PART X — ENVIRONMENTAL CONTAMINANTS 



Figure X-8 - 



AVERAGE ANNUAL LOSSES FROM CROP DISEASES 

 IN THE UNITED STATES 



The figures in this table represent potential production in the U.S. from 1951 to 

 1960, inclusive — i.e., the production that would have been realized had plant 

 diseases not been present. Most of the losses are due to rusts, smuts, viruses, 

 fungi, and molds that are viable biological material transported in the atmosphere 

 by the wind. 



as extensive acreages of monocultures, 

 wide use of genotypically identical 

 populations, unusual growth of foli- 

 age or fruit through use of chemical 

 fertilizers and irrigation, and elimina- 

 tion of associated and competing 

 species. Some aerobiologists see op- 

 portunities to study the cultural checks 

 and balances of plant diseases at the 

 centers of origin of the crop species, 

 and also opportunities to learn about 

 pathogenic germ-plasm variability, 

 survival, and migration. Out of such 

 studies of "origins and sources" of 

 plant diseases the United States Aero- 

 biology Program is endeavoring to de- 

 rive new biological information that 

 will constitute improved input for 

 the epidemiological models described 

 above. 



Human and Animal Diseases — Al- 

 though various human and animal 

 diseases are spread by transmission of 

 bacteria, spores, or viruses in the air, 

 most of the atmospheric transport is 

 probably over a short distance and 

 within a water droplet or on some 

 other particle. Studies of these par- 

 ticles have been confined to indoor air, 

 especially of hospitals. However, a 



number of pulmonary mycotic dis- 

 eases are acquired by the inhalation 

 of spore-laden dust or other organic 

 particles in the free air indoors or 

 outdoors. Histoplasmosis, coccidioi- 

 domycosis, North American blasto- 

 mycosis, cryptococcosis, and nocari- 

 dosis may result from exposure 

 of humans or animals to such infec- 

 tious materials. The fungi or fugus- 

 like microorganisms causing these 

 diseases are unique in that they are 

 free-living in nature but also find the 

 susceptible mammalian body a suit- 

 able growth environment. In a small 

 percentage of cases, the infectious 

 agent disseminates from the pulmo- 

 nary tract involving a multiplicity of 

 organs and tissues. 



From knowledge accumulated to 

 date it appears that some of these 

 etiologic agents exist in certain foci 

 in nature and are often associated 

 with avian or chiropteran species. 

 Some of these agents also exist 

 in sharply demarcated geographical 

 areas, such as a portion of a (Milan, 

 Michigan) schoolyard which was a 

 source of histoplasma infection. In- 

 fectious particles become airborne due 



to winds or mechanical disturbance 

 of soil in which the fungi are present. 

 Most of the work on control has been 

 directed toward eradicating the infec- 

 tious agent by chemical sterilization 

 of its natural habitat. Some studies 

 have been made on the ecology of 

 these fungi, but much more work re- 

 mains to be done. 



Airborne Allergens 



Allergenic pollen and spores in the 

 atmosphere have been under study 

 for nearly fifty years as clinical prob- 

 lems, with varying degrees of atten- 

 tion to botanical sources and phenol- 

 ogy of the airborne particles. Greater 

 uniformity in air sampling and report- 

 ing techniques, and better organiza- 

 tion and availability of accumulated 

 information on the distribution of 

 allergenic particles, are clearly neces- 

 sary for improved prediction of ex- 

 posure. Improvements of these kinds 

 are in progress nationally and inter- 

 nationally, fostered by appropriate 

 organizations including the IBP Aero- 

 biology Program. 



Research Needs — Especially in 

 connection with urban areas with high 

 levels of gaseous pollutants in the at- 

 mosphere, there is need for investiga- 

 tion of possible interactions between 

 biological (spores, pollen, fragments 

 of fungus mycelium, and similar ma- 

 terials) and nonbiological (gases such 

 as sulfur dioxide, hydrogen fluoride, 

 and so on) emissions in transit. Fur- 

 thermore, the extent to which these 

 two groups of agents may induce 

 synergistic effects on plants and ani- 

 mals is a subject that merits further 

 attention. Regarding atopic allergy, 

 there is strong suggestive evidence 

 that augmented respiratory changes 

 due to simple gaseous irritants may 

 be expected in persons with preexist- 

 ing inflammatory changes due to ex- 

 posure to inhalant or ingestant aller- 

 gens. The concept is growing that 

 specific segments of the general popu- 

 lation may be predisposed to experi- 

 ence adverse effects from air pollu- 

 tants; it would be valuable to explore 



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