Neonatal thyroxine level and perchlorate in drinking water

Environmental contamination of drinking water has been observed for perchlo rate, a chemical able to affect thyroid function. This study examines wheth er that exposure affected the thyroid function of newborns. Neonatal blood thyroxine (T-4) levels for days 1 to 4 of life were compared for newborns f rom the city of Las Vegas, Nevada, which has perchlorate in its drinking wa ter, and those from the city of Reno, Nevada, which does not (detection lim it, 4 mu g/L [ppb]). This study is based on blood T-4 analyses from more th an 23,000 newborns in these two cities during the period April 1998 through June 1999. No difference was found in the mean blood T-4 levels of the new borns from these two cities. Drinking water perchlorate levels measured mon thly for Las Vegas ranged during this study period from non-detectable for 8 months to levels of 9 to 15 ppb for 7 months. Temporal differences in mea n T-4 level were noted in both cities but were unrelated to the perchlorate exposure. This study was sufficiently sensitive to detect the effects of g ender, birth weight, and the day of life on which the blood sample was take n on the neonatal T-4 level, but it detected no effect from environmental e xposures to perchlorate that ranged up to 15 mu g/L (ppb).