Atrazine's reversible herbicidal mode of action:  Atrazine's mode of
action results from non-covalent, rapidly reversible binding to the D1
protein of photosystem II, and responses in plants are proportional to
exposure concentration and duration. The enclosed document, which shows
that the aquatic macrophyte Lemna gibba fully recovers from 14-day
exposures of atrazine at concentration up to 80 ppb, provides evidence
of the appropriateness of the use of a model that simulates the
community effects resulting from the short-term elevated exposures that
occasionally occur in Midwestern streams (see Charge Question #1).

