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April 2009 Williams and Denholm methods to achieve the desired concen- trativn of silver ion; • The majority of studies into acute and chronic effects of silver ion have used soluble silver nitrate; • A number of studies have shown that the toxicity of silver ion in water is signifi- cantly ameliorated by the presence in water of chloride ion, carbonate ion, sul- fide ion (reactive and other forms) and dissolved organic carbon. In addition, silver is strongly adsorbed onto particu- late matter in water. Findings from re- cent studies point to the fact that silver ion concentrations in natural waters are negligibly smail; - • The study by Johnston (2001) has shown that many of these factors exist in the KNP and, as a result, the bioavailability of siiver would be expected to be of the order of carrent background levels; • The research results reported by Johns- ton have been validated by extensive additional sampling and analyses for the relevant parameters; Background levels of silver occurring in snow in the KNP are generally less than 2x10'o g/L, while background level of sil- ver in stream runoff was below the detec- tion limit of 1x10 g/L for silver. This level is several orders of magnitude below the chronic toxicity level; The Snowy Hydro Limited (2005) as- sessment of background levels also showed silver to be present in the envi- ronment at concentrations ranging from 0.47 mg kg"' in soil at generator sites to 0.09 mg kg" in alpine humus in the tar- get area; The average mass of silver iodide used each year is 17.6 kg, dispensed from 13 separate locatons across a target area of approximately 1000 square kilometres The likelihood of any environmental im- pact, even in potential zones of accumu- latian is minimal because of the small quantities and because silver iodide is not water soluble and not readily bia available. Hence no acute or chronic toxic e(fects are expected; 91 The SPERP monitoring program has a high probability of detecting any adverse trend in silver concentration well before the GN is reached. A statistical power analysis of the SPERP monitoring data for generator sites has shown the moni- toring design to have sufficient power to detect any statistically slgnificant change in silver concentrations; and • Mean silver concentrations have all been shown to be well below the GN for all matrices, at all locations and for periods of sampling during the SPERP. The conclusion of this review of the literature, assessment of ameliorating factors and interpre- tation of results to date provides compelling evi- dence that the use of silver iodide for the SPERP will not result in an adverse ecotoxicological im- pact on the environment of the study area. REFERENCES Adams, N.W.H. and J.R. Kramer, 1998: Reactiv- ity of Ag+ ion with thiol ligands in the pres- ence of iron sulflde. Environmental Toxico!- ogy and Chemistry, 17, 625-629. Allen, H.E. and D.J. Hansen, 1996: The impor- tance of trace metal specfiation to water quality criteria. Water Environment Research, 68, 42-54. Ankley, G.T., 1996: Evaluation of inetal/acid- volatile suifide relationships in the prediction of inetal bioaccumulation by benthic macroin- vertebrates. Environmenta! Toxicology and Chemisfry, 15, 2138-2146. ANZECC and AMRCANZ, 2000: Guidellnes for Assessing Fresh and Marine Water Quality. National Water Quality Management Strat- egy. Australian and New Zealand Environ- ment and Conservation Council Agriculture and Resource Management Council of Aus- tralia and New Zealsnd. Beil, R.A. and J.R. Kramer, 1999: Structurai chemistry and geochemistry of silver-sulfur compounds: criticai review. Environmental Toxicology and Chemistry, 18, 9-22. Benoit, G., S.D. Oktay-Marshall, A. Cantu il, E.M. Hood, C.H. Coleman, M.O. Corapcioglu, and P.H. Santschi, 1994: Partitioning of Cu, Pb, Ag, Zn, Fe, AI, and Mn between filter- - Scientific Papers -