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<br />IR3 <br /> <br />SILVER IODIDE GENERATOR <br /> <br />277 <br /> <br />Automobile Exhaust. <br />1. Ca~bon monoxide; concentration 12,000 ppm. This concentration would <br />be fatal w'ithin an hour: hazardous. <br />2. Lead halides. These compounds are sOluble and are released in particle <br />sizes which are readily absorbed when inhaled: hazardous. <br />3. Other materials are present which were not considered in detail and <br />which contribute to air pollution. Among these are unburned and oxygenated <br />hydrocarbons, nitrogen oxides, nitrogen-containing organics, sulfur oxides, <br />aldehydes, acids, and phenols. All are substantial contributors to air pollution. <br /> <br />WATER POLLUTION <br /> <br />~ <br /> <br />In regard to possible water contamination or pOllution by the nucleating <br />material used to seed cloud systems, precipitation from treated and untreated <br />cloud systems has been analyzed for silver (the nucleating material used for <br />treatment. was silver iOdide). The silver content measured from natural <br />storms, npt seeded, was up to 20 X 10-12 g of silver per ml of precipitation. <br />In precipitation samples from seeded storms, the silver content ranged from <br />20 to 200 x 10-12 g of silver per ml (1). Iodine from AgI would be present in <br />nearly identical quantities (AgI is 0.46 Ag and 0.54 I by weight). <br />The U.S. Public Health Service water quality standards of 1962 (12) set <br />forth a maximum concentration for silver in drinking water as 5 x 10-8 g per <br />m1. If the amount of silver in precipitation from a seeded storm is assumed <br />to be 2 x 10-10 g per ml, this is less than one one-hundredth of the permis- <br />sible level. <br />As noted previously, the iodine which would be present in precipitation <br />resulting from seeding with silver iodide will be nearly identical to that of the <br />silver, that is, 2 x 10-10 g per ml or 0.2 ppb. . <br />Iodine is commonly added to table salt which is marketed as iodized table <br />salt. Federal regulations permit iodine to be added to table salt up to 0.02 % <br />or 200,000 ppb. To equal the amount of iodine a person would ingest from the <br />iodized (0.02 %) table salt he put on his breakfast eggs, he would have to drink <br />130 gal of precipitation from a storm seeded with silver iodide. <br />It is interesting to note that the concentration of both silver and iodine in <br />precipitation from seeded storms is substantially less than the most restricti ve <br />levels contained in the USPHS standards for drinking water which are for <br />phenol, cadmium, and selenium. <br />Materials employed as cloud nucleants other than silver iodide would be <br />found in precipitation in about the same order of magnitude as silver iodide. <br />The resulting concentrations in precipitation would consequently be about the <br />same as that produced by silver iodide seeding which are well below estab- <br />lished permissible values for all materials listed by the USPHS for drinking <br />water. <br /> <br />1 <br />~, <br /> <br />CONCLUSION <br /> <br />Examination of the effluent of a propane-acetone silver-iodide generator <br />reveals its chemical contents and their concentrations at the level where an <br />operator might encounter them present no hazard. These same materials are <br />released to the atmosphere in quantities so small, they may be disregarded <br />