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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Data waiving:
other justification
Justification for data waiving:
the study does not need to be conducted because the substance has a low octanol water partition coefficient and the adsorption potential of this substance is related to this parameter

Description of key information

logKoc = 0.6994 L/kg, Koc = 5.00 L/kg (Predicted)

Key value for chemical safety assessment

Koc at 20 °C:
5

Additional information

At a pH of 7, more than 99% of the substance exists in the neutral form (pKa 4.58, Perrin (1981)). A log Koc was estimated using the KOCWIN v2 QSAR equation where log Koc = 0.55313 log Kow + 0.9251 + correction factors (where n = 447, r2 =0.9). This QSAR is preferred for use since an experimental value of log Kow was available for the substance (logKow = -0.33, Hansch, 1995). A log Kow of -0.39 was predicted for the substance by KOWWIN. This is in reasonable agreement of the experimental value that was quoted in the KOWWIN experimental database. The log Koc was estimated to be 0.6994 L/kg. The substance lies within the molecular weight and log Kow range of the KOCWIN v2 training set. Other aromatic amines are also included within the KOCWIN training set. Aromatic amines can sorb via cation exchange, an example is aniline - which itself has a comparable pKa (expt pKa 4.63, CRC Handbook; pKa 4.61, ACD) and a higher log Kow (expt 0.9, Hansch, 1995). At pH values ranging from 4.5 to 7.8, the measured log Koc of aniline varied between 1-1.54 showing that sorption of cationic form (up to 55%) and neutral form (45-100%) did not increase the log Koc to a threshold of concern (Li, 2001). For these reasons, the predicted log Koc value of 0.699 L/kg (i. e. Koc = 5.00 L/kg) is considered reasonable and valid for use.

In addition, a sensitivity analysis performed on Koc values ranging from 1 to 1000 showed that the sediment and soil risk characterization ratio (RCR) remained less than 0.1. Therefore, this range of values shows that the adsorption coefficient is not an important factor for environmental behavior of the substance. See Chapter 9 exposure assessment for supporting documentation.

 

References 

Hansch C, Leo A and Hoekman D. Exploring QSAR. Hydrophobic, Electronic, and Steric Constants. ACS Professional Reference Book.: American Chemical Society.

Li H, Lee LS, Fabrega JR (2001). Role of pH in partitioning and cation exchange of aromatic amines on water-saturated soils. Chemophere, 44(4): 627-635).

CRC Handbook of Chemistry and Physics 51st edition (1970-1971) RC Weast (ed)

 

[LogKoc: 0.6994]