Substitution of Freshwater for Marine Data and Vice Versa

3 Substitution of Freshwater for Marine Data (and Vice Versa) 

Given the possible differences in sensitivity of freshwater and marine species, substitution from 1 data set to the other is not generally recommended except if insufficient freshwater or marine data are available for extrapolation to an EQS. 

In practice, there will sometimes be situations for which saltwater toxicity data are not available. In these situations, it may be deemed necessary to use freshwater data in lieu of data for marine species. However, several regulatory authorities (e.g., Australia, Canada, and the United States) would not extrapolate from freshwater data to set a definitive marine EQS. Based on acute SSDs, Wheeler et al. (2002) concluded that it is possible to use freshwater toxicity data to extrapolate to saltwater effects by applying an appropriate assessment factor. However, they did not propose a value for this factor moreover, looking in detail at their results (see Section 4.6.1), this extrapolation could be overprotective in some cases. 

Our consensus is that if a marine (acute or chronic) EQS is needed, then it should be based on experimental marine data and not extrapolated from freshwater studies. If data are substituted from freshwater systems to marine (or vice versa), the proposed standard should only be considered as tentative (see Zabel and Cole 1999). A tentative value of this type is likely to be unreliable if used for regulation. 

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