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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Discussion (sediment testing)
Studies are not available to assess the biodegradability of DTDP in sediment. Although there are no data specifically for the diester, there are biodegradation data for the monoester of DIDP (mono-isodecyl phthalate, MIDP) that showed an average half-life of 25 ± 6 hours in marine sediments based on results from two replicates (Otton et al., 2008). The investigators also evaluated the biodegradability of other mono phthalate esters (MPEs) in marine sediment and some MPEs in freshwater sediments and found that, in general, all the MPEs exhibited relatively similar half-lives in marine and freshwater sediment, ranging from 16 to 39 hours. Based on biodegradation data for other MPEs in freshwater sediments, MIDP would also be expected to exhibit a half-life in freshwater sediment equivalent to its half-life in marine sediment.
Because Di-isodecyl phthalate ester (DIDP) is an analog to DTDP, the mono ester of DTDP is expected to biodegrade in sediment at approximately the same rate as was exhibited by the mono ester of DIDP. Research suggests that the formation of the monoester occurs as the first step in the biotic degradation of di phthalate esters such as DIDP and DTDP (Staples et al., 1997). Because this step does not appear to be rate limiting, as evidenced by moderate to rapid biodegradation in ready tests, the degradation of the diester in sediment is expected to occur at a similar high rate to the monoester.

Key value for chemical safety assessment

Additional information

Studies are not available to assess the biodegradability of DTDP under simulated conditions (i.e., wastewater treatment). However, there are data for di-n-decyl phthalate (CAS No. 84-77-5; DnDP), an analog to DTDP, using treated wastewater that suggest DTDP would demonstrate a high extent of biodegradation under sewage treatment plant (STP) conditions (Furtmann, 1993). DnDP biodegraded 82% after 7 days based on the disappearance of the parent compound from the test system. The initial DnDP concentration was 7.8 μg/l and the DT50 was <1 day.

The elimination of DTDP in a STP through biodegradation and distribution was estimated using the SIMPLETREAT model. The model calculated that 92% of DTDP would be eliminated in a STP, which is consistent with the high loss reported by Furtmann (1993). The measured data for DnDP and the modeled data suggest that DTDP will be largely eliminated in a STP.