CIH Toxicology and Chemical Hazards 3 — Questions and Answers
Question 1: When two chemicals together produce a toxic effect greater than the sum of their individual effects, this interaction is called:
- Antagonism
- Additivity
- Synergism (Correct answer)
- Potentiation
Correct answer: Synergism
Synergism occurs when the combined toxic effect of two chemicals exceeds the sum of their individual effects (greater than additive).
Question 2: The IDLH (Immediately Dangerous to Life or Health) value for a substance represents:
- The concentration causing death in 1% of exposed workers
- The maximum concentration from which a worker could escape within 30 minutes without irreversible harm (Correct answer)
- The threshold limit value for a workday
- The concentration producing no observable adverse effects
Correct answer: The maximum concentration from which a worker could escape within 30 minutes without irreversible harm
IDLH is the maximum airborne concentration from which an unprotected worker could escape within 30 minutes without irreversible health effects or escape impairment.
Question 3: Which mechanism explains how carbon monoxide causes toxicity?
- Direct alkylation of DNA
- Competitive inhibition of cytochrome P450 enzymes
- High affinity binding to hemoglobin preventing oxygen transport (Correct answer)
- Displacement of calcium from bone
Correct answer: High affinity binding to hemoglobin preventing oxygen transport
Carbon monoxide binds to hemoglobin with approximately 200-240 times the affinity of oxygen, forming carboxyhemoglobin and preventing oxygen delivery to tissues.
Question 4: Methemoglobin-forming agents like aniline cause toxicity primarily by:
- Increasing oxygen-carrying capacity of blood
- Oxidizing ferrous (Fe2+) iron in hemoglobin to ferric (Fe3+) form (Correct answer)
- Destroying red blood cell membranes
- Blocking cellular uptake of oxygen
Correct answer: Oxidizing ferrous (Fe2+) iron in hemoglobin to ferric (Fe3+) form
Methemoglobin-forming agents oxidize the iron in hemoglobin from the ferrous (Fe2+) to ferric (Fe3+) state, which cannot carry oxygen.
Question 5: A substance classified as a 'sensitizer' is one that:
- Causes immediate irritation upon first contact
- Induces an allergic response after prior sensitization exposure (Correct answer)
- Destroys tissue at the point of contact
- Has a permissible exposure limit below 1 ppm
Correct answer: Induces an allergic response after prior sensitization exposure
A sensitizer causes an allergic response upon re-exposure after an initial sensitization period, not on first contact.
Question 6: The principle behind biological exposure indices (BEIs) is that they correlate with:
- The OSHA permissible exposure limit for the substance
- Health effects observed in epidemiological studies of exposed workers
- Air concentrations at or below the TLV (Correct answer)
- The no-observed-adverse-effect level (NOAEL) in animal studies
Correct answer: Air concentrations at or below the TLV
BEIs are designed to correlate with exposures at the TLV level, representing biomarker levels in healthy workers exposed at the TLV.
Question 7: Volatile organic compounds (VOCs) with high vapor pressure and low boiling points pose particular inhalation hazards because:
- They have high molecular weights that settle into lung tissue
- They evaporate readily at room temperature, producing high airborne concentrations (Correct answer)
- They react with moisture in the upper respiratory tract
- They are exclusively water-soluble and deposit in the nasopharynx
Correct answer: They evaporate readily at room temperature, producing high airborne concentrations
High vapor pressure substances evaporate quickly at ambient temperatures, generating elevated airborne concentrations that increase inhalation exposure potential.
CIH Toxicology and Chemical Hazards 3
When two chemicals together produce a toxic effect greater than the sum of their individual effects, this interaction is called: