LJWorld.com weblogs Dangerous Ideas
Spreading Junk Science
Based on the comments, the article "Soaring to new heights" in today's Journal World has provided yet another opportunity for some people to peddle misinformation about DDT. Perhaps rather than cite Fox News or the "Junk Science Web Site", these people ought to look more closely at the scientific literature on DDT and its effect on bird populations. Here for instance, is a review that classes DDE, a metabolite of DDT, as an endocrine disruptor. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1874172Meanwhile, a major 1995 study concluded that environmental pollutants appear to be the most important factor relating to productivity of eagle populations:http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1519271.For birds of prey the connection between DDT/DDE and reproductive failure seems pretty strong to me.Of course biology is rarely neat, and there are certainly studies that do not show a link between DDT and it's metabolites and changes in bird populations. For instance, a very recent filed study that shows that a population of herons is thriving in spite of exposure to PCB's and DDE's.http://www.news.uiuc.edu/NEWS/08/0116herons.htmlAnd consider this study which concluded that DDT, more precisely DDE, probably was not involved in the decline of California condors.http://www.blackwell-synergy.com/doi/abs/10.1046/j.1474-919X.2003.00132.xIndeed this study concludes that lead shot was probably the main factor in the decline of condors. The fact of the matter is, that bird species seem to vary widely in their response to DDT and its metabolites and other factors are important in the fate of many bird populations.So what are we to do in terms of policy about DDT? Perhaps the best answer we have on this issue, is this 1989 conclusion from the International Programme on Chemical Safety (IPCS)http://www.inchem.org/documents/ehc/ehc/ehc83.htm#SectionNumber:6.2"One of the most widely studied effects of DDT is eggshell thinningin birds, particularly in predatory species. The metabolite DDE, notDDT, has been shown to be responsible for this effect. Other effectson reproduction and survival of birds have been demonstrated. Largepopulation declines in birds of prey can be, at least partially,attributed to DDT. ...""Because of their lack of degradation, their resulting widespreadpersistence in the environment, their high acute toxicity to organismsat the base of food chains, and their high potential forbioaccumulation, DDT and its metabolites should be regarded as a majorhazard to the environment. DDT should not be used when an alternativeinsecticide is available."There may be some reason to consider DDT's limited use in malaria control as discussed here:http://pubs.acs.org/cen/government/84/8430gov1.html. However, the IPCS conclusions about DDT are still sound sound today. Indeed those interested in the controversy about the role of DDT in controlling Malaria should also see this article from the Washington Post.http://www.washingtonpost.com/wp-dyn/content/article/2005/06/04/AR2005060400130.htmlIn this article, entomologist May Berenbaum argues that DDT may have a limited role in managing malaria if mosquito populations can be monitored to assess the evolution of resistant strains but that we need to cut out the "overblown hype" about DDT. Perhaps this also applies to other aspects of the complex effects of man made chemicals on our environment.