Doctor: Shukrullah Ahmadi
Title: Lead exposure in children, sources of exposure and child growth in Benin
Supervisor: Florence Bodeau-Livinec
Doctoral school: ED 393 Epidemiology and Biomedical Information Sciences, Université Paris Cité
Date of thesis defense: 11/2020
Jury: Pascal Astagneau, Renaud Becquet, Jacques Gardon, Valérie Briand, Nathalie Costet-Deiber.
Lead exposure in children causes poor health outcomes including long-term impairments in neurocognitive functions. Lead exposure in children and its sources are known in many developed countries. However, there are limited studies on lead exposure in children, potential sources, and its health effects on child growth in Sub-Saharan Africa (SSA). The study of the determinants of growth can be done in two steps. First, the growth data is modelled and individual growth trajectories are estimated. In the second step, growth parameters derived from the growth modelling step are used as variables in the analysis of associations between lead exposure and child growth. Many growth models have been proposed. However, very few have studied their comparative merits in terms of Goodness-of-fit on child growth in rural SSA. This thesis aimed to investigate blood lead levels (BLLs) and sources of lead exposure in the children at six years of age in 2016-18 in the south of Benin, SSA. This thesis also aimed to identify a growth model that best describe the individual growth trajectories of children. For the first objective, BLLs and sources were assessed for 425 children. BLLs were analyzed by inductively coupled plasma mass spectrometry. Sources were assessed through questionnaire data. Multiple linear regression and quantile regressions were used to study potential sources of lead. A semi-structured interview guide was used for a qualitative study to assess practices about hunting, sale, and consumption of bushmeat harvested by lead ammunition. In this regard, 38 semi-structured interviews were undertaken with families, hunters, and sellers. For the second objective, we first modelled the child growth data (n=961). For this purpose, we compared goodness-of-fit of three structural growth models (Jenss-Bayley, Berkey-Reed and adapted Gompertz model) on longitudinal child growth data from birth to around six-years-of-age. The goodness-of-fit of three models was assessed using residual distribution over age and compared with the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). The geometric mean BLLs were 56.5 µg/L (95% CI: 53.4, 59.6) and 56.4 µg/L (95% CI: 54.1, 58.7) in children at one and six years of age, respectively. We found a persistently high prevalence (59.5%) of elevated BLLs >50 μg/L in children. This prevalence was comparable to the prevalence (54.8%) assessed at age one in 2011-13. However, the prevalence of children with very high BLLs i.e. above 100 μg/L decreased from 14.4% at one year of age to 8.2% at six years of age. The major sources of lead exposure were consumption of bushmeat harvested by lead ammunition and consumption of peanuts. Other potential sources of lead associated with BLLs with marginal significance were consumption of rice, paternal occupational exposure and presence of activity with the potential use of lead. The qualitative study explored in detail practices related to hunting of bushmeat; its sale, and consumption by families including children, and allowed a better understanding of the different stages of lead shot from the hunt to consumption by the child. Findings from growth modelling show that the Jenss-Bayley model presented the best fit amongst the three candidate models. This model estimated individual growth trajectories and growth velocities of children. It was estimated that about 1/3 of the children were wasted and underweight at six years of age. In conclusions, this thesis showed high levels of lead exposure in six-years-old children, as well as the diversity of possible sources of lead. Future research is needed to study the consequences of lead on the growth of children in this context of malnutrition. The findings highlight the need for prevention programs to protect children from lead exposure.