ABSTRACT
Mechanisms of action (MoAs) are the specific means by which chemicals induce effects in
organisms. Examples include narcosis, respiratory uncoupling, and inhibition of calcium
uptake. Modes of action are more general and phenomenological; a mode of action implies
a common toxicological outcome but not necessarily the same underlying mechanism.
Examples include acute lethality, tumorigenesis, feminization, teratogenesis, and hatching
failure. Note that the terms mechanism of action and mode of action are not used consistently
in the literature, and there is no agreed dividing line between them.
