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our
pollutants found in house dust add to the ability of a common
house hold insecticide to inhibit an enzyme important in neurologic
function in humans. Building on substantial evidence that the
insecticide chlorpyrifos inhibits cholinesterase, a biochemical
critical for nerve cell transmission, researchers at the Johns
Hopkins School of Public Health found that pollutants in house
dust increase this adverse effect in studies with purified enzyme.
The four pollutants, polycyclic aromatic hydrocarbons (PAHs)
that are among the most abundant components of house dust, are
pyrene, benzo(a)pyrene, fluoranthene, and anthracene. The study
appeared in the April 1999 issue of Toxicology Letters.
Lead
author David A. Jett, PhD, assistant professor, Environmental
Health Sciences, Johns Hopkins School of Public Health, said,
"When acetylcholinesterase was incubated with chlorpyrifos-oxon
together with the PAHs, the inhibitory effect on acetylcholinesterase
was additive. These data suggest that some PAHs have anticholinesterase
activity, and contribute in an additive manner to the inhibitory
effect of chlorpyrifos-oxon on acetylcholinesterase in the test
tube. Further research is needed to determine the toxicologic
relevance of these findings."
To study whether
the PAHs increased chlorpyrifos's inhibition of cholinesterase,
the researchers added specific concentrations of pyrene, benzo(a)pyrene,
fluor-anthene, and anthracene to an incubation mixture containing
chlorpyrifos and purified cholinesterase. They then measured
cholinesterase inhibition in the presence or absence of several
different concentrations of the four PAHs, noting the concentrations
that caused cholinesterase to be inhibited by 50 percent, as
well as the maximal activity of the enzyme.
The data suggested
that the combined effects of the PAHs were additive but not synergistic
with the effects of low concentrations of chlorpyrifos. Although
all four PAHs inhibited cholinesterase activity by themselves,
their potencies differed, with benzo(a)pyrene having the greatest
relative effect on cholinesterase in combination with chlorpyrifos,
and fluoranthene having the least. Perhaps most important, the
combined effects appeared to be greatest at low-level concentrations
of chlorpyrifos commonly encountered in environmental exposures.
A 1981 report
indicates that 90 percent of all homes in the United States use
pesticides, and usage is likely to be even higher today. The
primary source of exposure to pesticides for the general U.S.
population is in the indoor environment of the home.
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