BDE-47 sorption and desorption to soil matrix in single- and binary-solute systems
School of Environment, Tsinghua University, Beijing 100084, China.Chemosphere (Impact Factor: 3.34). 01/2012; 87(5):477-82. DOI: 10.1016/j.chemosphere.2011.12.034
Three loamy-clay soil samples (LC1-3) with different properties were collected as the geosorbents to preliminarily investigate the sorption and desorption of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in single system and binary system with the presence of decabromodiphenyl ether (BDE-209), which can provide information in order to further understand the sorption mechanisms and evaluate the adsorption sites. A concentration of 10 μg L(-1) BDE-209 suppressed the sorption of BDE-47, and the trend became more and more significant with the increase of BDE-47 equilibrium concentration, however, BDE-47 caused no competitive effect on BDE-209 sorption, which was related with the better accessibility of more hydrophobic molecules to adsorption sites. In the binary system, nonlinearity of the BDE-47 sorption isotherms for the three samples changed in different ways, which originated from the varied soil properties. Desorption hysteresis was observed in all cases, which was estimated due to irreversible surface adsorption between sorbent and sorbate. BDE-209 made desorption of BDE-47 more hysteretic from soil samples, which was estimated to be ascribed to the accelerated sorbent state transition and new sites creation caused by BDE-209 sorption.
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ABSTRACT: A study was conducted on the kinetics, equilibrium, and mechanisms of sorption and desorption of 17α-ethinyl estradiol (EE2) in six sorbents, which were two natural soils (Bulk1 and Bulk2) and their fractions obtained by alkaline extraction, namely, humic acids (HA1 and HA2), and mineral-bond humins (MHU1 and MHU2). These sorbents, characterized by total organic carbon (TOC), black carbon (BC), gas adsorption and Fourier transform infrared spectra, were shown to be porous solids containing aromatic (hard carbon) and aliphatic carbon (soft carbon). The two-compartment first-order model fitted the kinetics of sorption very well (R(2)>0.990). The fast and slow sorption rate constants ranged from 1.110h(-1) and 0.026h(-1) to 2.063h(-1) and 0.067h(-1), respectively. The slow sorption was attributed to the diffusion of EE2 in micropores rather than organic matter. The Freundlich model fitted the equilibrium of sorption and desorption very well. The nonlinearity of sorption took the order MHU>bulk soil>HA and was positively related to BC/TOC (p<0.01). The hysteresis in MHU2 with higher BC/TOC was stronger than that in Bulk2 with lower BC/TOC, but a contrary observation was found in MHU1 and Bulk1. This contradictory phenomenon could be attributed to the location difference of hard carbon which greatly affected the desorption process. These findings could give an insight into the sorption mechanisms and promote an accurate model for the transport, fate and risk assessment of EE2 in the environment.
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ABSTRACT: Tetrabromodiphenyl ether is one of the most abundant flame retardant additives detected in treated municipal wastewater, river water and sediments in China. When using treated municipal wastewater for recharging river-based natural groundwater, polybrominated diphenyl ether (PBDE) pollution might be a potential threat to underground aquifers. Lab-scale column experiments simulating recharge were conducted to investigate the migration and biodegradation of 2,2’,4,4’5-tetrabromodiphenyl ether (BDE-99) under different recharge modes. Three recharge columns were operated in continual sterilization recharge (CSR), continual recharge (CR), and wetting and drying alternative recharge (WDAR). The results showed that the attenuation effect of the BDE-99 was in the order of CR > WDAR > CSR, whereas the intermediate products of PBDE biodegradation were in the order of WDAR> CR > CSR. The attenuation rate constants of BED-99 in the CSR, CR and WDAR systems were 0.105, 0.139 and 0.127 m−1, respectively, which followed first-order kinetics. The primary debrominated metabolites were BDE-15, -28, -47 in the CR system, whereas high-brominated diphenyl ethers (BDE-153, -154, -183) and isomers of BDE-99 (BDE-100) were also produced during the biotransformation process in the WDAR system. The accumulation amount of BDE-99 was higher in WDAR soils than in the CR system, whereas the intermediate product concentration of PBDEs and OH-PBDEs were in reverse order. According to the high-throughput sequencing, the bacterial community in the upper layer was more diverse than in the bottom layer, which was related to the oxygen concentrations, BDE-99 and its halogenated intermediate concentrations in the water-soil system. The dominant groups were found to be proteobacteria, Acidobateria, and Firmcutes, including Gammaproteobacteria Betaproteobacteria, Alphaproteobacteria, Acidobateria-6, and Clostridia, suggesting that these microbes might play an important role in BDE-99 and intermediate metabolite degradation. The findings of this study provide an understanding of PBDE accumulation in natural groundwater recharge areas under different recharging operation modes and can facilitate the prediction of the fate of PBDEs in underground aquifers.
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ABSTRACT: When using treated municipal wastewater for recharging river-based natural groundwater, pentabromodiphenyl ether (BDE-99) pollution might be a potential threat to underground aquifers. Due to their strong affinity for black carbon (BC), the migration and bioavailability of PBDEs may be decreased in aquifer media with a high BC content. To properly examine the effect of black carbon on the migration and biodegradation of BDE-99, a lab-scale column was set up to simulate the recharge process. The filler media of the two columns mainly comprised silty clay (SC) and black carbon amendment silty clay (BCA). The results showed that the attenuation effect of BDE-99 was in the order of BCA > SC. The attenuation rate constants of BED-99 in the SC and BCA systems were 0.12 and 0.18 m−1, respectively, which followed first-order kinetics. The two turning points of the BDE-99 percentage with depth in the leachate were 0.15 m and 0.45 m due to fast sorption and biodegradation, respectively. The primary debrominated metabolites were not the only lower brominated ether congeners; high-brominated diphenyl ethers and isomers of BDE-99 were also produced during the biotransformation process. The accumulation of BDE-99 and PBDEs in the soil was higher in BCA soils than in the SC system. The bacterial community in the upper layer was more diverse than in the bottom layer. Five known bacterial classes (Gammaproteobacteria, Alphaproteobacteria, Betaproteobacteria, Acidobacteria and Clostridia) and seventeen known bacterial genera (three major genera: Halomonas, Pseudomonas and Shewanella) were considered to be PBDE-degradation-associated bacteria. The bacterial community diversity and percentage of PBDE-degradation-associated bacteria in the BCA system were marginally greater than those in the SC system. The higher bacterial diversity and adsorption capacity in the BCA system were able mitigate the migration of BDE-99 into groundwater.
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