GATE — Environmental Science and Engineering (ES) · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersHeavy metals, pesticides, plastics and emerging contaminants in soils: fate, toxicity to organisms and people, risk assessment, and remediation including phytoremediation and microbial methods.
In the exams: ICAR AICE subject 71 Unit 4 (soil pollution, remediation); GATE ES Sections 7 and 9 (soil contamination, health risk assessment); UGC NET Unit 6
GATE ES (Sections 7 and 9)
Human health risk assessment calculations (CDI, HQ, HI, cancer risk), toxicology terms (LD50, NOAEL, RfD), sorption (Kd = Koc x foc), retardation factor, first-order degradation and half-life, remediation technologies.
How our questions for GATE spread across the units of Soil Contamination, Toxicology & Remediation. Difficulty: 17 easy, 17 medium, 2 hard.
| Organic contaminants and xenobiotics | 4 | |
| Principles of toxicology: dose-response, LD50, NOAEL | 4 | |
| Human health risk assessment: hazard, exposure, dose, risk characterisation | 4 | |
| Bioremediation and phytoremediation | 4 | |
| Ecotoxicology and ecological risk assessment | 3 | |
| Permissible limits and soil screening values | 3 | |
| Physical and chemical remediation | 3 | |
| Contaminant leaching to groundwater | 3 | |
| Sources of soil contamination: industrial, agricultural, urban | 2 | |
| Heavy metals: forms, mobility and plant uptake | 2 | |
| Microplastics and emerging contaminants in agricultural soils | 2 | |
| Bioaccumulation and biomagnification | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Copper accumulates in vineyard and orchard soils mainly from:
C. Copper fungicides
Repeated Bordeaux mixture and other copper sprays build up copper.
A cabbage contains 0.8 mg/kg Cd (dry weight) grown on soil with 4.0 mg/kg Cd. What is the soil-to-plant transfer factor?
C. 0.20
TF = C_plant/C_soil = 0.8/4.0 = 0.20. Inverting the ratio gives 5.0; multiplying gives 3.2.
A pesticide degrades by first-order kinetics with a half-life of 30 days. What fraction remains after 90 days?
D. 12.5%
Three half-lives: 0.5^3 = 0.125 = 12.5%. Using e^(-t/t1/2) ignores ln 2.
A fish contains 50 mg/kg of a chemical present in water at 0.01 mg/L. What is the bioconcentration factor?
C. 5,000 L/kg
BCF = 50/0.01 = 5,000. Inverting the ratio or subtracting gives meaningless values.
The oral LD50 of a pesticide in rats is 50 mg/kg. Scaled directly to a 70 kg person, what dose does this correspond to?
D. 3,500 mg
50 x 70 = 3,500 mg; interspecies extrapolation is uncertain.
Which organism is the standard test species in OECD earthworm toxicity tests?
C. Eisenia fetida
Daphnia is aquatic, Danio a fish, Arabidopsis a plant. Eisenia fetida is the standard OECD earthworm species.
With CDI = 0.00064 mg/kg/day and RfD = 0.0035 mg/kg/day, what is the hazard quotient, and is there concern?
A. 0.18, below 1, low concern
HQ = 0.00064/0.0035 = 0.18 < 1. The reciprocal ratio or a product would misstate the hazard.
Which is the first step of the NRC (1983) risk assessment paradigm?
B. Hazard identification
Followed by dose-response, exposure and risk characterisation.
Which contaminant group is most amenable to bioremediation?
C. Petroleum hydrocarbons
Metals cannot be degraded; highly chlorinated compounds resist biodegradation.
A contaminant has Kd = 2.0 L/kg in soil with bulk density 1.6 kg/L and water content 0.3. What is the retardation factor?
C. 11.7
R = 1 + (rho_b/theta) Kd = 1 + (1.6/0.3) x 2.0 = 11.7. Omitting the 1 or inverting rho_b/theta gives wrong values.
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