NanoFe3O4 accelerates anoxic biodegradation of 3, 5, 6-trichloro-2-pyridinol

Research progress on remediation of organochlorine pesticide contamination in soil

Deteriorated soil pollution has grown into a worldwide environmental concern over the years. Organochlorine pesticide (OCP) residues, featured with ubiquity, persistence and refractoriness, are one of the main pollution sources, causing soil degradation, fertility decline and nutritional imbalance, and severely impacting soil ecology. Furthermore, residual OCPs in soil may enter the human body along with food chain accumulation and pose a serious health threat. To date, many remediation technologies including physicochemical and biological ways for organochlorine pollution have been developed at home and abroad, but none of them is a panacea suitable for all occasions. Rational selection and scientific decision-making are grounded in in-depth knowledge of various restoration techniques. However, soil pollution treatment often encounters the interference of multiple factors (climate, soil properties, cost, restoration efficiency, etc.) in complex environments, and there is still a lack of systematic summary and comparative analysis of different soil OCP removal methods. Thus, to better guide the remediation of contaminated soil, this review summarized the most commonly used strategies for OCP removal, evaluated their merits and limitations and discussed the application scenarios of different methods. It will facilitate the development of efficient, inexpensive and environmentally friendly soil remediation strategies for sustainable agricultural and ecological development.

Identification of two possible metabolic pathways responsible for the biodegradation of 3, 5, 6-trichloro-2-pyridinol in Micrococcus luteus ML

3, 5, 6-Trichloro-2-pyridinol (TCP) is a metabolite of the insecticide chlorpyrifos and the herbicide triclopyr, and it is higher toxic than the parent compounds. Microbially-mediated mineralization appears to be the primary degradative pathway and the important biological process of detoxification. However, little information is available on TCP complete metabolic pathways and mechanisms. In this study, the degradation of TCP was studied with a novel strain Micrococcus luteus ML isolated from a stable TCP degrading microbiota. Strain ML was capable of degrading 61.6% of TCP (50 mg/L) and 35.4% of chlorpyrifos (50 mg/L) at 24 h and 48 h under the optimal conditions (temperature: 35 °C; pH: 7.0), respectively. It could also degrade 3, 5-dichloro-2-pyridone, 6-chloropyridin-2-ol, 2-hydroxypyridine and phoxim when provided as sole carbon and energy sources. Seven TCP intermediate metabolites were detected in strain ML and two possible degradation pathways of TCP were proposed on the basis of LC-MS analysis. Both the hydrolytic-oxidative dechlorination pathway and the denitrification pathway might be involved in TCP biodegradation by strain ML. To the best of our knowledge, this is the first report on two different pathways responsible for TCP degradation in one strain, and this finding also provides novel information for studying the metabolic mechanism of TCP in pure culture.

Biodegradation mechanism of chlorpyrifos by halophilic bacterium Hortaea sp. B15

For decades, most of the developing nations have relied on chlorpyrifos for insecticidal activity in the agriculture sector. It is a common chlorinated organophosphorus pesticide that has been widely used to control insects to protect plants. This study aimed to investigate the effects of environmental characteristics such as salinity, pH, temperature, and surfactant on Hortaea sp. B15 mediated degradation of chlorpyrifos as well as enzyme activity and metabolic pathway. The highest bacterial growth (4.6 × 10¹⁶ CFU/mL) was achieved after 20 h of incubation in a 100 mg/L chlorpyrifos amended culture. The fit model and feasible way to express the chlorpyrifos biodegradation kinetics in normal condition and optimized was a first-order rate equation, with an R² value of 0.95-0.98. The optimum pH for chlorpyrifos biodegradation was pH 9, which resulted in a high removal rate (91.1%) and a maximum total count of 3.8 × 10¹⁶ CFU/mL. Increasing the temperature over 40 °C may inhibit microbial development and biodegradation. There was no significant effect of culture salinity on degradation and bacterial growth. In the presence of non-ionic surfactant Tween 80, the maximum chlorpyrifos degradation (89.5%) and bacterial growth (3.8 × 10¹⁶ CFU/mL) was achieved. Metabolites such as 3,5,6-trichloropyridin-2-ol and 2-pyridinol were identified in the Hortaea sp. B15 mediated degradation of chlorpyrifos. According to the findings, Hortaea sp. B15 should be recommended for use in the investigation of in situ biodegradation of pesticides.

The changing C/N of aggressive aniline: Metagenomic analysis of pollutant removal, metabolic pathways and functional genes

In order to optimize the degradation of high-concentration aniline wastewater, the operation of sequencing batch bioaugmentation reactors with different aniline concentrations (200 mg/L, 600 mg/L, 1000 mg/L) was studied. The results showed that the removal rates of aniline and COD in the three reactors could reach 100%. When the aniline increased to 600 mg/L, the nitrogen removal efficiency reached the peak (51.85%). The increase of aniline inhibited the nitrification, while denitrification was enhanced due to the increase of C/N ratio. But this change was reversed by the toxicity of high concentrations of aniline. The metagenomic analysis showed that when the aniline concentration was 600 mg/L, the abundance distribution of microbial samples was more uniform. The improved of aniline concentration had led to the increase of aromatic compounds degradation metabolic pathways. In addition, the abundance of aniline degradation and nitrogen metabolism genes (dmpB, xylE, norB) was also promoted.

Toxicity evaluation of chlorpyrifos and its main metabolite 3,5,6-trichloro-2-pyridinol (TCP) to Eisenia fetida in different soils

The present study utilized a biomarker response method to evaluate the effect of 3,5,6-trichloro-2-pyridinol (TCP) in artificial and natural soils on Eisenia fetida after 7, 14, 28, 42 and 56 days exposure. Results indicated that TCP induced excessive reactive oxygen species, caused oxidative stress and DNA damage to Eisenia fetida. Biomarker responses were standardized to calculate the Integrated Biomarker Response (IBR) index. The IBR index of three enzymes (superoxide dismutase, catalase and glutathione S-transferase) activities showed that TCP induced the oxidative stress to E. fetida in red clay was stronger than in the other three soils. Specifically, chlorpyrifos exposure group showed a lower toxicity than TCP exposure group after 28 days exposure but a higher toxicity than TCP exposure group after 56 days exposure. Despite the deficiencies of this study, the above information is of great significance for assessing the risk of chlorpyrifos and its metabolite TCP pollution in soil ecosystems.

The multi-process reaction model and underlying mechanisms of 2,4,6-trichlorophenol removal in lab-scale biochar-microorganism augmented ZVI PRBs and field-scale PRBs performance

This work developed calcium alginate (CA) embedded zero-valent iron (ZVI@CA) and CA embedded biochar (BC) immobilized microorganism (BC&Cell@CA) gel beads as alternative to conventional Fe⁰ permeable reactive barriers for treating groundwater contaminated with 2,4,6-trichlorophenol (2,4,6-TCP). Lab-scale and field-scale biochar-microorganism augmented PRBs (Bio-PRBs) were constructed and tested. The underlying mechanisms were revealed by a multi-source data calibrated multi-process reaction model, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high-throughput sequencing. Moreover, calibrated advection-dispersion (a) coupled with the two-site sorption (K_d) and chemical-biological multi-process reaction (λ) model were used for revealing 2,4,6-TCP transport behavior and optimizing Bio-PRBs. Compared to that in the ZVI@CA (0.004 h^-1) system, the reaction rate (0.011 h^-1) of 2,4,6-TCP increased by 175% in the combined chemical-biological batch system. Moreover, chemical-biological augmentation significantly improved the retardation effect of Bio-PRBs for 2,4,6-TCP. It came from that chemical-biological augmentation significantly decreased the dispersivity a (0.53 to 0.20 cm), and increased the distribution coefficient K_d (2.20 to 19.00 cm³ mg^-1), the reaction rate λ (2.40 to 3.60 day^-1), and the fraction (30% to 80%) of first-order kinetic sorption of 2,4,6-TCP in the lab-scale one-dimensional Bio-PRBs. Moreover, versatile functional bacteria Desulfitobacterium was crucial in the transformation of Fe (III) iron oxides. The diversity and richness of archaea in the reaction solution were improved by ZVI@CA gel beads addition. Furthermore, the field-scale reaction system was designed to remediate the chlorinated organic compounds and Benzene Toluene Ethylbenzene & Xylene contaminated groundwater in a pesticide factory site. The field test results demonstrated it is a promising technology to construct vertical reaction columns or horizontal Bio-PRBs for the efficient remediation of actually contaminated groundwater.

New insights into the biodegradation of chlorpyrifos by a novel bacterial consortium: Process optimization using general factorial experimental design

Himalayan mountains are subjected to the intensive and unjudicial application of chlorpyrifos (CP) in agricultural practices; hence it has spurred concerns over food safety and environmental consequences. These low-temperature mountainous regions are foremost ecosystems, representing the large-scale distribution of cold trapped CP residues. A bacterial consortium ECO-M was formed by isolating the CP degrading bacterial strains viz Agrobacterium tumefaciens strain ECO1, Cellulosimicrobium funkei strain ECO2, Shinella zoogloeoides strain ECO3 and Bacillus aryabhattai strain ECO4. At an initial concentration of 50 mg L^-1, consortium ECO-M degraded 100% of CP within 6 days. Emergence and subsequent degradation of the two metabolites, 3, 5, 6-trichloro-2-pyridinol (TCP) and 2-hydroxypyridine were confirmed by GC-MS analysis. A degradation pathway of CP by isolated strains has been proposed. A general factorial experimental design was effectuated to prognosticate the optimum biodegradation by manifesting the optimal biological and physicochemical factors. Fitness of the experimental design was affirmed experimentally by employing optimized factors i.e., temperature 30 °C, CP concentration 50 mg L^-1 and an inoculum size of 10% (v/v). The model appropriacy and the rationality of the optimization procedure were appraised by installing an in-situ microcosms experiment using the real contaminated soil collected from the Himalayan mountain ecosystem. The augmentation culture seems to be effectively conspicuous in stimulating maximum degradation up to 94.3% in the CP contaminated soil.

Fate of environmental pollutants: A review

A review of the literature published in 2019 on topics associated with the fate of environmental pollutants is presented. Environmental pollutants covered include pharmaceuticals, antibiotic-resistant bacteria and genes, pesticides and veterinary medicines, personal care products and emerging pollutants, PFAS, microplastics, nanomaterials, heavy metals and radionuclides, nutrients, pathogens and indicator organisms, and oil and hydrocarbons. For each pollutant, the occurrence in the environment and/or their fate in engineered as well as natural systems in matrices including water, soil, wastewater, stormwater, runoff, and/or manure is presented based on the published literature. The review includes current developments in understanding pollutants in natural and engineered systems, and relevant physico-chemical processes, as well as biological processes.