Reaction products of dimethyl phosphonate with 2-alkyl-2-alkylpropanediol and alkanediol

Endpoint summary

Description of key information

Abiotic degradation; Hydrolysis

The purpose of the key study was to investigate the hydrolysis of the test substance at 10 °C, 20 °C, and 30 °C in pH 4, 7, and 9 in sterile aqueous buffer solutions using the OECD Guideline for the Testing of Chemicals. Hydrolysis as a Function of pH, OECD Guideline No. 111 (April 13, 2004).

 

A preliminary test of test item stability in water was conducted during examination of water solubility and showed an increase of hydrogen ion concentration over time, which indicated possible hydrolysis. Additional testing was performed in sterile aqueous buffers prepared at pH 4, 7, and 9 at three temperatures (10, 20, and 30 °C).

Test solutions were prepared in pH 4, 7, and 9 buffers at approximately 0.5 mg/mL by weighing 0.5 g into each of 3, 1-L autoclaved volumetric flasks and bringing to volume with the respective buffers.Each dosing solution was distributed into an appropriate number of autoclaved 2-dram vials, which were filled leaving no headspace and sealed with PTFE lined caps. Subsets of vials for each pH were placed in temperature-controlled chambers set to maintain 10, 20, and 30 °C. The pH of each remaining dosing solution was measured. Vials containing buffers with no test material were prepared in the same way as the samples to check for background contamination.

Sampling for pH 4 at all temperatures was performed after approximately 1, 2, 3, 4, 5, 6, 23, 29, 48, and 53 hours by removing two vials at random and measuring pH and temperature immediately. This process above was repeated for pH 7 and 9 after approximately 2, 4, 5, 23, 29, 48, and 53 hours.

 

Following completion of the test period, the vials containing each buffer which had been stored at 30°C were removed for sterility check. An aliquot (1 mL) of each buffer was applied to individual 3M petrifilm plates while contained in a biological safety cabinet. The plates were placed in an incubator set at 35 °C for approximately 48 hours before being removed and visually observed for the presence of colonies.

 

It was noted that the correlation between hydrogen ion concentration and time was stronger at 30 °C for each pH level tested, and the strongest correlation was found in pH 7. This information supports the preliminary observations indicating the material may undergo hydrolysis in water.

Biodegradation

The ready biodegradability of the test item was determined in a key study by the Carbon Dioxide Evolution Test Method (OECD Guideline 301B and EU Method C.4C).

 

Tests of ready biodegradability are stringent tests that provide limited opportunity for acclimation and biodegradation to occur. In the CO2 test, inoculated mineral medium was dosed with a known amount of test substance as the nominal sole source of organic carbon and aerated with CO2-free air. The CO2 produced from the mineralization of organic carbon within the test chambers was displaced by the flow of CO2-free air and trapped as K2CO3 in KOH trapping solution. The amount of CO2 produced by the test substance (corrected for that evolved by the blank inoculum) is expressed as a percentage of the theoretical amount of CO2 (TCO2) that could have been produced if complete biodegradation of the test substance occurred.

The test contained a blank control group, a reference group and a treatment group, each with three replicates and a single toxicity control. The blank control was used to measure the background CO2 production of the inoculum and was not dosed with a carbon source. The reference chambers were dosed with sodium benzoate, a substance known to be biodegradable, at a nominal concentration of 10 mg C/L. The treatment group test chambers were used to evaluate the test material at a nominal concentration of 10 mg C/L. The toxicity control was used to evaluate the toxicity of the test substance to the inoculum and was dosed with both the reference (10 mg C/L) and test substances (10 mg C/L).

 

Results indicate that the activated sludge inoculum was active, degrading the reference substance an average of 96.1 % by the end of the test and that the test substance was not inhibitory to the inoculum at the concentration tested, as the toxicity control exceeded 25% degradation by Day 14 of the study. The average cumulative percent biodegradation for the test item was 27.4% by the end of the test.

Adsorption coefficient

The key study was performed to estimate the adsorption coefficient (Koc) of the test item in soil and sludge using a High Performance Liquid Chromatography (HPLC) based methodology. In this method, theretention times of test chemicals are correlated with those for reference standards with known adsorption coefficients. The guidelines applied were OECD Guideline for Testing of Chemicals, 121 Estimation of the Adsorption Coefficient (Koc) on Soil and Sewage Sludgeusing High Performance Liquid Chromatography (HPLC) Method (2001) and Estimation of the Adsorption Coefficient (Koc) on Soil and Sewage Sludge using High Performance Liquid Chromatography (HPLC) Method. Official Journal of the European Communities No. L225, Method C.19 (2001).

Five calibration standards of known log Koc were prepared from reference materials in the respective mobile phase at a nominal concentration range (10.0 to 200 mg/L) selected to provide desired ultraviolet (UV) detector response. Capacity factors were calculated for the five calibration standards using a sixth calibration standard, urea, to estimate the column dead time (i.e. the retention time of an unretained organic compound). The logarithms of the capacity factors were then plotted against published log Koc values for the five calibration standards with known log Koc to establish a linear regression equation.

 

Test substance solutions were prepared at nominal concentrations of 1.00 mg/mL and 5.00 mg/mL in 55% methanol (MeOH): 45% HPLC-grade reagent water (H2O). The calibration standard preparations were sequentially injected into the HPLC system followed by a single injection of the matrix blank preparation, single injections of each of the three 1.00 mg/mL test substance preparations, and a single injection of the 5.00 mg/mL test substance preparation. The calibration standards injection sequence was repeated following the test substance injections. The HPLC system was operated under standardised isocratic, reverse-phase operating conditions per the guideline.

 

The test substance eluted as three peaks and the corresponding Log Koc for the test substance by UV ranged from unretained (< urea) to 4.43.