ABT Environmental Toxicology 2 — Questions and Answers
Question 1: The EPA's Reference Dose (RfD) is defined as an estimate of daily exposure that:
- Causes a 1-in-a-million cancer risk over a lifetime
- Is likely to be without appreciable risk of deleterious effects over a lifetime (Correct answer)
- Represents the average human daily intake from all sources
- Is the LOAEL divided by an uncertainty factor of 10
Correct answer: Is likely to be without appreciable risk of deleterious effects over a lifetime
The RfD is an EPA estimate of daily oral exposure to a chemical that is likely to be without appreciable deleterious effects over a lifetime, used for non-carcinogens.
Question 2: Methylmercury exposure in humans primarily occurs through:
- Inhalation of industrial emissions
- Consumption of contaminated fish and seafood (Correct answer)
- Dermal contact with thermometers
- Drinking water from industrial runoff
Correct answer: Consumption of contaminated fish and seafood
Methylmercury bioaccumulates in fish and seafood, making dietary consumption of large predatory fish (tuna, swordfish) the primary human exposure route.
Question 3: Which class of pesticides inhibits acetylcholinesterase and was originally developed as nerve agents?
- Pyrethroids
- Organochlorines
- Organophosphates (Correct answer)
- Neonicotinoids
Correct answer: Organophosphates
Organophosphate pesticides are structurally related to nerve agents and inhibit acetylcholinesterase, causing accumulation of acetylcholine at synapses.
Question 4: Lead exposure in children is most commonly associated with which source in older US homes?
- Drinking water from copper pipes
- Lead-based paint chips and dust (Correct answer)
- Gasoline combustion residues in soil
- Food packaging leachates
Correct answer: Lead-based paint chips and dust
Lead-based paint used in homes built before 1978 is the most common source of lead exposure in US children through ingestion of paint chips and inhalation of dust.
Question 5: Dioxins (PCDDs) exert their toxic effects primarily through which molecular mechanism?
- Direct DNA alkylation
- Inhibition of cytochrome oxidase
- Activation of the aryl hydrocarbon receptor (AhR) (Correct answer)
- Disruption of sodium channel gating
Correct answer: Activation of the aryl hydrocarbon receptor (AhR)
Dioxins bind with high affinity to the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor that alters gene expression leading to diverse toxic effects.
Question 6: The 'cancer slope factor' (CSF) is used in risk assessment to estimate risk for which type of toxic endpoint?
- Threshold-based systemic toxicity
- Neurotoxicity endpoints only
- Linearized low-dose carcinogenicity risk (Correct answer)
- Reproductive toxicity endpoints
Correct answer: Linearized low-dose carcinogenicity risk
The cancer slope factor (CSF) is used in the linearized multistage model to estimate the incremental lifetime cancer risk per unit of daily exposure for carcinogens.
ABT Environmental Toxicology 2
The EPA's Reference Dose (RfD) is defined as an estimate of daily exposure that: