Introduction
Welcome to the ultimate Ecotoxicology MCQ quiz.
If you’re preparing for exams in Environmental Science, Ecology, or Toxicology, or simply want to test your understanding of pollutants, heavy metals, pesticides, and biomagnification, this is for you.
Ecotoxicology MCQs
- Ecotoxicology primarily studies
a) Animal physiology
b) Interaction of toxic substances with living organisms in ecosystems
c) Plant genetics
d) Ocean currents - The father of Ecotoxicology is
a) Rachel Carson
b) René Truhaut
c) Aldo Leopold
d) Barry Commoner - LD₅₀ represents
a) Least detectable dose
b) Lethal dose for 50 % of test organisms
c) Lowest dilution factor
d) Limiting degradation dose - Bioaccumulation refers to
a) Decrease of pollutants in an organism
b) Progressive accumulation of a chemical in an organism over time
c) Breakdown of toxins
d) Detoxification by microbes - Which of the following shows biomagnification most strongly?
a) Phosphates
b) Mercury
c) Nitrates
d) Carbon dioxide - The process of toxin concentration increasing along the food chain is called
a) Bioconcentration
b) Bioamplification
c) Biomagnification
d) Biodegradation - A chronic effect of a toxin means
a) Sudden death
b) Long-term low-dose exposure effects
c) Immediate poisoning
d) Mechanical injury - DDT primarily affects
a) Nervous system
b) Liver metabolism
c) Eggshell formation in birds
d) Photosynthesis in plants - The unit used for expressing concentration of toxicants in air is
a) ppm
b) μg/L
c) mg/kg
d) moles/m³ - Minamata disease was caused by
a) Lead
b) Arsenic
c) Mercury
d) Cadmium - The main organ for detoxification in animals is
a) Heart
b) Liver
c) Kidney
d) Brain - The test commonly used for acute aquatic toxicity is
a) Ames test
b) LC₅₀ test
c) ELISA
d) PCR - The Ames test is used to detect
a) Mutagenicity of chemicals
b) Heavy metal concentration
c) Pesticide residues
d) Organic load in wastewater - Biotransformation involves
a) Chemical alteration of toxicants by organisms
b) Physical adsorption
c) Sedimentation
d) Evaporation - Xenobiotics are
a) Natural nutrients
b) Foreign chemicals to biological systems
c) Enzymes
d) Vitamins - Detoxification in the liver involves mainly
a) Cytochrome P450 enzymes
b) Chlorophyll
c) DNA polymerase
d) ATP synthase - Persistent Organic Pollutants (POPs) are dangerous because they
a) Decompose rapidly
b) Are biodegradable
c) Persist, bioaccumulate, and biomagnify
d) Have short half-lives - Which of the following is a non-point source pollutant?
a) Factory effluent
b) Sewage outfall
c) Agricultural runoff
d) Industrial stack - The Stockholm Convention regulates
a) Ozone-depleting substances
b) Persistent Organic Pollutants
c) Radioactive waste
d) Greenhouse gases - Mercury is most toxic in which form?
a) Elemental Hg⁰
b) Methylmercury (CH₃Hg⁺)
c) HgS
d) HgCl₂ - The Bhopal gas disaster involved
a) Phosgene
b) Methyl isocyanate (MIC)
c) Sulfur dioxide
d) Ammonia - Which heavy metal causes Itai-Itai disease?
a) Lead
b) Arsenic
c) Cadmium
d) Chromium - The term NOAEL refers to
a) No observed adverse effect level
b) Normal oxygen activity emission level
c) Non-oxidative absorption energy level
d) None of these - Biomarkers in ecotoxicology indicate
a) Genetic ancestry
b) Physiological or biochemical changes due to exposure
c) Cell division rates
d) Energy production - The movement of toxic chemicals from water to air is called
a) Sorption
b) Volatilization
c) Sedimentation
d) Adsorption - Which insecticide was banned globally for its environmental persistence?
a) Parathion
b) DDT
c) Malathion
d) Carbaryl - The most common biological indicator of water pollution is
a) E. coli
b) Cyanobacteria
c) Zooplankton diversity
d) All of the above - Acid rain enhances toxicity of which metal?
a) Sodium
b) Aluminum
c) Calcium
d) Potassium - The bioconcentration factor (BCF) is the ratio of
a) Uptake to elimination rate
b) Concentration in organism to concentration in water
c) Intake to excretion
d) All of the above - Synergistic toxicity occurs when
a) Two chemicals neutralize each other
b) Combined effect is greater than the sum of individual effects
c) Both act independently
d) They reduce each other’s effect - Photochemical smog contains
a) PAN, ozone, aldehydes
b) Sulfur dioxide only
c) Carbon monoxide only
d) Methane and oxygen - A pollutant with high lipid solubility tends to
a) Excrete quickly
b) Bioaccumulate in fatty tissues
c) Be harmless
d) Dissolve only in water - Which organism level is most affected by biomagnification?
a) Producers
b) Primary consumers
c) Top carnivores
d) Decomposers - The most toxic form of lead is
a) Lead oxide
b) Tetraethyl lead
c) Lead carbonate
d) Lead sulfate - Which radioactive isotope accumulates in bones?
a) Sr-90
b) Cs-137
c) I-131
d) U-238 - Which gas causes methemoglobinemia (“blue baby syndrome”)?
a) Ammonia
b) Nitrous oxide
c) Nitrate/nitrite
d) Sulfide - The half-life of a toxicant indicates
a) Its toxicity level
b) Time taken for its concentration to reduce by half
c) Its atomic weight
d) Its reactivity - The main reason POPs persist is
a) They are insoluble in lipids
b) They resist chemical, biological, and photolytic degradation
c) They are volatile
d) They are biodegradable - Which pollutant is mainly responsible for acid mine drainage?
a) Iron sulfides
b) Carbonates
c) Phosphates
d) Nitrates - The Hazard Quotient (HQ) is defined as
a) Exposure dose / reference dose
b) Reference dose / exposure dose
c) Dose × concentration
d) Risk × probability - Risk = ___ × Exposure
a) Hazard
b) Threshold
c) Toxicity index
d) Response - A mutagen affects
a) Lipids
b) DNA
c) Enzymes
d) Cell wall - The most effective method for removing heavy metals from wastewater is
a) Chlorination
b) Ion exchange or precipitation
c) UV irradiation
d) Aeration - The octanol–water partition coefficient (Kow) is used to estimate
a) Solubility
b) Lipid affinity of chemicals
c) Boiling point
d) Radioactivity - In aquatic ecotoxicology, the test organism Daphnia magna is used to measure
a) Air pollution
b) Water toxicity
c) Soil pH
d) Light penetration - The major route of metal entry into fish is
a) Skin
b) Gills and diet
c) Scales
d) Muscles only - Sublethal exposure leads to
a) Immediate death
b) Behavioral or reproductive impairment
c) Immunity
d) Growth enhancement - Eutrophication increases ecotoxicological risk by
a) Reducing nutrient input
b) Increasing algal blooms and hypoxia
c) Improving biodiversity
d) Enhancing oxygen levels - The Threshold Limit Value (TLV) is
a) Highest safe concentration for humans at work
b) Minimum detectable limit
c) Median lethal dose
d) Air quality index - The study of how pollutants move through and affect ecosystems is
a) Environmental chemistry
b) Ecotoxicology
c) Bioinformatics
d) Epidemiology
Answers and Explanations
| No. | Answer | Explanation |
|---|---|---|
| 1 | b | Ecotoxicology = study of toxic effects on organisms in ecosystems. |
| 2 | b | René Truhaut coined the term “ecotoxicology” (1969). |
| 3 | b | LD₅₀ = dose lethal to 50 % test population. |
| 4 | b | Gradual accumulation within tissues. |
| 5 | b | Mercury biomagnifies through aquatic food webs. |
| 6 | c | Biomagnification = food-chain amplification. |
| 7 | b | Chronic = long-term exposure. |
| 8 | c | DDT interferes with calcium metabolism → thin eggshells. |
| 9 | a | Air pollutants are expressed in ppm or μg/m³. |
| 10 | c | Methylmercury poisoning in Japan. |
| 11 | b | Liver detoxifies via enzymatic pathways. |
| 12 | b | LC₅₀ = lethal concentration for 50 % aquatic organisms. |
| 13 | a | Ames test detects mutagenicity. |
| 14 | a | Biotransformation = metabolic conversion of toxins. |
| 15 | b | Xenobiotics = foreign compounds to organisms. |
| 16 | a | Cytochrome P450 family oxidizes toxins. |
| 17 | c | POPs persist, bioaccumulate, biomagnify. |
| 18 | c | Runoff from agriculture is diffuse. |
| 19 | b | Stockholm Convention controls POPs (2001). |
| 20 | b | Methylmercury = most bioavailable and toxic form. |
| 21 | b | MIC leak, 1984 Bhopal disaster. |
| 22 | c | Cadmium causes bone softening (Itai-Itai). |
| 23 | a | NOAEL = highest dose with no adverse effect. |
| 24 | b | Biomarkers show exposure effects. |
| 25 | b | Volatilization = transfer to atmosphere. |
| 26 | b | DDT banned under Stockholm Convention. |
| 27 | d | All used as biological indicators. |
| 28 | b | Acidic pH increases Al³⁺ toxicity. |
| 29 | b | BCF = [organism]/[water] concentration ratio. |
| 30 | b | Synergy = combined > sum. |
| 31 | a | Smog = ozone + PAN + aldehydes. |
| 32 | b | Lipophilic toxins store in fat. |
| 33 | c | Top predators accumulate maximum toxins. |
| 34 | b | Tetraethyl lead (fuel additive) = highly toxic. |
| 35 | a | Strontium-90 replaces calcium in bones. |
| 36 | c | Nitrate reduces to nitrite → methemoglobin. |
| 37 | b | Time for 50 % degradation/removal. |
| 38 | b | POPs resist breakdown. |
| 39 | a | Oxidation of FeS₂ → acidic drainage. |
| 40 | a | HQ = dose/reference dose; > 1 = risk. |
| 41 | a | Risk = Hazard × Exposure. |
| 42 | b | Mutagens damage DNA. |
| 43 | b | Ion exchange or precipitation removes metals. |
| 44 | b | Kow → lipophilicity indicator. |
| 45 | b | Daphnia bioassay for aquatic toxicity. |
| 46 | b | Gills major absorption route. |
| 47 | b | Non-lethal effects like behavior changes. |
| 48 | b | Excess nutrients → algal bloom → low O₂. |
| 49 | a | TLV = safe workplace exposure. |
| 50 | b | Definition of ecotoxicology. |
Decoding Biosphere 