Environmental Engineering Reference
In-Depth Information
occur in mixtures. Newer chemicals are less persistent than
the chlorinated hydrocarbon pesticides and do not generally
cause fish kills. However, they can produce sublethal effects
such as endocrine disruption, altered development and behav-
ior, reduced growth, and other effects. “Second-generation”
pesticides such as organophosphates and carbamates are
much less persistent in the environment, but if spraying coin-
cides with the time of reproduction and early life stages of sus-
ceptible organisms, they can harm sensitive early life stages.
Organophosphates break down in the environment in a mat-
ter of weeks. They were developed from chemical compounds
similar to nerve gas and, not surprisingly, they affect a chemi-
cal in the body that is important for the transmission of nerve
impulses. At high doses, organophosphates can overstimulate
the nervous system and cause nausea, dizziness, or in cases of
severe poisoning, convulsions and respiratory paralysis. One
organophosphate commonly used in salt marshes is temephos
(Abate
®
), which is considered hazardous to fish, birds, insects
(beneficial species as well as the pests), shrimp, and crabs.
Reductions in fiddler crabs and zooplankton have been seen
after its use for mosquito control, and it was found to accumu-
late in salt marsh organisms, including sheepshead minnows,
mussels, and fiddler crabs. Malathion can be applied as a fog
from a moving vehicle, and it will permeate through vegeta-
tion, killing adult mosquitoes. It is considered one of the safest
organophosphates, and has been used in large pest eradica-
tion programs. However, honeybees are quite sensitive to it,
and colonies are sometimes affected downwind from an appli-
cation. It degrades rapidly in the environment, especially in
moist soil, and has relatively low toxicity to estuarine organ-
isms, birds, and mammals. It is usually broken down within
a few weeks by water and sunlight and by bacteria in soil and
water, but it can affect nontarget estuarine organisms before
it is completely broken down. Current use pesticides are fre-
quently detected in the environment and tissues of animals,
even though they are less persistent than the earlier chemicals.
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