Evaluation of applying an alkaline green tea/ferrous iron system to lindane remediation impacts to soil and plant growth-promoting microbial community.

Application of in situ chemical oxidation or reduction (ISCO/ISCR) technologies for contaminated soil remediation and its subsequent impact on soil is gaining increased attention. Reductive reactivity, generated from green tea (GT) extract mixed with ferrous (Fe2+) ions under alkaline conditions (the alkaline GT/Fe2+ system), has been considered as a promising ISCR process; however, its impact on soil has never been studied. In this study, the impact of applying the alkaline GT/Fe2+ system on soil was evaluated by analyzing the variations of the soil microbial community, diversity, and richness using next-generation 16S rRNA amplicon sequencing while mimicking the lindane-contaminated soil remediation procedure. Lindane was reductively degraded by the alkaline GT/Fe2+ system with reaction rate constants of 0.014 to 0.057 µM/h depending on the lindane dosage. Environmental change to the alkaline condition significantly decreased the microbial diversity and richness, but the recovery of the influence was observed subsequently. Bacteria that mainly belong within the phylum Firmicutes, including Salipaludibacillus, Anaerobacillus, Bacillaceae, and Paenibacillaceae, were greatly enhanced due to the alkaline condition. Besides, the dominance of heterotrophic, iron-metabolic, lindane-catabolic, and facultative bacteria was observed in the other corresponding conditions. From the results of principal component analysis (PCA), although dominant microbes all shifted significantly at every lindane-existing condition, the set of optimal lindane treatment with the alkaline GT/Fe2+ system had a minimized effect on the plant growth-promoting bacteria (PGPB). Nitrogen-cycling-related PGPB is sensitive to all factors of the alkaline GT/Fe2+ system. However, the other types, including plant-growth-inducer producing, phosphate solubilizing, and siderophore producing PGPB, has less impact under the optimal treatment. Our results demonstrate that the alkaline GT/Fe2+ system is an effective and soil-ecosystem-friendly ISCR remediation technology for lindane contamination.

Assessment of green tea reductive degradation of halogenated solvents.

Green tea (GT) leaves can be brewed into a solution rich in polyphenols that serve as effective reducing agents, and the complexes formed by combining green tea with ferrous ion (GT/Fe(II)) can provide an elevated reduction potential. The dissociated GT polyphenols at alkaline pH can dramatically increase the formation of GT/Fe(II) complexes. This experimental work evaluated the reductive reactivity of alkaline GT solution and GT/Fe(II) complexes (at pH 10) on 14 halogenated volatile organic compounds (VOCs). Carbon tetrachloride (CT), with a highest carbon oxidation state (COS) of IV, was observed to be degradable by the alkaline GT solution, while all others proved ineffective. The GT/Fe(II) complexes are very reactive and capable of degrading halogenated methanes, ethanes, and ethenes, in which chemical structures exhibit zero or positive COS values, and the chlorine or bromine atom is bonded at the saturated carbon atom, such as CT, chloroform, bromoform, dibromomethane, 1,1,1-trichloroethane, and 1,1,1,2-tetrachloroethane. The linear free energy relationship (LFER) approach was used to determine the overall reduction potentials (EH0) of the alkaline GT solution and GT/Fe(II) complexes, which were found to be -0.131 V and -0.368 V, respectively. These findings demonstrated that GT/Fe(II) complexes exhibit the potential to remediate halogenated contaminants and the EH0 information obtained in this study may serve as a reference in determining probable reactivity that contributes to degradation of environmental contaminants.

Partition uptake of a brominated diphenyl ether by the edible plant root of white radish (Raphanus sativus L.).

Polybrominated diphenyl ethers (PBDEs) are of a class of emerging contaminants. In this study, the accumulation of 4-bromodiphenyl ether (BDE-3) by different parts of a live white radish was investigated. Different cultural media (hydroponics, silica sand, and soil) were used to sustain the radish plant during its uptake and in-plant translocation of BDE-3. The results showed that BDE-3 can be translocated from the roots to the aboveground organs and the accumulated levels of BDE-3 in different parts of the white radish followed the order for the three types of cultivation: fibrous roots > peels > main roots > leaves. The results were analyzed by the aid of the partition-limited model for the plant uptake. The relevant partition coefficients (KOC and Kd) and uptake parameters of BDE-3 with plant components (Kpt and Klip) were obtained for analyzing the BDE-3 distribution. The partition-limited model offers a significant insight into the uptakes of BDE-3 by the various components of live white radishes. The types of cultivation affected the total sorption level, translocation factors (TFs), extent to equilibrium (αpt), and root concentration factors (RCFs).