What Does Ddt Cause In Animal Populations

The Case of DDT: Revisiting the Impairment

Background

The fact that DDT (or ddt) played a role in the decline of bald eagle and other bird-of-casualty populations (e.g., ospreys, brown pelicans) is now commonly appreciated among most biologists. All the same, the link between Dichloro-diphenyl-trichloroethane and the eggshell thinning that caused reproductive failure in these birds was not initially recognized. Ultimately, the connection was made by re-examining the description of the impairment.

The get-go link betwixt DDT and diminishing baldheaded eagle and other birds of prey populations was the consistent observation of loftier body burdens of Ddt metabolites. In other words, there was co-occurrence of the declining bird populations and the candidate cause, DDT. In that location was also prove of a complete exposure pathway to birds based on body brunt of Dichloro-diphenyl-trichloroethane. Yet, extensive toxicity testing of Ddt on adult bird mortality revealed no human relationship. This suggested that the proposed mechanism, toxicity, was implausible. All the same, lethality was not the damage; decline of birds-of prey was the harm. A new conceptual model was required that considered other mechanisms that could consequence in declines in bird populations. In a reexamination of the overall analysis, it became apparent that the species chosen for testing had been relatively tolerant of DDT exposure compared to those that were afflicted in the wild, and that the endpoint observed in these tests (lethality) would non reverberate reproductive success or failure resulting from Ddt exposure.

Field observations somewhen revealed a potential plausible machinery of reproductive failure due to eggshell thinning among baldheaded eagles and other birds of prey. Laboratory experiments showed that DDE could cause eggshell thinning. Field studies showed that field exposures to DDE, a metabolite of Ddt, were sufficient to cause effects in many species of birds based on the stressor-response relationship. Together these findings provided lines of evidence by which Dichloro-diphenyl-trichloroethane might cause eggshell thinning and reduce reproductive success, a more specific damage than declines in bird population.

Outcome

In 1972, DDT was banned from most uses in the United states. In the years following the ban, baldheaded eagle and other bird-of-prey populations slowly recovered. The recovery of bird populations after the use of Ddt was banned, is an example of mitigation of the consequence following manipulation of the cause, and is very strong evidence that the use of DDT was, in fact, the true cause of bald eagle and other bird-of-prey population declines.