Contaminants are toxic substances that can harm fish, wildlife, plants
and people. Some environmental contaminants (including mercury, cadmium
and other metals) occur naturally in the environment. Human activities
can release these elements to the surrounding landscape. Natural deposits
can also serve as sources of these elements. Regardless of their source,
elevated concentrations of these contaminants can have adverse affects
on biological resources. 
A wide variety of chemical compounds are also used by society on
a regular basis. These compounds can be released into the natural
environment through spills, permitted discharges and other sources.
While some chemical compounds are virtually non-toxic, others affect
fish and wildlife when concentrations exceed a certain threshold.
Thresholds of concern differ among contaminant types and (individual)
organisms differ in their sensitivity to various contaminants. In
addition, the length of time an individual is exposed often influences
the degree of any adverse effect.
Some contaminants accumulate to a greater degree in predatory species.
Concentrations of some contaminants magnify through food chains, with
higher concentrations at the “top” of the food chain or
food web.
The field of environmental toxicology continues to evolve at a rapid
pace. New scientific studies are published every year, and with new
research comes better understanding of how contaminants affect various
species. Many factors are still poorly understood, for example little
is known about the effects of chemical mixtures and the implications
of long-term exposure to low levels of contaminants.
The U.S. Fish and Wildlife Service has been involved
with studying the effects of environmental contaminants on fish and
wildlife for several decades. As the main federal agency dedicated to
protecting wildlife and their habitat from pollution’s harmful
effects, the Service maintains an
Environmental
Contaminants Program with more than 75 offices around the country.
The Service’s major responsibilities include the conservation
of migratory birds, management of more than 500 national wildlife refuges,
enhancement of fish and wildlife habitat, management and restoration
of interjurisdictional fisheries, and recovery of endangered species.
Significant issues for the Environmental Contaminants Program in
Alaska includes study of contaminants in the Arctic, study of contaminants
in wildlife harvested for subsistence, evaluating the effects of contaminants in threatened,
endangered and declining species, identification and cleanup of contaminants
on National Wildlife Refuges, responding to oil and hazardous materials
spills that affect trust resources, and restoration of species and
their habitats injured by contaminant spills or releases.
