Potassium hexadecyl hydrogen phosphate

Endpoint summary

Additional information

Hydrolysis

A study was conducted to determine the rate of hydrolysis of potassium hexadecyl hydrogen phosphate at different environmentally relevant pH-values by quantifying the test item concentration after different incubation periods and at different temperatures according to OECD TG 111 and Regulation (EC) No 440/2008 method C.7. In a preliminary test the test item was dissolved in aqueous solutions buffered at pH 4, 7 and 9 and incubated at 50 °C ± 4.5 °C for a maximum of 5 days. No significant reduction of the test item concentration was observed in the samples incubated at pH 7 and 9 after 5 days of incubation (mean recovery > 90 % of the applied concentration). In the incubated samples at pH 4 a significant reduction of the test item concentration was observed after 5 days of incubation in phosphate and citric acid buffer, respectively (mean recovery 63 – 75 % of the applied concentration).

A main test was performed with a commercially available citric acid buffer solution at pH 4. The test item was dissolved and incubated at 18 °C ± 1.3 °C, 50 °C ± 0.6 °C and 60 °C ± 1.8 °C in the dark. Two test item concentrations (approx. 3 mg/L and 30 mg/L) were used. The concentration of the test item was determined after different incubation times. A LC-MS/MS method was used for quantification of the test item. In course of the test and also in course of sample storage the test item precipitated by the formation of white solid components. In order to execute the test at a pH between 4 to 7, test solutions were prepared with a concentration of approx. 3 mg/L and 30 mg/L. As buffer systems citric acid and acetate solutions were used, both at pH-values of 5 and 6. The solutions were stored at 20 °C ± 1.3 °C in the dark over a period of 13 days. In each case a precipitate was observed. With regard to the observations it was not feasible to investigate the hydrolytic properties of potassium hexadecyl hydrogen phosphate at a pH range of 4 - 6. Neither degradation rate nor corresponding half-life values were calculated as the test item was found to be stable at pH 7 and 9. At pH values of 4, 5 and 6 the test item (partly) precipitated in course of incubation, thus, hydrolysis endpoints could not be determined.

 

Biodegradation in water

Biodegradation of potassium hexadecyl hydrogen phosphate in water was examined in two studies in a weight of evidance approach. The first study which was performed according to OECD guideline 310 showed that the test substance is not readily biodegradable (37 % after 28 days) and the second study that was performed according to OECD guideline 302C showed that the test item is inherently biodegradable (86 % after 28 days).

 

The ready biodegradability was determined with a non-adapted activated sludge for potassium hexadecyl hydrogen phosphate over a test period of 28 days in the Headspace Test. The study was conducted according to OECD 310. Potassium hexadecyl hydrogen phosphate was tested with a concentration of 35 mg/L in triplicates, corresponding to carbon content (TOC) of 18.4 mg C/L in the test vessels. The biodegradation of the test item was followed by TIC analyses of the quantity of CO2 produced by the respiration of bacteria. The amount of TIC produced was calculated by correcting the results of the test and reference item for endogenous TIC production of the control groups.

The 10 % level (beginning of biodegradation) was reached after 12 days. The pass level of 60 % was not reached during the test period. The biodegradation of the test item came to a maximum of 37 % after 28 days. The 95 % confidence interval on day 28 was 32 - 42 %.

The percentage degradation of the functional control (activity of the test system sodium benzoate) reached the pass level of 60 % after 3 days and came to 87 % after 28 days. The 95 % confidence interval on day 28 was 83 - 91 %. The validity criteria according to the guideline were fulfilled.

The test item is considered to be primarily inherently biodegradable under the test conditions.

 

The inherent biodegradability of potassium hexadecyl hydrogen phosphate was determined by the manometric respirometry test according to the OECD guideline 302C. A measured volume of inoculated mineral medium, containing 30 mg/L test substance as the nominal sole source of organic carbon, was stirred in a closed flask at a constant temperature (± 1 °C) for up to 28 days. The consumption of oxygen was determined by measuring the quantity of oxygen required to maintain constant the gas volume in the respirometer flask. The amount of oxygen taken up by the microbial population during biodegradation of the test chemical (corrected for uptake by blank inoculum, run in parallel) was expressed as a percentage of ThOD. Potassium hexadecyl hydrogen phosphate undergoes an average of 86 % biodegradation after 28 days under the test conditions. Biodegradation proceeds steadily from the first day to the last, suggesting that solubilisation or hydrolysis is the limiting rate factor. Thus, potassium hexadecyl hydrogen phosphate was regarded as ultimately inherently biodegradable according to this test.

 

In conclusion, based on the weigh of evidance approach the test item is classified as inherently biodegradable.

 

Biodegradation in water and sediment

In accordance with column 2 of REACH annex IX, further degradation testing does not need to be conducted as potassium hexadecyl hydrogen phosphate was shown to be inherently biodegradable in a screening test. Thus, further simulation tests will not improve the chemical safety assessment. Safe use was shown for the developed exposure scenarios (CSR section 9 and 10).

 

Biodegradation in soil

In accordance with column 2 of REACH annex IX, further degradation testing does not need to be conducted as potassium hexadecyl hydrogen phosphate was shown to be inherently biodegradable in a screening test. Thus, further simulation tests will not improve the chemical safety assessment. Safe use was shown for the developed exposure scenarios (CSR section 9 and 10).

 

Bioaccumulation

In accordance with column 2 of REACH Annex IX, the bioaccumulation in aquatic species study does not need to be conducted as the substance has a low potential for bioaccumulation (the substance has a log octanol/water partition coefficient less than 3).

 

Adsorption /desorption

In an Adsorption/Desorption Test using a Batch Equilibrium Method according to OECD TG 106 the K_Foc of the substance at 20 °C was determined to be 112076 L/kg (arithmetic mean, n = 3; SD: 163631), corresponding to a log(K_Foc) ranging between 4.11 and 5.48, which indicates a strong to very strong adsorption to soil matrices.