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Environmental fate & pathways

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With reference to biodegradability, the existing studies provide conflicting results. The test substance ptBP was assessed for being readily biodegradable in a total of three different OECD 301 guideline-based studies. Additionally, ptBP was tested for inherent biodegradability using a Modified MITI test according to the OECD Guidelines for the Testing of Chemicals No. 302C (MITI, 1992). The substance has shown to be readily biodegradable in a DOC Die-Away test (OECD 301A, Huels, 1993) achieving a rate of 98% determined by DOC-removal within 28 days, but failed to pass the 10-day window criterion in the two other studies (OECD 301B CO2 Evolution, OECD 301F Manometric Respirometry), although showing a significant aerobic biodegradation of 60% within 28 days. However, the inoculum used in the DOC Die-Away test might have been adapted to ptBP, as it was taken from a predominantly municipal sewage treatment plant from a heavily industrialized area. On the other hand, the results from a Manometric Respirometry test and the Carbon Dioxide Evolution test show that ptBP is readily biodegradable, but failing the 10-day window criterion. This can be considered as a borderline case. The results also suggest that municipal sludge microorganisms need an adaptation period in order to be able to degrade ptBP rapidly. The modified MITI-test suggested that ptBP could not be considered as inherently biodegradable under the strict terms and conditions of the OECD Guidelines, but this result may be attributable to the inhibitory concentration of ptBP used resulting in a long lag phase under the test conditions. Overall, ptBP did not pass the 10 -days window for biodegradation in the key study, Manometric Respirometry test according to OECD 301F (Källqvist, 2003), but clearly the substance is readily biodegradable, but failing the 10-day window criterion.

Regarding the bioaccumulation potential, ptBP is unlikely to bioaccumulate in the food chain, considering the available data on biotransformation of ptBP and the rapid elimination of phenolic compounds from mammalian or aquatic organisms.