some of the arthropod poisons. Oysters and mussels have notable capacities for
biological concentration of pesticides, and oysters have been noted to accumulate DDT
to 70,000 times the concentration in ambient water. These levels of residue not only
pose a threat to the arthropods themselves, but also to the higher forms of life who feed
upon them.
d. Fish. Various species of fish have varying degrees of susceptibility to
pesticide intoxication, but concentrations of 5 ppm of DDT in trout eggs have caused
100 percent mortality in a fry. A few species of fish have developed resistance to
specific pesticides, but the resistant fish apparently have higher concentrations of
pesticide; therefore, they pose an increased threat to consumers, including man.
e. Birds. Birds have provided much of the significant evidence on the
worldwide effects of insecticides. Public and scientific concerns were alerted by early
reports of heavy mortalities among robins which had fed upon earthworms
contaminated during insect control programs. This concern was heightened by later
evidence on eagles and falcons and their failure to produce young. Significant is the
fact that the best-known cases of drastic population declines are among the carnivorous
eagles and hawks, which are at the end of the food chain. Concentrations of DDT as
high as 75.5 ppm in body weight have been found in the tissues of seagulls, who feed
on sea life which build up added residues with each link in the food chain. This buildup
is known as "ecological magnification."
f.
Mammals. Insecticide damage in mammals apparently has not been as
frequent or as serious as in birds and fish, although the available data are scarce. Field
sampling has shown that DDT and its derivatives are present in the fat of many species
of wild mammals. Only a few wild mammals have been sampled, but it is probable that
many or all have now been exposed to the persistent pesticides, that many have
accumulated measurable quantities, and that some have been adversely affected.
3-14. ROUTES OF CONTAMINATION
Contamination of the environment by pesticides occurs primarily through the
a. Air. One of the most common routes of contamination by pesticides is
through the air, either by aerial or surface application. Aerial dispersal is the distribution
of pesticides from aircraft in the form of sprays, dusts, mists, fogs, and granules. It is
designed to obtain maximum efficiency at minimum cost. Aerial dispersal provides
rapid coverage of large areas and breeding sources that are inaccessible by other
means. In 1963, the state of California used about 20 percent of the U.S. pesticide
production, 80 percent of which was applied by aerial treatment. In military use,
however, aerial application of pesticides is much more limited because of the inherent
hazards associated with this method of distribution. Factors that influence aerial
application are wind, temperature, rainfall, turbulence, terrain, vegetation, condition of
equipment, type of aircraft, and the ability of the pilot. Hazards include the inadvertent
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