Environmental pollution is the introduction of contaminants into the natural environment that cause an adverse change to the ecosystem. Pollutants can be any substance—solid, liquid, or gas—or a form of energy, such as heat or sound. These are released at a rate faster than the environment can safely disperse or decompose them. Understanding the diverse forms of pollution is fundamental to developing effective mitigation strategies and protecting public health and natural processes.
Atmospheric Pollution
Contaminants released directly into the air are classified as primary pollutants, emitted straight from their source in a harmful form. Examples include carbon monoxide (CO) from incomplete combustion, nitrogen oxides (NOx) from vehicle exhaust, and sulfur dioxide (SO2) from industrial processes and burning fossil fuels. These gases, along with particulate matter, represent the immediate chemical burden placed on the atmosphere.
Particulate matter (PM) consists of microscopic solid or liquid particles suspended in the air. PM is categorized by size, with PM10 referring to inhalable coarse particles less than 10 micrometers in diameter, and PM2.5 to fine particles 2.5 micrometers or smaller. The smaller PM2.5 particles pose the greatest health risk because they can penetrate deep into the lungs and enter the bloodstream.
Secondary pollutants form when primary pollutants undergo chemical reactions in the atmosphere, often triggered by sunlight or water vapor. Ground-level ozone, a major component of photochemical smog, forms when NOx and volatile organic compounds (VOCs) react in the presence of sunlight. The complexity of their formation makes secondary pollutants challenging to control, though they represent a substantial fraction of air quality issues.
Aquatic Pollution
Aquatic pollution involves the contamination of water bodies, including oceans, rivers, lakes, and groundwater, degrading water quality and disrupting aquatic life. Sources are distinguished as either point source or non-point source. Point source pollution originates from a single, identifiable location, such as a factory discharge pipe or a sewage treatment plant outfall.
Non-point source pollution is diffuse, resulting from land runoff that collects contaminants over a wide area and carries them into waterways. This includes agricultural runoff (pesticides and excess fertilizers) and urban stormwater (oil, heavy metals, and debris). Non-point pollution is generally more difficult to monitor and regulate.
Nutrient pollution, involving excessive nitrogen and phosphorus, stimulates rapid algal growth (eutrophication). This leads to algal blooms that deplete dissolved oxygen as the algae decompose, creating “dead zones.” Microplastics, tiny plastic fragments, persist in the environment and accumulate in aquatic organisms, potentially moving up the food chain.
Terrestrial Pollution
Terrestrial pollution focuses on the degradation of soil and land surfaces by contaminants, impacting the physical medium and supporting ecosystems. Improper disposal of solid waste is a significant source, as landfills leach hazardous liquids into the ground. This leachate, formed as water filters through decomposing waste, carries chemicals and heavy metals that contaminate the underlying soil and groundwater.
Hazardous waste contamination involves depositing industrial chemicals and heavy metals, such as lead and cadmium, in the soil. These substances can enter the food chain, reduce soil fertility, and pose long-term health risks. The chemicals alter the soil’s natural composition, potentially making the land unsuitable for future use or agriculture.
Agricultural practices also contribute through the excessive use of synthetic fertilizers and chemical pesticides. Pesticide residues persist in the soil, affecting soil-borne organisms and contaminating crops. Intensive cultivation can strip the land of its natural nutrients, leading to soil exhaustion and increased vulnerability to erosion.
Sensory and Energy-Based Pollution
Sensory and energy-based pollution involves introducing disruptive energy, rather than chemical substances, into the environment. These types of pollution disturb the natural processes and well-being of living organisms without chemically contaminating the air, water, or soil.
Noise pollution is unwanted or excessive sound that interferes with normal human activities like sleep and conversation. Sources include industrial machinery, construction sites, and transportation noise from aircraft and road traffic. Prolonged exposure to high decibel levels is linked to stress-related illnesses, high blood pressure, and hearing impairment.
Light pollution is the excessive, misdirected, or poorly chosen use of artificial outdoor lighting. This disturbance disrupts the circadian rhythms of humans and wildlife, notably by suppressing melatonin production in people. It also interferes with nocturnal habitats and astronomical observation, obscuring the night sky.
Thermal pollution refers to the alteration of natural water or air temperature, often through the discharge of heated water from industrial cooling processes or power plants. This temperature increase can cause thermal shock to aquatic life. It also reduces the amount of dissolved oxygen water can hold, severely impacting biodiversity.