Elevated prenatal methylmercury exposure in Nigeria: Evidence from maternal and cord blood

•Mercury is widespread globally but little is known about human exposures in Africa.•Mercury levels in Nigerian mothers and newborns are higher than other groups.•36% of participants had mercury levels exceeding the biomonitoring guideline. Methylmercury is a neurodevelopmental toxicant that is globally distributed though little is known about prenatal exposures in sub-Saharan Africa. The objective of the current study was to measure total mercury levels in cord blood and maternal blood from 95 mother-newborn pairs recruited from hospitals in Nnewi, Nigeria. The secondary aims of the study were to explore if demographic and dietary factors were associated with blood mercury levels, and to explore if mercury levels were associated with any self-reported health outcome and childbirth outcome. Maternal blood mercury levels averaged 3.6μgL−1 and ranged from 1.1μgL−1 to 9.5μgL−1. Cord blood mercury averaged 5.1μgL−1 and ranged from 1.2μgL−1 to 10.6μgL−1. The mean ratio of mercury in paired cord blood to maternal blood was 1.5 and it ranged from 0.4 to 3.2. Mercury in maternal and cord blood were significantly correlated (r=0.471). More than one-third of mothers reported eating fish at least once per day, and a weak (p=0.08) fish consumption-related increase in blood mercury was found. Cord blood mercury was positively and significantly associated with birth weight and length, and head and chest circumference. Mercury levels in 36% of the participants exceeded the biomonitoring guideline associated with the United States Environmental Protection Agency (U.S. EPA) reference dose for mercury. The study shows that pregnant women and their newborns are exposed to methylmercury and that their exposures are higher compared to general populations sampled from other regions of the world.