Ethyl 3-[[bis(1-methylethoxy)phosphinothioyl]thio]propionate

Bioaccumulation: aquatic / sediment

Description of key information

No experimental data on the test substance are available. Therefore the bioaccumulation potential of the substance was assessed in a weight of evidence approach using several QSAR calculations. The substance has a low bioaccumulation potential shown in the reliable model predictions.

Additional information

The bioaccumulation potential of the substance was assessed in a weight of evidence approach using several QSAR calculations. No reliable experimental data on the test substance are available. The logPow is 4 and below the screening criterion for B/vB (logPow >= 4.5). Several QSAR models have been used to properly assess the bioaccumulation potential in a weight-of-evidence approach. The single results are summarized in the table below.

 

Model/Study		BCF	Log BCF	Remarks
Catalogic v5.12.1		7	0.86	Main mitigating factor metabolism; 5.6% incorrect fragments (27.8% unknown)
T.E.S.T. v4.21		34	1.5
EPISuite v4.10	Regression-based estimate	253	2.4
	Arnot-Gobas upper trophic level	78	1.9	Including biotransformation rate estimates
	Arnot-Gobas mid trophic level	101	2.0	Including biotransformation rate estimates
	Arnot-Gobas lower trophic level	108	2.0	Including biotransformation rate estimates
VEGA CAESAR v2.1.14		3	0.5	*
VEGA Read across 1.1.0		9	0.95	*
VEGA Meylan v1.0.3		688	2.84	*

 *out of model applicability domain

Regarding the results, the calculated BCF values range from 3 (VEGA) to 253 (EPISuite v4.11, regression-based estimate).

 

Of the models, Catalogic and the Arnot-Gobas model from EPISuite v4.11 take into account mitigating factors, e.g. metabolism, water solubility and/or size. Catalogic revealed a corrected BCF of 7 but the compound is only to 66.7% in the model’s applicability domain.

The Arnot-Gobas model from EPISuite takes into account the biotransformation rate of the compound and calculates BCF values for the upper, mid and lower trophic levels. The values for the present compound range from 78 (upper trophic level) to 108 (lower trophic level). The substance is in the applicability domain of the model. the predicted logPow is similar to the experimental derived logPow of 1.

The T.E.S.T. package from the US EPA estimates BCF values using several different advanced QSAR methodologies. The recommended model of the T.E.S.T. package is the consensus method since it provides the most accurate prediction. This model estimates the BCF by taking an average of the predicted BCF values from the other applicable QSAR methods of the package. For the present substance the consensus method averaged the results from (1) the hierarchical clustering method, (2) the single model method, (3) the group contribution method, (4) the FDA method and (5) the nearest neighbor method. The resulting BCF value is approx. 34 but might have a low reliability.

The VEGA submodels were developed with several descriptors and are based on a dataset of 378 -860 compounds. They offer detailed information on the applicability domain. In the present case, the compound is out of the model’s applicability domains which makes the derived BCF values of 3, 9 and 688 not reliable. Furthermore the estimated logPow deviate significant from the experimental value of 4.0. Therefore, the VEGA estimations have a low reliability and are not further considered in the assessment.

 

In summary, in a weight-of-evidence approach balancing different QSAR estimations no significant accumulation of the compound in organisms is expected. Regarding the results, the calculated BCF values range from 7 (Catalogic) to 253 (EPISuite v4.11, regression-based estimate). Although some results might be uncertain, the results show a low bioaccumulation potential. The BCF was determined to be < 500 (threshold relevant for classification under Regulation 1272/2008/EC). However, due to the informative value of the QSARs it is not expected that the compound is above the “B” cut-off criterion of 2000. This assumption is supported by mammalian toxicological data. Therefore, the test substance does not accumulate in organisms. The highest determined BCF was 253 without considering biotransformation (EPISuite 4.11)

QSAR-disclaimer

 

In Article 13 of Regulation (EC) No 1907/2006, it is laid down that information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI (of the same Regulation) are met. Furthermore according to Article 25 of the same Regulation testing on vertebrate animals shall be undertaken only as a last resort.

 

According to Annex XI of Regulation (EC) No 1907/2006 (Q)SAR results can be used if (1) the scientific validity of the (Q)SAR model has been established, (2) the substance falls within the applicability domain of the (Q)SAR model, (3) the results are adequate for the purpose of classification and labeling and/or risk assessment and (4) adequate and reliable documentation of the applied method is provided.

 

For the assessment of the substance (Q)SAR results were used for bioconcentration. The criteria listed in Annex XI of Regulation (EC) No 1907/2006 are considered to be adequately fulfilled and therefore the endpoint(s) sufficiently covered and suitable for risk assessment.

 

Therefore, and for reasons of animal welfare, further experimental studies on bioaccumulation are not provided.