Human volunteers fed 35 mg of DDT per day over a period of 21 months reached a
steady storage level of residual material after about one year. When dosages were
discontinued, the residual deposits were rapidly depleted and storage levels decreased
until a lower level was reached. Surveys have shown that the fatty tissue of U.S.
inhabitants contains an average of 4 to 7 parts per million (ppm) DDT or its derivatives.
Fat storage of the chlorinated hydrocarbons has been a source of anxiety to many
people. However, despite numerous careful and detailed studies, no positive causal
relationship has been established between the presence of pesticide residues and
human disease. Still, authorities agree that active measures must be taken to prevent
the accumulation of pesticide residues. Both the Department of Health and Human
Services and the World Health Organization are trying to establish valid threshold levels
for the accumulation of pesticide residues in humans.
3-13. HAZARDS TO OTHER NONTARGET ORGANISMS
The hazards of pesticide employment are not limited to the toxicity to man. Man
is the only one of thousands of species in the living system of the earth. Most of these
organisms are considered to be essential to man's well being. When a pesticide is
applied to control specific pests, organisms other than those intended for eradication
are also killed. The "innocent bystanders" are referred to as nontarget organisms.
a. Phytoplankton. Drifting plant cells in natural waters carry on a large
portion of the photosynthesis on the earth's surface. These plant cells, or
phytoplankton, synthesize most of the earth's organic material, produce most of the
oxygen of the atmosphere, and participate in other essential ways in the chemical
cycles of the biosphere. Evidence indicates that pesticides may significantly reduce
b. Beneficial Insects. Not all insects are harmful or undesirable. Naturally
occurring parasitic and predacious insects control many insect pests. Some of these
parasitic and predaceous species are more susceptible to certain pesticides than are
the pest species. For example, when parathion was applied to a cole crop, the number
of predaceous and parasitic species was reduced by 95 percent, whereas the number
of plant-feeding species was reduced by only 8 percent. Following such a disruption,
population outbreaks of the plant-feeders occur explosively. Similar results were
observed in apple orchards where DDT applied against red mites kill predacious lady
beetles, but hardly affected the mite population. Subsequently, mite damage was quite
severe. Honey bee and wild bee pollinators have been found to be more susceptible to
carbaryl than many other species of insects. Therefore, the widespread use of this
chemical may reduce the pollination of both cultivated and wild plants.
Marine Invertebrates. In the coastal environment, several kinds of
organisms are unusually susceptible to chemicals contained in waters flowing from land.
Shellfish and other relatively immobile forms of life living on the bottom of bodies of
water must tolerate whatever reaches them since they cannot escape. Arthropods such
as shrimp and crabs are biologically similar to insects and mites, and highly sensitive to