Nitrates in drinking water and methemoglobin levels in pregnancy: a longitudinal study

Abstract

BackgroundPrivate 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.MethodsA 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.ResultsPregnant 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).ConclusionPregnant 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.

Seasonal variation of nutrient loads in treated wastewater effluents and receiving water bodies in Sedibeng and Soshanguve, South Africa

“…At higher concentration, it may lead to eutrophication of water systems which in turn result in the loss of biodiversity in the aquatic environment (CCME 2006). Nitrate concentration above 45 mg/L may result in the blue baby syndrome, anaemia in pregnant women and formation of carcinogenic nitrosamines (Manassaram et al 2010;Akan et al 2008). During the present study, the general geometric means of NO 3 (Fig.…”

Dietary nitrate facilitates an acetazolamide-induced increase in cerebral blood flow during visual stimulation

“…In adults, dietary intake of nitrate does not normally alter the plasma concentrations of methemoglobin (metHb) (25). However, in the blood, nitrite can potentially oxidize hemoglobin into metHb, which causes a higher T 1 relaxivity (22).…”

Genetic variation in CYB5R3 is associated with methemoglobin levels in preterm infants receiving nitric oxide therapy

“…When NO enters the blood stream, it quickly reacts with hemoglobin to form methemoglobin (MetHb) and, as a result, the hemoglobin is no longer able to bind oxygen 1,4,5 . The concentration of MetHb in the blood under normal conditions is typically less than 2% of all hemoglobin 6 . When levels of MetHb in the blood reach elevated concentrations, MetHb toxicity can occur 6–9 .…”

“…The concentration of MetHb in the blood under normal conditions is typically less than 2% of all hemoglobin 6 . When levels of MetHb in the blood reach elevated concentrations, MetHb toxicity can occur 6–9 .…”