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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The US EPA Arnot-Gobas BCF model was used to calculate the bioconcentration (BCF) or log BCF values in order to assess the bioaccumulative potential of the registered substance.  The calculated log BCF values for the main C20-C22 components ranged from 0.412 to 1.038.  The minor C18 and C24 components gave calculated log BCF values of 1.74 and 0.068, respectively.  Based on these findings, the registered substance is not expected to be bioaccumulative since the BCF values is well below the bioaccumulation (B) criterion value of 2000L/kg or log BCF 3.30.  Also it did not meet the very bioaccumulative (vB) criterion of 5000 L/kg or log BCF 3.699.  This finding is consistent with the fact that the registered substance is readily biodegradable and is expected to undergo rapid metabolism in the aquatic and terrestrial environment and organisms, thus limiting bioaccumulation.

Key value for chemical safety assessment

Additional information

Aquatic bioaccumulation studies in fish have not been reported for the registered substance. However, the US EPA EPI-Suite BCFBAF v3.0 program (US EPA 2009) using the Arnot-Gobas method has been used to calculate the bioconcentration (BCF) or log BCF values in order to assess the bioaccumulative potential of the registered substance. Log Kow values ranging from 10.02 to 11.07 for the main components (C20-C22) of the registered substance were used in the estimation method. The calculated log BCF values for the main C20-C22 components ranged from 0.412 to 1.038. The minor C18 and C24 components gave calculated log BCF values of 1.74 and 0.068, respectively. Based on these findings, the registered substance is not expected to be bioaccumulative since the BCF values is well below the aquatic bioaccumulation threshold value of 2000L/kg or log BCF 3.3. 

The calculated log BCF values indicating not bioaccumulative are consistent with the fact that the registered substance is readily biodegradable and not persistent. Rapid and extensive biodegradation lead to more water soluble metabolites and ultimately to carbon dioxide and mineralization products, processes which are not likely to contribute to bioaccumulation. In addition, the log BCF calculations are consistent with the general finding that materials that have high log Kow (>10) are not considered to be bioaccumulative. As pointed out in the ECHA PBT Assessment guidance document, Chapter R11.1.3.2 (bioaccumulation assessment, pg 28), “the aquatic BCF of a substance is probably lower than 2000 L/kg if the calculated Log Kow is higher than 10” (ECHA 2008b). The very high log Kow (>10) may be a mitigating factor that limits uptake across membranes due to bioavailability/membrane permeation constants. The registered substance has a calculated log Kow >10 based on its main components and under the above ECHA guidance document would not be considered bioaccumulative (B) or very bioaccumulative (vB)

Collectively, these findings support the conclusion that the registered substance, the reaction products of 1-decene, 1-dodecene, and 1-octene, hydrogenated, is unlikely to be bioaccumulative. 

Limitations of BAF Arnot-Gobas model(Registrant’s comments): 

While the BAF Arnot-Gobas model v3.0 is also available in US EPA EPI-Suite BCFBAF program, based on our knowledge and experience, it is not applicable to the registered substance because the BAF model does not accurately predict the bioaccumulative potential of petroleum hydrocarbon compounds such as branched alkanes and aliphatics hydrocarbons that can be metabolized in the gut and thus overestimates bioaccumulation predictions involving dietary exposures. Petroleum substances are not included in the model domain because this model was calibrated on non-metabolizable compounds such as PCBs and other recalcitrant compounds. As a result, petroleum hydrocarbon susceptible to gut biotransformation are not reliably predicted by the BAF model and bioaccumulation is overestimated since the contribution from dietary exposure is exaggerated. Therefore, it is not valid to consider predictions obtained from the current BAF Arnot-Gobas model for assessing the bioaccumulation potential of the registered substancegiven its limited domain of applicability. In contrast, the Arnot-Gobas BCF model does reliably address tissue biotransformation rates for petroleum hydrocarbons and is acceptable for use in estimating the log BCF value for the registered substance as discussed above. The BCF model does not suffer the same limitations as the BAF model because it was trained on a much broader set of chemicals including petroleum hydrocarbons. Registrant comments: The US EPA EPI-Suite modeling program has been extensively used in the OECD SIDS and the US EPA High Production Volume (HPV) programs and more importantly, the US EPI-Suite program is an integrated predictive tool in the OECD Toolbox to calculate physico-chemical and environmental fate properties for chemicals. Hence, the need to supply QMRF and QPRF for commonly applied EPI-Suite models is not warranted given its already accepted use in global regulatory notifications and its integration and underpinning in the OECD Toolbox for REACH