ABSTRACT
Life was certa inly simp ler in the old days . . . when we could ev aluate risk with a safety factor .
Doull (1984)
In mo st c ases, eco logical risk asses sment s must be based on exp osure-r esponse da ta for
specie s, life stage s, levels of organiz ation, a nd responses other than those specif ied by the
asses sment endpo ints. In so me cases, no exposure-r esponse data are avail able for the agent of
concern for an y relevan t or ganisms. For ex ample, the end point is bro ok trout produ ction an d
we have only a fathe ad minno w LC50 or only the structure of the ch emical. Hence, it is
necessa ry to use extrapo lation models based on assum ptions or statistica l an alyses to ex-
trapol ate to the endp oint specie s or communi ty or to estimate pa rameters for populatio n or
ecosyst em mod els (Chap ter 27 and Chapte r 28).
