Articles * Rogers et al.
mean ± SD) (Table 4). The amount of Cr hypothesized to have been in water from wells G and H, 240 Wgl, and the mean con- centration of Cr in the hair ofWoburn resi- dents who had access to this water, -2.8 pg/g, are consistent with the relationship between Cr in drinking water and Cr in hair reported by Rosas et al. (24). However, as we have already noted, the concentration of Cr in the hair ofWoburn residents who did not have access to the well water (and thus, presumably, were exposed to substantially less Cr via drinking water) was also on aver- age -2.8 pg/g. Furthermore, the concentra- tions of Cr in hair did not change as a finc- tion of access. Therefore, it appears that access to water from wells G and H cannot explain Cr levels measured in the hair of Woburn residents.
Another possible explanation for our negative findings is that our analysis lacked adequate temporal resolution. If the As and Cr concentrations to which a hair sample donor were exposed were temporally vari- able, a more powerful analysis could be achieved by measuring the axial distribution of As and Cr along individual hair strands. This approach has in fact been used by forensic scientists to distinguish chronic and acute As and Cr exposures (38-40). By contrast, our analysis of whole, unsegment- ed hair strands does not detect concentra- tion spikes along the strand.
There are several other sources of uncer- tainty associated with our methods that could also bear upon our results. The period of hair growth was overestimated for 14 of the samples grown between 1964 and 1979 because the month that the sample was cut was not known. The water distribution model used to estimate access is not entirely free oferror. In addition, As and Cr concen- trations in the hair samples could have changed during storage. While it is impor- tant to acknowledge that these (and possibly other) sources of uncertainty were inherent in our methods, we do not expect that greater knowledge of any of these uncertain- ties would significantly alter our findings.
Although we did not find evidence of increased As and Cr accumulation in the hair ofWoburn residents who had access to water from wells G and H, we did observe that As concentrations in the hair samples have changed over time. The plot of As concentrations in hair samples versus the year that the samples were cut (Fig. 3A) shows that concentrations ofAs in hair have decreased over the last half century. The concentrations of As in hair averaged over the periods 1938-1963, 1964-1979, and 1982-1994 [expressed as geometric means (GSD)] were 0.21 (3.0) pg/g (n = 26), 0.15 (2.4) pg/g (n = 36), and 0.06 (2.6) plg/g (n
= 20), respectively (Table 2). The reasons for this trend are not known; however, replacement of As-based pesticides by syn- thetic organic chemicals has undoubtedly reduced the amount of As to which people are exposed through diet and use of phar- maceutical products, and improvements in air pollution control technology have reduced the amount ofAs emitted into the atmosphere. Also, once the major producers of As-laden wastes ceased operating in Woburn (around 1930), natural attenua- tion processes, such as stabilization of As- containing particles by vegetation and deposition and burial in pond and lake sed- iments, may have acted to substantially reduce the amounts ofavailable As to which residents ofWoburn are exposed.
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Volume 105, Number 10, October 1997 * Environmental Health Perspectives