Interconversion between Methoxylated and Hydroxylated Polychlorinated Biphenyls in Rice Plants: An Important but Overlooked Metabolic Pathway

To date, there is limited knowledge on the methoxylation of polychlorinated biphenyls (PCBs) and the relationship between hydroxylated polychlorinated biphenyls (OH-PCBs) and methoxylated polychlorinated biphenyls (MeO-PCBs) in organisms. In this study, rice (Oryza sativa L.) was chosen as the model organism to determine the metabolism of PCBs in plants. Limited para-substituted 4′-OH-CB-61 (major metabolite) and 4′-MeO-CB-61 (minor metabolite) were found after a 5-day exposure to CB-61, while ortho- and meta-substituted products were not detected. Interconversion between OH-PCBs and MeO-PCBs in organisms was observed for the first time. The demethylation ratio of 4′-MeO-CB-61 was 18 times higher than the methylation ratio of 4′-OH-CB-61, indicating that formation of OH-PCBs was easier than formation of MeO-PCBs. The transformation products were generated in the roots after 24 h of exposure. The results of in vivo and in vitro exposure studies show that the rice itself played a key role in the whole transformation processes, while endophytes were jointly responsible for hydroxylation of PCBs and demethylation of MeO-PCBs. Metabolic pathways of PCBs, OH-PCBs, and MeO-PCBs in intact rice plants are proposed. The findings are important in understanding the fate of PCBs and the source of OH-PCBs in the environment

Reciprocal Transformation between Hydroxylated and Methoxylated Polybrominated Diphenyl Ethers in Young Whole Pumpkin Plants

Relationships among polybrominated diphenyl ethers (PBDEs), hydroxylated PBDEs (OH-PBDEs), and methoxylated PBDEs (MeO-PBDEs) have attracted considerable scientific interest. However, few studies have focused on the <i>in vivo</i> metabolism of these compounds by intact whole plants. In this work, interconversion between OH-tetraBDEs and MeO-tetraBDEs in young pumpkins was experimentally proven. Conversion ratios were higher for pumpkins exposed to OH-BDEs than for those exposed to MeO-BDEs. Twelve PBDE analogues showed different metabolic potential. The largest biotransformation ratio (12.4%) was observed for the transformation from 4-OH-BDE-42 to 4-MeO-BDE-42. The lowest interconversion ratios were found between 2′-OH-BDE-68 and 2′-MeO-BDE-68. Transformation products were mainly found in roots. Fewer metabolites were detected in stems, while no metabolites were detected in shoots. Root exudates were found to make only a small contribution to the conversion between OH- and MeO-PBDEs. This is the first study to demonstrate the reciprocal transformation of OH- and MeO-PBDEs in plants

Metabolites of 2,4,4′-Tribrominated Diphenyl Ether (BDE-28) in Pumpkin after <i>In Vivo</i> and <i>In Vitro</i> Exposure

There is currently limited knowledge on PBDE metabolism in plants although they could play an important role in the environmental transformation of these persistent organic pollutants. In this study, pumpkin (<i>Cucurbita maxima × C. moschata)</i> was chosen as the model to understand the fate of BDE-28 in plants. MeO-tri-BDEs, OH-tri-BDEs, and OH-tri-BDEs were found as metabolites in plant samples of both <i>in vivo</i> hydroponic and <i>in vitro</i> tissue culture exposure. Three MeO-tri-BDEs were further identified as para-substituted metabolites. MeO-BDEs and OH-BDEs, respectively, accounted for about 1.6% and 1.5% (recovery corrected) of initial amount of BDE-28 according to the semiquantitative results. Other PBDEs, especially less brominated PBDEs as impurities in the standard of BDE-28, were also detected. The impurities and evaporation of the standard must be considered when trace metabolites are studied in exposure experiments

Estimating Emissions and Environmental Fate of Di-(2-ethylhexyl) Phthalate in Yangtze River Delta, China: Application of Inverse Modeling

A georeferenced multimedia model was developed for evaluating the emissions and environmental fate of di-2-ethylhexyl phthalate (DEHP) in the Yangtze River Delta (YRD), China. Due to the lack of emission inventories, the emission rates were estimated using the observed concentrations in soil as inputs for the multimedia model solved analytically in an inverse manner. The estimated emission rates were then used to evaluate the environmental fate of DEHP with the regular multimedia modeling approach. The predicted concentrations in air, surface water, and sediment were all consistent with the ranges and spatial variations of observed data. The total emission rate of DEHP in YRD was 13.9 thousand t/year (95% confidence interval: 9.4–23.6), of which urban and rural sources accounted for 47% and 53%, respectively. Soil in rural areas and sediment stored 79% and 13% of the total mass, respectively. The air received 61% of the total emissions of DEHP but was only associated with 0.2% of the total mass due to fast degradation and intensive deposition. We suggest the use of an inverse modeling approach under a tiered risk assessment framework to assist future development and refinement of DEHP emission inventories

Identification of Tetrabromobisphenol A Allyl Ether and Tetrabromobisphenol A 2,3-Dibromopropyl Ether in the Ambient Environment near a Manufacturing Site and in Mollusks at a Coastal Region

Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants (BFRs) and has been frequently detected in the environment and biota. Recent studies have found that derivatives of TBBPA, such as TBBPA bis­(allyl) ether (TBBPA BAE) and TBBPA bis­(2,3-dibromopropyl) ether (TBBPA BDBPE) are present in various environmental compartments. In this work, using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) and liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (LC–Q-TOF-MS), TBBPA allyl ether (TBBPA AE) and TBBPA 2,3-dibromopropyl ether (TBBPA DBPE) were identified in environmental samples and further confirmed by synthesized standards. Soil, sediment, rice hull, and earthworm samples collected near a BFR manufacturing plant were found to contain these two compounds. In sediments, the concentrations of TBBPA AE and TBBPA DBPE ranged from 1.0 to 346.6 ng/g of dry weight (dw) and from 0.7 to 292.7 ng/g of dw, respectively. TBBPA AE and TBBPA DBPE in earthworm and rice hull samples were similar to soil samples, which ranged from below the method limit of detection (LOD, <0.002 ng/g of dw) to 0.064 ng/g of dw and from below the LOD (<0.008 ng/g of dw) to 0.58 ng/g of dw, respectively. Furthermore, mollusks collected from the Chinese Bohai Sea were used as a bioindicator to investigate the occurrence and distribution of these compounds in the coastal environment. The detection frequencies of TBBPA AE and TBBPA DBPE were 41 and 32%, respectively, and the concentrations ranged from below LOD (<0.003 ng/g of dw) to 0.54 ng/g of dw, with an average of 0.09 ng/g of dw, for TBBPA AE, and from below LOD (<0.008 ng/g of dw) to 1.41 ng/g of dw, with an average of 0.15 ng/g of dw, for TBBPA DBPE