The Organochlorine Insecticides - Organic Pollutants: An Ecotoxicological Perspective - page 119

the principal primary detoxication of dieldrin, endrin, and heptachlor epoxide is by
monooxygenase attack.
In mammals, dieldrin and endrin are also converted into keto metabolites
(Figure 5.5). In the rat, the keto metabolite is only a minor product, which, because
of its lipophilicity, tends to be stored in fat. With endrin, a keto metabolite is formed
by the dehydrogenation of the primary monohydroxy metabolite. In mammals, the
trans diol of dieldrin is converted into a diacid in vivo (Oda and Muller 1972).

5.3.3 e n v i r of n m e n T a l f a T e o f c y c l of d i e n e s
During the 1950s, cyclodiene insecticides came to be widely used for a number of
different purposes. They were used to control agricultural pests, insect vectors of dis-
eases, rodents, and ectoparasites of farm animals, to treat wood against wood-boring
insects, and to mothproof fabrics. Because of their very low solubility in water, such
insecticides were usually formulated as emulsifiable concentrates or wettable pow-
ders. Following the discovery of their undesirable environmental side effects, the
use of cyclodienes for many purposes was discontinued during the 1960s and early
1970s in Western Europe and North America. The following account will focus on
the environmental fate of aldrin, dieldrin, and heptachlor—three insecticides that
gave rise to persistent residues and were shown to cause serious and widespread
environmental side effects. Other cyclodienes were less widely used, and some (e.g.,
endrin and endosulfan), although highly toxic, were far less persistent.
As mentioned earlier (Figure 5.5), aldrin and heptachlor are rapidly metabolized to
their respective epoxides (i.e., dieldrin and heptachlor epoxide) by most vertebrate spe-
cies. These two stable toxic compounds are the most important residues of the three
insecticides found in terrestrial or aquatic food chains. In soils and sediments, aldrin and
heptachlor are epoxidized relatively slowly and, in contrast to the situation in biota, may
reach significant levels (note, however, the difference between aldrin and dieldrin half-
lives in soil shown in Table 5.8). The important point is that, after entering the food chain,
they are quickly converted to their epoxides, which become the dominant residues.

taBLe 5.8
Half-Lives of cyclodienes

compound material/organism Half-Life

Dieldrin Soil 2.5 yr

Aldrin Soil 0.3 yr

Heptachlor Soil 0.8 yr

Dieldrin Male rat 12-15 d

Dieldrin Pigeon 47 d (mean)

Dieldrin Dog 28-32 d

Dieldrin Man 369 d (mean)

Sources: Soil data from Edwards (1973). Data for pigeon from Robinson et
al. (1967b). Other data from Environmental Health Criteria 91.