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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

not bioaccumulative, no testing required (log Dow of individual constituents between -2.37 and 2.33) 

Key value for chemical safety assessment

BCF (aquatic species):
19.1 L/kg ww

Additional information

No bioconcentration studies are available for DOPA-Glycinate, however, estimates of bioconcentration, based on the procedures described in the Guidance on information requirements and chemical safety assessment, are available for the aquatic environment. These estimates rely on physical chemical properties of the test substance, specifically the log Kow (3.81) based on the weighted mean of the overall log Kow. The BCF in freshwater fish was estimated to be 345.54 L/kg wwt, which would not qualify the substance as being bioaccumulative.

However, BCF estimations for DOPA-Glycinate based on the log Kow are not considered to be reliable due to the physicochemical properties of the substance.

In the case of the individual constituents of the test substance such experimental and computational determination of BCF utilising the partition coefficient is considered not to be feasible. DOPA-Glycinate is a complex mixture of long chain aliphatic alkyl aminoacetic acids (mono- and dicarboxylate) and azaalkanes with a total active matter content of 20% (w/w) in aqueous solution. In addition, some of the molecules may exist as hydrochlorides. Such substance characteristics do not fit with the experimental and computational determination of BCF, this is primarily related to the (i) surface active properties of the products, and (ii) the ionic nature of the approx. 20 constituents, comprised of difunctional amine structures with caboxylation grades ranging from 0 – 2.

The ‘Guidance on Information requirements and chemical safety assessment, chapter R.7a: Endpoint specific guidance, Nov 2012’ – Guidance on Regulatory compliant Kow determination for ionisable substances and salts, indicates that ‘substances which dissociate within environmentally relevant pH range (pKa 5 -9), values for Kow shall be derived from the neutral form, and preferably also for the dissociated form. In some cases a factor of 4 - 5 has been recorded between the log Kow of both species. The value for the dissociated molecule determined around a pH of 7 (sometimes referred to as Dow) is considered more realistic for PBT and chemical safety assessment’.

The ionic nature of the constituents of DOPA-Glycinate implies that the charge of each individual molecule will be strongly pH dependent. Therefore, for ionisable substances such as DOPA-Glycinate, a log Dow (distribution coefficient) instead of a log Kow, should be derived. The distribution coefficient is the ratio of the sum of the concentrations of all forms of the compound (ionized plus un-ionized) in each of the two phases. For measurements of distribution coefficient, the pH of the aqueous phase is buffered to a specific value such that the pH is not significantly perturbed by the introduction of the compound. The logarithm of the ratio of the sum of concentrations of the solute's various forms in one solvent, to the sum of the concentrations of its forms in the other solvent is called log D:

Log D (octanol/water) = log ( [solute, octanol] / ([solute, ionized, water] + [solute, neutral, water]))

Log Dow values were calculated which take into account all (including ionisable) dissociation species of a molecule. Overall, at neutral pH (pH 7) the Log Dow values for the individual constituents of DOPA-Glycinate ranged between -2.37 and 2.33. The BCF was calculated to be 19.1 L/kg wwt using the equation log BCF(fish) = 0.85 x log Dow - 0.7.

 

Conclusion

DOPA-Glycinate is highly water-soluble and has been demonstrated to be readily biodegradable. Due to the physicochemical properties of DOPA-Glycinate molecules the BCF estimations based on the log Kow are not considered to be reliable. According to the Guidance on information requirements and chemical safety assessment, chapter R.7a, log Dow values are considered more realistic for an assessment of bioaccumulation.Log Dow values for the individual constituents of DOPA-Glycinate ranged between -2.37 and 2.33. The predicted BCF in freshwater fish based on a log Dow of 2.33 was estimated to be 19.1 L/kg wwt indicating that the substance is not bioaccumulative.