ASRB NET and ARS / SMS / STO (Agricultural Scientists Recruitment Board) · India · Agricultural Scientists Recruitment Board
Original practice questions written to the published syllabus · not past papersWater and air hygiene, waste and carcass disposal, disinfection, pollution and climate change as they affect animal and human health.
In the exams: NAVLE environmental health and safety 5%
How our questions for ASRB NET and ARS / SMS / STO spread across the units of Environment & Environmental Hygiene. Difficulty: 3 easy, 26 medium, 17 hard.
| Air hygiene | 8 | |
| Climate change and livestock | 8 | |
| Waste management on livestock farms | 7 | |
| Water hygiene | 6 | |
| Environmental pollution | 5 | |
| Carcass disposal | 4 | |
| Disinfection | 3 | |
| Experimental animal medicine | 3 | |
| Biomedical waste | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In membrane filtration testing of water, the pore size of the filter normally used to retain coliform bacteria is:
C. 0.45 µm
A 0.45 µm membrane retains coliforms while allowing water through at a practical rate; colonies on the filter are counted directly per 100 mL. 4.5 µm and 45 µm would let bacteria pass; 0.02 µm is an ultrafiltration size that would clog quickly.
Further reading: APHA Standard Methods
Why is chlorination more effective in water at pH 6.5 than at pH 8.5?
D. More of the free chlorine is present as hypochlorous acid
Free chlorine exists as hypochlorous acid (HOCl) and hypochlorite ion (OCl−); HOCl dominates at lower pH and is the far more effective biocide because it is uncharged and penetrates cells. Hypochlorite ion is the weaker form that dominates at high pH. Chloramines are slower, weaker disinfectants.
Further reading: WHO Guidelines for Drinking-water Quality; McDonnell, Antisepsis, Disinfection and Sterilization
Which statement about dairy cow THI thresholds is correct?
B. Work on high-yielding cows places the onset of milk loss near THI 68, below the older threshold of 72
Higher yield means more metabolic heat, so modern high-producing cows lose milk at lower THI; studies placed the onset near 68 compared with the older 72. Different THI formulas give slightly different values, so a threshold must be applied with the formula it was derived from.
Further reading: Zimbelman et al. (2009); Armstrong (1994)
Which statement comparing COD and BOD of the same farm effluent is correct?
A. COD is always equal to or greater than BOD
COD oxidises organic matter chemically with strong oxidants, including material microbes cannot break down, so COD ≥ BOD. BOD measures only the biologically oxidisable fraction over five days.
Further reading: APHA Standard Methods
In a BOD test, 6 mL of dairy effluent is diluted to 300 mL. Dissolved oxygen is 8.6 mg/L at the start and 3.4 mg/L after 5 days at 20 °C. What is the BOD5 of the effluent?
C. 260 mg/L
BOD = (DO initial − DO final) / P, where P = 6/300 = 0.02. BOD = (8.6 − 3.4) / 0.02 = 5.2 / 0.02 = 260 mg/L. 5.2 forgets the dilution; 255 uses 6/294 (sample to diluent) instead of sample to total volume; 52 uses a factor of 10.
Further reading: APHA Standard Methods
Under EU Regulation 1069/2009, the carcass of a pet dog is classified as:
A. Category 1 animal by-product
Pet, zoo and circus animals are Category 1 because of the drugs and unknown risks they may carry; they are incinerated or processed and then incinerated. Category 2 covers fallen farm stock and manure; Category 3 covers material fit for, but not destined for, human consumption.
Further reading: Regulation (EC) No 1069/2009
The increase in concentration of a persistent pollutant such as DDT at each higher level of a food chain is called:
B. Biomagnification
Biomagnification is the rise in concentration between trophic levels; bioaccumulation is build-up within one organism over time. Biotransformation is metabolism of a chemical; bioremediation is the use of organisms to clean up pollution.
Further reading: Environmental toxicology texts
A drug has a no-observed-adverse-effect level (NOAEL) of 5 mg/kg body weight per day in the most sensitive animal study. Using the usual safety factor of 100, what is the acceptable daily intake for a 60 kg person?
A. 3 mg per day
ADI = NOAEL / 100 = 0.05 mg/kg/day. For 60 kg: 0.05 × 60 = 3 mg/day. 300 mg multiplies the NOAEL by body weight without the safety factor; 0.05 mg is the per-kg ADI, not per person; 30 mg uses a factor of 10.
Further reading: JECFA principles for ADI derivation; Codex Alimentarius
A cow emits 107 kg of enteric methane per year. Using the AR5 GWP100 for methane of 28, what is this in CO2-equivalent?
D. About 3.0 t CO₂-eq
107 × 28 = 2,996 kg = 3.0 t CO₂-eq (about 2.9 t with the AR6 value of 27). 0.11 t is the methane mass itself without conversion; 0.3 t is a decimal slip; 28.4 t uses the N2O GWP of 265.
Further reading: IPCC AR5 WG1
The feed additive 3-nitrooxypropanol reduces enteric methane by:
B. Inhibiting methyl-coenzyme M reductase, the final enzyme of methanogenesis
3-NOP is a structural analogue of methyl-coenzyme M and inhibits methyl-coenzyme M reductase. Nitrate supplementation is a different strategy (alternative hydrogen sink with nitrite risk); ionophores act on bacteria; defaunation targets protozoa.
Further reading: Animal nutrition and climate mitigation literature
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