Burn to kill: Wood ash a silent killer in Africa
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Aside the emissions, burning of wood in traditional cookstoves (TCs) also generates substantial amount of ash
containing hazardous pollutants such as polycyclic aromatic hydrocarbons (PAHs) and toxic metals. But, their
concentrations in the ash, particularly in Africa where over 70% of the population utilize TCs, remain unknown.
Here, we determined concentrations of sixteen PAHs and eleven heavy metals in ashes from twelve different
African TCs, comprising six three-stone fires (TSFs) and six built-in-place cookstoves (BIPCs), burning common
African wood species under real world situation. For each TC, ash samples were collected for six consecutive
days (Monday–Saturday), and a total of seventy-two daily samples were collected from January–June 2019.
Ash yields were measured gravimetrically, and concentrations of the pollutants were determined following stan�dard analytical protocols. The results were used alongside secondary data (annual fuelwood consumption,
African fuelwood densities, population proportion using fuelwood and surface human population density) to es�timate annual tonnage, exposure potential and risk to health in Africa, using Monte Carlo simulation technique.
The ash yields from all TCs studied exceeded 1% on dry weight basis, indicating that ash is a major waste by�product of wood combustion in TCs. TSFs produced more ash (5.7 ± 0.7%) than BIPCs (3.4 ± 1.0%). Concentra�tions of As, Cd, Hg and Pb in ashes were significantly higher (α = 0.05) for TSFs than BIPCs. In contrast, concen�trations of PAHs were higher in ashes from BIPCs than TSFs. Assuming ash consumption rates rang 500 mg/day for young children weighing 10 to 30 kg, the upper dose (μg/kg-day) of Pb (0.2–3.9) or Σ16PAHs (0.02–0.34), for instance, surpasses the 0.3 μg/kg-day of Pb or PAH recognized as causing adverse effects in chil�dren, indicating a concern. The top five countries with the highest annual tonnage or exposure potential to toxic pollutants are Nigeria>Ethiopia>DR Congo>Tanzania>Uganda, or Rwanda>Burundi>Uganda>Nigeria>
Guinea-Bissau, respectively
Keywords
Q Science (General), QD Chemistry