| | More on DDT and DDE (a metabolite of DDT) ...
In the Adami Tulu district in Ethiopia -- in a mere 2-week week interval during the peak malaria transmission season in 2003 -- a fifth of the kids under age 5 had fevers (were "febrile")! Mosquito nets cut the odds of fever by 60%, spraying the house with DDT cut the odds by 20%, and sharing the house with the family cow and chickens increased the odds by 30%.
*Note the term: "95% CI" (95% Confidence Interval) for my discussion found below.
Of 3873 children, 21% had experienced fever in the past 2 weeks. Household ownership of a mosquito net (odds ratio (OR)=0.4, 95% CI 0.3-0.7) and prior spraying of the house with aerosols (OR=0.7, 95% CI 0.5-0.9) or DDT (OR=0.8, 95% CI 0.6-0.9) were associated with lower risk of febrile illnesses, whilst sharing the house with livestock increased the risk (OR=1.3, 95% CI 1.1-1.6).--Trans R Soc Trop Med Hyg. 2007 Jun 27; [Epub ahead of print] Some studies seem hell-bent on finding problems with DDT. One of the ways to stack-the-deck in favor of your pet theory is to arbitrarily reduce the specificity of the search for findings while increasing the sensitivity to pick up any stray findings. This is done by reducing something called a confidence interval. A confidence interval does what it says: it lets you know how confident you can be that the findings found correspond to the reality of the situation as it is. The scientific "industry standard" for a confidence interval is 95 percent CI. If a researcher chooses to analyze recorded data with anything lower than that (such as a 90percent CI), then the findings are presumed somewhat specious.
Also, the study below mentions a standardized mortality ratio (SMR). Imagine a snapshot of a population where the proportion of folks who died at each age is recorded. Now, the SMR would show up as a graphed line (or a simpler bar graph, with each bar dedicated to a 1- to 10-year age-range), and if a study finds the same proportion of folks dying at the same ages, then the reported SMR would be 100 (%) -- with numbers higher than 100 meaning that more people were dying at a given age, than a standard group would have. ...
Standardized mortality ratios (SMR) were calculated on the basis of the age, sex, and cause specific mortality rates prevailing during the same calendar years in the province of Rome. The SMR from all causes for the whole cohort was 103.8 (90 percent CI 86 124). The SMR for all cancers was 106.0 ( 90 percent CI 75-146). An increased risk was observed for the exposed for cancer of the gallbladder (SMR 723.8 90 percent CI 129-2279), of the liver (SMR 596.3, 90 percent CI 204-1365) and for cancer of the nervous system (SMR 529.2, 90 percent CI 144-1368).
All increases were statistically significant, but no association was found between the increased risk of these cancers and the longer duration of exposure. The increase in risk of the three cancers mentioned above (liver, nervous system and gallbladder), was further increased, when the analysis was restricted to the workers exposed prior to the 1978 ban of DDT and products containing arsenic.--Int J Immunopathol Pharmacol. 2006 Oct-Dec;19(4 Suppl):61-5. <SCRIPT language=JavaScript1.2>
... Note the use of a 90 percent CI. Specious. Note also how, in the discussion, the researchers arbitrarily "lumped" findings of DDT with arsenic, instead of separating them out and giving us a true picture of the relative effects of each. Hmmm. Anyone smell a (DDT-contaminated) rat? And, perhaps more important than any thing else, note that the all-cause mortality and the death rate from all cancers (for those exposed to DDT) didn't statistically change. In plain terms, this study failed to find evidence that DDT causes more cancers or shortens your life-span -- even after "relaxing" the standards for findings!
;-)
Question: So, when might DDT (or its metabolite, DDE) exposure hurt humans? Answer: In potential offspring, exposed during the first trimester of pregnancy.
OBJECTIVES: Our goal was to assess the prenatal DDE exposure window and its effect on the psychomotor development index (PDI) and mental development index (MDI) during the first year of life.
We evaluated PDI and MDI of the Bayley Scales for Infant Development (BSID-II), at 1, 3, 6, and 12 months of age. We adjusted for quality of the home environment and maternal intellectual coefficient (IQ). We used generalized mixed-effects models for statistical analysis.
RESULTS: Third-trimester DDE level (7.8 +/- 2.8 ppb) was significantly higher than the level at baseline, first, and second trimesters, but the differences never exceeded 20%. Only DDE levels during the first trimester of pregnancy were associated with a significant reduction in PDI (every doubled increase of DDE level reduced the PDI 0.5 points). DDE was not associated with MDI.
CONCLUSIONS: A critical window of exposure to DDE in utero may be the first trimester of the pregnancy, and psychomotor development is a target of this compound.--Environ Health Perspect. 2007 Mar;115(3):435-9.
Ed
(Edited by Ed Thompson on 7/26, 3:20pm)
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