Extrapolation methods for setting ecological standards for water quality: statistical and ecological concerns

: Extrapolation methods form the basis for most recent techniques used to set 'safe' levels of toxicants for ecosystems. Most methods use information from several single species toxicity tests to predict safety factors for protecting all species in all communities in a nation or group of nations. There are a number of statistical and ecological concerns with this approach. These include assumptions about the shape of the distribution of tolerance to a toxicant, the ability to extrapolate information on laboratory species and condition to field species and condition and to the condition of communities and ecosystems, and assumptions about the appropriateness of laboratory measures relative to ecosystem measures. The approach has not been validated for safety and, before the approach is fully applied, needs to be validated. Other methods can be used with the extrapolation approach to reduce uncertainties.