Cupressaceae pollen in the atmosphere of Alentejo: disruption of pollen grain during air transport

Abstract

Background Cupressaceae family include several species that are widely used as ornamental plants pollinating in late winter - early spring, depending on the temperature. Despite being considered moderately allergenic, it might be responsible for winter allergic outbreaks. As ornamental trees, they are found scattered throughout the territory but are more abundant in pockets of wild forest, outside Alentejo. Despite being more common in mountain, this pollen type is captured in considerable amounts in Alentejo, Portugal, where its aerobiological features and allergenic impacts are poorly characterized. The aim of this work is to characterize the aerobiology of Cupressaceae pollen, to evaluate the effect the meteorological conditions and the source of this allergenic pollen type in the atmosphere of Evora, Alentejo.

Materials and methods Pollen were collected using a Hirst type 7-day pollen trap and pollen was identified following standard methodology. Temperature (ºC), relative humidity (RH; %), precipitation (mm) and wind speed and direction were obtained from ICT/CGE platform. Back trajectories (12-hour) of air masses arriving at Évora were calculated using the HYSPLIT model (Hybrid Single-Particle Lagrangian Integrated Trajectory). All trajectories have been computed at 12:00 and 15:00 UTC at different height levels.

Results Elevated daily concentrations of Cupressaceae pollen were detected, reaching maximum value of ~1600 grain/m3; One remarkable feature was that a significant amount of the pollen grains, ranging between 18% and 50% on different days, were disrupted, showing a distended intine and released cellular content. Higher levels of disrupted pollen coincided with RH>70%. Temperature, wind speed or direction did not correlate with elevated pollen grain disruption. Hourly counts, performed for days with the highest pollen loads, have shown that pollen peaked around 13h, suggesting local origin. Back trajectory analysis suggested that pollen was mostly from local origin, but did not exclude the contribution of long-range transport.

Conclusions To our knowledge, this is the first report of a considerable fraction of disrupted Cupressaceae pollen grains reaching the sampler, releasing cell contents, which may significantly increase ambient free allergen and contribute to enhance allergenic activity of this pollen type. A better understanding of this phenomenon may contribute to improve allergy risk management.