Quiz: Calculation of Predicted No-effect Concentration (PNEC)
Little Pro on 2016-08-11
This is the answer to a quiz on how to derive predicted no-effect concentration (PNEC) for a substance (Koc=10) for 4 environmental compartments (water, soil, STP and sediment) based on available data. The original quiz and tutorial can be accessed here.
Answer
| Compartment | Available data | Method | PNEC |
|---|---|---|---|
| PNEC-Fresh water |
|
AF=10 | 0.1mg/L |
| PNEC-STP microorganism | EC50(activated sludge inhibition test)=20mg/L | AF=100 | 0.2mg/L |
| PNEC-soil | LC50 (earthworm acute toxicity) =500mg/kg |
PNEC(AF=1000)=0.5mg/kg PNEC (EQM)=0.029mg/Kg |
0.029mg/kg |
| PNEC-sediment | No data | EQM | 0.1mg/L |
Q2. If the concentration of the substance in water is 0.05mg/L, the risk is acceptable.
Explanation
For PNEC-water, long-term results (NOEC) from three species are available. An assessment factor of 10 is assigned to the lowest NOEC value of the 3 species.
- PNEC-water=Lowest NOEC/10=1mg/L/10 (AF)=0.1mg/L.
For PNEC-STP microorganism, only short-term EC50 from activated sludge respiratory inhibition study is available. An assesment factor of 100 is assigned to the EC50.
- PNEC-STP microorganism=EC50/1000 (AF)=20mg/L/100=0.2mg/L.
For PNEC-soil, only one acute test result with soil dwelling organisms is available. PNEC-soil is calculated on the basis of this result using both assessment factor approach and on the basis of the equilibrium partition method (EPM).
- PNEC-soil(assessment factor)=LC50/1000(AF)=0.5mg/kg
- PNEC-soil(EPM)=(0.1176+0.01764*Koc)*PNEC-water=0.029mg/kg
In the end, the lowest PNEC-soil value (0.029mg/kg) will be used for soil risk assessment.
For PNEC-sediment, no test data is available. Only EPM can be used.
- PNEC-sediment=(0.783+0.0217*Koc)*PNEC-water=0.1mg/L
If the concentration of the substance in water is 0.05mg/L and it is less than PNEC-water, the risk is acceptable.
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