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

ContextNitrate 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.MethodTwo 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).ResultsIn 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.