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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Two tests using the batch equilibrium methodology, one according to OECD guideline 106 and one not according to the guidelines but of of good quality were performed on 54 different soil samples. The results show that TFA is poorly absorbed to the soil and is considered as a mobile organic compound in the majority of soils investigated. The Kd ranged between 0.19 to 20 L/kg for organic and mineral soils (the organic horizon exhibiting greater retention) giving a geometric mean of 0.94 L/kg (SD=4.86, n= 20) at 25°C. Based on these results no further information on adsorption/desortion is required according to column 2 of REACH Annex IX.

Key value for chemical safety assessment

Koc at 20 °C:
6.22

Other adsorption coefficients

Type:
log Kp (soil-water)
Value in L/kg:
0.94
at the temperature of:
25 °C

Additional information

An adsorption screening test carried out according to OECD guideline 106 with three soil types (humous acid sandy soil, sandy loam with a low organic matter content, slightly alkaline loamy soil). The soil/water-system consisted of about 2 g soil and about 10 mL 0.01 M Ca(CH3COO)2 solution spiked with NaTFA (sodium trifluoroacetate) on a level of about 5 mg/L. Six blanks (without NaTFA), three controls (without soil) and six test soil (two replicates per soil) were performed during the test. The conclusion drawn from these results is that the TFA-anion poorly adsorbs to the different soil components because after 16 hours of agitating in a soil/water system less than 3% of the initial amount of TFA had disappeared from the water phase. Due to the fact that less than 25% is adsorbed, no further testing is required by the OECD guidelines.

Another batch equilibrium study not performed according to standard guideline but scientifically acceptable and well documented is reported. TFA was retained by 34 of 54 soils collected from diverse locations and a subset of 12 soils were chosen as representative of the TFA retention characteristics found in this study. Organic soils that exhibited higher retention of TFA sorbed between 20 and 60% of added TFA. In contrast, mineral soils retained 0 -15% of added TFA. Classifying mobility of TFA on the basis of Kd values suggests that TFA would be considered immobile (Kd> 10) in only 3 of 54 soils studied characterized by elevated organic matter content (> 70%). Eight soils exhibited low TFA mobility (Kd=2 -10), 15 soils intermediate mobillity (Kd=0.5 -2) and TFA should be considered as mobile in eight of soils (Kd=0.1 -0.5). No significant TFA retention was found in 20 of the soils studied. The retention of TFA increased with decreasing pH and decreased with increasing concentrations of F-, Cl-, and SO42 -. It is expected that rates of TFA leaching from soils will depend on soil types, organic content, soil pH, inputs of competing anions and atmospheric deposition rates of TFA. TFA was considered as a mobile organic compound in soils at the majority of sites investigated and measured Kd value ranged between 0.17 to 20 L/kg for all soil locations. An average Kd of 0.94 L/kg at 25°C (SD= 4.86, n= 20) based on the geometric mean of reported values for representitive soils retaining TFA was calculated.

A Koc is needed for the exposure assessment of the sediment.

By default, EUSES and CHESAR use QSAR calculation according to equation from Sabljic and Güsten (1995), as reported in the EU TGD (2003), using the class of non hydrophobic chemicals. In the case of trifluoacetic acid, the class "organic acid" is more relevant. Therefore the Koc is calculated as follows: logKoc = 0.6 * logKow + 0.32, with LogKow = 0.79

[LogKoc: 0.794]