Japanese cedar (Cryptomeria japonica) pollinosis is the most popular pollinosis in Japan. In recent years, it was reported that the most Cryptomeria japonica pollen allergenic species were scattered as fi ne particles in the urban atmosphere. It is thought that allergenic fi ne particles are responsible for inducing asthma by breaking into lower respiratory tract; this phenomenon was observed in fi eld investigations during sunny days after rainfall. Hence, it is considered that the release of fi ne allergenic species derived from pollen grains may be induced during rainfall events. For this reason, we investigated the releasing behaviour of Cryptomeria japonica pollen allergenic species in rainwater containing air pollutants, through rainwater sampling and laboratory experiments. The pollen grain counts, pollen burst ratios, ionic concentrations and pH in each rainwater sample were measured, when rainwater samples were separately collected in Saitama City, a suburban area north of Tokyo metropolis. Additionally, three simulated rainwater (SR) samples were prepared to investigate the releasing behaviour of pollen allergenic species. In the samplings, the most pollen grains were trapped into initial rainwater (IR). Moreover, burst pollen grains were observed in many rainwater samples. Burst ratio of pollen grains were positively correlated with pH and ionic concentrations in rainwater. Therefore, it was thought that pollen grains were washed out by IR containing air pollutants. On the other hand, for the laboratory experiments, the elution of allergenic Cry j 1 and Cry j 2 was observed when pollen grains were exposed to different SR samples. A time-dependent increase of Cry j 1 was observed, but the elution of Cry j 2 was not observed from pollen grains exposed to SR samples. In particular, the elution of Cry j 1 increased by contact with SR samples under conditions of Asian dust events. The results demonstrated that the burst of pollen grains is associated with the production of fi ne particles containing pollen allergenic species, and that the release of allergenic species was induced by rainwater containing air pollutants.
High airborne concentrations of fine allergenic particles of Cryptomeria japonica pollen were determined during the pollen scattering spring seasons in Japan. In particular, this phenomenon was observed in field investigations during sunny days after rainfall. It is considered that the release of daughter allergenic species derived from pollen grains may be induced during urban rainfall events. Hence, it is necessary to do research in order to find the evidence of this phenomenon.There are two major daughter allergenic species produced by pollen in Japan, which are called Cry j 1 and Cry j 2 of Cryptomeria japonica pollen. Allergenic Cry j 1 mainly exists in the pollen wall surface (Ubisch body), while allergenic Cry j 2 is present as a starch granule in the pollen grain, it can be thought that the release mechanism of allergenic Cry j 1 and Cry j 2 species in rainfall should be different. Since the release mechanisms are still not clear, therefore, the aim of this study is to clarify the important mechanisms of elution rate of two kinds of daughter allergenic species when pollen grains are washed out by rainfall and exposed to polluted air.From the analytical results of rainwater samples and model laboratory experiments of simulated rainfall, it was indicated that a great number of pollen grains were trapped in initial rainfall. At the same time, many bursts of pollen grains were also observed in the rainwater. Thus, it is possible that the two daughter allergenic species will be released from the fractions of cell wall, burst Air Pollution XX 387pollen and the surfaces of pollen grains. Moreover, ionic concentrations in initial rainfall were higher than following wet deposition, because air pollutants were also abundantly trapped in the initial rainfall. Especially, it was found that the elution rate of allergenic Cry j 1 was increased when in contact with rainwater containing high ionic concentrations. In this case, elution of allergenic Cry j 1 was rapidly increased when in contact with a weak basic solution with high Ca 2+ concentrations. Similarly, elution of allergenic Cry j 2 was also prompted from burst pollen washed out by rainfall and exposed to polluted air. Therefore, it is one important factor for the fast release of daughter allergenic species from pollen grains washed out by rainfall and exposed to polluted air including abundantly crustal particles such as road dust and Asian dust.
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