Silver is tightly bound by sewage sludge and elevated levels of silver are often associated with sewage outfalls receiving minimal treatment. In the absence of sewage, silver associates with iron oxides and humic substances. Silver-inorganic complexes are probably the most common in the marine environment. Silver-chlorides are generally not bioavailable except for silver chloride. Activated sludge organisms may bioaccumulate silver at 100 times the concentration in the effluent.
Silver has low toxicity to vertebrate animals and is eliminated rapidly when ingested orally.
It is not a cumulative toxin. Since surface waters in Canada generally contain low levels of silver and there are few data on chronic silver toxicity to animals, no criteria seem to be justified at this time for wildlife, livestock or laboratory animal drinking water. Wildlife, free range and confined livestock and laboratory animals can safely drink water which meets the aquatic life criteria. Maximum and 30-day average criteria have been set despite the paucity of data for marine fish since fish are not sensitive to silver at concentrations over 10 times the levels that affect most invertebrates and algae. Criteria are set to protect the most sensitive lifestage of the most sensitive species.