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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The QSAR determination of the carbon partition coefficient for tetrachlorophthalic anhydride using the model KOCWIN included in the Estimation Program Interface (EPI) Suite v 4.1 revealed values of 1524 L/kg (logKow method) and 22.69 L/kg (MCI method) for the unaffected molecule of the substance as any decomposition (e.g. hydrolysis) of the substance is not taken into account by the program. Therefore the results are only of theroretical interest, because tetrachlorophthalic anhydride rapidly hydrolysed in water. The revealed values for the hydrolysis product tetrachlorophthalic acid (CAS 632-58-6) were 117.5 L/kg (logKow method) and 1308 L/kg (MCI method). The results relate to the neutral form of the substance. Estimated pka1 is 3.01 and pKa2 is 0.55, indicating that tetrachlorophthalic acid exists predominately in its dissociated form at environmentally relevant pH. Therefore the Koc was calculated (logKow method) for the deprotonated form, the obtained Koc was 0.1243 L/kg based on a logKow of -2.18 (EPI Suite). The Koc value of 0.1243 L/kg considers the anionic character of the substance and is taken into account for further assessment.

Key value for chemical safety assessment

Koc at 20 °C:
0.124

Additional information

Neither for tetrachlorophthalic anhydride nor for the hydrolysis product tetrachlorophthalic acid (CAS 632-58-6) no experimental results describing the adsorption properties are available.

The distribution of tetrachlorophthalic anhydride and the hydrolysis product tertachlorophthalic acid between the organic phase of soil or sediments and the porewater was calculated by using QSAR with the Estimation Program Interface (EPI) Suite v 4.1. Koc values of 1524 L/kg (logKow method) and 22.69 L/kg (MCI method) were obtained for tetrachlorophthalic anhydride. As any decomposition of the substance (e.g. due to hydrolysis, photolysis) is not taken into account by the program, the values for tetrachlorophthalic anhydride are only of theoretical interest.

In order to predict the mobility and fate of the substance in soil and sediments the organic carbon partition coefficient was calculated for the hydrolysis product tetrachlorophthalic acid. Koc values of 117.5 L/kg (logKow method) and 1308 L/kg (MCI method) for the neutral form were estimated. For tetrachlorophthalic acid the estimated pKa1 is 3.01 and pKa2 is 0.55, indicating that the substance exists predominately in its dissociated form at environmentally relevant pH. This property is not incorporated by the estimation program. Therefore the Koc was calculated for the deprotonated form, the obtained Koc was 0.1243 L/kg (logKow method) based on a logKow of -2.18 (EPI Suite). The Koc value of 0.1243 L/kg considers the anionic character of the substance and is taken into account for further assessment.

The Koc of 0.1243 L/kg suggest that the substance has a negligible sorption potential to soil and sediment, and a rapid migration potential to groundwater. For all estimations ambient temperature was assumed.

Under environmental relevant pH-values, tetrachlorophthalic acid exists predominantly in the dissociated form, based upon its pKa values. At pH 5 to 9, the substance will be deprotonated resulting in the corresponding anion. As cationic substances in particular generally adsorb strongly, an adsorption potential of the dissociated form of tetrachlorophthalic acid is not expected.