Endocrine-Disrupting Chemicals and Their Environmental Impacts - Organic Pollutants: An Ecotoxicological Perspective - page 291

and strength of interactions with different environmental estrogens. This illustrates
the need for care when extrapolating for effects of chemicals between in vitro and
in vivo studies and across species. The dangers in cross-species extrapolations for
the effects of chemicals is especially well illustrated in the case of diclofenac, where
adverse effects are bringing about potential extinction of wild vulture populations
in Asia owing to their high susceptibility to the drug, which was not predicted from
laboratory studies on mammals.
Research into the biological effects of EDCs has clearly shown they can have inter-
active effects, and this is a priority for further work if we are to develop an accurate
picture of their potential effects on wildlife populations. Studies on EDCs have also
served to emphasize that chemicals that affect behaviors can potentially impact popu-
lations through altering breeding patterns and changing the normal genetic structure
of populations. It is the author's opinion that testing strategies for EDCs should take
these facts into account and incorporate a more intelligent approach to the hazard
identification process, rather than necessarily simply applying present standardized
tests. Modifications of the present OECD and USEPA testing programs for chemicals
are presently under way to incorporate endpoints more suitable for detecting EDCs,
but they do not include some important systems affected, including behavior.
It is unlikely that any chemical-testing strategy developed will predict all adverse
outcomes, especially those that arise as a consequence of chronic exposures to low
levels of chemicals. The American Chemical Society lists over 246,000 inventoried
or regulated chemicals worldwide (http://www.cas.org/cgi-bin/cas/regreport.pl), and
this does not include their products of degradation, conjugates, or metabolites. The
challenges for testing and screening of chemicals for endocrine-disrupting activity
are therefore considerable. Endocrine disruption as an environmental issue arose
through observations of adverse effects in wildlife populations, not through sys-
tematic screening and testing of chemicals, and it is the opinion of these authors
that long-term environmental monitoring programs of wildlife populations need to
be included as part of any effective and well-integrated hazard identification and
risk management program for EDCs. We accept that the challenges associated with
disentangling adverse effects in wildlife populations with causative agents are con-
siderable, but such programs can nevertheless provide warning signals regarding
which pragmatic chemical identification programs can be mounted. Environmental
monitoring programs ideally need also to include analytical chemistry to measure
for exposure concentrations. This, however, also involves considerable associated
challenges. For example, EDCs such as EE 2 can induce biological effects at concen-
trations difficult to quantify accurately in environmental samples (at parts of a ng/L
in water), even using some of the most sophisticated analytical techniques. Further
support for the need for wildlife monitoring programs comes from the argument
that individual-level consequences of toxicant exposure can be weak predictors of
population-level consequences (Forbes and Calow 1999). Modeling approaches are
gaining increasing favor to support investigations into the potential for population-
level effects of EDCs and other chemicals. These approaches, however, require high-
quality empirical data for both their development and validation, again drawing on
the need for data from monitoring programmes of wildlife populations.