Agriculture Reference
In-Depth Information
extract and purified pyrethrins are contained in various commercial products,
commonly dissolved in petroleum distillates. Some are packaged in pressur-
ized containers ("bug-bombs"), usually in combination with the synergists
piperonyl butoxide and n-octyl bicycloheptene dicarboximide. The synergists
retard enzymatic degradation of pyrethrins. Some commercial products also
contain organophosphate or carbamate insecticides. These are included because
the rapid paralytic effect of pyrethrins on insects ("quick knockdown") is not
always lethal.
Pyrethrum and pyrethrin products are used mainly for indoor pest control.
They are not sufficiently stable in light and heat to remain as active residues
on crops. The
synthetic insecticides
known as pyrethroids (chemically similar
to pyrethrins) do have the stability needed for agricultural application.
Toxicology and Mode of Action
Crude pyrethrum is a dermal and respiratory allergen, probably due mainly
to noninsecticidal ingredients. Contact dermatitis and allergic respiratory reac-
tions (rhinitis and asthma) have occurred following exposures. A strong
cross-reactivity with ragweed pollen has been recognized. Single cases exhib-
iting anaphylactic and pneumonitic manifestations have also been reported.
The refined pyrethrins are probably less allergenic, but appear to retain some
irritant and/or sensitizing properties.
Pyrethrins are absorbed orally and by inhalation, but only slightly across
intact skin. They are very effectively hydrolyzed to inert products by mam-
malian liver enzymes. This rapid degradation combined with relatively poor
bioavailability probably accounts in large part for their relatively low mam-
malian toxicity. Dogs fed extraordinary doses exhibit tremor, ataxia, labored
breathing, and salivation. Similar neurotoxicity rarely, if ever, has been ob-
served in humans, even in individuals who have used pyrethrins for body lice
control (extensive contact) or pyrethrum as an anthelmintic (ingestion).
In cases of human exposure to commercial products, the possible role of
other toxicants in the products should be kept in mind. The synergists
piperonyl butoxide and n-octyl bicycloheptene dicarboximide have low toxic
potential in humans, but organophosphates or carbamates included in the
product may have significant toxicity. Pyrethrins themselves do not inhibit
cholinesterase enzyme.
There are presently no practical tests for pyrethrin metabolites or pyrethrin
effects on human enzymes or tissues that can be used to confirm absorption.
2.
Nicotine
Nicotine is an alkaloid contained in the leaves of many species of plants,
but is usually obtained commercially from tobacco. A 95% solution of the
free alkaloid in organic solvent has been marketed in the past as a greenhouse
