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Environmental fate & pathways

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The atmospheric oxidation half-life of isophthalic acid was estimated using the AOPWIN v1.91QSAR model available from the US EPA. The estimated atmospheric oxidation DT50 of isophthalic acid ranged from 8.18 days (default settings) to 12.27 days, estimated by applying the recommended northern hemisphere settings that are considered relevant in a European context.


Since isophthalic acid is readily biodegradable, a formal study of the hydrolysis behaviour of IPA at three pH values is not required and has not been performed. Nevertheless, some insight is provided by a study of the toxicity of IPA (converted to its sodium salt(s) prior to test initiation) to unicellular aquatic algae (Knacker et al., 1993c). The IPA-equivalent concentrations, initially dosed to non-sterile aqueous algal growth test medium at 67.9, 298 and 1023 mg/L (measured), were reduced by - on average - ca. 16% over the course of 96-h incubation at pH ca 7and 23 degrees C. Although this small reduction may have been the result of biodegradation, photolysis, hydrolysis or any combination of these processes, these data (DT50 > 4 days) provide clear evidence that IPA is not prone to rapid hydrolysis in the aquatic environment.


Similarly, no studies are required or have been performed to investigate the phototransformation of isophthalic acid in water, however the results of the same algal study, in which IPA remained stable following continuous bright illumination for 96 hours, suggests that isophthalic acid is not prone to rapid photodegradation.


In summary isophthalic acid is generally resistant to physico-chemical degradation processes under the range of conditions likely to be encountered in the aquatic and terrestrial environment. Other data (see Point 5.2.1) show that isophthalic acid is readily biodegradable, with >60% mineralisation (oxidation to CO2) occurring within 5 to 7 days. Biodegradation may therefore be considered a more significant dissipation mechanism than physico-chemical processes tor IPA in the environment.