ERA relies on the derivation of two values, the Predicted Environmental Concentration (PEC) and the Predicted No Effect Concentration (PNEC). Factors that contribute to the calculation of the PEC include the amount of the chemical that is in use, transport between the various environmental compartments and its degradation, by physical, chemical or biological means.
The PNEC is derived from the results of studies of effects on micro-organisms, plants and animals. As these studies cannot represent the whole range of organisms that are in the real world the results are subjected to “safety factors” to ensure that the overall conclusions of the ERA are precautionary. If the amount of effects data available is limited then high levels of safety factors are applied. If there are comprehensive data on a wide range of organisms, over complete life-cycles, then lower levels of safety factors can be applied.
Once the PEC and PNEC have been derived they can be placed in a simple PEC/PNEC ratio as an expression of risk. The magnitude of the ratio will depict the “level of concern”.If applicable concerns will be addressed by further refinement of the risk assessment, are our predictions of the PEC reduced if we understand degradation of the substance better, or can the effects safety factors be reduced if we understand longer term effects. The tests used to refine the ERA are known as Higher Tier tests. If, even after refinement, the PEC/PNEC ratio still shows potential concern then the compound will need to be the subject of regulatory controls.
