Urban Forestry & Urban Greening 16 (2016) 9–12 Contents lists available at ScienceDirect Urban Forestry & Urban Greening journa l h om epage: www.elsevier.com/locate/ufug A contribution to the study of airborne Citrus pollen in Córdoba, southern Spain Purificación Alcázar ∗ , M a José Velasco-Jiménez, Eugenio Domínguez-Vilches, Carmen Galán Department of Botany, Ecology and Plant Physiology, University of Córdoba, Campus Universitario Rabanales, 14071 Córdoba, Spain a r t i c l e i n f o Article history: Received 3 June 2015 Received in revised form 2 December 2015 Accepted 26 January 2016 Available online 29 January 2016 Keywords: Orange trees Airborne pollen Allergy Health impact Urban planning a b s t r a c t Citrus species, and especially oranges, are widely grown in Córdoba (southern Spain) both as ornamentals (Citrus aurantium) and as cash crops (Citrus sinensis). There has been little research into the incidence of orange-pollen allergy in the local population. Given the abundant presence of orange trees in Córdoba, a study was designed to determine local Citrus pollen counts at human height in areas where these trees are densely planted. Although standard aerobiological studies report negligible airborne Citrus pollen counts, the samplers used are located at greater heights and in open areas; as a result, large Citrus pollen grains are not recorded. It was found that when Hirst-type volumetric samplers were placed on the roof of a building – the recommended position for aerobiological research – airborne Citrus pollen counts were very low. By contrast, portable samplers placed at human breathing height recorded very high counts, reaching around 2000 pollen grains/m 3 during the peak day. This finding suggests that greater attention should be paid to the potential negative impact on the local population, given that the sparse research has highlighted the allergenic nature of orange pollen. Citrus pollen could have an adverse local health impact in areas where orange-trees are densely planted, particularly given reported cross-reactivity with other pollen types. However, further aerobiological and clinical research into Citrus pollen is required in order to draw wholly reliable conclusions. © 2016 Elsevier GmbH. All rights reserved. 1. Introduction The genus Citrus, a member of the Rutaceae, comprises around 12 species of Asiatic origin, all greatly valued both as cash crops and as ornamentals. In Spain, Citrus sinensis (L.) Osbeck is widely grown for its sweet, succulent oranges, while the bitter orange Citrus aurantium L. is a widespread ornamental throughout the Mediter- ranean area. Both species are evergreens, with highly-fragrant hermaphrodite flowers pollinated by insects. Citrus species are commonly used as ornamentals in parks and sidewalks in southern Spain. The most abundant species in urban green spaces in Córdoba is C. aurantium. In Córdoba province, C. sinensis is grown as a cash crop. Allergy to orange fruits is reportedly associated with three major allergens: Cit s 1, Cit s 2 and Cit s 3 (Ahrazem et al., 2006; Bendersky and Lupas, 1960; Iba ˜ nez et al., 2004; López-Torrejón et al., 2005; Morimoto et al., 2004; Ortolani et al., 1989; Zhu and Yest, 1989). ∗ Corresponding author. Tel.: +0034 957218719. E-mail address: bv2altep@uco.es (P. Alcázar). Yet while oranges have been identified as a key allergenic plant food in a public survey of food allergies (Sloan and Powers, 1986), there has been little research into allergy to oranges and other citrus fruits, which is often associated with pollinosis and sensitization to other plants (Iba ˜ nez et al., 2004; Iorio et al., 2013). Clinical reports of allergic reactions to orange-tree pollen are scarce: El-Qutob López et al. (2006), reporting on a C. sinensis pollen allergy reaction in a sensitive patient, noted that the positive skin prick test for orange- blossom pollen and the detection of serum specific IgE indicated a hypersensitivity mechanism, and concluded that both the clini- cal history and the results of physical examination were consistent with an IgE-mediated allergic reaction to orange-blossom pollen. Although most reports focus on citrus fruit allergies, some studies highlight the presence of 2 major allergens for Citrus pollen, Cit s 1 and Cit s 3 (Iorio et al., 2013). Insect pollination and large pollen grain size hinder pollen dis- persal and transport. As a result, airborne pollen counts recorded using samplers placed at a considerable height above ground level – with a view to avoiding obstacles – tend to be negligible. However, airborne Citrus pollen levels may be significant at human height and in the immediate vicinity of trees, as reported in local studies http://dx.doi.org/10.1016/j.ufug.2016.01.009 1618-8667/© 2016 Elsevier GmbH. All rights reserved.