CPA Pesticide Toxicology and Mode of Action

Question 1

What term describes the dose of a pesticide required to kill 50% of a test animal population under specified conditions?

Accepted Answer

LD50

Answer

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?

Accepted Answer

Organophosphates

Answer

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?

Accepted Answer

Block sodium channel inactivation

Answer

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?

Accepted Answer

Acute toxicity

Answer

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?

Accepted Answer

Highly toxic (Category I)

Answer

Category I (Highly Toxic) includes pesticides with oral LD50 values less than 50 mg/kg, which carry the DANGER signal word on the label.

(CPA) Certified Pesticide Applicator Practice Test