chapter 11 - herbicides and pesticides

cholingeric stimulation

stimulation of the nerve fibers utilizing acetylcholine as a neurotransmitter

superoxide anion

oxygen molecule with an extra, unpaired electron; a charged free radical

hemodialysis

process by which a foreign substance is removed from the blood of a poisoned patient by allowing it to diffuse across a semipermeable membrane while the blood is pumped through a filtering machine

hemoperfusion

process by which a foreign substance is removed from the blood of a poisoned patient by allowing it to pass through mechanical equipment. where it is absorbed by activated charcoal

skink

australian reptile

pesticide

a substance that has been specifically designed or chosen for selective toxicity to certain organisms

why are pesticides a concern?

they may be toxic to non-target organisms and may be toxic to humans via acute or chronic exposure

what is an example of an accidental pesticide poisoning?

organic mercury fungicides used to treat seed grain

is chronic or acute exposure more difficult to quantify?

chronic because when chronically exposed the amount of pesticide in human blood is very low

what are the four classes of pesticides?

insecticides, herbicides, fungicides, rodenticides

insecticides

organophosphorus compounds; carbamate and organochlorines, natural products

herbicides

chlorophenoxy compounds; triazines, bipyridyls, substituted ureas, aromatic amides, dinitrophenols, carbamates

fungicides

alkyl mercury compounds; chlorinated hydrocarbons, dialkyldithiocarbamates, organotin compounds

rodenticides

inorganic agents, anticoagulants, red squill, phosphorous, metals, a-napththylthiourea, fluorinated aliphatics

what are examples of selective toxicity poisons?

• warfarin as rodenticide

• malathion

nematicides

kills worms; fumigants, botanical, organophosphorus, oxime carbamate

DDT is:

(a) an organophosphate

(b) lipid soluble

(c) toxic to mammals

(d) metabolized by loss of Hal

(e) inhibits cholinesterase

b, d

it is an organochlorine pesticide, which has low mammalian toxicity and does not destroy plants. it does not inhibit cholinesterase. it is not directly toxic to eggs although it may contribute to their breakage as a result of eggshell thinning

parathion is an insecticide that:

(a) has low toxicity to humans

(b) is not metabolized

(c) acts by inhibiting Na-K ATPase

(d) causes excessive cholingeric stimulation

(e) results in bronchoconstriction

d, e

parathion is an organophosphate insecticide which is toxic to humans. it is metabolized to paragon which inhibits cholinesterase leading to elevated levels of acetylcholine. the result is excessive cholingeric stimulation producing symptoms such as broncocontriction

paraquat:

(a) is an organochlorine insecticide

(b) is metabolized to diquat by SOD

(c) causes lipid peroxidation

(d) is concentrated in lung tissue

(e) causes liver fibrosis

c, d

paraquat is a bipyridyl herbicide. it is actively incorporated into lung tissue by the putrescine uptake system. it is concentrated in the lungs where it is responsible for stimulation of lipid peroxidatioi, production of reactive oxygen species and fibrosis. the reactive oxygen radicals are detoxified by superoxide dismutase (SOD) but is over-whelmed when large amounts of paraquat are ingested

describe the mechanism of toxicity of fluoroacetate

fluoroacetate is toxic as a result of intermediary metabolism when it is first converted to fluoroacetyl CoA. the resultant product is incorporated into the TCA cycle, forming fluorocitrate. this analog of citrate, however, cannot be further metabolized by the next step to cisocanitate as the fluorine atom is not removed.. therefore, the TCA cycle is blocked; ATP production is compromised, and mammals die of heart failure

describe the mechanism of paraquat toxicity. draw formulas to support the answer

paraquat selectivity accumulates in pulmonary alveolar type I and II cels. PQ preferentially accumulates in the lungs because of structural similarity with diamines and polyamides. the intramolecular distance between the 2 nitrogens in paraquat enables in=ts incorporation into a selective active transport system in alveolar cells for which polyamides are the normal substrate.

explain why malathion is used as an insecticide

it is metabolized by hydrolysis in mammals, so it is not toxic towards them, but in insects it is metabolized by oxidation to malaoxon, which inhibits cholinesterase

what is the difference between pesticides that demonstrate selective toxicity and those that don’t?

ones that do not demonstrate selective toxicity are toxic to many mammalian organisms since they do not just affect target organs

what type of pesticide is DDT?

insecticide

where does DDT localize?

adipose tissue

what was one of the main problems caused by using DDT?

bird population decreased to due DDT causing eggshells to thin

what are some of the problems associated with the ban of DDT?

• number of malaria cases increased

• other more toxic pesticides were developed

what are some symptoms of organophosphate pesticides?

• cholinergic shock

• excessive cholinergic stimulation

• neuromuscular paralysis

• central depression

what is an organophosphate mechanism?

excessive cholinergic stimulation

what type of pesticide is malathion?

organophosphate pesticide; insecticide

what type of pesticide is paraquat?

herbicide

what is the target organ for paraquat?

lung - causes progressive fibrosis

how does one become poisoned by paraquat?

ingestion

what are some treatments for paraquat?

hemodialysis, hemoperfusion, high-flow oxygen, fullers earth to absorb

what is special about fluoroacetate?

it is a naturally occurring pesticide produced from plants; targets mammals, though Australian species are more tolerant

how is one poisoned by fluoroacetate?

oral administration and absorption through the gut, and then affects the Krebs cycle