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- 2 - industry, and industrial waste products, leave persistent residues that add to the contamination in the biosphere. The breakdown of a pesticidal chemical alters the parent molecule, and the alteration often results in a less toxic product. Some pesticidal chemicals break down and disappear soon after application. Others degrade or dissipate slowly, and their residues remain in decreasing but measurable concentrations for varying periods of time; it is to these that the relative term "persistent" is applied. Some persistent pesticidal chemicals remain in the environment for months or years, the rate of degra- dation varying with the local environmental conditions. Some of the organochlorine insecticides and certain other persistent pesticides are disseminated by natural forces throughout the biosphere, and they have characteristics that favor accumulation and storage by organisms. Much of the present public concern is directed to pesticides having these characteristics. This report discusses environmental contamination resulting from the use of persistent pesticides in the continental United States. However, the Committee is well aware that, because of the mobility of some persis- tent chemicals in the atmosphere and in water, contamina- tion of the biosphere must be viewed as a global problem. NEED FOR PESTICIDES During the past quarter of a century, nations in all parts of the world have benefited from increasing use of the synthetic organic pesticidal chemicals. Through use of these chemicals, spectacular control of diseases caused by insect-borne pathogens has been achieved, and agricul- tural productivity has been increased to an unprecedented level. No adequate alternative for the use of pesticides for either of these purposes is expected in the foreseeable future. The President's Science Advisory Committee pointed out in a 1967 study that, in the developed countries, most of the increase in the use of pesticides has been in
- 3 - agriculture, whereas, in the developing countries, most of the increase has been due to efforts to control insect vectors of disease.* Moreover, as a result of the greatly reduced incidence of diseases in some developing countries, more food is needed--to feed those saved from disease. These countries must turn to more intensive agriculture to support their growing populations. Modern agricultural productivity depends on coordinated increase in the use of pesticides, fertilizers, machinery, and better crop varieties. Pesticides that persist in a biologically active form offer certain advantages. If the material breaks down slowly, frequency of application can be reduced and labor costs are correspondingly lowered. If, as a result of its being present in the environment over an extended period, the material accumulates in the tissues of the target species, low initial application rates may well provide effective control. Certain of the persistent compounds have additional advantages over many nonpersistent compounds: they are less hazardous to the persons handling them, and there is less likelihood of immediate harm to nontarget animal and plant species in the treated area. Farmers sometimes apply more pesticide than the amount needed for controlling pests. The public has come to insist on attractiveness in produce, and this insistence weighs heavily in determining market acceptability. Consequently, extra applications of pesticide are made with the aim of raising the level of control of insects or disease agents from good, or reasonable, to the level of almost perfect. The producer of vegetables for commercial canning may be caught between two tolerance limits--one for pesticide residues and the other for insect parts that are legally defined as "filth." Both tolerances were set indirectly by the decisions of society at large. In some instances, *President's Science Advisory Committee, Panel on the World Food Supply, The World Food Problem (Washington, u.s. Government Printing Office, 1967), pp. 138-139.
- 4 - it may be desirable to reexamine the basis of market quality in the interest of reducing pesticide residues in the environment. In home gardening and household uses, pesticides may be applied at excessive rates because the user does not know the proper type of pesticide for best results and because he applies them improperly. In doubt as to proper quantity, he may reason that "if some is good, more is better" and thus may apply too much. Under some conditions, persistent pesticides are the most effective means of controlling pests; under others, they are the only practical means. Many serious public health problems associated with insect vectors of human disease still require the use of persistent pesticides in some countries, either because a suitable short-lived alternative is not available or because the developing countries cannot bear the cost of nonpersistent pesticides, which are usually more expensive than persistent pesticides. Reasonably priced alternative chemicals or nonchemical means may be found in time. Meanwhile, any action to reduce the availability of persistent pesticides needed by developing countries might have serious health conse- quences in those countries. There is no satisfactory alternative to persistent pesticides for protecting wood against insects. Long-lived materials may be placed in the soil, or timber may be impreg- nated to achieve long-term protection, without danger of contaminating the environment. In the United States, persistent pesticides have some uses for which satisfactory alternatives do not exist. Economic entomologists state that at present, the only chemicals that effectively control certain insects are the persistent ones. The insects to which they refer include certain pests of cotton, corn, wheat, alfalfa, fruit, forest trees, lawns, and turf. Despite the present need for persistent pesticides, their availability must not inhibit the search for more desirable means of pest control.
