Populations 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 reproduce. Wildlife 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.
The embryo is the most sensitive life stage of animals to the hazards posed by these chemicals. Current contamination in wildlife has reached levels in some regions at which there are known sublethal effects sufficient to impair populations. Many 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.