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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Based on the experimentally determined Koc values of 282,624 and 2,658,608 (log Koc: 5.5 to 6.4) for read-across substance, C16-18 TMAC is also expected to adsorb onto soil and be classified as immobile. 

Key value for chemical safety assessment

Koc at 20 °C:
2 658 608

Additional information

A guideline study was conducted on the read-across substance C12-C16 ADBAC to determine the soil adsorption / desorption properties of the test substance using the batch equilibrium method. The test substance adsorbs onto soil (soil 1: Kadsoc = 18,251; soil 2: Kadsoc = 16,679; soil 3: Kadsoc = 812,943) and does not desorb easily for the three soil types used, therefore it can be classified as immobile. The high concentrations of the test substance used in the study (0.5 g test substance for 1 g soil) leads to a less accurate extrapolation to lower concentrations. Adsorption is likely to be higher at lower concentrations than suggested by the outcome of this study (Geffke T, 1999).

In another guideline study, the adsorption / desorption coefficients and constants of C12-C16 ADBAC were determined by equilibrating with four soil types (i.e., sand, sandy loam, clay loam, silt loam). Based on the very high percent of14C-test substance adsorption onto the test soil, i.e., 95.2 to 97.3% in a preliminary study conducted with a 1 to 20 soil to water ratio, the definitive study was carried out at 1: 200 soil:water ratio. Nominal test concentrations of 0, 0.1, 0.5, 1 and 2 µg/mL (i.e., equivalent to a measured concentration of 0.689, 0.441, 0.887 and 1.85µg/mL) were prepared by pipetting appropriate aliquots of isotopically diluted purified primary stock solution of14C-test substance directly into bottles containing 0.01 M CaCl2solution and soil samples. Liquid scintillation counting analysis was employed to measure the test substance concentrations in the aqueous phase. The amount of the test substance remaining adsorbed on the soil was determined by combustion/radio analysis. Although the percentages of14C-test substance adsorbed onto the four test soils was well above the 20 to 80% range recommended to ensure Freundlich isotherms, excellent correlations were obtained ranging from 0.9682 to 0.9983. In addition, the14C-mass balance for the four soils types ranged from 95.3 to 103.2%. The Freundlich constants determined for the 4 soil types were:

The #32 sand at 0.1% organic carbon had an adsorption Kd and Koc of 6,172 and 6,171,657 respectively and a desorption Kd and Koc of 7,137 and 7,137,310 respectively.

The #45 silt loam at 0.5% organic carbon had an adsorption Kd and Koc of 10,797 and 2,159,346 respectively and a desorption Kd and Koc of 14,083 and 2,816,590 respectively.

The #59 sandy loam at 0.8% organic carbon had an adsorption Kd and Koc of 5,123 and 640,389 respectively and a desorption Kd and Koc of 96,540 and 12,067,457 respectively.

The #58 clay loam at 2% organic carbon had an adsorption Kd and Koc of 32,429 and 1,663,039 respectively and a desorption Kd and Koc of 165,556 and 8,490,062 respectively.

No apparent degradation of the test substance occurred in any of the four soils.

Under the conditions of the study, the test substance was considered to have little or no potential for mobility in the soil and therefore should not pose an environmental risk for contamination of ground water (Daly D and Cranor W, 1988).