Sorption Behavior Of Typical Pbdes In Soil Matrix And The Effect On Biodegradability Of PBDEs

Polybrominated diphenyl ethers (PBDEs) are included as persistent organicpollutants (POPs) by Stockholm Convention. Heavy soil contamination has beentriggered by PBDEs production, utilization and post-treatment, which could induceserious environmental risks. In this study, the mechanism of interactions betweenPBDEs and soil organic matter fractions and its impact on the biodegradability ofPBDEs were studied, which would pave a better way for further risk assessment andmanagement of PBDEs contaminated sites.2,2’,4,4’-Tetrabromodiphenyl Ether (BDE-47), one typical PBDEs congener whichis included in persistent organic pollutants (POPs) list and frequently detected in naturalenvironment at high concentration level, is selected as the model PBDEs to explore itsinteraction with the tested sorbents: bulk soils, inorganic minerals, and the isolatedorganic fractions (humic acid and black carbon). Based on the characterization ofsurface and structural properties, sorption/desorption experiments were conducted toexplore the sorption characteristics of each sorbent. It was shown that compared tominerals, the major contribution to soil behaviors with BDE-47was attributed to soilorganic matter among which black carbon fraction displayed more pronouncednonlinear sorption isotherm and desorption hysteresis. Even for the different samples ofone same soil organic fraction, pronounced sorption affinity differences were observed.Based on pp-LFER model, the single-point adsorption equilibrium constant (Koc) atthree C_elevels (C_e=0.001S_w,0.005S_w,0.05S_w) was correlated with four majorparameters (surface functionalities, microporosity, aromaticity and hydrophobicity)using multiple parameter linear analysis accompanied by significance test. The resultsindicated that at low concentration, surface microporosity representing pore fillingcontributed significantly to this relationship, while as concentration increased to higherlevels, functionality related to surface adsorption began to take the dominant role, whichwas further confirmed by results of Polanyi-based modeling. Given to above, a dualmode model based on Dubinin-Radushkevich (DR) and de Boer-Zwikker equations wasadopted to quantitatively assess the changes of significance of surface adsorption aswell as that of pore filling with sorption process developed. In addition, UV andinfrared spectra of four typical aromatic compounds which represented the key structural fragments of biochars before and after interactions with BDE-47wereanalyzed and proposed π-π electron-donor-acceptor interaction to contribute greatly tosurface adsorption.The effects of soil organic matter-BDE-47interactions on the biodegradability ofBDE-47by Pseudomonas putida TZ-1were examined. The presence of all tested modelsoil organic fractions decreased the biodegradation rate as the degradation of solid phaseBDE-47was slower than that of liquid phase BDE-47for the desorption hysteresis fromsoil organic fractions. In terms of potential biodegradability, the microporous soilorganic fractions contributed to a significant negative impact, while the effects ofnon-porous soil organic fractions were negligible, as BDE-47sorbed within deepmicropores would be resistant to rigorous chemical extraction and long-term desorption.