Pollen harvested from trees as a biomonitor of atmospheric pollution by semi-volatile compounds in an urban area: benzo(a)pyrene extracted from samples of Cupressus sempervirens pollen grains and PM10

Abstract

Benzo(a)pyrene (BaP), a known toxic air pollutant regulated by ambient air quality regulations, can adhere to pollen grains from the gaseous phase or bound to adsorbed atmospheric particles. This study investigated the applicability of a method based on microwave extraction and HPLC-FD (fluorescence detection) to measure BaP attached to airborne pollen samples of Cupressus sempervirens collected from the urban area of Badajoz (Spain) during the species' peak pollination month (February) to assess the variability of BaP levels. After testing the analytical quality of the method, we sampled and assayed pollen samples collected from trees located in Badajoz (Southwest Spain) urban areas, finding BaP levels ranging between 84.9 and 140.6 μg kg⁻¹. The results were significantly higher than those measured in pollen samples collected at a rural unpolluted site (mean value 87.7 μg kg⁻¹). As a reference, we simultaneously measured PM concentration (PM₁₀, PM_2,5 and PM₁) and BaP concentration in PM₁₀ samples collected by high-volume sampling at an official air quality surveillance unit in the city (range 2.39–11.29 mg kg⁻¹). BaP levels in the pollen samples assayed reflect the urban variability in terms of emission sources contributing to BaP pollution, with higher values in pollen collected from trees in urban locations exposed to dense traffic and lower values in quiet pedestrian areas. These results suggest that Cupressus sempervirens pollen grains harvested from trees could be effective air pollution biomonitors for atmospheric BaP in urban areas.