Page 826 - The Toxicology of Fishes

806 The Toxicology of Fishes

O
O
H C
3
C C C O
H C
3
Pyrethrin I H C
3

O C N
O
Cl C C O C

Fenvalerate

O
Cl F
C C C O F
CF 3
Tefluthrin F CH 3
F

O
CH 3

C OH 5 C O
2
CH 3

Ethofenprox

FIGURE 20.1 Structures of one natural and three synthetic pyrethroid insecticides.

of the natural pyrethrins. The use of more stable side-chains and rings, as well as the inclusion of
chlorine, bromine, and fluorine, resulted in synthetic pyrethroids that were much less susceptible to
oxidation, hydrolysis, and photolytic reactions. The new types of pyrethroids were labeled photostable,
but they persisted for much longer times in water and soil, as well as on plant surfaces. Figure 20.1
shows one natural pyrethrin and three synthetic analogs that all generate essentially the same toxic
symptoms and effects, despite quite divergent structures.
When the chlorinated hydrocarbon insecticides were introduced 60 years ago, accidental fish kills
became commonplace. DDT, dieldrin, endrin, heptachlor, chlordane, toxaphene, endosulfan, and other
related toxic, lipophilic, and persistent pesticides are extremely toxic to fish, with LC values in the
50
range of micrograms per liter (parts per billion) to nanograms per liter (parts per trillion). There were
also serious effects from chronic exposures to the ubiquitous low-level residues in water and sediment.
The exceptional persistence and lipophilicity of the chlorinated hydrocarbons led to numerous delete-
rious effects on reproduction, growth, and survival. Biomagnification of the residues occurred upward
through trophic relationships; simple uptake across gills also increased concentrations in fish tissues.