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Adsorption / desorption

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Description of key information

The estimated Log Koc of TBBPA is 5.62 (equivalent to a Koc of 416 869 mL/g), estimated value using EPIwin and based on chemical structure.

Key value for chemical safety assessment

Koc at 20 °C:
416 869

Additional information

The log Koc value was estimated using software recommended in the REACH Guidance and based on the chemical structure. The

PCKOC v1.66 program within the Estimations Programs Interface for Windows, EPIwin v3.20 was used.

The estimated Log Koc of TBBPA is 5.62 (equivalent to a Koc of 416 869 mL/g). Based on this, TBBPA is expected to be highly bound to particulate matter.

Evidence for this in terms of sorption to soil and sediment was observed in laboratory studies investigating toxicity to soil and sediment organisms and in biodegradation studies. 

Furthermore, TBBPA sorption to soil has also been reported in the literature. The mobility and sorption of TBBPA was studied in a Glyndon silt loam soil and standard laboratory sand as comparison (Larsen et al. 2001). TBBPA sorption was investigated using a batch equilibration technique. TBBPA was applied to the soil at the upper concentrations found in contaminated Swedish sediment (500 ppb).

A dried Glyndon silt loam was evenly packed in a glass column (8.4 x 15.2 cm; 842 mL) with a stainless steel end cap. Sandwiched between the soil and the end cap were a 40 mesh stainless steel screen and six layers of cheesecloth. The soil was wetted with 0.01 M CaCl₂ solution from the bottom over a 24 h period. A steady-state flow velocity was then established with 0.01 M CaCl₂ from the top of the column and a pulse of [14C] TBBPA was applied to the soil surface and eluted with 0.01 M CaCl₂. The effluent flowing out of the column was fraction collected and analysed for 14C. The soil column was extruded from the column and cut into one cm sections. The sections were dried and assayed for 14C by combustion analysis. Selected sections were individually extracted sequentially with toluene, ethyl acetate and methanol. TLC analysis on these fractions was conducted.

As a comparison, standard, washed laboratory sand was packed in the same size column as the soil. The sand was saturated with a solution of 0.01 M CaCl₂ from the bottom over a 24 h period and a steady-state flow velocity established with 0.01 M CaCl₂ from the top of the column. A pulse of [14C] TBBPA was applied to the sand surface and eluted with 0.01 M CaCl₂. The effluent flowing out of the column was fraction collected and analysed for 14C. The sand column was then eluted with methanol and extruded in four sections and analysed for 14C by LSC.

Additionally, TBBPA sorption was done using a batch equilibration technique. The soil used was the Galesburg loam. 14C-spiked TBBPA was added so that the solution concentrations were 2.5, 0.25, and 0.025 g/mL in 0.01 M CaCl₂ in separate vials. The slurries were agitated by rotation of the vial. At 48, 96 and 168 h, the bottles were centrifuged, samples removed and radioactivity analysed by LSC.

No radioactivity from was eluted from the soil column. Combustion analysis of the soil sections showed 16.2% of the 14C from TBBPA remained in the first centimetre of soil with six to seven percent in each of the next four sections. Generally, radioactivity in the remaining sections of the column appeared to taper off from four to two percent. In the ASE extraction, only the toluene extract of each section contained 14C, which was shown to be TBBPA by chromatography in both TLC systems. Although it appeared that TBBPA was strongly sorbed to the soil because there was no radioactivity in the column effluent, there was significant redistribution of the TBBPA to a depth of 15 cm.

A small amount of 14C (4.5%) was found in the effluent of the sand column in the fractions from between 0.86 to 1.4 pore volumes (260 to 430 mL). Nearly 73% of the TBBPA, as determined by two TLC systems, was recovered when the column was eluted with methanol. Virtually no 14C was detected in sand from any of the four methanol rinsed sections.

Batch studies at 48 h showed that 97.9, 92.6, and 93.6% of the 0.025, 0.25, 2.5 μg/mL [14C] TBBPA, respectively, were bound to the soil. Sorption of [14C] TBBPA to the soil at the later time points were the same.

These results show that TBBPA is sorbed extensively by loam soil and sand. Therefore, TBBPA, in the environment would be expected to sorb largely to sediment and organic matter in the soil.

[LogKoc: 5.62]