TOXICITY OF PESTICIDES
a. Insecticides. Toxicities of the insecticides discussed in this subcourse for
which data are available are presented in Table 1-1. In reading this table, it must be
recognized that the data are based on laboratory experiments with small animals.
Unfortunately, humans do not always react in the same way as small animals; therefore,
the lethality of these chemicals to man may vary considerably from the test data.
General statements on the toxicities of various insecticides are included in succeeding
(1) Inorganic insecticides. Most of the inorganic insecticides are
formulated from the heavy metals and are extremely toxic to warm-blooded animals.
Arsenic poisoning, for example, produces symptoms of severe irritation of the
gastrointestinal tract accomplished by vomiting and albuminuria. Chronic arsenic
poisoning may result from prolonged exposure to small amounts because of absorption
through the lungs, skin, or alimentary tract. An apparent tolerance to ingestion of
arsenic may appear, though this is not a systemic tolerance, but is based on diminished
absorption from the alimentary tract. Normally, workers with this pesticide are
simultaneously exposed to inhalation and skin absorption. Symptoms of chronic
poisoning may go unnoticed at first. Bronchial irritation may be attributed to infection or
to smoking. Loss of appetite, nausea, vomiting, and diarrhea may be attributed to some
other pesticide. Prolonged chronic exposure eventually leads to anemia and multiple
neuritis of the extremities; skin changes and even loss of hair and fingernails may occur.
Paralysis and liver damage are late manifestations. In 1956, the latest year for which
detailed records are available, 55 percent of all fatal accidents caused by pesticides in
the United States involved inorganic ones, especially arsenic and phosphorous.
(2) Botanicals. Nicotine pesticides, used chiefly in the control of plant
pests, are highly toxic to mammals. The poison is readily absorbed through the skin.
Depending upon the concentration and duration of contact, symptoms of poisoning may
appear. Rotenone is another botanical pesticide that is frequently used for a variety of
pest problems and as a deliberate fish poison. The mammalion toxicity of rotenone
varies considerably among animal species, though normal precautions in its use are
adequate to protect humans. Pyrethrum is one of the least toxic of all pesticides to
(3) Synthetic organic insecticides.
(a) Chlorinated hydrocarbons. Many of the items used in military
pest control programs belong to this group of chemicals. Some of them are quite
hazardous as concentrates and a single exposure is capable of causing illness and
death. There is a wide range of toxicity and hazard. Repeated exposure to dilute
solutions also may be hazardous; therefore, maximum use of protective measures
should be employed. Pesticides in this group of chemicals usually affect the nervous
system. The result is spastic inability to coordinate muscular activity, which progress to
convulsions. If death occurs, respiratory failure is usually the immediate cause.