Disodium 2-(3-oxo-6-oxidoxanthen-9-yl)benzoate

Biodegradation in water and sediment: simulation tests

Description of key information

Estimation Programs Interface (EPI) Suite (2016) prediction model was run to predict the half-life in water and sediment for the test compound disodium 2-(3-oxo-6-oxidoxanthen-9-yl)benzoate (CAS no. 518 -37 -8). Half-life of disodium 2-(3-oxo-6-oxidoxanthen-9-yl)benzoatein water is estimated to be 37.5 days (900 hrs.) while in sediment it is 337.5 days (8100 hrs). Based on these half-life values of disodium 2-(3-oxo-6-oxidoxanthen-9-yl)benzoate, it is concluded that the chemical is not persistent in water and persistent in sediment.

Key value for chemical safety assessment

Half-life in freshwater:

37.5 d

at the temperature of:

25 °C

Half-life in freshwater sediment:

337.5 d

at the temperature of:

25 °C

Additional information

A number of studies and predicted data for the test compoundSodium fluorescein(CAS no 518-47-8) were reviewed for the biodegradation end point which are summarized as below:

Estimation Programs Interface (EPI) Suite (2016) prediction model was run to predict the half-life in water and sediment for the test compound disodium 2-(3-oxo-6-oxidoxanthen-9-yl)benzoate (CAS no. 518 -37 -8). Half-life of disodium 2-(3-oxo-6-oxidoxanthen-9-yl)benzoatein water is estimated to be 37.5 days (900 hrs.) while in sediment it is 337.5 days (8100 hrs). Based on these half-life values of disodium 2-(3-oxo-6-oxidoxanthen-9-yl)benzoate, it is concluded that the chemical is not persistent in water and persistent in sediment.

 

The Biodegradation study involve the use of two OECDs (301D and 301F) tests and a screening water sediment test (WST) to investigate the biodegradability of Uranine. An artificial matrix was introduced to achieve higher reproducibility and stability of the test system. All components of the artificial medium (sediment, inoculum, mineral medium) were standardized and based on OECD guidelines (Lukasz Gutowski et. al; 2015).

The sediment was placed in the test vessels (230 g wet weight) with a water layer above containing mineral medium and inoculum. Separately, in vessels conditioned for ‘sterile control’ contained no inoculum and addition of sodium azide in sediment and water. These vessels were acclimated for 7 days under the test conditions. Conditioning allows stabilization of important parameters e.g. pH, redox potential, and adaptation of bacteria and their growth on the sediment. During the conditioning the pressure development and BOD were measured to monitor the processes inside the sediment.

Briefly, the water sediment test (WST) consisted of five different series (details can be found in: blank, quality control, test, toxicity control and sterile control; each run in three parallels. Each of the series was placed in glass bottles (1 L) equipped with two septum sealed bottle nozzles. With water phase (500 mL) and artificial sediment (230 g) volumetric ratio was 1:5. The aniline (used as quality control) and test substance concentrations were prepared in a way that they corresponded to 40 mg/ L of theoretical oxygen demand (ThOD). The nominal concentrations were 17.2 and 24.4 mg/L for aniline and uranine, respectively. To obtain abiotic conditions in the sterile control, sodium azide was added in a concentration of 400 mg/ L in water phase and 800 mg/kg in sediment. All assays were incubated in the dark at 20 °C in closed vessels. Test duration was 28 days as in related OECD tests. The water phase in the bottles was gently stirred to improve water exchange between water and sediment without disturbing the sediment. During the experiment, pressure change inside the vessels was monitored by pressure sensors.A substance was considered to be toxic if measured toxicity control was lower than 25%, which corresponded to less than 50% degradation of aniline. If the measured toxicity control was lower than calculated, a substance was assumed to have inhibitive or toxic impact on the inoculum. The primary elimination was monitored by means of HPLC-FLD (Prominence series Shimadzu, Duisburg, Germany). Sample injection volume was 5 μL and the oven temperature was settled at 30 °C, flow rate was 1.0mL/min. Retention time for UR was 6.0min. The total time of chromatographic run was 16 min. The excitation and detection wavelengths were set to 476 and 515 nm, respectively. The limit of detection (LOD) and the limit of quantification (LOQ) for UR were 1.0μg/l and 3.0μg/l respectively.

During the Water Sediment screening Tests [WST], the inoculum was of sufficient activity (‘quality control’ 79 ± 5% biodegradation). The biodegradability of Uranine (UR) was slightly higher and reached 28 ± 16% compared with 0% in Manometric Respirometric Tests [MRT]. The explanation of slightly higher degradation rates in WST in comparison to MRT could be the higher bacterial diversity of the inoculum used for this test, which in fact was a mixture of bacterial cultures from several natural water bodies and secondary effluent from sewage treatment plant. UR was not toxic to the inoculums as biodegradation in ‘toxicity control’ reached 53 ± 7%. At the end of WST the HPLC-FLD analysis showed elimination of 2.4 mg/l (11.7%) of initial UR concentration from the water phase. This might be a result of partial sorption to the sediment particles or due to the bacterial metabolism. In the WST, 93% of sediment mixture consisted of quartz sand, while the rest was clay and peat. Hence sorption cannot be excluded. However, the low degree of mineralization was observed indicating that the UR was not fully degraded but transformed into TP’s [Transformation Products]. TPs were assumed to be possibly mono- and di-hydroxylated derivatives of UR. The hydroxylation could take place in any of the UR aromatic rings. The fragmentation patterns confirmed that TP1a,b and TP2 are hydroxylated products whereas TP3a,b belong to the carboxylated compounds. However, due to many possible addition sites to the aromatic ring of UR, it is difficult to know the exact position of either the hydroxyl or the carboxyl groups.The study demonstrated that Uranine was not readily biodegradable in nature,

Thus, based on the above experimental data, it can be concluded that the substance is not readily biodegradable and on the basis of the estimation model, it is evident that the substance is not persistent in water but persistent in sediment compartment.