[en] Highlights: • Contaminants stress shifted microbial community structures in soil. • Biochar and OA mediated the shifts of soil microbial communities stressed by PAH. • Biochar and OA stimulated the functional genes participating in PAH degradation. • Tandem biochar-rhizoremediation may be feasible to improve PAH-polluted soil. -- Abstract: It remains unclear whether biochar amendment can mediate changes in soil microbial communities caused by organic contaminants in the rhizosphere. In this study, phenanthrene-contaminated soil was amended with biochar and oxalic acid (OA) alone or in combination and incubated for 21 days. Phospholipid fatty acids (PLFAs) and high-throughput sequencing were used to evaluate shifts in bacterial and fungal community structure. Phenanthrene stress led to significant shifts in both soil bacterial and fungal community structure, in particularly, 82% of microbial phyla decreased in abundance. Biochar and/or OA improved the phenanthrene-polluted soil by positively mediating shifts in soil microbial communities stressed by phenanthrene. Specifically, biochar and/or OA led to the survival of certain microbial taxa that were inhibited by phenanthrene stress. In addition, many functional microbial individuals and genes participating in polycyclic aromatic hydrocarbon (PAH) degradation were positively stimulated by high phenanthrene stress and further stimulated by the simultaneous application of biochar and OA. Based on these findings, tandem biochar and rhizoremediation may be a feasible strategy for relieving PAH toxicity to soil microbial communities.

[en] Batch incubation experiments were conducted to study the effects of different nitrogen (N) fertilizers (NH₄HCO₃, CO(NH₂)₂, and NaNO₃) on hexachlorobenzene (HCB) dechlorination in an acidic paddy soil. Results showed that NH₄HCO₃ and CO(NH₂)₂ had similar effects on HCB dechlorination, and their application amount was a crucial factor on reductive dechlorination. The addition of a proper amount of 0.14 g NH₄HCO₃- or CO(NH₂)₂-N to 500 g soil promoted HCB dechlorination, however, the application of a high amount (0.84 g) of NH₄HCO₃- or CO(NH₂)₂-N inhibited HCB dechlorination. Additional NaNO₃ served as an electron acceptor and led to lower soil pH, thus inhibited HCB dechlorination. Detected dechlorinated products showed that the dominant pathway of HCB dechlorination was HCB → pentachlorobenzene (PeCB) → 1,2,3,5-tetrachlorobenzene (TeCB) → 1,3,5-trichlorobenzene (TCB), and PeCB was the main metabolite. The role of methanogenic bacteria in HCB dechlorination was uncertain and conditions-dependent.

[en] Highlights: • Hydroxyl radical was revealed with great impact on aerobic biodegradation of BDE-47. • Hydroxylations initiated by ∙OH were theoretically studied with DFT computation. • Electrophilic addition at brominated-site may lead preferentially to dihydroxylation. • Hydrogen abstraction was indicated as a favorable path for generation of 5-OH-BDE-47. Polybrominated diphenyl ethers (PBDEs) are a group of persistent pollutants in the environment. Though aerobic biodegradation of PBDEs have been extensively studied, the involved hydroxylation mechanism decisive for whole biotransformation is not clear yet. During the effective biodegradation of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) by B. xenovorans LB400, the depletion of endogenous ∙OH by scavenger could bring about the significant decrease of biodegradation efficiency whereas $·{\mathrm{O}}_2^{-}$ was nearly not influential. Given the importance of ∙OH in hydroxylation, the reaction mechanisms along major pathways of electrophilic addition and hydrogen abstraction were theoretically examined by density functional theory (DFT). For the less demand of activation energy, the relative preference of electrophilic addition was shown at aromatic C3-site. When the secondary reaction was considered after addition at C4-site, the barrierless association of ∙OH at C3-site and deprotonation by H₂O was validated as the energetically-favorable pathway that may cause dihydroxylation of BDE-47 into 3,4-dihydroxyl-BDE-17. The electrophilic addition followed by seconary barrierless trans-association of ∙OH and then dehydration seemed favorable for monohydroxylation as regards energetic barrier merely up to 194.01 kJ mol⁻¹, while the hydrogen abstraction by ∙OH from C5-site was more privileged actually. The theoretical insights would help well understand the hydroxylation mechanism of PBDEs by aerobes.

[en] The leaf-air transfer of organochlorine pesticides (OCPs) in three kinds of vegetables, namely lettuce, romaine and garlic leaves was investigated. It was found that although the uptake of OCPs by the three selected vegetables was similar under controlled conditions, the depuration varied significantly among chemicals and plant species in terms of elimination rate, final residue of each OCPs, as well as the effect of temperature on the residue of OCPs in the vegetables. The results indicated that neither QCB nor HCB could be trapped tightly by any of the three selected vegetables, in contrast, p,p'-DDT could be retained effectively by all of them; the retainment of α-HCH, γ-HCH, p,p'-DDE, was dependent on the vegetable species, of which the garlic leaf had the biggest ability to trap them. Our work provided insight into the behavior of OCPs in the agroecosystem. - The leaf-air transfer of OCPs varied significantly among chemicals and the three selected vegetables