1st May, 2021 Prelims


Note: Common Environmental Terminologies which are already explained in standard books like Shankar IAS are not repeated here.

Acute Toxicity

The ability of a substance to cause poisonous effects resulting in severe biological harm or death soon after a single exposure or dose. Also, it is any severe poisonous effect resulting from a single short-term exposure to a toxic substance.

Assimilation Efficiency

In an animal, the percentage of the energy content of ingested food that is absorbed across the gut wall. In plants, the percentage of solar visible light that is fixed by photosynthesis. The term may also be used to refer to the percentage assimilation of ingested inorganic nutrients (such as nitrate or phosphate) by plants or animals, or of drugs by animals.

Atmospheric Inversion (Temperature Inversion)

A relatively stable atmospheric condition in which cool air is trapped beneath a layer of warmer air.


In evolutionary biology, abiogenesis, or informally the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds.


The field within ecology that deals with the study of individuals and species.

Allopatric Speciation

Allopatric speciation is speciation that happens when two populations of the same species become isolated from each other due to geographic changes. Speciation is a gradual process by which populations evolve into different species. A species is itself defined as a population that can interbreed, so during speciation, members of a population form two or more distinct populations that can no longer breed with each other.

Adaptive radiation

Adaptive radiation refers to the adaptation (via genetic mutation) of an organism which enables it to successfully spread, or radiate, into other environments. Adaptive radiation leads to speciation and is only used to describe living organisms. Adaptive radiation can be opportunistic or forced through changes to natural habitats.

Air Gap

An open vertical drop, or vertical empty space, that separates a drinking (potable) water supply to be protected from another water system in a water treatment plant or other location. This open gap prevents the contamination of drinking water by backflow because there is no way raw water or any other water can reach the drinking water.

Air Sparging

An in-situ treatment technology that uses injected air to help remove harmful vapors from polluted soil and groundwater below the water table by injecting air directly into the saturated subsurface to encourage the solvents and gasoline to evaporate faster, which makes them easier to remove with a vacuum.

Air Stripping

A treatment system that removes or “strips” VOCs from contaminated groundwater or surface water as air is forced through the water, causing the compounds to evaporate. Often the compounds are then captured using air filters.


A geologic formation (usually a layer of material such as clay) that creates an underground barrier to the flow of groundwater.

Assimilative Capacity

The difference between the baseline water quality concentration for a pollutant and the most stringent applicable water quality criterion for that pollutant.

Auto Shredder Fluff

The non-metallic waste product that results from the reclamation process of recyclable ferrous and non-ferrous metals. The primary source of recyclable materials comes from automobiles, truck, buses and common household appliances such as washers, dryers and refrigerators.

Baseline Risk Assessment

An assessment conducted before cleanup activities begin at a site to identify and evaluate the threat to human health and the environment. After remediation has been completed, the information obtained during a baseline risk assessment can be used to determine whether the cleanup levels were reached.

Biogeochemical Prospecting

Prospecting for metal ores using observations of high metal concentrations in plants, soil, or surface rocks.


The retention and concentration of a substance by an organism.


A test which determines the effect of a chemical on a living organism.


The accumulation of a chemical in tissues of an organism (such as fish) to levels that are greater than the level in the medium (such as water) in which the organism resides.

Biological Degradation

A process by which micro-organisms break down waste materials. Nutrient additives may be introduced into a contaminated area (such as groundwater or soil) for the specific purpose of encouraging biodegradation.


Refers to treatment processes that use microorganisms (usually naturally occuring) such as bacteria, yeast, or fungi to break down hazardous substances and pollutants. Bioremediation can be used to clean up contaminated soil and water.


An in-situ remediation technology that combines soil vapor extraction methods with bioremediation. It uses vapor extraction wells that induce air flow in the subsurface through air injection or through the use of a vacuum. Bioventing can be effective in remediating releases of petroleum products, such as gasoline, jet fuels, kerosene, and diesel fuel.


Water that contains animal, human, or food waste.


An infertile, acidic, unproductive wetland that develops in cool but wet climates

Boreal Coniferous Forest

A northern forest dominated by coniferous trees, usually species of fir, larch, pine, or spruce. See also boreal forest.


Abandoned, idled, or underused industrial and commercial facilities where expansion or redevelopment is complicated by real or perceived environmental contamination.

Broad-Spectrum Pesticide

A pesticide that is toxic to other organisms as well as the pest.

Buffering Capacity

The ability of a solution to resist changes in pH as acid or base is added

Close-loop Recycling

A recycling system in which a product made from one type of material is recycled into a different type of product (e.g. used newspapers into toilet paper). The product receiving recycled material itself may or may not be recycled.


A shrub-dominated ecosystem that occurs in south- temperate environments with winter rains and summer drought.


Microorganisms that harness some of the potential energy of certain inorganic chemicals (e.g., sulphides) to drive their fixation of energy through chemosynthesis. Compare with photoautotroph.


Autotrophic productivity that utilizes energy released during the oxidation of certain inorganic chemicals (such as sulphides) to drive biosynthesis. Compare with photosynthesis.


This occurs when species interact in ways that affect their reciprocal survival, and so are subject to a regime of natural selection that reinforces their mutual evolutionary change.

Commercial Extinction

Depletion of a natural resource to below the abundance at which it can be profitably harvested.

Convergence (Evolutionary Conversion)

This occurs when unrelated species with similar niches and living in comparable environments are subjected to parallel regimes of natural selection, resulting in their evolution to be similar in morphology, physiology, and behaviour.

Critical Load

A threshold for pollutant inputs, below which it is thought ecological damages will not be caused.

Cultural Eutrophication

Eutrophication caused by anthropogenic nutrient inputs, usually through sewage dumping or fertilizer runoff. See also eutrophication.

Cultural Evolution

Adaptive evolutionary change in human society, characterized by increasing sophistication in the methods, tools, and social organizations used to exploit the environment and other species.

Cumulative Environmental Impacts

Environmental impacts that result from a proposed undertaking, in addition to those caused by any past, existing, and imminent developments and activities.

Deep Drainage

Soil water that has drained to below the lower limits of plant roots.

Dose-Response Relationship

The quantitative relationship between different doses of a chemical and a biological or ecological response.


A philosophical and political movement that applies feminist ideas to environmental concerns.

Ecological Conversion

A long-term change in the character of the ecosystem at some place, as when a natural forest is converted into an agricultural land use.

Ecological Economics

A type of economics that involves a full accounting of costs associated with ecological damages and resource depletion. Compare with conventional economics.


A population specifically adapted to coping with locally stressful conditions, such as soil with high metal concentrations.


The largest biophysical zones in the national ecological classification of Canada.

Environmental Citizenship

Actions taken by individuals and families to lessen their impacts on the environment.

Environmental Racism

Discrimination against a group of people defined by racial attributes, which results in them suffering a disproportionate amount of degradation or pollution of their living or work environment.

Extinction Vortex

An accelerating spiral of endangerment and extinction caused by worsening environmental conditions.

Ecological Footprint

The area of ecoscape (i.e., landscape and seascape) required to supply a human population with the necessary food, materials, energy, waste disposal, and other crucial goods and services.

Ecological Integrity (Ecosystem Health)

A notion related to environmental quality, but focusing on changes in natural populations and ecosystems, rather than effects on humans and their economy. See also environmental quality.

Ecological Justice

A worldview in which all species (i.e., not just humans) have a right to equitable access to the necessities of life and happiness. See also social justice.


The relationship between economic output (product, service, activity) and environmental impact added caused by production, consumption and disposal.

Carbon Absorption Unit (CAU)

A control device that uses activated carbon to absorb volatile organic compounds from a gas or liquid stream. (The VOCs are later recovered from the carbon.) It is commonly known as a granular activated carbon (GAC) unit.

Catalytic converter

An air pollution abatement device that removes pollutants from motor vehicle exhaust, either by oxidizing them into carbon dioxide and water or reducing them to nitrogen.

Chlorinated Hydrocarbons

Chemicals containing only chlorine, carbon, and hydrogen. These include a class of persistent insecticides that linger in the environment and accumulate in the food chain like DDT, aldrin and chlordane etc.


The application of chlorine to water, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results.


Microorganisms found in the intestinal tract of humans and animals. Their presence in water indicates fecal pollution and potentially adverse contamination by pathogens.

Effluent-Dependent Water (EDW)

A surface water that consists of a point source discharge of wastewater. Without the point source discharge of wastewater, it would be an ephemeral water.

Environmental Sustainability

Maintenance of ecosystem components and functions for future generations.

Ephemeral Water

Surface water that has a channel that is at all times above the water table and flows only in direct response to precipitation.

Evaporation Ponds

Areas where sewage sludge is dumped and dried.

Fugitive Emissions

Emissions not caught by a capture system.

Flue-Gas Desulphurization

A process to remove SO2 from the waste (flue) gases of a power plant or smelter, before they are discharged into the atmsophere.

Geographical Information System (GIS)

A system designed to capture, store, manipulate, analyze, manage, and present all types of spatial or geographical data.

Gray Water

Wastewater generated from kitchen sinks, washing machines, wash-hand basins, showers and baths, which can be recycled for landscape irrigation and constructed wetlands.

Green cleaning

Refers to the use of cleaning methods and products with environmentally friendly ingredients designed to preserve human health and environmental quality. Green cleaning techniques and products avoid the use of chemically reactive and toxic products which contain various toxic chemicals.

Gausse Law

The idea that if two competing species coexist in a stable environment, then they do so as a result of differentiation of their realized niches; but if there is no such differentiation, or if it is precluded by the habitat, then one competing species will eliminate or exclude the other.

Gaia hypothesis

A notion that envisions Earth’s species and ecosystems as a “superorganism” that attempts to optimize environmental conditions toward enhancing its own health and survival.

Heat Island Effect

A "dome" of elevated temperatures over an urban area caused by structural and pavement heat fluxes, and pollutant emissions.


A homoplasy is a shared character between two or more animals that did not arise from a common ancestor. A homoplasy is the opposite of a homology, where a common ancestor provided the genes that gave rise to the trait in two or more animals. Often, a homoplasy will occur when two very different groups of animals evolve to do the same thing. This is known as convergent evolution, or convergence.

Intermittent Water

A stream or reach that flows continuously only at certain times of the year, as when it receives water from rainfall or snow melt.

K-selected Organisms

Refers to organisms that produce relatively small numbers of large offspring. A great deal of parental investment is made in each progeny, which helps to ensure their establishment and survival. Compare with r-selected.

Keystone Species

A dominant species in a community, usually a predator, with an influence on structure and function that is highly disproportionate to its biomass.

Landscape Ecology

Study of the spatial characteristics and temporal dynamics of communities over large areas of land (landscapes) or water (seascapes).

Lentic Ecosystem

A freshwater ecosystem characterized by nonflowing water, such as a pond or lake.

Limiting Factor

An environmental factor that is the primary restriction on the productivity of autotrophs in an ecosystem.

Load-On-Top (LOT) Method

A process used in ocean-going petroleum tankers to separate and contain most oily residues before ballast waters are discharged to the marine environment

Particulate matter

Any finely divided airborne solid or liquid material with a diameter smaller than 100 micrometers while it is in the air. Examples of particulate matter include dust, smoke, soot, pollen and soil particles.

Lotic Ecosystem

A freshwater ecosystem characterized by flowing water, such as a stream or river.


The evolution of species or higher taxonomic groups, such as genera, families, or classes.

Maximum Sustainable Yield (MSY):

The largest amount of harvesting that can occur without degrading the productivity of the stock.


Local disruptions that affect small areas within an otherwise intact community. Compare with community-replacing disturbance.


Relatively subtle evolutionary changes occurring within a population or species, sometimes within only a few generations, and at most leading to the evolution of races, varieties, or subspecies.

Marine Snow

Marine snow refers to organic particulate matter that constantly falls from the upper waters into the deeper waters of the ocean. Marine snow serves to provide food and energy from the productive upper waters exposed to sunlight to the marine organisms that reside in the deeper regions of the water column.

Net Ecosystem Productivity

The amount of ecosystem-level productivity that remains after respiration is subtracted from gross productivity.

Net Primary Production (NPP)

Primary production that remains as biomass after primary producers have accounted for their respiratory needs. See also respiration and gross primary production.


An acronym for “not in my backyard”. It signifies one’s opposition to the locating of something considered undesirable example waste products in one’s neighborhood (could be a developing country).

Nutrient Budget

A quantitative estimate of the rates of nutrient input and output for an ecosystem, as well as the quantities present and transferred within the system.

Nutrient Capital

The amount of nutrients present in a site in soil, living vegetation, and dead organic matter.

Nutrient Cycling

Transfers and chemical transformations of nutrients in ecosystems, including recycling through decomposition.

Old-Growth Forest

A late-successional forest characterized by the presence of old trees, an uneven-aged population structure, and a complex physical structure.

Pesticide Treadmill

The inherent reliance of modern agriculture and public-health programs on pesticides, often in increasing quantities, to deal with pest problems.

Particulate Matter (Inhalable)

Any finely divided airborne solid or liquid material with a diameter smaller than 10 micrometers while it is in the air.


The expressed characteristics of an individual organism, due to genetic and environmental influences on the expression of its specific genetic information.

Phenotypic Plasticity

The variable expression of genetic information of an individual, depending on environmental influences during development.

Punctuated Equilibrium

Punctuated equilibrium is a theory that states that evolution occurs primarily through short bursts of intense speciation, followed by lengthy periods of stasis or equilibrium. The model postulates that nearly 99% of a species’ time on earth is spent in stasis, and change happens very quickly.

Particulate Matter-10 (PM10)

Dust, particulate matter measuring 10 microns or less. A dust particle of 10 microns is one-seventh the width of a human hair.

Particulate Matter-2.5 (PM2.5)

Particulate matter measuring 2.5 microns or less. A major pollutant source, it is generated by smoke from wildfires, prescribed burns and fireplace activity.

Perched Aquifer

A relatively small, localized aquifer that lies above the regional aquifer and is underlain by a confining layer. Perched aquifers may be formed when the groundwater table drops and water is trapped above a confining layer. They are usually discontinuous and are not usually sources for drinking water.


A manufactured salt that is found in rocket fuels, explosives, flares, fireworks, some bleach products, and some herbicides. Perchlorate can impair thyroid function.

Point Source

Refers to a specific, identifiable source from which waste or pollution is released into the environment.

Photochemical Air Pollutants

Ozone, peroxy acetyl nitrate, and other strongly oxidizing gases that form in the atmosphere through complex reactions involving sunlight, hydrocarbons, oxides of nitrogen, and other chemicals.

Political Ecology

This integrates the concerns of ecology and political economy to consider the dynamic tensions between natural and anthropogenic change, and also the consideration of damage from both natural and anthropogenic perspectives; the latter includes the broad range of concerns from individual people to all of society.

Ppb (Part Per Billion)

A unit of concentration, equivalent to 1 microgram per kilogram (µg/kg), or in aqueous solution, 1 µg per litre (µg/L).

Ppm (Part Per Million)

A unit of concentration, equivalent to 1 milligram per kilogram (mg/kg), or in aqueous solution, 1 mg per litre (mg/L).

Precautionary Principle

An approach to environmental management, adopted by many countries at the 1992 Earth Summit, which essentially states that scientific uncertainty is not a sufficient reason to postpone control measures when there is a threat of harm to human health or the environment.

Principle of Limiting Factors

A theory stating that ecological productivity (and some other functions) is controlled by whichever environmental factor is present in least supply relative to the demand.

R-selected Organisms

Refers to organisms that produce relatively large numbers of small offspring. Little parental investment is made in each offspring, but having large numbers of progeny helps ensure that some will establish and survive.

Radiatively Active Gases (RAGs)

Atmospheric gases that efficiently absorb infrared radiation and then dissipate some of the thermal energy gain by reradiation.

Replacement Fertility Rate

The fertility rate that results in the numbers of progeny replacing their parents, with no change in size of the equilibrium population.

Residence Time

(1) The time required for the disappearance of an initial amount;

(2) The length of time that a stressor or other environmental influence remains active.


Radioactive particle, man-made (anthropogenic) or natural, with a distinct atomic weight number. Radionuclides can have a long life as a soil or water pollutant.


A common radioactive gas emitted from ordinary soils and rock. Radon has no smell, taste or color and can seep into homes, building up to dangerous levels if there is not enough ventilation. Exposure to high levels of radon gas over a long period of time increases the risk of developing lung cancer.

Reclaimed Water

Former wastewater that is treated to remove solids and impurities in compliance with standards in regulation, which may then be used for agriculture, landscape irrigation, recharge of groundwater aquifers, and power generation supplies, industrial and other uses.


Cleanup or other methods used to remove or contain a toxic spill or hazardous materials.


A hydroelectric development that directly harnesses the flow of a river to drive turbines, without creating a substantial impoundment for water storage.

Riparian Habitat

Areas adjacent to rivers and streams with a differing density, diversity, and productivity of plant and animal species relative to nearby uplands.


An air pollution device that uses a spray of water or reactant or a dry process to trap pollutants in emissions.


A semi-solid residue from any of a number of air or water treatment processes. Sludge can be a hazardous waste.


A watery mixture of insoluble matter resulting from some pollution control techniques.


Water that originates during rainfall events and snow or ice melt and runs off into water courses, lakes and other water bodies and sewers.

Synthetic Organic Chemical (SOC)

Man-made (anthropogenic) organic chemicals. Some SOCs are volatile; others tend to stay dissolved in water instead of evaporating.


Discrimination (by humans) against other species purely on the basis that they are not human, especially as manifested by cruelty to or exploitation of animals, or merely by a lack of consideration of their interests.

Species Richness

The number of species in some area or place.


The study of relationships among species within communities.

Tail Water

The runoff of irrigation water from the lower end of an irrigated field.

Total Dissolved Solids (TDS)

The total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water.

Total Maximum Daily Load (TMDL)

A calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards, and an allocation of that load among the various sources of that pollutant.

Total Suspended Solids (TSS)

A measure of the suspended solids in wastewater, effluent, or water bodies, determined by tests for total suspended non-filterable solids.


A cloudy condition in water due to suspended silt or organic matter. The degree of turbidity is measured with a turbidometer.

Zero Population Growth (ZPG)

When the birth rate plus immigration equal the death rate plus emigration.