Biotransformation kinetics and pathways of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and its hydroxylated and methoxylated derivatives (6-OH-BDE-47 and 6-MeO-BDE-47) in earthworms (Eisenia fetida)

Detection and O-methylation of bromocatechols, brominated/hydroxylated analogs of diphenyl ethers and dibenzo-p-dioxins in thorny oyster (Spondylus squamosus) and pen shell (Atrina vexillum) from the Philippines

Marine algae in the Asia-Pacific region are known for producing brominated phenols in abundance. This study investigated the presence of brominated catechols and their transformation into brominated dimethoxy diphenyl ethers (diMeO-BDEs) and monomethoxy-dibenzo-p-dioxins (MeO-BDDs) in two bivalve species collected from the coast of Luzon island, the Philippines. Species-difference in brominated profiles were observed between thorny oyster (S. squamosus) and pen shell (Atrina vexillum). In the immature S. squamosus, we identified di- and tribrominated catechols/guaiacols, dihydroxylated tetra-/pentaBDEs (diOH-BDEs), and monohydroxylated tri-/tetrabromo-dibenzo-p-dioxins (OH-BDDs). During the immature stage of S. squamosus, the concentrations of phenolic products were higher in the order of bromocatechols > OH-BDDs > diOH-BDEs. Corresponding MeO analogs, however, increased in the order of MeO-BDDs > diMeO-BDEs > bromoveratroles. It was estimated that 1-2 % of bromophenols and catechols undergo O-methylation, whereas diOH-BDEs and OH-BDDs are nearly completely O-methylated. The interconversions within phenolic products were minimal. The results suggest that S. squamosus produces or acquires phenolic and catecholic products in early larval stage and may undergo O-methylation as it grows, resulting in the accumulation of diMeO-BDEs and MeO-BDDs. This understanding provides important insights into the sources of diOH-BDEs and OH-BDDs, as well as the accumulation mechanisms of their methoxylated derivatives in marine top predators.

Polybrominated diphenyl ethers in bivalves: metabolites, accumulation, quantification and ecological risks

Polybrominated diphenyl ethers (PBDEs) are extensively used as flame retardants in plastics but have emerged as persistent environmental pollutants due to their bioaccumulation and toxicity. Analysis of 74 studies from 2000 to 2024 highlights the increasing research interest in PBDE contamination, particularly in aquatic ecosystems and bivalves. Recurring themes such as "health risk," "bioaccumulation," and "risk assessment" dominate the discourse, emphasizing the need for deeper investigations into PBDE pathways and impacts. This trend underscores the critical importance of evaluating PBDE contamination in seafood species like oysters, mussels and clams, which are integral to human diets and aquatic food chains. Building on these insights, this study focused on analyzing PBDEs and their metabolites (MeO-BDE, OH-BDE) in commonly consumed bivalve species. Advanced methods for extraction, purification and simultaneous analysis revealed significant variations in PBDE concentrations: oysters (29-101 ng/g lw), mussels (10-274.8 ng/g lw) and clams (23-64,900 ng/g lw). Notably, metabolites MeO-BDE and OH-BDE were frequently detected, sometimes surpassing PBDE levels, indicating complex bioaccumulation processes. Bioaccumulation and bio-sediment accumulation factors (BAF and BSAF) showed that PBDEs and their metabolites accumulate more effectively through water pathways than sediment. Trophic magnification factor (TMF) analysis further revealed higher TMF values for PBDEs compared to their metabolites, categorizing PBDEs and MeO-BDE as low-risk TMFs. These findings align with citation analysis trends, which emphasize "risk assessment" as a pivotal theme, particularly concerning human exposure. The human health risk assessment based on bivalve consumption highlights potential exposure concerns in regions with high seafood intake. This study not only enriches the understanding of PBDE distribution and bioaccumulation in bivalves but also emphasizes the importance of effective monitoring, regulatory control and continued investigation into their ecological and human health impacts.

Fate and Persistence of Bisphenol AF (BPAF) in Agricultural Soils: Role of Nonextractable Residues

Bisphenol AF (BPAF), a polyfluorinated compound and widely used substitute for bisphenol A, is ubiquitous in the environment. However, the fate of BPAF in soil is still obscure. Here, we used [ring-U-14C]-labeled BPAF to investigate its fate in three agricultural soils for 240 days, based on a four-compartment fate model. BPAF dissipated in the soils with a half-life of 35-110 days, accompanied by low mineralization (8.5-11.3% of the initial radioactivity). The main fate of BPAF in the soils was formation of nonextractable residues (NERs) (44.2-65.3%), mostly (>90%) via physicochemical sequestration (31.2-42.7%) and ester bonds (10.0-22.6%). Notably, the sequestered free BPAF in the NERs increased the half-life by 1.4-2.5 times. Six transformation products (TPs) were identified, including BPAF mono- and dimethyl ethers, monosulfate ester, and three single-ring monophenolic compounds. BPAF monomethyl ether was the predominant extractable TP, while the polar TPs were the predominant physico-chemically sequestered and ester-linked TPs in the NERs. Three transformation pathways for BPAF in the soils are proposed, including type II ipso-substitution, O-methylation, and sulfate conjugation. Our study provides the first quantitative information on the fate of BPAF in soil, and highlights the importance of NERs in determining the persistence of BPAF.

Transformation and environmental fate of 6-OH-BDE-47 and 6-MeO-BDE-47 in oxic and anoxic sediments

Pollutants often exhibit different environmental behaviors at varying redox potentials, and the fate and microbial response of 6-OH-BDE-47 and 6-MeO-BDE-47 under these conditions remain unclear. Herein, 14C-labeled 6-OH-BDE-47 and 6-MeO-BDE-47 were used to investigate their fate in water-sediment systems at different redox potentials. For 6-OH-BDE-47, aerobic microorganisms and nitrate electron acceptors promoted nonextractable residues (NERs) formation and anaerobic microorganisms facilitated their release and was highest formed in the O2-containing group. For 6-MeO-BDE-47, aerobic microorganisms, electron acceptors, and anaerobic microorganisms promoted NER formation, and was highest formed in the nitrate group. Microorganisms markedly promoted 6-OH/MeO-BDE-47 transformation. For 6-OH-BDE-47, the degradation followed the order nitrate group (29.6 %) > O2-containing group (6.5 %) > sulfate group (1.45 %) > anaerobic group (0 %), while for 6-MeO-BDE-47, the order was O2-containing group (8.8 %) > nitrate group = sulfate group = anaerobic group (0 %). The complexity of the 6-OH-BDE-47 and 6-MeO-BDE-47 microbial community network was consistent with the results of redox potentials, where microbial networks connectivity linking were more complex under O2-containing and nitrate conditions. Overall, our study comprehensively revealed the fate of 6-OH-BDE-47 and 6-MeO-BDE-47 under different redox conditions, showing that electron acceptors can alter microbial community structure and regulating interactions. It provided guidelines for selecting electron acceptors in the remediation of 6-OH-BDE-47 and 6-MeO-BDE-47.

Bioaccumulation, Trophic Transfer, and Biotransformation of Polychlorinated Diphenyl Ethers in a Simulated Aquatic Food Chain

Polychlorinated diphenyl ethers (PCDEs) are detected in aquatic environments and demonstrate adverse effects in aquatic organisms. However, data regarding the environmental behavior of PCDEs in aquatic ecosystems are lacking. In the present study, a simulated aquatic food chain (Scenedesmus obliquus-Daphnia magna-Danio rerio) was constructed in a lab setting, and the bioaccumulation, trophic transfer, and biotransformation of 12 PCDE congeners were quantitatively investigated for the first time. The log-transformed bioaccumulation factors (BCFs) of PCDEs in S. obliquus, D. magna, and D. rerio were in the range of 2.94-3.77, 3.29-4.03, and 2.42-2.89 L/kg w.w., respectively, indicating the species-specific bioaccumulation of PCDE congeners. The BCF values increased significantly with the increasing number of substituted Cl atoms, with the exception of CDE 209. The number of Cl atoms at the para and meta positions were found to be the major positive contributing factors for BCFs in the case of the same number of substituted Cl. The lipid-normalized biomagnification factors (BMFs) of S. obliquus to D. magna, D. magna to D. rerio, and the whole food chain for the 12 PCDE congeners ranged at 1.08-2.27, 0.81-1.64, and 0.88-3.64, respectively, suggesting that some congeners had BMFs comparable to PBDEs and PCBs. Dechlorination was the only metabolic pathway observed for S. obliquus and D. magna. For D. rerio, dechlorination, methoxylation, and hydroxylation metabolic pathways were observed. ¹H nuclear magnetic resonance (NMR) experiments and theoretical calculations confirmed that methoxylation and hydroxylation occurred at the ortho position of the benzene rings. In addition, reliable quantitative structure-property relationship (QSPR) models were constructed to qualitatively describe the relationships between molecular structure descriptors and BCFs for PCDEs. These findings provide insights into the movement and transformation of PCDEs in aquatic ecosystems.