Estimation of long-term exposure to PM2.5 based on short-term personal measurements in mother-child pairs in rural Ghana

Abstract

BACKGROUND AND AIM: Air pollution epidemiological studies usually rely on estimates of long-term exposure to air pollutants, which are difficult to ascertain. This problem is accentuated in low- and middle-income countries where sources of personal exposure often differ from those of ambient concentrations. METHODS: We used a well-characterized cohort of mother and child pairs in 29 communities in rural Ghana and evaluated modeled long-term predictions of PM2.5 exposure. The models relied on three types of short-term measurements: personal exposure to PM2.5 in mother-child pairs, ambient PM2.5 concentration at the community level, and ambient PM2.5 concentration at a central site. Intra-class correlation coefficients (ICC) were computed to assess sources of variability in community ambient and personal exposure. Empty models were linear mixed models with a random intercept for the community or for the participant. Additional predictors included time-varying factors for the community and time-invariant characteristics for the household and participant. Personal exposure in mother and children were modeled separately. Models were evaluated using leave-one-out cross validation and the lowest root-mean-square-error (RMSE) was used to select the best performing model. RESULTS:We analyzed 240 community-days and 251 participant-days of PM2.5. Means (sd) of daily PM2.5 were 30.2 (24.9) μg/m³ for the central site, 43.5 (36.2) μg/m³ for the communities, 83.0 (53.2) μg/m³ for mothers, and 82.3 (43.6) μg/m³ for children. The ICCs (95% CI) for community ambient and personal exposure were 0.30 (0.17, 0.47) and 0.74 (0.65, 0.81) respectively. The sources of variability differed during the Harmattan season. Children’s daily exposure was best predicted by models that used community ambient compared to mother’s exposure as a predictor (log-scale RMSE: 0.165 vs 0.325). CONCLUSIONS:Our results support the feasibility of predicting long-term personal exposure to PM2.5 using short-term measurements in settings similar to rural Ghana and suggest that mother’s exposure may not be the best proxy for child’s exposure. KEYWORDS: Particulate matter, long-term exposure, children's environmental health