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Toxicity to aquatic algae and cyanobacteria

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Description of key information

 


α-Pinene is a bicyclic monounsaturated monoterpene and (-)-α-pinene is an enantiomeric form of α-pinene. Therefore, data on (-)-alpha pinene can be extrapolated to alpha-pinene. (see read-across justification document in section 13).


The recalculated 48h-NOErC for freshwater algae for (-)-alpha-pinene is 0.131 mg/L.


 

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
0.131 mg/L

Additional information

α-Pinene is a bicyclic monounsaturated monoterpene and (-)-α-pinene is an enantiomeric form of α-pinene. Therefore, data on (-)-alpha pinene can be extrapolated to alpha-pinene. (see read-across justification document in section 13).


An algal toxicity study was performed on Pseudokirchneriella subcapitata with (-)-alpha-pinene in accordance with GLP and OECD Guideline 201.


A slight inhibition (38.5 %) was recorded at 24 h at the limit test concentration in comparison to control cultures, but no significant inhibition of the growth rate was recorded during the remainder of the test (8 % at t = 48 h and 0 % at t = 72 h).


Chemical analyses revealed severe test item losses in the presence and absence of algae from the first day. These test item losses were more likely due to a photodegradation phenomenon or another abiotic degradation characteristic of the test item. The 48-h LOEC and NOEC values of (-)-alpha pinene on Pseudokirchneriella subcapitata were first estimated to be 0.494 and 0.247 mg/L, respectively.


To express a more conservative exposure of algae, the exposure concentration was calculated with the biotic samples.The concentration of 2.259 mg/L is a better representation of the real exposure of organisms and the concentration of 0.905 mg/L represents the minimum exposure concentration (after significant volatility loss which occurred outside of the study during sample analysis).


At 24 and 48 h the substance is detected, the concentration is assumed to be 0.05 mg/L (half of the quantification limit, close to the detection limit).The exposure concentration over 48h was 0.131 mg/L, calculated as the mean geometric of 0.905, 0.05 and 0.05 mg/L (concentrations at 0, 24 and 48h).


The 48-h NOEC values of (-)-alpha pinene on Pseudokirchneriella subcapitatawas estimated to be 0.131 mg/L.


 After 72 h, no effect of the test item on Pseudokirchneriella subcapitatawas observed at the solubility/saturation limit of the test item in the test water.


 In order to support the experimental result, iSafeRat® High-Accuracy QSAR models were used on (-)-alpha-pinene. The model for non-polar narcosis (or MOA1 according to Verhaaret al.;1992) dedicated to algae toxicity was constructed using high quality data for water solubility and algal growth inhibition test for 40 substances with the same mode of action. This mechanism of toxicity is based on the principle of biological membrane disruption by a reversible accumulation of chemicals into the membrane induced by hydrophobic interactions. (-)-α pinene as an alkene (terpene) is attributed to the class of non-polar narcotic compounds (MOA1).


All chemical groups within the molecular structure are taken into account by the model.


The water solubility of (-)-α pinene was predicted at 3.11 mg/L (or -4.64 in log (mol/L) using the iSafeRat® solubility module. This value was given as the input in the QSAR model to determine the algae toxicity. The water solubility value given as the input to the iSafeRat® Holistic HA-QSAR model falls just beyond the regression domain of the model between a log water solubility (in log (mol/L)) of -4.38 to 0.49. It falls in an intermediate domain between a log water solubility (in log (mol/L)) of - 9.34 to -4.38 where baseline toxicity cannot be experimentally measured accurately because the thermodynamic equilibrium is unlikely to be reached within the exposure duration of the study. Therefore the toxicity is likely to be greater than the water solubility limit. Based on a statistical k-NN (k Nearest Neighbours) approach (k = 3), the predicted toxicity of the test item can still be extrapolated using the linear regression since the closest neighbours have a ErC50 below their solubility limit. It should be noted that the regression can therefore be considered a worst case toxicity scenario for the algae under these conditions.


The 72h-ErC50 of (-)-α pinene to algae was extrapolated as equal to 0.31 mg/L with a 95% confidence interval (α = 0.05) of 0.27 to 0.36 mg/L.


 


It is considered that the experimental OECD 201 study fulfils the information requirement laid down in Annex VII, Section 9.1.2 of the REACH regulation and considers this study as key study. Under the test conditions, the 48 h-NOErC for the registered substance to freshwater algae is 0.131 mg/L.


 


Thus the experimental NOEC value is valid for key value for chemical safety assessment.