Prenatal PBDEs and Neurodevelopment: Herbstman et al. Respond to Goodman et al. and to Banasik and Strosznajder

A 469 over time could have altered any observed exposure–response associations. In addition, the authors did not indicate how assessments of individual children changed over time. If different children contributed to associations at different ages, the reported findings may not be indicative of a causal role for PBDEs. Notably, most associations were found at earlier ages, suggesting that even if PBDEs were causal, effects were reversible. Herbstman et al. (2010) reported that all PBDEs were correlated with one another, as were repeated develop mental scores. Yet associations varied both among PBDEs for the same tests and among repeated tests for the same PBDEs. If PBDEs are truly causal and acting via similar mechanisms of action, results should be repeatable across PBDEs and repeated tests. This is not the case, thus suggesting that chance or some other factor (e.g., alcohol, caffeine, poor diet, methyl­ mercury, poly chlorinated biphenyls) is a more likely explanation. In addition, all of the mothers in the study were pregnant and lived near the World Trade Center (WTC) on 11 September 2001. Given this proxim­ ity, there is no way of knowing whether other unmeasured exposures or other factors (e.g., psychological, behavioral) contributed to neuro logical effects. Herbstman et al. (2010) used the Bayley Scales of Infant Development, Second Edition (BSID­II) to measure develop mental impairment, which is based on a mean ± SD of 100 ± 15 to define normal development (Bayley 1993). This means that in 68% of the standard population, scores ranged from 85 to 115. The authors reported that through uni variate analysis, the change in the BSID­II score from the 25th percentile of PBDE level to the 75th percentile was –5.57. This degree of change is well within the SD of the test, which makes it impossible to determine whether the relation ship observed was due to PBDEs or simply the inter individual variability inherent to the test. Because the authors did not assess the association between PBDE levels and those scoring outside the SD of the test (compared with those scoring within), it is impossible to determine whether a clinically significant asso­ ciation between PBDE cord blood levels and develop mental impairment exists. Changes in IQ scores are not very meaningful unless they are put directly into context with the scoring ranges in the test design; Herbstman et al. did not provide much information as to the scores that were actually …