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Environmental fate & pathways

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The atmospheric oxidation half-life of dimethyl terephthalate was estimated using the AOPWIN v1.91QSAR model available from the US EPA. The estimated atmospheric oxidation DT50 of dimethyl terephthalate ranged from 18.64 days (default settings) to 27.96 days, estimated by applying the recommended northern hemisphere settings that are considered relevant in a European context.

Since dimethyl terephthalate is readily biodegradable, a formal study of the hydrolysis behaviour of DMT at three pH values is not required and has not been performed. Nevertheless, some insight is provided indirectly from other sources. Hydrolysis of dimethyl terephthalate is exploited as one of the commercial production methods of terephthalic acid, but this process requires high temperatures (260 to 280 degrees C) and pressures (4500 to 5500 kPa) and on this basis DMT may be considered unlikely to hydrolyse rapidly under normal environmental conditions. Further insight is provided by a study of the toxicity of DMT to unicellular aquatic algae (BASF, 2010a). The concentration of dimethyl terephthalate, initially dosed to non-sterile aqueous algal growth test medium at 29.4 mg/L (measured), was reduced by 10% over the course of 72-h incubation at pH 8.1 and 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 > 3 days) provide clear evidence that DMT is not prone to rapid hydrolysis in the aquatic environment.

Similarly, no studies are required or have been performed to investigate the phototransformation of dimethyl terephthalate in water, however the results of the same algal study, in which DMT remained stable following continuous bright illumination for 72 hours, suggest that dimethyl terephthalate is not prone to rapid photodegradation.

In summary dimethyl terephthalate is generally resistant to physico-chemical degradation processes under the range of conditions likely to be encountered in the aquatc and terrestrial environment. Other data (see Point 5.2.1) show that dimethyl terephthalate is readily biodegradable, with >60% mineralisation (oxidation to CO2) occuring within 14 days. Biodegradation may therefore be considered a more significant dissipation mechanism than physico-chemical processes tor DMT in the environment.