By necessity, first estimates of the safety of a pesticide must be based on its 
toxicity in experimental animals. Such study may provide essentially all the information 
that is necessary inevaluating the probable results of acute exposure such as that involved 
in accidentally eating the compound. However, additional studies must be made if the 
mode of action of the compound is to be understood and the danger of occupational 
poisoning is to be evaluated. The study of dermal toxicity in animals is more useful than 
the study of oral toxicity in predicting occupationalhazards. However, there are sufficient 
differences in the reactions of different species to the same compound that studies must 
eventually be made in man himself. Such studies, in man, have been made of a number 
of compounds including DDT, schradan, dimefox, parathion, Dipterex, malathion, tetraethyl 
pyrophosphate, and dinitrophenol. 
It may be nearly as valuable to know the magnitude of exposure by different routes 
as to know the toxicity of a compound. It has been known for some time, on the basis of 
animal experiments, that many of the newer pesticides, except DDT, are absorbed 
easily through the skin, even when not in solution. This property has been associated 
correctly with cases of poisoning following massive skin exposure, but the importance 
of dermal absorption in the more ordinary cases of occupational illness frequently has 
been missed. Actual chemical measurement of the exposure of applicators to several 
compounds used in agriculture or in vector control has shown that skin exposure is 
greater and sometimes very much greater than respiratory exposure when liquid sprays 
are used. However, not all work situations have been explored and additional studies 
need to be made. It has been necessary to develop new techniques for measuring the 
exposure to pesticides because the older methods used for measuring exposure in 
factories and mines proved inadequate. The newer methods are useful not only in 
evaluating different routes of exposure, but may be used also in studying the efficiency 
of protective clothing and devices. 
Incidental or environmental exposure to pesticides has been a source of difficulty 
only rarely, as for example, the allergic reactions of a few people exposed to vaporized 
lindane. Excluding acute poisoning following massive exposure, any ill effects are to be 
expected in persons whose exposure is intensive and prolonged. A study of such people 
is also the best single source of information about the potential long-term hazard to 
the general population in the use of any particular compound. 
Nothing is now known to justify the suggestion from some sources that pesticides 
currently constitute a serious threat to human health and that they are now a significant 
cause of blood dyscrasias and other diseases. However, it is the duty of the Public 
Health Service to keep alert to such possibilities. In addition to our own planned studies, 
we welcome reports of cases or any other relevant information. 
There is now a considerable amount of information about the clinical effects of 
poisoning by a wide range of pesticides inman. At least 48 of these compounds are known 
to have produced human poisoning. Some useful information on the treatment of poisoning 
by many of them is available. However, much remains to be learned about symptomatology 
and treatment, as well as about the prevention of poisoning. 
In conclusion, the human safety record of the newer compounds is good in some 
technically advanced countries, largely owing to careful labeling. In countries where 
labeling is poor, or where illiteracy or irresponsibility tend to vitiate labeling, hundreds 
of cases of human poisoning have occurred. Because of the usefulness of economic 
poisons in the control of vector-borne diseases and also in the control of a wide range 
of pests of field crops, livestock, forests, and stored products, it should be our aim to 
improve their safety so that they may be fully exploited. 
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