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Page Title: Toxicokinetics
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conduction across myoneural junctions in skeletal muscle, and interference of
CNS synaptic transmission. The signs and symptoms of poisoning, which are the
same as those for the organophosphate insecticides, are typically cholinergic
with lacrimation, salivation, miosis, convulsion, and death. The associated
symptoms mimic the muscarinic, nicotinic, and CNS actions of acetylcholine and
the severity of the effects is dose-dependent.
Acute toxicities, represented by the oral LD50 in male rats, ranged from
0.8 mg/kg for aldicarb to 850 mg/kg for carbaryl (Klaassen, Amdur, and Doull
1986). Carbaryl is considered one of the least acutely toxic carbamate
insecticides. Long-term dietary exposures to carbaryl in rats resulted in kidney
and liver toxicity levels similar to those observed for rat cholinesterase inhibition
in a separate chronic study (IRIS 1997).
Carbaryl is teratogenic in several experimental animals with widely varying
no-observed effect levels. However, in most species, the doses for effects on
fetuses were near the maternal toxic doses. Although the lowest effect levels
were observed for dogs (a tenth of the toxic dose to the mother), these studies
were judged inappropriate for human health risk assessment because of
differences in the metabolism of carbaryl between dogs and humans (IRIS 1997).
Chronic toxicity test results indicate carbaryl as a potential carcinogen and
mutagen, while aldicarb has been indicated as a suspect mutagen (Briggs and
Council 1992). Carbaryl has not been evaluated by the USEPA for its human
carcinogenic potential.
Toxicokinetics
Organophosphates are absorbed by the respiratory tract, mucous membranes,
skin, and gastrointestinal tract. The carbamate insecticides are direct inhibitors
of acetylcholinesterase and do not require metabolic activation (Klaassen,
Amdur, and Doull 1986). Hydrolytic reactions result in metabolites that lack
anticholinesterase activity. Various oxidation steps are catalyzed by mixed
function oxidases. The products formed by these reactions are not always less
toxic than the parent compound (Klaassen, Amdur, and Doull 1986). Unlike the
organophosphates, the organocarbamates are reversible inhibitors of
cholinesterase, and their duration of action is relatively short. Atropine alone is
the recommended antidote for organocarbamate poisoning.
Ecological effects
Bees are extremely sensitive to the organocarbamate insecticides, which can
also disrupt schooling behavior of fish, and are considered teratogens in fish
(Briggs and Council 1992). Certain organocarbamates are toxic to earthworms
and invertebrate populations. Aldicarb is reported to be highly toxic to birds,
fish, and aquatic insects, while carbaryl is highly toxic to fish, crustaceans,
earthworms, aquatic worms, and aquatic insects (Briggs and Council 1992).
Neither aldicarb nor carbaryl are expected to bioconcentrate significantly in
aquatic organisms.
D55
Appendix D Toxicological Profiles

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