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Adsorption / desorption

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Description of key information

The study does not need to be conducted because the substance has a low octanol water partition coefficient and the adsorption potential of this substance is related to this parameter (study scientifically not necessary). Moreover, the substance is readily biodegradable and decompose hence rapidly. However, using QSAR the log Koc of isobutyl acrylate was determined to be 1.53 (Koc = 33.8).

Key value for chemical safety assessment

Koc at 20 °C:
33.8

Additional information

Non-submission justification

In accordance with column 2 in Annex VIII to Regulation (EC) No 1907/2006 (REACH) the study on adsorption/desorption does not need to be conducted if based on the intrinsic properties of the substance low potential for adsorption is to be expected, e.g. when the substance has a low octanol water partition coeffiicient and the adsorption potential of this substance is related to this parameter. The experimental log Pow of isobutyl acrylate was determined to be 2.38 (please refer to IUCLID section 4.7) indicating that adsorption is very unlikely. Moreover, the substance was assessed to be readily biodegradable which implies that it decompose rapidly in the environment (please see IUCLID section 5.2.1). Therefore, additional studies are scientifically not justified and this endpoint was waived.

 

Supporting information

There are no experimental data on the potential adsorption of isobutyl acrylate or the source substance tert-butyl acrylate to solid phases available. Thus, the adsorption behaviour of isobutyl acrylate and tert-butyl acrylate was only assessed by using QSAR estimates. One guideline study, supported by a QSAR prediction, is available for the source substance n-butyl acrylate.

 

isobutyl acrylate

There are no experimental data on the potential adsorption of isobutyl acrylate to solid phases. Based on an estimated Koc of 33.8 calculated by SRC PCKOCWIN v1.66 (corrected log Koc = 1.53), adsorption to solid soil phase is not expected (BASF SE, 2008).

 

n-butyl acrylate

The adsorption and desorption characteristics of n-butyl acrylate to five soils, a loamy sand, a clay loam, two loams and an aquatic sediment, were determined in a guideline study according to EPA guidelines - CFR 40 section 796.2750 and GLP regulations (BAMM 1991). The organic carbon content of the soils and sediment used ranged from 0.46 % to 4.58 %. 14C-butyl acrylate was used in following the movement of the compound for one adsorption and three desorption steps. Six concentrations of butyl acrylate in 0.1 N calcium nitrate solution were used in these experiments. The concentrations of butyl acrylate ranged from 0.5 to 8.5 µg/mL of the carrier solutions. The amount of butyl acrylate in solution was measured by liquid scintillation counting. The amount of n-butyl acrylate on the soil was calculated from differences in solution concentrations for the adsorption and first two desorptions. The amount on the soil after the third desorption was determined directly by combustion of the soil. Overall, replicate 14C balances ranged from 71.8 to 99.5 %.

 

Butyl acrylate was weakly adsorbed onto the soils and sediment. As related to the carbon content of the individual soils, the average Koc for the adsorption step was 88.4. This places -butyl acrylate in a medium to high mobility class for adsorption to soils. The substance was less readily desorbed from the soils once adsorption had occurred. Related to the carbon content of the individual soils, the average Koc for the combined desorption steps was 254.6. These results are supported by QSAR calculations. Based on an estimated Koc of 35.37 calculated by SRC PCKOCWIN v2.00 (corrected log Koc = 1.6), adsorption to solid soil phase is not expected (BASF SE, 2015).

 

tert-butyl acrylate

For tert-butyl acrylate Koc values were calculated to be 138.9 L/kg (log Koc =2.1428) and 23.14 L/kg (log Koc =1.3643) when based on the log Kow method and the MCI method, respectively (BASF SE, 2017). Based on a log Koc of <3 adsorption to solid phases is not expected.

 

Conclusion

The experimental study on adsorption / desorption was waived based on a low Kow of 2.38 in accordance with REACH Annex VIII. QSAR estimations showed that neither the target substance isobutyl acrylate nor the source substances n-butyl acrylate and tert-butyl acrylate potentially adsorb to solid phases. For isobutyl acrylate the log Koc was calculated to be 1.53 (Koc = 33.8).

 

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.

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 tert-butyl acrylate (Q)SAR results were used for adsorption / desorption.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.