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EC number: 216-374-5 | CAS number: 1569-02-4
Derivation of PNECs for fresh and marine water
Through a combination of using data on the substance, data from read across substances and reliable QSARs, sufficiently robust data is available to derive acute EC50 or LC50 values for all three trophic levels. The acute toxicity data indicate that algae are the most sensitive species and fish the least sensitive. The EC50 for algae is likely to be greater than 1000mg/l. There is also data on chronic toxicity for a suitable read across substance. The experimental data in combination with the data from QSARs suggests that the order of relative chronic toxicity will be the same as for acute toxicity, with algae again the most sensitive species and fish the least sensitive., although the QSAR data suggests little difference between daphnia and algae. The overall data base is consistent too with the acute to chronic toxicity ratios typical of organic substances and the order of relative toxicity established by ECETOC (“Aquatic hazard assessment II”, Technical report 91, ECETOC, Brussels, 2003). Therefore an appropriate starting place for establishing the PNEC is the NOEC established from an assessment of all of the relevant data on chronic toxicity. Using a read across approach and the known trend of toxicity within the P series of glycol ethers, the NOEC for algae is likely to be between 500-1000mg/l. A conservative choice is a NOEC of 500mg/l, based on the observed NOEC for propoxypropanol, which would be expected to be more toxic. There is also data available to inform on the likely chronic toxicity to both fish and invertebrates. The experimental data is from limit studies, which therefore do not provide absolute NOECs. However, as stated above, the weight of evidence from the acute and QSAR data does strongly support the argument that algae are a sensitive species and starting from them to derive the PNEC is justified. On this basis, it would be justified to conclude that an assessment factor of 10 can be used to derive the PNEC for freshwater, since there is chronic data available for all three species and data from the most sensitive trophic level is used as a starting point. However, taking into account a more conservative approach and recognising that some may argue that the chronic fish study is not to a modern protocol, a more cautious conclusion is that a factor of 50 is more appropriate as would be used if chronic data was only available from 2 trophic levels to derive the PNEC of 10mg/l. An alternative approach would be to take the NOECs selected for each trophic level (even if these are derived from limit studies.) The lowest value available is a NOEC of 100mg/l (daphnids and algae). Since data is available for all three trophic levels, an assessment factor of 10 is justified, which would lead to the same PNEC value of 10mg/l.
For marine water, the PNEC is taken as one tenth of the freshwater PNEC.
Appendix - calculations used in partitioning method to calculate PNECs for soil and sediment
Formula for the calculation of PNECsed using the equilibrium partitioning approach for sediment:
PNEC(sed) = (Ksed-water x PNEC(aqua) / RHOsed) * 1000
PNEC(sed) Predicted No Effect Concentration in sediment [mg/kg, wet weight]
Ksusp-water partition coefficient sediment / water [0.94 m3/m3]
RHOsed bulk density of sediment matter [1150 kg/m3]
PNECaqua Predicted No Effect Concentration in water [as above]
Formula for the calculation of PNECsoil using the equilibrium partitioning approach for soil:
PNEC(soil) = (Ksoil-water x PNEC(aqua) / RHOsoil) * 1000
PNEC(soil) Predicted No Effect Concentration in soil [mg/kg, wet weight]
Ksoil-water partition coefficient sediment / water [0.294 m3/m3]
RHOsoil bulk density of soil matter [1700 kg/m3]
Because ethoxypropanol is readily biodegradability, it does not meet the criteria for classification for environmental toxicity.
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