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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption, other
Remarks:
estimation
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
Testing was conducted between 2009-04-29 and 2009-04-30
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Meets generally accepted scientific standards, well documented and acceptable for assessment
Justification for type of information:
QSAR prediction: migrated from IUCLID 5.6
Qualifier:
no guideline followed
Principles of method if other than guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC)) could not be followed due to interference of test material with the test method. In place of experimental data, an estimate of the Quantitative Structure Activity Relationships (QSARs), the details of which are provided in the technical guidance documents in support of Commission Directive 93/67/EEC on risk assessment for new substances.
GLP compliance:
yes (incl. QA statement)
Remarks:
Date of Inspection: 2009-08-19; Date of Signature 2009-03-04
Type of method:
HPLC estimation method
Media:
other: Not applicable
Radiolabelling:
no
Test temperature:
Not applicable
Details on study design: HPLC method:
Not applicable
Analytical monitoring:
no
Details on sampling:
Not applicable
Details on matrix:
Not applicable
Details on test conditions:
Not applicable
Computational methods:
PROCEDURE

A value for the partition coefficient of the test material was sourced from the International Chemical Safety Card for Cas No. 1477-55-0 by the United States National Institute for Occupational Safety and Health (NIOSH). This value was log10 Pow = 0.18

CALCULATION

The QSAR calculation for the chemical class of nonhydrophobics is shown below:

log10Koc = 0.52 x log10 Pow + 1.02

Where
Koc = adsorption coefficnet
Pow = Partition coefficient
Type:
log Koc
Value:
3.11 dimensionless
Details on results (HPLC method):
Not applicable
Adsorption and desorption constants:
The adsorption coefficient (Log10 Koc) of the test material was estimated to be 1.11. However, the guidance document cautioned that the adsorption coefficient of alkyl amines may be systematically underestimated by the method by up to 2 log units. Therefore, the maximum possible correction factor was added to the result to represent a worst case scenario for persistence in soils, thus giving a final estimated adsorption coefficient (Log10 Koc) value of 3.11.
Recovery of test material:
Not applicable
Concentration of test substance at end of adsorption equilibration period:
Not applicable
Concentration of test substance at end of desorption equilibration period:
Not applicable
Details on results (Batch equilibrium method):
Not applicable

The discrepancy between partition coefficient and adsorption coefficient for amines was as expected, as partitioning forces with the organic carbon content of soils was not anticipated to be the dominant force controlling the mobility of cationic substances in soils. Strong ionic interaction with clay particles and similar may also influence the fate of the molecule in soils and therefore the apparent adsorption coefficient may not correlate with the hydrophilic character evident from the partition coefficient value. From experimental experience of studying cationic, quaternary amine containing compounds in soil/water systems using the OECD Method 106, this extremely hydrophilic chemical class typically shows a very high affinity for soils. An example available from the literature is that of paraquat dichloride, which has a partition coefficient of log10Pow equals -4.5 and is soluble at approximately 620 g/L in water, but has a distribution coefficient (Kd) greater than 1 x 104 (Tomlin CDS (editor) The Pesticide Manual, 2000, British Crop Protection Council, Surrey). With soils typically containing less than 10% organic carbon, the resulting apparent value of log10Kocwould be greater than 5.

 

The correction factor applied to the QSAR result was also supported by a second, alternative estimation method. Using the specialised chemical estimation software, KOCWIN, version 2.00, © 2000 to 2008 US Environmental Protection Agency, the adsorption coefficient of the test material was estimated to be log10KOCequals 2.71. The software uses a molecular connectivity index (MCI) and a series of statistically derived fragment contribution factors to apply this technique to polar compounds.

Validity criteria fulfilled:
not applicable
Conclusions:
Using a QSAR calculation, the adsorption coefficient of the test material was estimated to be log10 Koc 3.11

Description of key information

Log Koc 3.11 (QSAR)

Key value for chemical safety assessment

Koc at 20 °C:
1 288

Additional information

The test material is predicted to maintain at least a single cationic charge over the entire environmentally relevant pH range of 5.5 to 7.5. Therefore, in place of experimental data, an estimate of the adsorption coefficient was obtained by calculation and a value of 3.11 was reported for Log Koc.

The discrepancy between partition coefficient and adsorption coefficient is as expected since partitioning forces with the organic carbon content of soils is not expected to be the dominant force controlling mobility of cationic substances. Strong ionic interaction with clay particles and similar may also influence the fate of the molecule in soils and the apparent adsorption coefficient may not correlate with the hydrophilic character evident from the partition coefficient value.