Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

DIUP has been shown to biodegrade to a high extent in tests of ready and inherent biodegradability using standard OECD test guidelines. DIUP biodegraded 70.9% in 28 days and was readily biodegradable within the 10-day window. Based on the high extent of biodegradability measured using various standard test procedures, DIUP and its degradation products are expected to biodegrade to a high extent under simulated conditions (i.e., wastewater treatment) and in sediment and soil. Additional data for a mono ester indicate that the metabolites of DIUP would also be biodegraded. A mono-n-octyl/n-decyl-phthalate (MC8/10PE) was shown to biodegrade to approximately 90% after 28 days and the results met the ready biodegradable criteria. The mono ester of DIUP would be mono-undecyl-phthalate and is expected to exhibit an equally high extent and rapid rate of biodegradation as was demonstrated by MC8/10PE.

Studies are not available to assess the biodegradability of DIUP 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 hours in marine sediments based on results from two studies (Ottonet al., 2008). Research suggests that the formation of the monoester occurs as the first step in the biotic degradation of DIDP (Stapleset al., 1997b). Because this step does not appear to be rate limiting, as evidenced by the high extent of biodegradation demonstrated by DIDP in a ready test, the degradation of the diester in sediment is expected to occur at a similar rate. Because Di-isodecyl phthalate ester (DIDP) is an analog to DIUP, the mono ester of DIUP is expected to biodegrade in sediment at approximately the same rate as was exhibited by the mono ester of DIDP.

Studies are not available to assess the biodegradability of DIUP specifically in soil. However, data for an analog substance di-isononyl phthalate (DINP) can be used to estimate the loss rate of DIUP in soil. DINP exhibited a half-life in soil of approximately 51 days, based on the loss of parent substance (ExxonMobil, 2009). These data were developed in an earthworm toxicity test conducted in soil in which the concentration of DINP was monitored over a 56-day period. During that period DINP concentration decreased from 982 to 441 mg/kg soil (wet weight). Because DIUP and DINP exhibited similar extents of biodegradation in ready biodegradability tests, they would be expected to biodegrade in soil at similar rates and to similar extents.