the last five decades many wildlife populations across the North
American continent have experienced severe and often sudden declines
that in some cases have led to extirpation. While some of these
declines are attributable to natural biological events such as epidemics
caused by microbial pathogens and well-established human causes
such as overharvesting, habitat changes, and introduction of exotic
species, many of these declines have not been satisfactorily explained
by these factors. During this time a number of man-made compounds
were introduced into the environment that caused the declines of
some wildlife populations through adult and embryonic mortality.
man-made contaminants can alter embryonic and early postnatal development.
The consequences of this interference are irreversible, in some
cases leading to early death, but in other cases not manifested
until the individual reaches adulthood with resultant loss of fertility.
Through subtle biochemical and physiological changes the contaminants
interfere with the development of the reproductive, endocrine, immune,
and nervous systems of embryos, and therefore are likely candidates
for causing some of the declines and failure of wildlife populations
to recover even after regulatory prohibition of activities involving
these compounds. In light of this knowledge, 23 wildlife experts
were gathered in retreat at Wingspread, Racine, Wisconsin, 10-12
December, 1993, to discuss the topic of "Environmentally Induced
Alterations in Development: A Focus on Wildlife." Participants reported
on their observations of alligators, bald eagles, beluga whales,
boreal toads, bottle-nosed dolphins, Caspian terns, common terns,
Florida panthers, Forster's terns, great blue herons, herring gulls,
leopard frogs, old squaw ducks, polar bears, roseate terns, scoters,
sea turtles, slider turtles, spectacled eiders, water fleas, white
croakers, and wood ducks. Participants were expected to reach some
conclusions concerning the nature, magnitude, and geographic scope
of the problem on the North American continent.
following consensus was reached by participants at the workshop.
We are certain of the following:
in a number of species and many taxa (including plants) are in
progress on the North American continent. Some of these declines
are related to exposure to man-made chemicals. Such declines are
not solely a US or North American problem but are occurring on
a global scale.
is a special cause for concern for long-lived species which may
or may not (at this time) show overt signs of reproductive impairment.
Examples of species that are near extirpation at the population
level are those that are annually replenished by outside stock,
not by intra-regional reproduction, such as Great Lakes lake trout
and shoreline bald eagles, and Lake Apopka, FL alligators and
of many long-lived species are declining, some to the verge of
extinction, without society's knowledge. The presence of breeding
adults and even healthy young does not necessarily reflect a healthy
population. Detailed population analysis is needed to determine
whether offspring have the functional capacity to survive and
are exposed to compounds that disrupt development of the reproductive,
immune, nervous, and endocrine systems and thereby can lead to
population instability. The pollutants of greatest concern affect
cellular and molecular processes that regulate developmental,
endocrine, and immunological functions. Hormones are natural substances
that control normal development of all embryos and fetuses. Many
of the contaminants mimic and/or interfere with female and male
hormones, thereby modifying development and reproduction.
embryo is the most sensitive life stage of animals to the hazards
posed by these chemicals.
contamination in wildlife has reached levels in some regions at
which there are known sublethal effects sufficient to impair populations.
Unless the continuing release of man-made toxic chemicals is prohibited
immediately in certain well-studied North American major aquatic
systems, populations of important top predator species may become
persistent contaminants do not remain at the site of release.
Chemical releases on one continent may not only affect animals
on that continent but animals on other continents and in other
hemispheres. They are carried as particulates or gases in the
air, surface waters, groundwater, and ocean currents across or
between continents and by animals that travel long distances from
the site of contamination. The contaminant, therefore, can enter
the food web in places remote from the site of release.
is no longer sufficient to approach population/species revitalization
passively by providing appropriate habitat and expecting threatened
or extirpated populations to recover. Contamination of apparently
useful habitat is not always visible and may not cause overt lethality.
Instead, contaminants may cause population-threatening changes
in functionality. For example, populations may not be able to
infectious diseases because of immunosuppression;
the inability to obtain sufficient food, avoid predators,
and the loss of parenting instinct because of neurotoxicological
the result of abnormal sexual development of anatomy or behavior
because of endocrine disruption.
has been difficult to document causal relationships between population
declines and failures with the chemicals suspected to have caused
them. The difficulty can only be successfully addressed through
multidisciplinary research linking ecological, wildlife, human,
and laboratory animal research and by building bridges between
the human, veterinary, and environmental health sciences.
collaboration and exchange of information between wildlife, laboratory
animal, and human investigations is essential. This requires a
redefinition or broadening of the role of federal agencies and
the institutionalization of causal investigations (environmental
detective work). This work must be supported by federal agencies
to investigate the declines and their causal relationships.
have been made between some effects and specific man-made chemicals.
Other chemical-effect linkages, which in fact may exist, have
not been made for several reasons because (1) it is difficult
to distinguish individual effects of the numerous man-made chemicals
present in the environment because many have similar biological
effects; (2) other biotic and abiotic factors play a role in population
instability; (3) testing for the presence of such chemicals is
so expensive; and (4) additional research is required to clarify
these connections (see below).
regulatory action depends upon knowledge of the specific physiological
and/or biochemical endpoint of a chemical. However, we have yet
to identify many biomarkers which are specifically diagnostic
of a substance or an effect. Because few such biomarkers have
been developed, there is clearly a need for more physiological
and molecular-oriented biomarker-based research. However, we believe
that the prerequisite of documenting the mode of toxic action
and development of specific biomarkers to make cause and effect
links before taking regulatory action leads to unnecessary delays
that continue to result in injury and potential extirpation of
more populations and species.
issues addressed in this statement are fundamental to the concepts
of "biodiversity", "sustainable development", and "ecosystem health"
and call for responsible global citizenship. They assume a preemptive,
rather than a reactive, role for scientists, wildlife agencies,
and environmental regulators (see below).
We estimate with confidence that:
many cases wildlife and humans have exceeded their capacity to
compensate for exposure to chemicals.
more areas of the North American continent are surveyed and a
wide variety of multigenerational consequences are taken into
consideration, more evidence of damage will be revealed among
wildlife and human populations. Many effects are taking place
that are not easily observed, but they do exist. Too much attention
has been directed toward the health of the
current population, the directly exposed individuals, and not
enough on the offspring. Our current regulatory focus on adult
mortality is not sufficient to preserve reproductively successful
populations. Rather, we must ensure that successive generations
an animal is exposed at the same time to many chemicals that individually
are at non-toxic levels, additivity, antagonism, potentiation,
and synergy can result in unpredictable consequences. Concomitant
exposure to multiple chemicals can cause massive or subtle, but
potentially tragic effects.
chemically induced syndromes have been indentified in the past,
it has been difficult to establish cause and effects relationships
and to do so has frequently taken decades. The basic tenets of
epidemiology have proved valuable in organizing information to
infer causal relationships. The tenets include (1) time order
(exposure must precede the effect); (2) strength of association
(relative risk); (3) specificity of a compound to an effect (does
X lead to Y?); (4) consistency on replication (results are supported
across studies, geographic areas, and over time); (5) coherence
with biological theory (the relationship must be biologically
plausible); and (6) performance on prediction (does the test stand
up in the field?).
are reliable sentinels of effects of chemicals on human populations.
Lesions at every level of biological organization provide parallels
and excellent models for assessing the response of humans exposed
to the same chemicals. Effects seen at the cellular to the population
levels among wildlife populations should be an integral part of
assessments of risk or injury to human health.
There are many uncertainties in our predictions because:
implications of cumulative exposure to the vast number of chemicals
released in the environment are difficult to determine. Although
data may become available on the mechanisms of action of certain
chemicals, there is no way to account for the interaction of the
large number of chemicals to which an animal is exposed.
differences in land-use practices, industrial activity, and geophysical
characteristics must be factored into a cumulative, multimedia
exposure model. Migratory species pose additional difficulties
when determining sources of exposure.
systematic, coordinated effort has been undertaken to determine
the geographic extent to which contaminants contribute to the
degradation of wildlife populations. While there is evidence in
areas where researchers have suspected and looked for wildlife
damage, there are many more areas of the continent that have not
yet been surveyed. Consequently, the magnitude of the damage is
incompletely understood for major wildlife taxa.
and Canadian governmental agencies no longer appear willing to
commit sufficient long-term, fiscal resources for documenting
the effects of chemical exposure in wildlife. Until responsible
parties are designated and given adequate appropriations to address
wildlife health problems, biodiversity will continue to decline.
We believe that:
To improve our assessment of dangers posed by chemicals:
assessments of risks posed by single chemicals are not adequate
for assessing the risks for embryos exposed to multiple chemicals.
tenets of epidemiology have been successfully used to infer causal
associations between certain syndromes and exposures to multiple
systems for characterizing wildlife population declines can help
to determine the magnitude and scope of the problem. Initial efforts
must concentrate on a suite of contaminants thought to have the
most serious consequences. It is imperative to replicate the damage
observed in the field under laboratory conditions in order to
confirm cause and effect linkages.
chemicals licensed for environmental release should be tested
throughout a minimum of two generations for a wide variety of
effects including reproductive, immunological, endocrinological,
and neurological endpoints.
abate the scope and severity of wildlife population declines,
we must endeavor to bring the message into our homes, schools,
and the political arena. Until more people understand the insidious
nature of developmental toxicants, little will change. More popular
press articles and other media should broadcast the message about
the effects of developmental toxicants using the wildlife/human
connection. A major popular press publication is needed to get
the message to the public. Pressure must be exerted on legislators
and public health officials to take action to restore damaged
populations and to prevent further damage from occurring.
balanced and comprehensive assessment of wildlife declines and
diseases caused by chemicals on a global basis is imperative.
These assessments must include both retrospective as well as prospective
must be forthcoming to support interdisciplinary investigations,
the use of non-traditional organisms (such as wildlife), and research
that focuses on functionality in addition to obvious damage. It
is imperative to establish a central coordinating office and interdisciplinary
teams that can report on sites where subtle effects are occurring
and be responsible for directing where field samples can be shipped
for initial and rapid evaluation of effects and identification
of suspected chemical causes.
electronic network should become available to wildlife biologists
to improve networking and to increase opportunities for collaboration.
In light of the strenuous and unpredictable nature of field research,
networks could increase the maximum utilization of sampling and
the power of each study.
is an urgent need to have integrated funding mechanisms established
to facilitate these studies, possibly by creation of a National
Institute of the Environment.