There is evidence, however, that hormonal levels around the time of conception are associated with the sex ratio of offspring [ 22], and there is compelling evidence that exposure to particular chemicals does lead to changes in the sex ratio of offspring [ 23- 27], as seen, for example, with exposure to dioxins following an explosion at an herbicide plant in Seveso, Italy [ 26, 27].
For example, with exposure during week 15 of gestation, NNHs for PM2.5 and LPTB correspond to 5,587, meaning that for every 1-μg/m increase in ambient PM2.5 concentrations for 5,587 pregnant women, 1 LPTB occurs (assuming associations are causal).
We described several approaches to study timing of vulnerability using an example with few exposure windows and few covariates.
For example, with less exposure to heat, our bodies can fail to acclimatize physiologically to summer conditions, while we develop a mental dependence on cooling.
For example, with methoxychlor exposure of rats, F1 males had significantly elevated levels of splenic antibody-forming cells, unlike their exposed mothers, whereas F1 females had a significantly reduced percentage of CD8+ T cells (at all doses examined) with no corresponding effect in the exposed dams (White et al. 2005).
Differences between results do occur; for example, with EC exposures in early pregnancy, we found elevated RDs, though not for all PTB categories.
For example, with respect to exposure measurement error, Jurek et al. (2006) sampled papers from three epidemiology journals over 1 year and found that only 61% of the articles made any mention of exposure measurement error, and only 46% of those qualitatively described the possible effects.
The authors conclude that optimal doses for EM maps at low and intermediate resolutions are much higher than the 10-20 e-/Å2 determined previously using crystalline samples, for example with a pre-exposure of 50 e-/Å2 a map at better than 6 Å resolution could be obtained.
There is also a clear potential for off-target harm with acute exposure (for example, raised intracranial pressure, pulmonary hypertension), and with exposure for prolonged periods (for example, increased risk of infection) or at high doses.
Animals served as their own controls, that is, the responses of animals that were assessed for STD (using low-frequency stimulation [LFS] alone) were compared with the subsequent responses of the animals when, for example, LFS was given together with exposure to novel pictures.
In this way, these studies undoubtedly add valuable information to the ongoing debate, prompting further questions, suggesting differences may rest, for example, with possible risk factor exposure, but failing to provide any definitive answers in this complex and multifaceted topic.
