The large variation among species (>3 orders of magnitude)
presents a challenge for the establishment of sensible environmental regulation of Cu since it will be impossible to test all
organisms, including endangered species, and thus capture the
full range of sensitivity. Considering the wide range in sensitivity for a relatively small number of species tested the most
sensitive (and tolerant) species likely have yet to be identified.
This challenge is best met by understanding the sources of the
variation in sensitivity within and among species to allow for extrapolation to organisms for which data cannot be obtained.
Such an understanding must include an understanding of the physiological basis for variation in sensitivity, a point which
becomes even more important when considering Cu toxicity in marine and estuarine environments.