Spatial prediction of Pb, Zn and Fe air pollution in urban environments: A case of Douala, Cameroon

Overview & Synopsis

Plant biomonitoring is widely used as a tool to characterize and monitor air quality in complex urban environments. Trees are reliable bio-accumulators of atmospheric pollutants and can provide valuable information on the chemical composition of vehicular particulate emissions through their bark. In this study, geostatistical techniques were applied to analyze the concentrations of Zn, Fe and Pb in 234 tree bark samples collected across the city of Douala, Cameroon, using a portable X-ray fluorescence (XRF) instrument. Ordinary kriging was used to predict heavy metal levels at unsampled locations, while universal kriging was applied to estimate Pb concentrations in samples where values were below the instrument's detection limit, based on correlations with Zn and Fe. The results revealed that Zn, Fe and Pb concentrations exceeded the World Health Organization (WHO) reference limit for medicinal plants at several high-traffic intersections and surrounding areas. These findings indicate that the city of Douala is experiencing a critical level of air pollution. Therefore, urgent mitigation measures should be integrated into the city's urban development plan, including the establishment of green infrastructure and the strategic selection of tree species capable of efficiently trapping airborne chemical elements.