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Environmental fate & pathways

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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. Metabolites of TBBPA were observed in anaerobic sediment and anaerobic sludge, but not identified definitively.

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. Half-lives calculated for TBBPA ranged between 48 and 84 days at a concentration of 10 and 1000 µg/L, respectively.

The biodegradability of 14C-TBBPA was tested for 102 days under anaerobic conditions in freshwater aquatic-sediment systems from two sources (Turkey Creek and Choptank River) at a nominal concentration of 50 µg/kg dry sediment at approximately 20 °C. The DT50 values for TBBPA in the whole test systems for Turkey Creek and Choptank River were 28 and 24 days, respectively.

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 DT50 value in the biotic sludge systems was 19 days.

The transformation of 14C-TBBPA was tested for 6 months in aerobic and anaerobic soil systems. Volatile metabolites were identified (CO2 at 17.2 to 21.4% after 6 months) as were residues (declining from 89.6 to 92.5% at day 0 to 1.7 to 2.4% after 6 months). The DT50 was 5.3-7.7 days in aerobic soils.

The biodegradability of 14C-TBBPA was tested under aerobic and anaerobic conditions in three soil types; TLC showed biodegradation of TBBPA in all soil types. Under aerobic conditions, less than or equal to 6% of the applied radioactive TBBPA was recovered in the volatile traps, indicating partial degradation to CO₂. Under anaerobic conditions, less than 0.5% of the radiolabel was recovered in the volatile traps, indicating little degradation to CO₂. The recovered radioactivity in all traps was almost exclusively CO₂. Under both aerobic and anaerobic conditions, degradation products (2 or 3 depending on soil type) were not specifically identified, but the dimethyl and diethyl derivatives of TBBPA were ruled out based on TLC characteristics of authentic standards.

Based on the data presented and the supporting information from the scientific literature, it can be concluded that under anaerobic conditions, TBBPA undergoes biodegradation and the biodegradation pathway is through sequential debromination, resulting in BPA formation. BPA is further mineralized under aerobic conditions. Under aerobic conditions, o-methylation could occur. Further discussions on the biodegradation/transformation products are included as part of the PBT assessment.