Reaction mass of disodium 2-[[2-hydroxy-3-[[methyl-(2-oxido-2-oxoethyl)amino]methyl]-5-nonylphenyl]methyl-methylamino and sodium 2-[(2-hydroxy-5-nonylphenyl)methyl-methylamino]acetate

Endpoint summary

Description of key information

Hydrolysis

The hydrolytic stability of the test item, Reaction mass of disodium N,N'-[(2-hydroxy-5-nonylphen-1,3-ylene)bis(methylene)]bis[N-methylaminoacetate] and sodium N-[(2-hydroxy-5-nonylphenyl)methyl]-N-methylaminoacetate, was assessed at a GLP accredited laboratory according to the OECD Guideline 111, “Hydrolysis as a function of pH” (Fox, 2019).

 

Test systems consisted of buffer solutions at pH 4, 7 and 9 treated with test item at nominal concentrations of 50 mg/L. Test solutions were incubated in the dark at 50.0 ± 0.5°C for a period of 120 hours. Duplicate samples were taken for test item concentration analysis (via HPLC-UV) from test solutions at 0, 24 and 120 hour periods.

 

The estimated half-life and rate constant (in parentheses) of the test item at 50°C were 399 hours (1.74E-3 h-1) and 117 hours (5.93E-3 h-1) at pH 7 and 9, respectively. The test item was hydrolytically stable at pH 4, showing <10% hydrolysis after 5 days at 50°C (equivalent to a half-life >1 year at 25°C).

Biodegradation

The ready biodegradability of Reaction mass of disodium N,N'-[(2-hydroxy-5-nonylphen-1,3-ylene)bis(methylene)]bis[N-methylaminoacetate] and sodium N-[(2-hydroxy-5-nonylphenyl)methyl]-N-methylaminoacetate, was assessed under aerobic conditions at a GLP accredited laboratory according to the OECD Guideline 301B, “Ready biodegradability; CO₂ evolution test” (Best, 2018).

 

In an initial experiment conducted using a test item concentration equivalent to 10 mg carbon/L, the toxicity control vessel, containing both the test item and reference substance (sodium benzoate), showed <25% biodegradation after 14 days, indicating that the test item had inhibitory effects on the microbial inoculum activity. The definitive test therefore exposed activated sludge micro-organisms with mineral medium to a reduced test item concentration equivalent to 5 mg carbon/L. Tests were conducted in sealed culture vessels in the dark at temperatures between 22-24°C for 28 days.

 

The reference substance attained 79% biodegradation after 14 days, with >60% degradation within a 10-day window, thereby confirming the suitability of the inoculum and test conditions. All other validity criteria specified by the OECD 301B Guideline were also met.

 

The test item attained 0% biodegradation (based on CO₂ evolution) after 28 days and is therefore concluded to be not readily biodegradable.

Adsorption / desorption

Reaction mass of disodium N,N'-[(2-hydroxy-5-nonylphen-1,3-ylene)bis(methylene)]bis[N-methylaminoacetate] and sodium N-[(2-hydroxy-5-nonylphenyl)methyl]-N-methylaminoacetate was shown to be a surface active material, therefore (as stated in the OECD 121 Guideline for estimation of the adsorption coefficient (Koc)) an experimental HPLC method to determine the Koc is not applicable. Therefore, a Koc value was estimated based on the weighted averages of components using the (Q)SAR model KOCWIN v2.01 integrated in the EPISuite 4.11 software. In order to perform estimations via the Molecular Connectivity Index (MCI) method, KOCWIN removed Na, hence such Koc estimations represent a worst-case with respect to adsorption capacity.

Based on the MCI method, a weighted average Koc of 56600.23 L/kg was estimated, whereas based on the Kow method a weighted average Koc of 629.30 L/kg was estimated. Based on these two weighted averages, an overall Koc value of 28614.76 was derived and the substance is therefore considered to have strong adsorption capacity and thus low mobility in soils.