Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

The threshold that triggers the need to investigate a potential bioconcentration/bioaccumulation tendency experimentally is a log10 Kow value greater than or equal to 3.0. The US EPA's KOWWIN model predicts a log Kow of 1.76 for terephthalic acid (TPA) and the database on which the model is constructed contains a published value of 2.00 for TPA (Hansch, C. et al., 1995 - data attributed to Chan, T. & Hansch, C., Pomona College, unpublished results). Both these log10 Kow values lie below the trigger of 3.0 and terephthalic acid is therefore not expected to exhibit significant bioconcentration or bioaccumulation tendencies. The US EPA's model BCFBAF v3.00 predicts a bioconcentration factor in fish of 3.16 L/kg wet weight, derived from the measured log Kow value. Studies of bioconcentration/bioaccumulation are not triggered for TPA.

It may be concluded that terephthalic acid is not bioaccumulative (not B).

Terephthalic acid is not expected to remain stable in the form of the free acid under environmental conditions. Aquatic ecotoxicology studies have been conducted with TPA after converting it to its disodium salt to increase its solubility and the range of achievable exposure concentrations. This is considered representative of the likely behaviour of TPA in the environment. The increased aqueous solubility of terephthalate salts relative to that of the free acid implies a corresponding decrease in log10 Kow and hence an even lower bioconcentration/bioaccumulation potential.

This is confirmed by measured data available for isopthalic acid. Isophthalic acid is a structural analog of TPA that has an identical KOWWIN log Kow estimate of 1.76. The octanol/water partition coefficient of isophthalic acid has been determined according to the shake-flask procedure, in a system buffered to pH 7 (see Point 4.7, Hatoum & Garthwaite, 1992). The mean log Kow obtained for IPA under these conditions was -2.34. This value implies a much higher relative solubility of IPA in the aqueous phase than the log Kow indicated by KOWWIN QSAR. This is likely to have been caused by the presence of the buffer used to maintain the test system at pH 7: IPA would have been converted under these conditions to salts with higher aqueous solubility than that of the free acid. Similar behaviour, with a log Kow similarly lower than that of the free acid, may be expected for TPA under comparable conditions, following conversion of the parent monomer to its more soluble salts.