![]() ![]() The picture below summarizes common assessment factors used for PNEC calculation (from ECHA guidance on chemical risk assessment). More data on more species in the same environmental compartment can also reduce uncertainties, thus further decreasing assessment factors. Assessment factors applied for long-term tests are smaller because the uncertainty of the extrapolation from labs to natural environment is reduced. How to Choose Appropriate Assessment Factors?Īssessment factors (AFs) are used to address the differences between laboratory data and natural conditions, taking into account of interspecies differences and intraspecies differences. Usually PNECs are only derived for 4 compartments: fresh water, soil, STP micro-organism and sediment. It is not always necessary to derive PNECs for all mentioned environmental compartments. Required when log Kow>3 or BCF >100 and there is no mitigating property such as ready biodegradability or hydrolysis.NOEC bird/mammal=NOAEL bird/mammal* conversion factors(8-40 for different species) if only NOAEL is available.The lowest value of LC50 bird, NOEC bird or NOEC mammal divided by assessment factors (30-3,000).Important for gases and highly volatile substances.The lowest NOEC/EC10/EC50 value from activated sludge inhibition test or biodegradability studies divided by assessment factors (1~100).The lowest LC50/NOEC/EC10 value for soil living organisms divided by assessment factors (10~100) or.Larger assessment factor for marine sediment.Using the equilibrium partitioning method (EPM) when only aquatic toxicity data is available.The lowest NOEC/EC10 value for sediment living organisms divided by assessment factors (10~100) or.If there is not enough ecotox data on marine organisms, PNEC- marine water = PNEC -fresh water/10.Bigger assessment factor for marine water.Derived only when exposure to marine water is possible. ![]() The lowest value of EC50, LC50, NOEC, etc from aquatic toxicity studies (algae, daphnia and fish) divided by assessment factors.PNECs need to be derived for various environmental compartments (water, sediment, soil, air, etc.). The table below summarizes the types of PNECs you may need to derive and how to calculate them. How Many Predicted No-Effect Concentrations (PNECs) You Need to Derive? If the actual concentration of the substance in aquatic environment is 2mg/L, the substance will cause unacceptable risks to aquatic enviroment. An assessment factor of 10 is used to take into account of the differences between laboratory conditions and natural conditions. For aquatic environment, toxicological data ( 10mg/L) from the most sensitive species (Daphnia) is used for PNEC- water calculation. In above case, PNEC- water is calculated as 1mg/L. LC50 (earthworm acute toxicity) > 1000mg/kg If PEC/PNECs 1000mg/L (activated sludge inhibition test) In environmental risk assessment, PNECs will be compared to actual or predicted environmental concentration ( PEC) to determine if the risk of a substance is acceptable or not. Predicted No-Effect Concentration (PNEC) is the concentration of a substance in any environment below which adverse effects will most likely not occur during long term or short term exposure. How to Calculate Predicted No-Effect Concentration (PNEC) ![]()
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