The life stage, size of the organisms, length of time of exposure, species sensitivity and salinity all contribute to the variation in toxicity reported in the literature. This lack of free silver ion is generally not accounted for in the literature where most values are given as total silver and the actual toxic forms of the silver would be a considerably smaller value. This factor accounts for much of the wide variation in toxicity values reported in the literature, for while salinity is generally reported, it is rarely considered as a factor affecting toxicity. The total silver measurements reflect the worst-case scenario, which should be considered when setting any water quality criteria in order to protect the most sensitive life stages of the most sensitive species. This worst-case scenario is particularly important for estuaries, where salinity can fluctuate quite dramatically.
Silver is one of the most toxic of the heavy metals to freshwater micro-organisms.
Water hardness, length of exposure, size of the organism and life stage of the organism all affect the toxicity values. Invertebrates and embryos of fish are generally much more sensitive than juvenile and adult fish. The effect of speciation on the acute and chronic toxicity of silver was compared using the fathead minnow as the test organism. Silver sulfide, silver thiosulfate and silver chloride were compared to the silver ion, added as silver nitrate. The tests were flow-through in soft water at 25 degrees C. Silver chloride was found to be 300 times less toxic, silver sulfide was 15,000 times less toxic, and silver thiosulfate was 17,500 times less toxic than silver nitrate.