Development of chronic aquatic water quality criteria and standards for silver.

U.S. Environmental Protection Agency (EPA) is updating its aquatic life ambient water quality criteria (aqAWQC) for a number of parameters, including silver. The silver aqAWQC was last issued in 1980. At that time only an acute aqAWQC was established. With the increased reliance on water quality criteria to drive and prioritize the United State's efforts to improve water quality, the scientific basis of new and modified water quality criteria must be both strong and transparent. Although few, if any, natural waters in the United States have suffered water quality impairments because of silver, the lack of valid silver chronic toxicity data in combination with the misapplication of the current U.S. EPA guidelines on deriving chronic aqAWQC could lead to derivation of chronic criteria (by U.S. EPA) and chronic standards (by states, tribes, etc.) that are not supported by scientific data. This misapplication could result in U.S. EPA and the states listing many waters as impaired by silver where, in fact, no silver-related water quality problem exists. This Research Note reviews available information on studies of both acute and chronic silver toxicity to aquatic organisms, as well as U.S. EPA's 1985 procedure for adopting chronic water quality criteria. It identifies existing gaps in the underlying research data base and identifies additional work necessary to derive valid chronic water quality criteria and standards for silver.