Species based models, uncertainty analysis

The Predicted No Effect Concentration may be derived from laboratory, field or theoretical data. Studies conducted on single species such as acute toxicity to fish (IX so) over a relatively short time scale (normally 40 or % h) and with death as the only recorded endpoint is, by itself, only of limited value in deciding whether or not a predicted environmental level of a dye is, or, is not, acceptable. Extrapolation from acute effects to chronic and ecosystems effects involves numerous uncertainties. In order to protect the ecosystem, conservative assessment factors have been introduced based on the statistical analysis of a set of data [17] for chronic exposure. The US-EPA [18] has proposed to apply a factor of KXX) for a single acute L(E)Cso value or 100 to the lowest value if all 3 tests are available (fish, daphniae, algae). These models have in common that they assume steady state concentrations in the aquatic environment. 

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