964 PESTICIDES
National Academy of Sciences study (1987) concluded that
nearly 80% of the estimated oncogenic risk to humans is from
residues to 10 pesticides. The study concluded that 98% of the
oncogenic dietary risk could be eliminated by revoking the
registrations of 28 carcinogenic pesticides.PESTICIDES IN WILDLIFEThe widespread use of pesticides has occasioned much con-
cern about adverse affects on wildlife. Significant reviews
of this important subject include Hunt (1966), Dustman and
Stickel (1966, 1969), and Cope (1971). Concern in this area
has moved from studies of acute toxicity (Rudd and Genelly,
1956) to physiological, behavioral, and ecological implica-
tions of the toxicity to non-target organisms (Cope, 1966;
Newsom, 1967; Johnson, 1968; Pimentel, 1971). Despite
the implications of selective toxicity inherent in pesticide
application it is evident that pesticide usage often has delete-
rious effects on non-target organisms. As Pimentel (1971)
points out, pesticide usage in the United States is aimed at
about 2000 pest species of plants and animals, but many of
the remaining 200,000 non-target plants and animals, the
great majority of which are necessary for human survival,
are affected directly or indirectly. The anthropomorphic con-
cepts of pest and beneficial species are not valid ecologically
and it is obvious that both target and non-target organisms
respond to pesticide contamination in a variety of essentially
similar ways (Newsom, 1967).Acute Toxicity of PesticidesAn important first step in assessing pesticide effects on
organisms is the determination of the acute toxicity as LD 50in terms of dose applied, eaten, or injected; or LC 50 in terms
of concentration in the water, causing 50% mortality of an
animal population. Knowledge of the comparative toxici-
ties of a variety of pesticides to representative organisms is
important in selecting pesticides for various uses and in
assessing risks to non-target species. Unfortunately most
of the large amount of data on quantitative toxicology deals
with effects of a few compounds on a wide variety of spe-
cies and there is little uniform data on a wide representation
of species for the important pesticides. Table 8 presents a
selection of toxicity values to a variety of organisms for the
widely used pesticides for which adequate data is available.
From the comparative viewpoint, the table shows the impos-
sibility of profound generalizations about pesticide toxicity.
Methoxychlor and malathion, two of the very safest materials
to mammals and birds, are highly toxic to fish and inverte-
brates. Carbaryl, with low toxicity to mammals, birds, and
fish is highly toxic to invertebrates. Zectran and carbofuran,
among the most toxic compounds to mammals and birds, are
of low toxicity to fish. Endrin, phorate, disulfoton, and para-
thion are general biocides, highly toxic to nearly all animals.
Only the herbicides such as dalapon, dicamba, diquat, diuron,
endothall, paraquat, 2,4-D, 2,4,5-T and simazine seem rela-
tively safe to all the animals listed.Ecological MagnificationThis descriptive term applies to the ability of living organisms
to concentrate stable, lipid soluble, water insoluble substances
in their bodies either through successive accumulation in food
chains or directly from water by partitioning. In this manner
residues of substances such as DDT and dieldrin have been
concentrated in fish 1 10 6 and 1 10 5 fold respectively
over the concentration of the water. The first demonstrationTABLE 7
Average daily intake and incidence of pesticides in U.S. human diet compositesaPesticideDaily intake from
total diet mg/kg % positive samplesFAO-WHO acceptable
intake mg/kgDDT 0.0005 37.4 0.01
Dieldrin 0.00009 20.2 0.0001
Lindane 0.00006 13.6 0.0125
Heptachlor epoxide 0.00004 12.6 0.0006
Carbaryl 0.0012 4.7 0.02
Malathion 0.001 4.5 0.02
Aldrin 0.00003 4.5 —
2,4-D 0.00005 3.5 0.017
Diazinon 0.000014 3.0 —
Dicofol 0.00011 2.5 —
Pentachlorophenol 0.00006 2.5 —
Endrin trace 2.3 —
a Data from Duggan (1969).C016_004_r03.indd 964C016_004_r03.indd 964 11/18/2005 11:00:07 AM11/18/2005 11:00:07 AM