CIH Toxicology & Health Risk Assessment 2 — Questions and Answers
Question 1: A Threshold Limit Value-Ceiling (TLV-C) is a concentration that should:
- Never be exceeded at any time during the work shift (Correct answer)
- Not be exceeded for more than 15 minutes
- Not be exceeded on average over 8 hours
- Only apply to skin contact situations
Correct answer: Never be exceeded at any time during the work shift
TLV-C is the ceiling concentration that should never be exceeded, even instantaneously, during any part of the working exposure.
Question 2: Which organization publishes Threshold Limit Values (TLVs) for occupational chemical exposures?
- OSHA
- NIOSH
- ACGIH (Correct answer)
- EPA
Correct answer: ACGIH
The American Conference of Governmental Industrial Hygienists (ACGIH) publishes TLVs annually based on the best available scientific evidence.
Question 3: Carbon monoxide causes toxicity primarily by:
- Directly destroying lung tissue
- Binding to hemoglobin with greater affinity than oxygen (Correct answer)
- Inhibiting the enzyme acetylcholinesterase
- Causing lipid peroxidation in cell membranes
Correct answer: Binding to hemoglobin with greater affinity than oxygen
Carbon monoxide binds to hemoglobin approximately 200–250 times more strongly than oxygen, forming carboxyhemoglobin and preventing oxygen transport to tissues.
Question 4: In toxicology, a 'sensitizer' is a substance that:
- Causes immediate irritation on first contact
- Can induce an allergic response upon repeated exposure (Correct answer)
- Destroys nerve tissue on contact
- Requires very high doses to cause any effect
Correct answer: Can induce an allergic response upon repeated exposure
A sensitizer causes an allergic response that develops after repeated exposures; once sensitized, even minute amounts can trigger severe reactions.
Question 5: The No-Observed-Adverse-Effect Level (NOAEL) is defined as:
- The lowest dose causing a statistically significant adverse effect
- The highest tested dose producing no detectable adverse health effect (Correct answer)
- The dose resulting in 50% response in the population
- The regulatory exposure limit divided by a safety factor
Correct answer: The highest tested dose producing no detectable adverse health effect
NOAEL is the highest dose in a study at which no statistically or biologically significant increase in adverse effects is observed compared to controls.
Question 6: Which organ is primarily responsible for biotransformation (metabolism) of toxic chemicals in the body?
- Kidney
- Lung
- Liver (Correct answer)
- Spleen
Correct answer: Liver
The liver is the primary site of biotransformation, using enzyme systems (especially cytochrome P450) to metabolize and detoxify foreign chemicals.
Question 7: When a worker is simultaneously exposed to multiple chemicals, the combined exposure is evaluated using the mixture formula. If the sum of (C1/L1 + C2/L2 + ... Cn/Ln) exceeds 1, this indicates:
- The exposure is within acceptable limits
- The TLV of the most toxic chemical is exceeded
- The combined exposure has exceeded the acceptable limit (Correct answer)
- Individual chemicals are below their limits so no action is needed
Correct answer: The combined exposure has exceeded the acceptable limit
When the sum of the fractions of each chemical's concentration divided by its limit exceeds 1.0, the combined mixture exposure has exceeded the permissible level.
CIH Toxicology & Health Risk Assessment 2
A Threshold Limit Value-Ceiling (TLV-C) is a concentration that should: