Centers for Disease Control and Prevention, National Center for Environmental Health, Health Studies Branch, 4770 Buford Highway, MS F-57 Chamblee, GA 30341, USA.
Environ Health. 2010 Oct 14;9:60. doi: 10.1186/1476-069X-9-60.
Private water systems are more likely to have nitrate levels above the maximum contaminant level (MCL). Pregnant women are considered vulnerable to the effects of exposure to high levels of nitrates in drinking water due to their altered physiological states. The level of methemoglobin in the blood is the biomarker often used in research for assessing exposure to nitrates. The objective of this study was to assess methemoglobin levels and examine how various factors affected methemoglobin levels during pregnancy. We also examined whether differences in water use practices existed among pregnant women based on household drinking water source of private vs. public supply.
A longitudinal study of 357 pregnant women was conducted. Longitudinal regression models were used to examine changes and predictors of the change in methemoglobin levels over the period of gestation.
Pregnant women showed a decrease in methemoglobin levels with increasing gestation although <1% had levels above the physiologic normal of 2% methemoglobin, regardless of the source of their drinking water. The multivariable analyses did not show a statistically significant association between methemoglobin levels and the estimated nitrate intake from tap water among pregnant women around 36 weeks gestation (β = 0.046, p = 0.986). Four women had tap water nitrate levels above the MCL of 10 mg/L. At enrollment, a greater proportion of women who reported using water treatment devices were private wells users (66%) compared to public system users (46%) (p < 0.0001). Also, a greater proportion of private well users (27%) compared to public system users (13%) were using devices capable of removing nitrate from water (p < 0.0001).
Pregnant women potentially exposed to nitrate levels primarily below the MCL for drinking water were unlikely to show methemoglobin levels above the physiologic normal. Water use practices such as the use of treatment devices to remove nitrates varied according to water source and should be considered in the assessment of exposure to nitrates in future studies.
私人供水系统的硝酸盐含量更有可能超过最大污染物水平（MCL）。由于生理状态的改变，孕妇被认为容易受到饮用水中高硝酸盐暴露的影响。血液中亚甲蓝水平是研究中常用的评估硝酸盐暴露的生物标志物。本研究的目的是评估亚甲蓝水平，并研究怀孕期间各种因素如何影响亚甲蓝水平。我们还研究了孕妇基于家庭饮用水来源（私人与公共供应）是否存在用水习惯差异。
对 357 名孕妇进行了纵向研究。使用纵向回归模型来检查妊娠期内亚甲蓝水平的变化及其变化的预测因素。
尽管<1%的孕妇亚甲蓝水平超过生理正常的 2%，但随着妊娠的进行，孕妇的亚甲蓝水平呈下降趋势，无论其饮用水来源如何。多变量分析并未显示 36 周左右孕妇自来水中估计硝酸盐摄入量与亚甲蓝水平之间存在统计学显著关联（β=0.046，p=0.986）。有 4 名妇女的自来水中硝酸盐含量超过 10mg/L 的 MCL。在入组时，报告使用水处理设备的妇女中，私人水井使用者（66%）比公共系统使用者（46%）比例更高（p<0.0001）。此外，与公共系统使用者（13%）相比，私人水井使用者（27%）中更多的人使用能够去除水中硝酸盐的设备（p<0.0001）。
孕妇可能接触的硝酸盐水平主要低于饮用水的 MCL，不太可能出现亚甲蓝水平高于生理正常水平。根据水源，用水习惯（如使用处理设备去除硝酸盐）存在差异，在未来的研究中应考虑将其作为评估硝酸盐暴露的因素。
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