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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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The partition coefficient of the substance was measured to be >6.2 by means of the HPLC method. The limit value is due to the limitation of the method. It was therefore considered appropriate to undertake an estimation of the partition coefficient by means of QSAR estimation based upon the SMILES code of the molecule using US EPA KOWWIN v1.67 of the EPI Suite v4. Based upon structural fragmentation drawn from a database of >40,000 substances, including aryl phosphate esters and aromatic species predicted for the fragmentation estimates, the log Pow is estimated to be 11.79.

Based on these data, the substance may be considered to be of concern as potential for bioaccumulation, according to screening criteria for bioaccumulation in ECHA guidance (Chapter R.11 PBT Assessment). The likely reliability of the log Pow is, however, considered to diminish above a value of 6, as noted in Appendix R.11-1 Annex 1 of ECHA guidance on PBT Assessment. Substances with log Pow between 4.5 and 6 are considered likely to be highly accumulating; however no substantial bioconcentration is assumed for compounds having log Pow with values less than 4.5 or greater than 6. For compounds having log Pow greater than 6, a gradual decrease of the BCF is observed and it has been hypothesised within the published literature that a high log Pow is more an effect of solubility than a tendency of the substance to be lipophilic. 

Considering that the measured log Pow is a limit value at 6.2 and has been estimated based on structure to be 11.79, it is considered that the results indicate that the substance is likely to be non-bioaccumulating based on the partition coefficient.

A fish bioaccumulation study has been conducted using common carp and according to the OECD 305 test guideline which concludes that the BCF is <0.02 based on whole body weight after 56 days. The study was, however, conducted primarily for notification in Japan and, due to the low water solubility, the test formulations were prepared using a dispersing agent of 3%v/v Tween 80-dimethylformamide. The use of a dispersing agent is considered to affect the uptake of the test item to the fish reducing the reliability of the result.

In support of these data, two separatein silicoQSAR estimations have been undertaken using the EPIWIN and CAESAR database systems. The EPIWIN QSAR estimates that the BCF for the substance is 8.99 L/Kg while the CAESAR QSAR estimates the BCF for the substance to be 6 L/Kg. These data support the consideration that the use of the dispersing agent affects the uptake of the substance to the test organism but suggest that the BCF for the substance is below the threshold of concern.

Summary:

Based on a weight of evidence approach of study data with reduced reliability and two separate QSAR estimation techniques, PX-200 is considered to be not bioaccumulative with a BCF <100. It is, therefore, considered to not meet the DSD criteria of ≥ 100 nor the CLP criteria of ≥ 500.