Use of cleaner-burning biomass stoves and airway macrophage black carbon in Malawian women

Exposure to particulate matter (PM) from burning of biomass for cooking is associated with adverse health effects. It is unknown whether or not cleaner burning biomass-fuelled cookstoves reduce the amount of PM inhaled by women compared with traditional open fires. We sought to assess whether airway macrophage black carbon (AMBC) - a marker of inhaled dose of carbonaceous PM from biomass and fossil fuel combustion - is lower in Malawian women using a cleaner burning biomass-fuelled cookstove compared with those using open fires for cooking. AMBC was assessed in induced sputum samples using image analysis and personal exposure to carbon monoxide (CO) and PM were measured using Aprovecho Indoor Air Pollution meters. A fossil-fuel exposed group of UK women was also studied. Induced sputum samples were obtained from 57 women from which AMBC was determined in 31. Median AMBC was 6.87 μm2 (IQR 4.47–18.5) and 4.37 μm2 (IQR 2.57–7.38) in the open fire (n = 11) and cleaner burning cookstove groups (n = 20), respectively (p = 0.028). There was no difference in personal exposure to CO and PM between the two groups. UK women (n = 5) had lower AMBC (median 0.89 μm2, IQR 0.56–1.13) compared with both Malawi women using traditional cookstoves (p < 0.001) and those using cleaner cookstoves (p = 0.022). We conclude that use of a cleaner burning biomass-fuelled cookstove reduces inhaled PM dose in a way that is not necessarily reflected by personal exposure monitoring.