III. True or False

1. False

2. True

3. True

4. True

5. False

28
References

Aotc. (2023, July 21). Types of hazardous waste disposal methods - AOTC.
Alpha-Omega Training & Compliance, Inc. https://a-otc.com/
hazardous-waste-disposal-methods/

Benefits of proper solid waste management to our health. (2021, October,

21).
National Nutrition Council. https://nnc.gov.ph/regional-offices/visayas
/region-vii-central-visayas/6221-benefits-of-proper-solid-waste
management-to-our-health

Benisek, A. (2021, November 9). What is Noise Pollution?. WebMD.

https://www.webmd.com/a-to-z-guides/what-is-noise-pollution.

Biodegradable And Non-Biodegradable Materials. (n.d.). Aakash.

https://www.aakash.ac.in/important-concepts/chemistry/biodegradable -and-
non-biodegradable-materials

Environmental Hazards Services. (n.d.). What are the 4 types of hazardous

waste?. https://leadlab.com/what-are-the-4-types-of-hazardous- waste/

Four Characteristics of Hazardous Waste. (n.d.). Mli Environmental.

https://mlienvironmental.com/blog/four-characteristics-hazardous- waste/

Greenfield, E. (2022, March 11). Sources of Noise Pollution. Sigma Earth.

https://sigmaearth.com/sources-of-noise-pollution/

Mayuga, J. (2021, January 10). The garbage conundrum. DENR News Alert.
https://www.denr.gov.ph/images/DENR_News_Alerts/DENR_
News_Alerts_10_January_2021_Sunday.pdf

Nathanson, J. A. (2023, August 29). hazardous-waste management.

Encyclopedia Britannica. https://www.britannica.com/technology/
hazardous-waste-managment.

29
National geographic. Pollution.https://education.nationalgeographic.org/
resource/pollution/

Noise pollution: how to reduce the impact of an invisible threat?. (n.d.).

Iberdrola. https://www.iberdrola.com/sustainability/what-is-noise-
pollution-causes-eff
cts-solutions

Noise pollution.(2023, July 19). National Geographic Society.

https://education.nationalgeographic.org/resource/noise-pollution/

Nriagu, J. O., Kulkarni, P. S., Crespo, J. G. C., & Afonso, C. A. M. (2011).

Dioxins. In Enyclopedia of Environmental Health (pp. 83–92).

Pollution. (n.d.). National Geographic. https://education.nationalgeographic.

org/resource/pollution/

Singh, G., & Yadav, P. K. S. (2022). Chapter 6 - Hazardous waste

characteristics and standard management approaches. In Hazardous
waste management: An overview of advanced and cost-effective
solutions (pp. 145–164).

Solid Waste Management. (n.d.). evreka.

https://evreka.co/blog/solidwaste- let-the-garbage-do-the-job/

Solid waste management techniques. (2021, April 5). ENVPK. https://www.

envpk.com/solid-waste-management-techniques/

Solid waste – types, sources, and effects. (2021, April 5). ENVPK.
https://www.envpk.com/solid-waste-types-sources-and-effects/

Wolters, C. (2019, June 26). Toxic waste, explained. National Geographic.

https://www.nationalgeographic.com/environment/article/toxic-waste

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