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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption, other
Study period:
This study was conducted between 01 June 2017 and 21 October 2017
Data waiving:
study technically not feasible
Justification for data waiving:
other:
Justification for type of information:
No determination of the adsorption coefficient was possible by the HPLC estimation method, Method C19 Adsorption Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001. This was since the method was invalid for the test item. The method is not valid for organic bases.

The dissociation constants of the amine functional groups were predicted to be between 6.2 and 9.4, using structural information supplied by the Sponsor and specialized software ACD pKa, Advanced Chemistry Development, Inc., Toronto, Canada, Algorithm Version v12.1.0.50374. Therefore the test item would maintain at least a single cationic charge over the entire environmentally relevant pH range of 5.5 to 7.5, applicable for the method. Cationic species have been demonstrated to interact with the HPLC column stationary phase by mechanisms other than partitioning, thus invalidating the estimation of the adsorption coefficient of the test item by comparison to the capacity factors of reference substances of known adsorption coefficient values. In addition, the regulatory methods lack any cationic reference substances with which to generate a valid calibration plot.

For the test item, a fully unionized form will exist only at a pH of approximately 11.4 or greater and therefore it is not relevant to environmental assessment when addressing the adsorption coefficient. With respect to possible experimental analysis of the remaining ionized form found at an approximately neutral pH, experience supports the method guideline caution of validity for this chemical class. The HPLC column stationary phase required by the guidelines is that of cyanopropyl groups established on a silica backbone. Critically however, this silica backbone contains a number of free silanol groups (Si-OH) which present an anionic charge at a neutral mobile phase pH as required by the method. This presents a significant opportunity for retention of a cationic substance by secondary ionic interactions, as opposed to partitioning onto the cyanopropyl groups, as intended by the method.

This has been demonstrated internally by the analysis of cationic substances under neutral and acidic conditions. Under neutral conditions, the silanol groups are ionized and under acidic conditions, the silanol groups revert to a unionized form. Both the stationary phase as defined by the OECD guideline and the ionized state of the cationic molecule remains the same under both sets of conditions, yet a difference in the retention time of the analyte is observed based on whether the secondary ionic interactions from the silanol groups is activated on not. This indicates a very significant influence of these free silanol groups on the final estimated adsorption coefficient value. Although there is the option of performing the analysis at an acidic pH to eliminate the silanol interaction, this is not performed due to possible conflict on submission of the data, as it would be generated outside of the environmentally relevant pH range.

In addition, overall the actual concept of an organic carbon normalized adsorption coefficient for a cationic molecule is limited, as the organic carbon content of a soil or sludge may not be the critical factor for the mobility of the substance. This explains the absence of a correlation between partition coefficient and apparent adsorption coefficient for this chemical class.
No alternative estimation method was available for the determination of the adsorption coefficient of this test item. However, examples of cationic structures available from literature were that of diquat dibromide and paraquat dichloride. With reference to MacBean C (editor), The Pesticide Manual, 2012, British Crop Protection Council, Hampshire, UK, both substances are stated to adsorb rapidly and strongly to sediments and soils, and the potential to leach into groundwater is negligible.

Therefore, in conclusion, from available literature, the test item was predicted to have a very high affinity for soils.
Guideline:
EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))
Version / remarks:
EC NO. 440/2008 of 30 May 2008
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Version / remarks:
22 January 2001
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Information as provided by the Sponsor.
Identification: 1,3-Benzenedimethanamine, reaction products with glycidyl tolyl ether
Appearance/Physical state: clear, colorless, viscous liquid
Batch: WA 1508
Purity: 100% UVCB
Expiry date: 01 January 2021
Storage conditions: room temperature, in the dark
Conclusions:
No determination of the adsorption coefficient was possible by the HPLC estimation method, Method C19 Adsorption Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001. This was since the method was invalid for the test item. The method is not valid for organic bases
Executive summary:

No determination of the adsorption coefficient was possible by the HPLC estimation method, Method C.19 Adsorption Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001. This was since the method was invalid for the test item. The method is not considered valid for organic bases.In addition, the overall actual concept of an organic carbon normalized adsorption coefficient for a cationic molecule is limited, as the organic carbon content of a soil or sludge may not be the critical factor for the mobility of the substance. This explains the absence of a correlation between partition coefficient and apparent adsorption coefficient for this chemical class. 

 

No alternative estimation method was available for the determination of the adsorption coefficient of this test item. However, examples of cationic structures available from literature were that of diquat dibromide and paraquat dichloride. With reference to MacBean C (editor), The Pesticide Manual, 2012, British Crop Protection Council, Hampshire, UK, both substances are stated to adsorb rapidly and strongly to sediments and soils, and the potential to leach into groundwater is negligible. Therefore,in conclusion, from available literature, the test item was predicted to have a very high affinity for soils.

Description of key information

For REACH registration purposes a study to determine the adsorption coefficient by the

HPLC estimation method, Method C19 Adsorption Coefficient of Commission Regulation (EC)

No 440/2008 of 30 May 2008 and Method 121 of the OECD Guidelines for Testing of

Chemicals, 22 January 2001 was commissioned O’Connor B.J. (2018) (Envigo Study Number

VP81MK). However, it was concluded that the method was invalid for the test item as the

test material is an organic base.

For risk characterisation purposes a Log KoC value is required for PNEC derivation and for

risk assessment purposes it was considered appropriate to calculate a weighted average KoC

and Log KoC value based on the molecular structure of six components present at 0.5 to

44% within the UVCB substance.

The results indicate that the MCI method provides the most conservative estimate and

therefore weighted KoC and LogKoC values of 9954 and 0.351 respectively will be used for

risk characterisation.

Key value for chemical safety assessment

Koc at 20 °C:
9 954

Additional information

[LogKoc: 0.351]