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<br />Seeding Agents <br /> <br />Silver iodide is the only seeding agent that is of concern. The issues facing us are reassessment <br />and redefinition of the purpose and methods of monitoring for cloud-seeding silver in the <br />environment and the need for further research devoted to biospheric impacts of cloud-seeding <br />silver. Past research has answered in the negative to all the questions except those related to <br />long-term accumulations, and has confined long-term concerns to the assimilation of silver iodide <br />to the same forms as naturally occurring silver and its subsequent effects in the environment. <br />For long-term impacts, the particular form of silver used for cloud seeding is unimportant. The <br />quantity used, and the resulting concentration of assimilated forms of silver in the natural <br />environment, are important. <br />However, we have recently found that both the quantities used for precipitation management <br />and the resulting concentrations are very much smaller than the corresponding natural transports <br />and concentrations of silver within the aquatic and terrestrial domains. Furthermore, both the <br />quantities and the concentrations of silver used for cloud seeding are very small compared with <br />those dispersed into t~e environment by industrial pollution and by the use of fertilizers. <br />A prime issue then becomes the priority for biological studies of the impact of cloud-seeding <br />silver relative to that from other, much stronger sources of silver dispersion into the environment. <br />In the face of the determination by the Environmental Protection Agency and the National <br />Institute of Environmental Health Sciences that cloud seeding is a negligible source of silver <br />pollution. compared to other sources, and that all sources together do not constitute an <br />environmental threat, what should be the role of Skywater? <br />Long-term biological impacts of silver, if they are real, should be apparent to a much greater <br />degree in connection with naturally high-soil concentrations of silver, and in connection with <br />industrial and agricultural dispersals that have been going on in certain areas for many decades. <br />Possible issues concern to what degree added silver may accumulate in one compartment or <br />another, in one type of organism or another, the rate of accumulation under realistic conditions, <br />the likely maximum concentration that will result from the accumulation process when an <br />equilibrium is reached between the addition of silver and its escape, and how does this <br />concentration compare with tolerance thresholds for both un acclimated and acclimated <br />organisms? <br />Within this area of concern, what issues apply directly to conditions that may reasonably be <br />expected to result from widespread and prolonged application of precipitation management? <br />What research specifically in support of Project Sky water is appropriate in the area of biological <br />impacts of silver? How should it relate to research addressed to the possible impacts of industrial <br />and agricultural pollution sources? <br />An auxiliary issue is that of monitoring. Neither past experience nor present calculations give <br />us any realistic expectation that monitoring procedures now available, applied in areas of cloud <br />seedi_ng, will be capable of detecting changes in silver related to precipitation management. <br />Natural variations of silver content in materials so far monitored are much larger than changes <br />that precipitation management can reasonably be expected to produce. Other pollution sources <br />are potentially far more powerful. <br /> <br />24 <br /> <br />.€ <br /> <br />~ <br />