Water Effect Ratio (WER)
EnviroScience’s Bioassay Laboratory routinely performs Water Effect Ratio (WER) evaluations. Water Effect Ratios may be used to derive site-specific limits for certain metals from national and state aquatic life criteria that were originally developed using laboratory toxicity data.
National aquatic life criteria for metals are intended to protect the aquatic life in most, but not all, surface waters. In some cases, such a criterion might not adequately protect the aquatic life at a given site. More commonly, though, these criteria are overprotective because most surface waters have greater hardness and often higher pH than the laboratory water which was used in toxicity tests that formed the basis for the standard.
Because a national aquatic life criterion might be more or less protective than intended for the aquatic life in most bodies of water, USEPA established federal guidelines to derive site-specific criteria for certain metals including arsenic, cadmium, chromium(III), chromium(VI), copper, lead, mercury, nickel, selenium, silver, and zinc. A number of physical and chemical characteristics of site water and a metal can affect the toxicity of that metal to aquatic organisms in particular surface water. When deriving site-specific aquatic life criteria for a metal, the difference between the toxicity of the metal in laboratory water and site water may be adjusted with a site water effect ratio.
Toxicity differences of site water and synthetic laboratory water are compared in the laboratory, and evaluated for differential lethal concentrations. The toxicity endpoints from these two tests are used to calculate the WER, which is then multiplied by the national or state aquatic life criterion to calculate the site-specific limit.
Please contact one of the EnviroScience biologists at (800) 940-4025 to determine whether a WER is appropriate for your facility’s permit situation.
Chemistry analysis on Effluent Water
