days, the residual decreases by about 50 percent. After two months, only about 1/190th
of the original toxicant is present.
d. Inorganic Pesticides. The inorganic pesticides, principally arsenic
compounds and the heavy metals, may be considered permanent rather than persistent
in that they combine chemically with the soil and actually become part of the soil. Of
these, mercury has caused the greatest concern; it is no longer used in pesticide
e. Natural Organics. The natural organic pesticides, of which pyrethrum is
the only one the military stock list, are rapidly biodegradable and thus have virtually no
adverse effect on the environment.
Herbicides. Herbicides do not constitute a separate chemical
classification, but rather fall into a number of different chemical groups including, but not
limited to, the classes into which we group insecticides. Accordingly, the degree of
persistence may vary from a few weeks (as with dalapon, a carbamate) to one or two
months (as with 2, 4-D and dicamba) to periods of 8 to 18 months (as with diuron,
monuron, simazine, and picloram). Picloram has been known to last up to three years,
with very heavy applications.
3-12. HAZARDS TO MAN
a. Acute Poisoning. Acute poisoning occurs from improper handling and use
of pesticides and the unwise practice of storing them in food or beverage containers.
Within the various groups, there is a wide range of acute toxicity. For example, DDT is
relatively safe in terms of acute intoxication, whereas other chlorinated hydrocarbons
have produced many cases of acute poisoning. A characteristic of organochlorine
poisoning is difficulty in establishing the correct diagnosis. The symptoms are
nonspecific and therapeutic measures do not exist. The organophosphate pesticides
include some of the most toxic materials used by man. However, their effect --
cholinesterase inhibition -- results in a well-defined clinical pattern of intoxication that
can be readily diagnosed. Specific therapeutic measures are available and, if applied
with speed and vigor, are highly effective. Carbamate pesticides are also
cholinesterase inhibitors, but the measurement of cholinesterase activity is not a reliable
guide to exposure. As with organophosphates, the toxic potential of some members of
the carbamate group is very great.
b. Chronic Poisoning. Studies of the effects on humans of prolonged low-
level exposure to pesticides have been inconclusive thus far. The chief area of concern
today is the accumulation of pesticide residues in foods, particularly in animal tissues.
Chlorinated hydrocarbons, when ingested by warm-blooded animals, are deposited in
the fat of body tissues. Although a number of pesticide residues have been identified in
animal tissues, DDT is by far the most prevalent. DDT residues in humans tend to
achieve an equilibrium between absorption, storage, and excretion. Storage levels
reach a plateau after relatively long periods and are little disturbed by additional intake.