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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The organic carbon normalised adsorption coefficient (Koc) was estimated by calculation using KOCWIN Program (v2.00) found in EPI Suite and was found to be 940.8 L/kg (log Koc = 2.97). The Koc was also estimated using the Gerstl correlation, as reported in ECHA REACH Guidance Document R.7a, and found to be 158 L/kg at 25 °C. The geometric mean of 941 and 158 L/kg is 386 L/kg (log Koc = 2.59) at 25 °C and this value used for the chemical safety assessment.
No data on desorption are available.

Key value for chemical safety assessment

Koc at 20 °C:
386

Additional information

ECHA Guidance Document R.7a indicates that "Estimation methods for Koc are not appropriate for surface active or ionisable (at environmentally relevant pH) substances." Therefore, a screening level estimation of Koc for the test substance is appropriate if it can be shown that the substance will not ionise at environmental pH. For ionisable substances, the adsorption coefficient will be highly dependent on the acid dissociation constants of the hydrolysable protons. For the test substance, the SPARC Performs Automated Reasoning in Chemistry (SPARC) Program estimates pKa1 and pKa2 values of 10.5 and 10.7, respectively for the two phenolic hydrogen atoms. Using the Henderson-Hasselbalch equation, it can be shown that > 99 % of the test substance will exist in the non-ionised form at environmental pH of 7:

pH = pKa + log ([A-]/[HA])

7 = 10.5 + log ([A-]/[HA])

-3.5 = log ([A-]/[HA])

[A-]/[HA] = 0.00032

[A-] = 0.00032[HA]

0.00032[HA] + [HA] = 1

[HA] > 0.99

Based on this result (>99 % non-ionised at environmental pH), the use of calculations to estimate the Koc is scientifically acceptable. KOCWIN, found in EPI Suite, estimates a Koc of 940.8 L/kg (log Koc = 2.97) for DMBPC at 25 °C. ECHA REACH Guidance Document R.7a (ECHA, 2008) indicates that the Gerstl correlation (Gerstl, 1990) is an acceptable method of estimation for non-ionised substances. The Gerstl correlation estimates a Koc of 158 L/kg for DMBPC.

ECHA REACH Guidance Document R.7a (ECHA, 2008) specifies that the geometric mean of multiple estimations should be taken as the key value for the chemical safety assessment. The geometric mean of 941 and 158 L/kg is 386 L/kg (log Koc = 2.59) at 25 °C. This value cannot be extrapolated to 20 °C; therefore, it will be used for the chemical safety assessment.

In accordance with section 9.3.3 of Column 2 of Annex IX, the further information on adsorption/desorption study does not need to be conducted if based on the physicochemical properties the substance can be expected to have a low potential for adsorption (e.g., the substance has a low octanol water partition coefficient). DMBPC has a log Kow of 3.1, indicating a low potential for adsorption. It is therefore considered to be justified to omit this study.

Furthermore, this substance is not manufactured or imported as such on the EEA market, but is only available as a reacted monomer in an imported polymer with residual levels below 0.1 %. Consequently the exposure and emissions to the environment are considered to be negligible. Therefore, this testing is not required.

References

European Chemicals Agency (ECHA). 2008. Guidance on information requirements and chemical safety assessment, Chapter R.7a: Endpoint specific guidance. May 2008.

Gerstl Z. 1990. Estimation of organic chemical sorption by soils. J. Contaminant Hydrology, 6, 357-75, as cited in: European Chemicals Agency (ECHA). 2008. Guidance on information requirements and chemical safety assessment, Chapter R.7a: Endpoint specific guidance. May 2008.

SPARC Performs Automated Reasoning in Chemistry (SPARC). October 2011 release w4.6.1691-s4.6.1687. Available at: http://archemcalc.com/sparc/test/login.cfm?CFID=148855&CFTOKEN=98109949. Accessed on: 09.02.2012.

[LogKoc: 2.59]