Modern Environmental Health Hazards in Africa: Additional Comments
Dorea, Jose G., Environmental Health Perspectives
I commend Environment Health Perspectives for publishing the work of Nweke and Sanders (2009); this significant contribution brought to light interesting aspects of environmental health hazards on the African continent that can be universalized for scientifically unrepresented less developed countries and regions of the planet. In this dimension, existing studies [World Health Organization (WHO) 1989] of that continent compel us to share additional results of studies of heavy metals (mercury, lead, and cadmium) related to early exposure in children. I would like to address the WHO (1989) study of breast milk concentrations used to monitor mother-infant contamination in selected African countries (Nigeria and Zaire). I would also like to point out an often neglected but universal source of Hg exposure during pregnancy and throughout infancy and childhood--ethylmercury (etHg) in thimerosal-containing vaccines (TCVs).
Concentrations of Hg and Pb in breast milk are important indicators of prenatal exposure, the period when most neurotoxic insults of these elements occur. In a review in which I summarized the WHO (1989) study, I showed that mean Hg concentrations were similar in both Nigeria and Zaire (Dorea 2004), but these concentrations were among the highest reported in that review (Dorea 2004). However, the concentrations of milk Pb were higher than that of milk Hg for both countries; in the case of Pb, mean Pb concentrations in rural Zairians were twice that of urban dwellers. On a molar basis, there was twice as much Pb as Hg in these African countries (Dorea 2004); however, the ratios of Se and Ca concentrations (attenuators of neurotoxicity of Hg and Pb) were quite different between the two countries.
Nweke and Sanders (2009) realized that the earliest stages of neurodevelopment are most vulnerable to the toxic effects of Hg. Therefore, I find the figures of occupational exposure involving mothers to be disturbing; women occupationally exposed to gold processing from amalgam range from 5% of the population in South Africa to 50% in Mali. Also, African women are exposed to Hg in soap and through traditional fish consumption. However, Nweke and Sanders (2009) did not mention that tetanus vaccines are used in countries following WHO recommendations to control or eradicate maternal and neonatal tetanus. These vaccines are preserved with thimerosal. In any part of the developing world where TCVs are in widespread use, a newborn is exposed to high concentrations of etHg depending on the child's weight and vaccine brand (Dorea and Marques 2008). Indeed, because the hepatitis-B vaccine is given within hours of birth, Hg concentrations can reach extremely high levels of acute exposure, depending on birth weight and vaccine manufacturer (Dorea and Marques 2008). These exposures are higher than the ones estimated for occupationally exposed mothers working with gold extraction (Dorea 2009). Nweke and Sanders (2009) covered environmental hazards as a result of exposure to hazardous pollutants in tandem with development activities, as well as evidence of their adverse effects on African populations. …