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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

Biodegradation data include results from aerobic freshwater/sediment, anaerobic freshwater/sediment, anaerobic digester sludge, and sediment/soil studies. Biotic degradation and binding to sediment/soil/sludge was observed in all studies. 

Key value for chemical safety assessment

Half-life in freshwater:
19 d
at the temperature of:
25 °C
Half-life in freshwater sediment:
26 d
at the temperature of:
25 °C

Additional information

The biodegradation potential of TBBPA in water and sediments (simulation tests) was investigated in 4 studies:

1) Fackler (1989): The biodegradability of 14C-TBBPA was tested for 56 days under aerobic conditions in a sediment/water microbial test system using natural river sediment and water at concentrations of 10, 100 and 1000 µg/L. The test conditions were pH 5.5, field moisture capacity 15.9%, temperature 24 -25 °C, and composition of the soil (6.8% Carbon) was 92% sand, 6% silt and 2% clay. Biodegradation occurred in all tested concentrations. Half-lives calculated for TBBPA in the sediment/water microbial test systems ranged between 48 and 84 days at a concentration of 10 and 1000 µg/L, respectively.

2) Schaefer and Stenzel (2006a): The biodegradability of 14C-TBBPA was tested for 102 days under anaerobic conditions in freshwater aquatic-sediment systems at a nominal concentration of 50 µg/kg dry sediment. Anaerobic sediments and waters were collected from two freshwater sources, Turkey Creek and Choptank River and incubated at approximately 20 °C. TBBPA was readily adsorbed to the sediments in the first 14-day interval for both test systems. The DT50 values for TBBPA in the whole test systems for Turkey Creek and Choptank River were 28 and 24 days, respectively.

3) Schaefer and Stenzel (2006b): The biodegradability of 14C-TBBPA was tested for 120 days at 35 °C at a nominal concentration of 50 μg/L with anaerobic digester sludge collected from a municipal wastewater treatment plant. The digester sludge was used to prepare various test vessels containing both biotic and abiotic systems. TBBPA was immediately adsorbed to solids in both biotic and abiotic sludge systems. The DT50 value in the biotic sludge systems was 19 days.

4) Ravit et al. (2005): A supporting study has also been provided (Ravit et al., 2005) in which the effect of two salt marsh macrophyte species (Spartina alterniflora and Phragmites australis) on the sediment microbial community responsible for the biotransformation of TBBPA (microbial community function) was measured. Under the conditions of this study, the test material was reductively dehalogenated resulting in the transient formation of two intermediates, identified as tribromobisphenol A and dibromobisphenol A, and the formation and accumulation of bisphenol A (BPA) as the end product.

Discussion

Metabolites of TBBPA were observed in anaerobic sediment and anaerobic sludge, but not identified definitively due to the low and environmentally relevant TBBPA concentration used for these tests (50 µg/kg).In the two anaerobic studies performed in aquatic sediments and digester sludge by Schaefer and Stenzel (2006), three unknown HPLC peaks were observed between TBBPA and bisphenol-A (BPA). The kinetics of the unknown peaks between TBBPA and BPA show an increase and then a decrease in their concentrations during the experimental period, indicating that these are indeed intermediates. Although not definitively identified, these peaks can be attributed to three dehalogenated intermediates: tribromobisphenol-A (Br3-BPA), dibromobisphenol-A (Br2-BPA) and monobromobisphenol A (Br-BPA). However, as more information on the dehalogenation mechanism in which TBBPA is degrading to BPA under anaerobic conditions is well described in the literature for the soil and sediment compartments, this information can be used to support the degradation pathway in the studies performed.

In the supporting study provided (Ravit et al., 2005), in which the effect of two salt marsh macrophyte species on the sediment microbial community responsible for the biotransformation of TBBPA was measured, TBBPA was reductively dehalogenated resulting in the transient formation of two intermediates, identified as tribromobisphenol A and dibromobisphenol A, and the formation and accumulation of bisphenol A (BPA) as the end product.

There are also a number of scientific papers available that address the degradation pathway of TBBPA. A summary of the main papers addressing this point is as follows:

- Bisphenol A was reported as a degradant of TBBPA in eustuarine sediments under conditions promoting either methanogenesis or sulfate reduction (Voordeckers et al., 2002). The EU Risk Assessments on TBBPA and BPA concluded that this degradation pathway would not significantly affect the environmental levels of bisphenol A.

- Ronen and Abeliovich (2000): The anaerobic metabolism of TBBPA was examined in sediments collected from the vicinity of an industrial complex in the northern Negev in Israel. The intermediate metabolites of the biodegradation products of TBBPA were determined by HPLC and GC-MS methods. Br3-BPA and Br2-BPA were identified using HPLC. BPA was identified as the final metabolite under the anaerobic conditions. The further degradation of BPA under aerobic conditions was studied by using a pure culture of a bacterium that was isolated from soil. Degradation products of BPA under aerobic conditions were also identified by a mass spectral method. The first proposed mechanistic degradation pathway was for the full dehalogenation of TBBPA to BPA under anaerobic conditions. The second proposed mechanistic degradation pathway was for the cleavage and full mineralization of BPA.

- Voordeckers et al. (2002): The degradation of TBBPA was investigated in sediments under methanogenic and sulfidogenic conditions. Sediment grab samples were collected from the Arthur Kill tidal strait located between Staten Island and New Jersey, USA. Under both conditions, debromination of TBBPA to BPA was demonstrated. Based on the study results, the authors claim that TBBPA seems to be readily dehalogenated to BPA under both methanogenic and sulfate-reducing conditions.

- Ronen and Arbeli (2003): A full dehalogenation mechanism with identification of intermediate metabolites is described in this publication. Sediment samples were taken from the vicinity of an industrial complex in the northern Negev desert, Israel. The debromination and transformation of TBBPA to BPA was investigated under anaerobic conditions. GC-MS and HPLC analytical methods were used for identification of the metabolites. The kinetics of TBBPA biodegradation were investigated with full identification of three intermediate metabolites: Br3-BPA, Br2-BPA and Br-BPA. These results further support the dehalogenation mechanistic degradation pathway of TBBPA to BPA under anaerobic conditions.

- Chu et al. (2005): The biodegradation mechanism of TBBPA in sludge and sediments was investigated using an HPLC-ESI(-) -MS-MS analytical method developed for simultaneous determination of BPA, TBBPA and debrominated TBBPA derivatives. Surface sediment samples were taken from Lake Erie in Canada and analyzed for TBBPA and its potential debromination metabolites. In 65% of the55 samples, BPA, TBBPA, and Br3-BPA were detected. Although, Br2-BPA and Br-BPA were not detected in these samples, the detection and quantification of BPA in these samples indicate that debromination processes are occurring.

In addition, analyses were also performed on sewage sludge samples collected from Little River Waste Water Treatment Plant and from the West Windsor Pollution Control in Canada. In these samples, BPA, TBBPA, Br3-BPA, Br2-BPA and Br-BPA were identified. The full debromination pathway is presented in this paper.

O-methylation of TBBPA

Based on scientific literature and monitoring data, the o-methylation of TBBPA can occur in the environment. Although the significance of this pathway is not conclusive, monitoring data show that the methyl ether TBBPA can be found at low levels (µgs/kg ) in suspended particular matter in rivers in Europe. However, the dimethyl ether TBBPA is much less frequently found and only in highly contaminated rivers (Mersey and Tees in the UK). In fish, the methylated ether was found at very low levels, mostly below the LOQ of 0.8 µg/kg, while the dimethyl ether was not found at all.

- George and Häggblom et al. (2008): The biodegradation of TBBPA in sediments was tested using initial concentrations of 5 mg/kg. The paper demonstrated o-methylation of TBBPA to its mono- and di-methyl ether derivatives by microorganisms present in different sediments; transformation rates to the monomethyl ether were 25 and 5% after 60 and 80 days, respectively, in the different sediments, and transformation rates to the dimethyl ether were 35% and 5% respectively.

- Peng et al. (2014): Transformations of TBBPA by 6 freshwater green microalgae was investigated. The results showed that TBBPA could be transformed with nearly complete removal by Scenedesmus quadricauda and Coelastrum sphaericum following 10-day incubation. Four transformation products were identified by mass spectrometry: TBBPA sulfate, TBBPA glucoside, sulfated TBBPA glucoside, and tribromobisphenol-A. In addition, in one species (Scenedesmus quadricauda), the monomethyl ether TBBPA was identified.

- Kotthoff (2015): A 7 year monitoring project (2007 – 2014) was undertaken. Samples of fish were collected annually from selected rivers in Europe and one lake. In addition, suspended particular matter (SPM) was collected from the same rivers and sediment cores were collected from the lake. These samples were analysed for the presence of TBBPA, methyl ether TBBPA and dimethyl ether TBBPA. The Limits of Quantification (LOQ) of TBBPA in all matrices were 0.45 μg/kg (ww for fish and dw for SPM/sediment). The LOQs of TBBPA-MME in all matrices were 0.80 μg/kg (ww for fish and dw for SPM/sediment). The LOQ of TBBPA-DME was 1.6 μg/kg ww for the fish and 0.70 μg/kg dw for the SPM/sediment samples.

TBBPA could be quantified in 13 of 36 bream samples (range ~0.5 - 1.2 μg/kg ww) and 7 of 7 sole muscle samples (range ~0.5 – 0.7 μg/kg ww). Further, it could be quantified in 11 of the 14 SPM samples (range ~0.5 – 9.4 μg/kg dw) and in both of the sediment core samples (2.3 – 2.6 μg/kg dw). TBBPA-MME could be quantified in 12 of 36 bream and 4 of 7 sole muscle samples (range ~0.8 – 1.8 μg/kg ww). Further, it could be quantified in 10 of the 14 SPM samples (range ~ 2.3 – 4.5 μg/kg dw) and in both of the sediment core samples (5.2 – 5.5 μg/kg dw). Dimethyl-TBBPA was only rarely detectable and could be quantified above the LOQ in no sample.