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

Abstract

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 6.87μm² (IQR 4.47-18.5) and 4.37μm² (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 0.89μm², 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.

Keywords: Air pollution; Cookstove; Macrophage black carbon; Particulate matter.

Graphical abstract

Fig. 1

Flow chart of recruitment to study and samples analysed.

Fig. 2

Airway macrophages from the samples obtained in Malawi demonstrating large amounts of visible black carbon in clumps (airway macrophage black carbon, AMBC) (x100 under oil immersion).

Fig. 3

Airway macrophages from the UK samples showing some large clumps of black carbon along with smaller scattered visible particles (airway macrophage black carbon, AMBC) (x100 under oil immersion).

Fig. 4

Microscope image demonstrating large sheets of bacteria obscuring the macrophages (x100 under oil immersion).

Fig. 5

Single macrophage with phagocytosed bacteria (x100 under oil immersion).

Fig. 6

Comparison of Airway macrophage black carbon results between the traditional cookstove group and the intervention cleaner cookstove group, each dot represents a separate individuals mean AMBC (per 50 macrophages), p < 0.05 by Mann Whitney.

Fig. 7

Dotplots comparing AMBC subgroup lung function data, each dot represents a single participants result.. a. shows % predicted FEV₁. b. shows % predicted FVC. c. shows FEV₁:FVC ratio. FEV₁, forced expiratory volume in 1 s. FVC, forced vital capacity.

Fig. 8

Comparison of Airway macrophage black carbon results between the traditional cookstove group and the intervention cleaner cookstove group and the healthy UK controls, each dot represents a separate individuals mean AMBC (per 50 macrophages), p < 0.05 by Kruskall Wallis and post hoc testing.

Fig. 9

Individual scatter plots of mean AMBC against; a. FEV₁% Predicted, b. FVC% Predicted, c. PM_2.5, d. CO. All correlations are non-significant (see Table 5). FEV₁, forced expiratory volume in 1 s. FVC, forced vital capacity. AMBC, airway macrophage black carbon (mean per 50 macrophages per subject). CO, carbon monoxide. PM_2.5, particulate matter <2.5 μm.