Liang Meng

The increasing contamination of global groundwater by organic chlorine solvents poses a major threat to environmental and human health; however, there is a lack of structurally stable and effective materials for removing organic chlorine pollutants. In this study, biochar-based composite microspheres embedded with zero-valent iron (ZVI) and soybean oil were prepared and their effects on 1,1,1-trichloroethane (1,1,1-TCA) removal and the microbial community in simulated groundwater system were investigated. The composite microspheres achieved a remarkable 85.79% removal rate of 1,1,1-TCA after 360 h in groundwater, which was 1.63 times higher than that of ZVI + biochar microspheres (52.69%) and 1.33 times higher than that of soybean oil + biochar microspheres (64.50%). The composite microspheres also significantly reduced the oxidation–reduction potential to − 248.52 mV and maintained a neutral pH range of 6.8–7.2, thereby creating favorable conditions for long-term reductive dechlorination. The surface morphology of the composite was stable during degradation, reflecting its potential for long-term usage. The rich network structure of microspheres and the micropore structure of the biochar were conducive to the capturing of pollutants, safety of microorganisms, and slow release of organic carbon. 16S rDNA sequencing demonstrated that the composite significantly affected the diversity and stability of the microbial community, especially promoting the growth and interaction of dechlorinating and fermentative microorganisms in the groundwater and composite microspheres. The preliminary removal mechanisms included biochar-induced adsorption and ZVI-induced chemical reduction in the early stage and biochemical coupling of dechlorination in the middle and last stages. The biochar-based composite microspheres significantly enhanced the effectiveness and consistency of 1,1,1-TCA removal, potentially being applied to in situ enhanced reductive dechlorination of organochlorine solvents in site groundwater. Moreover, considering the abundant porous structure and easy availability of biochar, it can effectively promote the sustainability and cost-efficiency of the microspheres during application. Graphical abstract

2,6-Dichloro-1,4-benzoquinone (2,6-DCBQ) is an emerging chlorinated disinfection byproduct (DBP) in bodies of water. However, this compound poses an unknown toxic effect on cyanobacteria. In this study, the toxicological mechanisms of 2,6-DCBQ in Microcystis aeruginosa (M. aeruginosa) were investigated through physiological and nontargeted metabolomic assessments. The results show that 2,6-DCBQ inhibited the growth of M. aeruginosa, reduced its photosynthetic pigment and protein contents, increased the levels of reactive oxygen species, damaged the antioxidant defense system, and aggravated the cytomembrane. Meanwhile, 2,6-DCBQ stimulated the production and release of microcystin-LR (MC-LR) and altered the transcripts of genes associated with its synthesis (mcyA, mcyD) and transport (mcyH). In addition, nontargeted metabolomics of M. aeruginosa cells exposed to 0.1 mg/L 2,6-DCBQ identified 208 differential metabolites belonging to 10 metabolic pathways and revealed the considerable interference caused by 2,6-DCBQ among ABC transporters, the two-component system, and folate biosynthesis. This study deepens the understanding of the physiological and nontargeted metabolomic responses of M. aeruginosa exposed to 2,6-DCBQ, offers insights into the toxic effect of 2,6-DCBQ on M. aeruginosa, and provides a theoretical basis for the ecological risk assessment of emerging DBPs in accordance with water quality criteria.

Taipu River is an important transboundary river and drinking water source in the Yangtze River Delta, China. This study collected 15 topsoil samples along the Taipu River banks and subsequently determined the polycyclic aromatic hydrocarbons (PAHs) concentrations, sources, and ecological and health risks. The sum of toxic 15 PAHs concentrations ranged from 83.13 to 28342.53 ng/g, with a mean of 2828.69 ng/g. High molecular weight (HMW) PAHs were the dominant components and Indene (1,2,3, -cd) benzopyrene (InP) accounted for the highest proportion in individuals. The average PAH concentration in residential land was the highest, followed by those in industrial and agricultural land. The PAH concentration was positively related to contents of total carbon, total nitrogen, ammonium nitrogen, and aminopeptidase activity in soils. The mixed combustion of biomass, coal, and petroleum and traffic emissions could be the primary PAH contributors. The total PAHs at over half of sampling points had relatively high risk quotients and incremental lifetime cancer risk (ILCR) values, posing potential or great ecological threats and health risks.

1,1,1-Trichloroethane (1,1,1-TCA) is a typical organochloride solvent in groundwater that poses threats to human health and the environment due to its carcinogenesis and bioaccumulation. In this study, a novel composite with nanoscale zero-valent iron (nZVI) supported by polycaprolac-tone (PCL)-modified biochar (nZVI@PBC) was synthesized via solution intercalation and liquid-phase reduction to address the 1,1,1-TCA pollution problem in groundwater. The synergy effect and improvement mechanism of 1,1,1-TCA removal from simulated groundwater in the presence of nZVI@PBC coupling with Shewanella putrefaciens CN32 were investigated. The results were as follows: (1) The composite surface was rough and porous, and PCL and nZVI were loaded uniformly onto the biochar surface as micro-particles and nanoparticles, respectively; (2) the optimal mass ratio of PCL, biochar, and nZVI was 1:7:2, and the optimal composite dosage was 1.0% (w/v); (3) under the optimal conditions, nZVI@PBC + CN32 exhibited excellent removal performance for 1,1,1-TCA, with a removal rate of 82.98% within 360 h, while the maximum removal rate was only 41.44% in the nZVI + CN32 treatment; (4) the abundance of CN32 and the concentration of adsorbed Fe(II) in the nZVI@PBC + CN32 treatment were significantly higher than that in control treatments, while the total organic carbon (TOC) concentration first increased and then decreased during the culture process; (5) the major improvement mechanisms include the nZVI-mediated chemical reductive dechlorination and the CN32-mediated microbial dissimilatory iron reduction. In conclusion, the nZVI@PBC composite coupling with CN32 can be a potential technique to apply for 1,1,1-TCA removal in groundwater.