Drinking water nitrate and prevalence of methemoglobinemia among infants and children aged 1-7 years in Moroccan areas

Context: Nitrate is ubiquitous in environmental media (air, water and soil) and other sources (some medicines, inorganic fertilizers and household's chemicals). It is a hemoglobin-oxidizing agent that can cause methemoglobinemia. The effect of nitrate on infants is well known but less is known about nitrate-induced methemoglobinemia in young children. Method: Two cross-sectional studies were carried out in Salé, Morocco to determine the prevalence of methemoglobinemia among 411 infants and children aged 1-7 years in two adjacent areas that were similar in terms of the air quality, available vegetables and medicines but different in terms of the drinking water quality (nitrate-contaminated well water versus municipal water). Results: In the exposed area, nitrate concentration was measured in 78 wells and ranged from 15.39 to 246.90 mg/l as NO3-. Nitrate levels were higher than 50 mg/l in 69.2% of the surveyed wells, and 64.2% of the participants were drinking nitrate contaminated well waters. The prevalence of methemoglobinemia among study children was 36.2% in the exposed area, and 27.4% in the non-exposed area. Study children drinking well water with a nitrate concentration >50 mg/l were significantly more likely to have methemoglobinemia than those drinking well water with a nitrate concentration <50 mg/l (p=0.001 at 95% CI=[1.22-2.64]) or than those drinking municipal water (p<0.01 at 95% CI=[1.16-2.21]). In the exposed area, the mean methemoglobin (MetHb) level increased with age (R2= 0.79, p=0.04), whereas in the unexposed area, the mean MetHb level remained relatively stable in the first 6 years of life (R2=0.21, p=0.44). Mean MetHb was normal when the nitrate concentration in water was below 50 mg/l as NO3-, and reached an abnormal level, when the nitrate concentration in water ranged between 50 and 90 mg/l as NO3-. This last level was statistically similar to mean MetHb at nitrate level above 90 mg/l as NO3- (up to 246.9 mg/l as NO3-). No association was observed between methemoglobinemia prevalence and gender. This is the first study about methemoglobinemia conducted in Morocco. © 2007 Elsevier GmbH. All rights reserved.