CPA Pesticide Toxicology and Mode of Action 1 — Questions and Answers
Question 1: What term describes the dose of a pesticide required to kill 50% of a test animal population under specified conditions?
- LC50
- LD50 (Correct answer)
- ED50
- TD50
Correct answer: LD50
LD50 (Lethal Dose 50) is the standard measure of acute oral or dermal toxicity, expressed in mg of pesticide per kg of body weight.
Question 2: Which pesticide class inhibits acetylcholinesterase, preventing the breakdown of acetylcholine and causing continuous nerve stimulation?
- Pyrethroids
- Organophosphates (Correct answer)
- Neonicotinoids
- Strobilurins
Correct answer: Organophosphates
Organophosphates and carbamates inhibit acetylcholinesterase, leading to acetylcholine accumulation and overstimulation of the nervous system.
Question 3: What is the primary mode of action of pyrethroid insecticides such as permethrin and cypermethrin?
- Inhibit mitochondrial electron transport
- Block sodium channel inactivation (Correct answer)
- Inhibit acetylcholinesterase
- Disrupt chitin synthesis
Correct answer: Block sodium channel inactivation
Pyrethroids keep voltage-gated sodium channels open, causing prolonged nerve depolarization and repetitive nerve firing in insects.
Question 4: Which type of toxicity results from a single or short-term exposure to a high dose of a pesticide?
- Chronic toxicity
- Subchronic toxicity
- Acute toxicity (Correct answer)
- Cumulative toxicity
Correct answer: Acute toxicity
Acute toxicity refers to adverse effects that occur from a single dose or short-term exposure, often appearing within 24–96 hours.
Question 5: A pesticide has an oral LD50 of 5 mg/kg body weight. How would this pesticide be classified under EPA toxicity categories?
- Slightly toxic (Category III)
- Moderately toxic (Category II)
- Highly toxic (Category I) (Correct answer)
- Practically non-toxic (Category IV)
Correct answer: Highly toxic (Category I)
Category I (Highly Toxic) includes pesticides with oral LD50 values less than 50 mg/kg, which carry the DANGER signal word on the label.
Question 6: For most pesticide applicators during routine fieldwork, which route of pesticide exposure is generally considered the most significant?
- Oral ingestion
- Inhalation
- Dermal contact (Correct answer)
- Ocular absorption
Correct answer: Dermal contact
Dermal exposure accounts for the majority of pesticide exposure for applicators because skin contact occurs throughout mixing, loading, and applying operations.
Question 7: What term describes the potential of a pesticide to cause cancer in exposed organisms?
- Mutagenicity
- Teratogenicity
- Carcinogenicity (Correct answer)
- Neurotoxicity
Correct answer: Carcinogenicity
Carcinogenicity refers to a substance's ability to cause cancer, and EPA evaluates this through weight-of-evidence classifications for pesticide registration.
CPA Pesticide Toxicology and Mode of Action 1
What term describes the dose of a pesticide required to kill 50% of a test animal population under specified conditions?