Kelly - DDT (and its breakdown and metabolic products DDE [more potent] and DDD [generally less potent]) affects different bird species differently wrt egg shell thinning. There is no question that egg shell thinning is an effect of exposure to DDT/DDE in many birds of prey (including the condors), yet gallinaceous birds (e.g. chickens) do not exhibit similar sensitivity for that effect.
DDT is used as a technical congener of o,p (ortho, para) and p,p forms. In general o,p DDE is weakly estrogenic - maybe 1/1000th as potent as estrogen (estradiol), while p,p DDE is anti-androgenic. Since it's the balance between the androgens and estrogens that help determine function, in some ways the effects of the two forms of DDE/DDT will induce similar effects - such as feminization of male alligators (see L. Guillette's work for example). However, some species seem to have a different response patterns= , so this is an "in general" statement above. Different animals are differentially sensitive - sometimes due to species-related genetics, sometimes due to individual genetic, exposure or environmental [e.g. co-exposure] differences, sometimes due to lifestyle or life stage or gende= r differences, which of course overlaps the previous modifying factors. Just in case you think, "weakly estrogenic" means not effective, and is thu= s not a concern, realize that DDE/DDD does not readily decompose, nor is it readily broken down (metabolized) in the body. As a result, DDT/DDE/DDD ar= e environmentally persistent, and bioaccumulative in the body. Over time, concentrations build up in organisms to effective/toxic levels. This bioaccumulation tends to occur faster in higher trophic level organisms due to the phenomenon of biomagnification. The higher the trophic level, the more of the lower trophic level organisms you eat, and the more you accumulate of what they have previously accumulated. In addition, DDT is/was used at pretty high doses, and large amounts were dumped in single areas. So the environmental concentrations can and could be pretty high in certain situations. Realize that estrogen is effective in the body within the range of 10^-12 - 10^-9 - ie up to nM. Pesticides tend to be used in the uM (ie 10^-6) to mM (ie 10^-3) range - resulting (especially after bioaccumulation) in potential body levels that are easily more than 1000x the estrogen concentration. Thus, even exposure to a weak estrogen can cause adverse (endocrine disrupting) effects when exposure is at a high enough dose. Diane Henshel On 8/27/07, Abraham de Alba A. <[EMAIL PROTECTED]> wrote: > > Dear Kelly: > > Don=B4t know about the revutal to R. Carson's allegations, but there > are tons of info (I am in the middle of M=E9xico, a bit far from a librar= y, > and so I am at a disadvantage to give you relevant references ) on > estrogen-like compounds that result from the breakdown of DDT, and that`s > the concern with aquatic organisms, fish, amphibians and reptilians. I do > remember a good paper in American Scientiest a while back if you want a m= ore > precise answer. > > > > > Kelly Stettner <[EMAIL PROTECTED]> wrote: > Date: Mon, 27 Aug 2007 06:06:18 -0700 > From: Kelly Stettner <[EMAIL PROTECTED]> > Subject: [ECOLOG-L] DDT question > To: [email protected] > > While I whole-heartedly agree that the larger and long-term picture must > be considered with regards to ecology, I also think that emotional, > knee-jerk reactions need to be tempered with real scientific investigatio= n. > Before our imaginations get too fired up over sensationalism, we need to = be > responsible and look at ALL the evidence, not just that which supports ou= r > hypothesis. > > For some reason, I thought that Rachel Carson's allegation about sea bird > eggshells had been disproven? Can someone point to some of the research o= n > both sides of the issue? Also, have there been studies on DDT's effects o= n > animals, through groundwater or as an airborne spray or some other vector= ? > > What are these 'adverse impacts to polar bears and penguins' that you > mention? How does it get there, does it last that long in the upper > atmosphere to be carried to the poles on the wind? > > Sex reversal in fish ~ I'd also like to know about studies on this > particular issue, since I've never heard of it, either. Are the fish > affected when DDT moves through groundwater? What happens to DDT when it > hits soil or water? Does it break down into component molecules? > > Thank you for considering my questions. > > Kelly Stettner > Springfield, Vermont > > > > > Black River Action Team (BRAT) > 45 Coolidge Road > Springfield, VT 05156 > [EMAIL PROTECTED] > > http://www.blackriveractionteam.org > > ~Making ripples on the Black River since 2000! ~ > > > --------------------------------- > Need a vacation? Get great deals to amazing places on Yahoo! Travel. > > > > Abraham de Alba Avila > Terrestrial Plant Ecology > INIFAP-Ags > Ap. postal 20, > Pabell=F3n Arteaga, 20660 > Aguascalientes, MEXICO > > Tel: (465) 95-801-67, & 801-86 ext. 118, FAX ext 102 > alternate: [EMAIL PROTECTED] > cel: 449-157-7070 > > > --------------------------------- > Pinpoint customers who are looking for what you sell. > --=20 Diane Henshel Indiana University 1315 E 10th #340 Bloomington, IN 47405 812 855-4556 P 812 855-7802 F [EMAIL PROTECTED]
