PART X — ENVIRONMENTAL CONTAMINANTS 



Figure X-9 — DISTRIBUTION OF RAGWEED POLLEN IN THE UNITED STATES 



Ragweed pollen is responsible for more than 90 percent of all the pollinosis in the 

 United States. Some 50 species of ragweed are known; they are found in all fifty 

 of the United States, but the highest concentrations are in the North Central and 

 Northeastern states. They grow alongside highways, in plowed fields, and in other 

 disturbed areas. Since there is more and more disturbed soil each year, there 

 is more and more ragweed, and, hence, there are more and more pollen and hay- 

 fever sufferers. 



but the location of local sources that 

 affect specific receptors is often not 

 known. Seasonal patterns of occur- 

 rence are fairly well documented for 

 most important species, but diurnal 

 patterns have been studied for only a 

 few, and the relationships between 

 these patterns and other variables are 

 little known. Sources of fungus 

 spores are less well known than 

 sources of pollen, and diurnal and 

 seasonal spore concentration patterns 

 have seldom been studied. 



Although the dispersion mecha- 

 nism plus the source strength will 

 determine the concentrations that are 

 sampled at any given point of inter- 

 est, quantitative studies of pollen 

 transport and dispersion from known 

 sources have been made by only two 

 research groups in this country. 

 These studies have indicated that 

 pollens are dispersed much like inert 

 particles of similar size, and that 

 meteorological diffusion theory may 

 be applied if particle characteristics, 



source configuration, and output rate 

 are known. 



Concentrations of aeroallergens at 

 sampling locations may vary by at 

 least several orders of magnitude. 

 Close to a local source, such as a 

 field of ragweed, concentrations can 

 average over 75,000 grains per cubic 

 meter during a several-hour period. 

 Short-period peak concentrations 

 probably exceed this value by several 

 times. At locations distant from 



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