Enforcement Officer / Accounts Officer (EO/AO) 2017 recruitment test. Transcribed from the Commission's own booklet (series A, GRS-A-TNS); answer as per the official UPSC final answer key. This question is in Part B. Answer last reviewed 24 August 2026.

Bio-remediation is a technology which is being extensively utilized in controlling

(a)global warming
(b)melting of glaciers
(c)ozone depletion
(d)heavy metal pollutions

Answer

Why

Correct — D, (d) heavy metal pollutions. Bio-remediation is the use of living organisms — bacteria, fungi, algae and higher plants — to remove, break down or immobilise pollutants in soil, water and industrial effluent. Everything it can do, it does to a contaminated medium that can be treated: a stretch of soil, a body of water, a tank of effluent. That is why heavy metal contamination is its natural target and why the other three options are not.

Heavy metals are a special case within bio-remediation and the difficulty is instructive. Unlike an organic pollutant, a metal cannot be degraded — an atom of cadmium remains an atom of cadmium whatever is done to it. So bio-remediation of metals works by moving them or by changing their form rather than by destroying them. Microorganisms bind metal ions to their cell surfaces, a passive process called biosorption, and take them up into their cells, an active one called bioaccumulation. Some bacteria change the oxidation state of a metal, converting it into a less soluble and therefore less mobile form, so that it stays put instead of travelling through groundwater. And plants do the same work on a larger scale in phytoremediation, drawing metals out of soil and water into their roots and shoots, from which they can be harvested and disposed of. Laboratory and field work has demonstrated this on cadmium, lead, chromium, mercury, nickel and arsenic among others.

The reason the other three options fail is the same for all of them, and worth stating as a rule: they are atmospheric problems, global in scale, and they have no contaminated medium that an organism can be applied to. Global warming, glacier melt and ozone depletion are all matters of the composition of the atmosphere over the whole planet. Bio-remediation is a site-scale technology, applied to a particular volume of soil or water, and there is no way to inoculate the stratosphere.

The wider family is worth having in view. Bio-remediation is used on oil spills, where hydrocarbon-degrading bacteria are the classic application; on pesticide residues; on solvents and industrial organics; and on heavy metals, as here. It may be done in place, called in situ bio-remediation, or by excavating the contaminated material and treating it elsewhere, called ex situ.

Why the others are wrong

(a)global warming — Global warming is caused by the accumulation of carbon dioxide, methane, nitrous oxide and other greenhouse gases in the atmosphere, and it is addressed by emitting less of them, by capturing carbon at source, and by increasing the biological sinks that take carbon out of the air. Growing forests does use living organisms to absorb carbon dioxide, which is the honest root of the confusion, but afforestation and carbon sequestration are not what the term bio-remediation names. Bio-remediation means the biological treatment of a contaminated site or medium; you cannot treat the atmosphere as a site, and no biological agent applied at a location can lower a global gas concentration.
(b)melting of glaciers — The melting of glaciers is a physical consequence of rising temperature, not a form of contamination, so there is nothing in it for a biological agent to act upon. Nothing can be degraded, adsorbed or accumulated. The only route to slowing it is to slow the warming that causes it, which returns to the discussion under option (a). This option is on the page because it belongs to the same cluster of well-known environmental problems as the other two wrong answers, and a candidate who has not fixed what bio-remediation actually means will choose among the four by familiarity rather than by fit.
(c)ozone depletion — Ozone depletion happens in the stratosphere, where chlorofluorocarbons and related halogenated compounds release chlorine and bromine atoms that catalytically destroy ozone. The remedy has been regulatory rather than biological — the Montreal Protocol of 1987 phased the offending substances out of production, and the ozone layer has been recovering since. There is nothing here for an organism to do. It is worth keeping ozone depletion and global warming apart in the first place, since they are commonly conflated: one is a stratospheric chemistry problem caused by halogenated compounds, the other a tropospheric radiation-balance problem caused by greenhouse gases.

Concept

Bio-remediation uses living organisms to clean up contaminated soil, water and effluent. Its central mechanism for organic pollutants is metabolic: bacteria and fungi already possess enzymes that break down complex carbon compounds, and given the right conditions of oxygen, moisture, temperature and nutrients they will break down petroleum hydrocarbons, solvents and many pesticides into carbon dioxide, water and simple residues. Practitioners distinguish bio-stimulation, in which the nutrients and oxygen a native microbial population needs are supplied so that it can multiply and do the work, from bio-augmentation, in which specially selected or engineered organisms are introduced. The treatment may be in situ, carried out where the contamination lies, or ex situ, with the material excavated and treated in a bioreactor or a prepared bed. Metals need a different approach, because they cannot be degraded at all: biosorption binds them to the surface of microbial cells, bioaccumulation takes them inside, microbial reduction converts them to less soluble and less mobile forms, and phytoremediation uses plants that take metals up into harvestable tissue. The great advantages of the technology are its low cost and the fact that it works with natural processes and produces little secondary waste; its limits are that it is slow, that it needs conditions favourable to the organisms, and that it works on a site rather than on a region. The last of those limits is what this question is really testing.

Environmental science items in EPFO papers usually test whether a technical term has been placed in the right scale and the right medium. A candidate who knows only that bio-remediation is good for the environment cannot answer this question, because all four options name environmental goods. A candidate who knows that bio-remediation is applied to a contaminated site can answer it in a few seconds, because three of the four options are atmospheric and planetary. The habit to build is to ask, of any environmental technology, what exactly it is applied to and at what scale: soil and water at site scale for bio-remediation, the atmosphere at global scale for greenhouse gas control, the stratosphere and international regulation for ozone.

Key facts

Bio-remediation is the use of living organisms to remove, degrade or immobilise pollutants in soil, water and effluent.
It works at the scale of a contaminated site or medium, which is why it cannot be applied to atmospheric or global problems.
Metals cannot be degraded, so metal bio-remediation relies on biosorption, bioaccumulation, change of oxidation state to a less mobile form, and phytoremediation.
Phytoremediation uses plants to draw metals such as cadmium, lead, chromium, nickel and arsenic out of soil and water into harvestable tissue.
Bio-stimulation supplies nutrients and oxygen to the native microbial population; bio-augmentation introduces selected organisms.
Treatment may be in situ, where the contamination lies, or ex situ, after excavation.
Hydrocarbon-degrading bacteria used on oil spills are the best known application of the technology.
Ozone depletion is a stratospheric problem caused by chlorofluorocarbons and was addressed by the Montreal Protocol of 1987, not by any biological technique.

Bio-remediation is applied to a site; three of the four options are the atmosphere

(d) Heavy metal pollution→A contaminated medium that can be treated — a stretch of soil, a body of water, a tank of effluent — which is exactly what the technology needs. Living organisms, bacteria, fungi, algae and higher plants, are used to remove, break down or immobilise the pollutant in it.

Why metals are a special case→A metal cannot be degraded: an atom of cadmium remains an atom of cadmium whatever is done to it. So the work is done by moving it or changing its form — biosorption binds metal ions to microbial cell surfaces, bioaccumulation takes them inside, microbial reduction converts a metal to a less soluble and less mobile form, and phytoremediation draws it into harvestable plant tissue.

The rule that disposes of the other three→Global warming, glacier melt and ozone depletion are atmospheric problems, global in scale, with no contaminated medium that an organism can be applied to. Bio-remediation is a site-scale technology, applied to a particular volume of soil or water, and there is no way to inoculate the stratosphere.

(a) Global warming — the honest confusion→Growing forests does use living organisms to absorb carbon dioxide, which is the root of the temptation. But afforestation and carbon sequestration are not what the term bio-remediation names, and no biological agent applied at a location can lower a global gas concentration.

(b) Melting of glaciers→A physical consequence of rising temperature rather than a form of contamination, so there is nothing in it for a biological agent to act upon — nothing to be degraded, adsorbed or accumulated. The only route to slowing it is to slow the warming that causes it.

(c) Ozone depletion→A stratospheric chemistry problem: chlorofluorocarbons and related halogenated compounds release chlorine and bromine atoms that catalytically destroy ozone. The remedy was regulatory — the Montreal Protocol of 1987 — and the layer has been recovering since. Worth keeping apart from global warming, which is a tropospheric radiation-balance problem caused by greenhouse gases.

Study next

Bio-remediation techniques — bio-stimulation, bio-augmentation, in situ and ex situ methodsPhytoremediation and hyperaccumulator plantsHeavy metal pollution in India — arsenic in groundwater, fluoride, chromium and lead contaminationThe distinction between ozone depletion and global warming, and the Montreal and Paris agreementsBiological methods in sewage treatment — activated sludge, trickling filters and oxidation ponds

Common traps

Choosing whichever environmental problem is most famous. All four options name real problems; only one has a treatable medium.
Confusing bio-remediation with carbon sequestration by forests. Both use living organisms, but only one is the treatment of a contaminated site.
Assuming bio-remediation destroys heavy metals. Metals are immobilised, taken up or converted; they are never degraded.
Conflating ozone depletion with global warming, which have different causes, different atmospheric layers and different remedies.

Environmental technology terms come up in these papers about once a paper and are tested by their application rather than by their definition. Prepare each term with the medium it acts on and the pollutant class it handles: bio-remediation for contaminated soil and water, including hydrocarbons and heavy metals; bio-magnification for the movement of persistent pollutants up a food chain; eutrophication for nutrient enrichment of water bodies. A term learnt with its medium answers the applied question; a term learnt as a definition often does not.

Related PYQs

EPFO_EOAO_2017_Q98Open & attempt →

Beauty of some historical monuments is greatly affected by the growth of certain living organisms. These living organisms belong to which one of the following groups?

(a) Amphibious plants
(b) Lichens
(c) Bacteria
(d) Viruses

Answer(b) Lichens

Asks which organisms damage the beauty of historical monuments and keys lichens — the neighbouring item in this paper’s biology run, and the other one that turns on what living organisms do to a physical environment.

Practice

practice — not a real PYQ
The use of green plants to remove heavy metals from contaminated soil and water is known as
- (a)bio-magnification
- (b)phytoremediation
- (c)eutrophication
- (d)biological oxygen demand
Answer(b) phytoremediation
practice — not a real PYQ
The depletion of stratospheric ozone is caused principally by
- (a)carbon dioxide and methane
- (b)chlorofluorocarbons and related halogenated compounds
- (c)oxides of sulphur
- (d)suspended particulate matter
Answer(b) chlorofluorocarbons and related halogenated compounds

Why