Atmospheric Transportation of Marihuana Pollen from North Africa to the Southwest of Europe

--As a result of aerobiological samples taken on the Costa del Sol (S. Spain), Cannabis sativa L. (marihuana) pollen was detected from May to September 1991-1996, always sporadically and usually during the afternoons. Sampling was by two volumetric spore traps set up in Malaga and Estepona, two coastal towns approximately 90 km apart. A study of the days when this pollen was recorded points to the movement of air masses from North Africa to southern Spain. Furthermore, the isentropic air trajectories calculated for these days reinforce the possibility of the pollen originating in marihuana plantations in northern Morocco (Rif). This study demonstrates the application of aerobiology to the control of the source, quantity and phenology of the crop. © 1997 Elsevier Science Ltd Key word index: Aerobiology, long-distance transport, isentropic air trajectories, phenology, crop. I N T R O D U C T I O N Cannabis sativa L. is an annual plant, sometimes monoicous, originating in Central Asia, which is cultivated for its fibrous stems to produce hemp and for its seed (hempseed), which is used as a commercial bird food. Some varieties are cultivated to produce drugs (marihuana, hemp) from the resin found in stems, young leaves and flowers. It is also found in cereal crops and fallow lands of the temperate regions of Europe (Moore et al., 1991). The plant produces abundant pollen, 70,000 grains in one anther (Faegri and Iversen, 1989). Since the stamens are free and the masculine inflorescences are found at the top of the plant, wind pollination is favoured and pollen has been identified in airborne pollen samples in a wide variety of places as South Africa (Cadman and Dames, 1993), India (Malik et al., 1991; Gupta and Chanda, 1991), Florida (Jelks, 1991) and North Africa (Reille, 1992; Calleja et al., 1993). In Europe it has only been cited in Madrid {Central Spain) (Sfienz and Guti~rrez, 1983), and in the coastal areas of South Spain (Recio et al., 1995), where it was registered in two volutAuthor to whom correspondence should be addressed, Fax: 34-5-2131944; e-mail: [email protected]. metric traps in two separate parts of this coast during May-September 1991-1996. In order to ascertain the origin of this pollen the meteorological characteristics of the days when it was recorded were examined and the isentropic trajectories were calculated. The importance of identifying the origin lies not only in attempts to control the illegal movement of drugs but also in the possibility of the pollen producing allergenic reactions in some sensitive individuals, as has happened in the northcentral regions of North America where Cannabis was widely grown (Maloney and Brodkey, 1940; MacQuiddy, 1955). Many papers on medium or long-range transport of other pollen grains have been published (Tampieri, 1977; Mandrioli et al., 1980, 1982, 1984; Johansen and Hafsten, 1988; Peeters and Zoller, 1988; Hjelmroos, 1991; Franzen et al., 1994; Rantio-Lehtim~iki, 1994), but this is the first on marihuana pollen. ANALYSIS OF THE ATMOSPHERIC POLLEN CONTENT Methods By using a spore trap sited 15-20 m above ground level in an open area with no nearby buildings to interrupt the free movement of air, it is possible to get a good idea of the atmospheric pollen content of an area of approximately 50 km radius (Faegri and