The toxicity of ammonia to fishes has been attributed to the un-ionized ammonia chemical species present in aqueous solution. Because the percent of total ammonia present as un-ionized ammonia (NH3) is so dependent upon pH and temperature, an exact understanding of the aqueous ammonia equilibrium is important for toxicity studies. A critical evaluation of the literature data on the ammonia–water equilibrium system has been carried out. Results of calculations of values of pKa at different temperatures and of percent of NH3 in aqueous ammonia solutions of zero salinity as a function of pH and temperature are presented.

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The toxicity of nitrite to rainbow trout is pH-dependent within the range considered acceptable to most freshwater aquatic life (pH 6.5–9.0). Both of the nitrite species, NO2− and HNO2, are toxic. It is recommended that nitrite criteria to protect freshwater aquatic life be based on total nitrite, and that such criteria reflect the pH dependence of nitrite toxicity. Variation in the toxicity of nitrite in the presence of chloride, sulfate, phosphate, and nitrate anions has also been demonstrated. It is concluded that the toxicity of nitrite to fishes, in addition to being pH-dependent, is also dependent in varying degrees upon many of the anions that are commonly found in natural aquatic environments.Key words: nitrite, pH, chloride, phosphate, sulfate, toxicity, rainbow trout, Salmo gairdneri

Metal-C02 complexes have attracted attention from both fundamental and applied viewpoints.1 First, C02 is an abundant Q molecule that serves as nature's photosynthetic building block.Second, C02 exhibits a variety of binding modes to metals.1"6 Third, the reactivity of metal-C02 complexes should provide insight regarding C02 activation and the design of new catalytic reactions.7 We have previously described the synthesis of the Scheme I. Representative Syntheses and Reactions of Rhenium/ Main-Group-Metal Bridging Carboxylate Complexes Ci c C MH R3SnCI /jv, ON/(TXPPh3

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