Environmental Engineering Reference
In-Depth Information
application of pesticides indoors occurred in occupants of some 2.5 million
homes in the U.S. during 1976-1977.
Many of the compounds that have been, and continue to be, used as
insecticidal pesticides are chlorinated hydrocarbons or organophosphorous
compounds. Though they have different chemical structures and toxicities
relative to each other, both compound groups have similar modes of action.
They are neurotoxic compounds that interfere with nerve signal transmission
by inhibiting the enzyme acetylcholine esterase. Depending on the exposure
dose and innate toxicity of substances to which humans have been exposed,
a variety of symptoms that affect the central nervous system can be expected.
For example, severe acute symptoms include muscular tremors.
In many reported acute pesticide exposure cases, symptoms may have
been caused by exposure to active pesticidal ingredients, solvents used in
pesticidal formulations, or both. Solvents used with pesticides are them-
selves neurotoxic. In diagnosing the cause of symptoms allegedly associated
with such exposures, tests showing significantly depressed acetylcholine
esterase activity indicate that the active pesticidal ingredient(s) was the more
likely cause of some, if not all, reported symptoms.
b. Cancer.
Chlorinated hydrocarbons such as chlordane, heptachlor,
lindane, dieldrin, and PCP are known animal and suspected human carcin-
ogens. As a consequence, their use has been restricted by USEPA. Subterra-
nean termite treatments with chlordane and heptachlor were permissible
under USEPA rules in the 1970s and 1980s because they were believed to
pose a low probability of human exposure. However, data obtained in stud-
ies of military housing indicate that these low-volatility substances are in
fact mobile, entering building spaces through the movement of soil gases.
Although exposure concentrations are low, such compounds have relatively
long half-lives (12 to 13 years in the ambient environment) so that exposures
can continue to occur for decades. This would also be the case with exposures
associated with PCP-treated logs and other wood materials.
In response to exposure concerns, a committee of the National Research
Council conducted a risk assessment of pesticides used in termite control.
They proposed guideline exposure levels of 5
µ
g/m
3
chlordane, 2
µ
g/m
3
g/m
3
chlorpyrifos, using
occupational exposure limits and relative tumor incidence in animals.
Based on this assessment, chlorpyrifos, the active ingredient used in most
termiticidal treatments in the U.S. between the years 1980 and 2000, would
have posed the lowest risk of cancer to humans in long-term exposures
associated with residences.
Chronic exposure to pesticides is a major public health concern since
many pesticides have been shown to be animal carcinogens or potential
human carcinogens. Of 51 pesticides evaluated by the National Cancer Insti-
tute and National Toxicology Program (as of 1990), 24 have been demon-
strated to be carcinogenic in chronic animal exposure studies. These include
herbicides such as atrazine, amitrole, and trifluralin; organochlorine insecti-
heptachlor, 1
µ
g/m
3
aldrin/dieldrin, and 10
µ
