Tetramethylammonium hydrogen phthalate

Adsorption / desorption

Description of key information

The Koc of read-across candidates TMAH pentahydrate and TMAC  was determined in three different soils, in accordance with OECD guideline 106 and GLP (see read-across justification in IUCLID section 13)
The  Koc value of TMAH pentahydrate was 87, 585 and 1017 in three different soils  (mean Koc 563).
The  Koc value of TMAC was 92, 567 and 979 in three different soils  (mean Koc 546).
The mean Koc value of TMAH and TMAC was 555.

Key value for chemical safety assessment

Koc at 20 °C:

555

Additional information

When TMHP is dissolved, it will dissociate completely in a tetramethylammonium cation and a phtalate anion.

There are three relevant studies available:

Else et al. (1994) carried out an OECD 106 study with TMHP, but since the analytical measurements were most likely carried out for the phtalate anion only, the results are considered representative for the phtalate anion.

Brands (2013a,b) carried out OECD106 studies with TMAH pentahydrate and TMAC which can be regarded as representative for the tetramethylammonium cation. The mean Koc values (for 3 tested soil types) were 563 and 546forTMAH pentahydrate and TMAC, respectively. The fact that these values do not differ significantly indicates that the different anions (hydroxide and chloride) did not influence the adsorption.

The L(E)C50 values of TMHP are significantly lower than those of phtalic acid (which has L(E)C50 values to fish, daphnia and algae that are all > 100 mg/L, source: OECD SIAR, 2001). Therefore the tetramethylammonium cation is considered to be relevant for the environmental risk of TMHP and the mean Koc value of the studies of Brands (2013) with TMAH and TMAC of 555 is considered to be the key value for CSA.

Else et al. (1994) (TMHP):

The Koc of TMHP was 11, 62 and 154 in three different soils respectively. The average Koc value is 76.

The study was carried out in accordance with OECD guideline 106 (1981) and GLP. Insufficient validation details (such as the identity of the analyte, linearity, LOD and recovery) of the analytical method are included in the report. The reviewer determined that the measured concentration in the controls containing test solution with no soil (after 48 hours) are within 90-110 % of the nominal concentration of 8.22 mg/L which indicates that the test substance was stable during the test, did not adsorb at the test system and the recovery of the analytical method was sufficient.

The phtalate moiety contains an aromatic ring and therefore in principle shows significant UV absorption. The TMA does not contain any bonds which will show significant UV absorption. Furthermore, as the mobile phase of the HPLC method contains TBA (tetrabutylammonium), these substances will not influence the detector signal. The HPLC chromatogram of the standard solution shows one peak which therefore most probably results from the phtalate moiety. The tetramethylammonium cation is expected to have a higher adsorption due to the fact that clay compounds in the soil have a negative charge. Therefore, the test is considered to be only representative for the phtalate ion and a reliability 2 was assigned. Together with representative results for the tetramethylammonium ion, which can be obtained from studies with TMAH pentahydrate and TMAC (Brands, 2013a,b), it provides sufficient information with respect to adsorption.

Brands(2013a) (TMAH pentahydrate):

The adsorption behavior of TMAH pentahydrate was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64).

Adsorption kinetics were determined at an initial TMAH pentahydrate concentration of approximately 10 mg/L. A rapid increase of the adsorption of TMAH pentahydrate to the soils in the first 3 hours contact time was observed for all three soils. The adsorption plateau was reached after 24 hours for all three soils.

Adsorption isotherms were determined over a TMAH pentahydrate concentration range of 0.25 – 25 mg/L and a contact time of 24 hours. TMAH pentahydrate adsorption isotherms could be described by the Freundlich equation. KFoc was determined to be 87.3 (1/n=0.84) , 585 (1/n=0.64) and 1017 (1/n=0.77) mL/g for the soil Speyer 2.2, Speyer 2.3 and Speyer 6S, respectively. The mean Koc for the three soils was 563 mL/g.

The study is classified as reliable without restrictions according to OECD Guideline 106.

Brands (2013b)(TMAC):

The adsorption behavior of TMAC was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64).

Adsorption kinetics were determined at an initial TMAC concentration of approximately 10 mg/L. A rapid increase of the adsorption of TMAC to the soils in the first 3 hours contact time was observed for all three soils. The adsorption plateau was reached after 3 hours for all three soils.

Adsorption isotherms were determined over a TMAC concentration range of 0.25 - 25 mg/L and a contact time of 24 hours. TMAC adsorption isotherms could be described by the Freundlich equation. KFoc was determined to be 91.5 (1/n=0.82) , 567 (1/n=0.64) and 979 (1/n=0.78) mL/g for the soil Speyer 2.2, Speyer 2.3 and Speyer 6S, respectively. The mean Koc for the three soils was 546 mL/g.

The study is classified as reliable without restrictions according to OECD Guideline 106.