Emergence of per- and poly-fluoroalkyl substances (PFAS) and advances in the remediation strategies.

A group of fluorinated organic molecules known as per- and poly-fluoroalkyl substances (PFAS) have been commonly produced and circulated in the environment. PFAS, owing to multiple strong CF bonds, exhibit exceptional stability and possess a high level of resistance against biological or chemical degradation. Recently, PFAS have been identified to cause numerous hazardous effects on the biotic ecosystem. As a result, extensive efforts have been made in recent years to develop effective methods to remove PFAS. Adsorption, filtration, heat treatment, chemical oxidation/reduction, and soil washing are a few of the physicochemical techniques that have shown their ability to remove PFAS from contaminated matrixes. However these methods also carry significant drawbacks, including the fact that they are expensive, energy-intensive, unsuitable for in-situ treatment, and requirement to be carried under dormant conditions. The metabolic products released upon PFAS degradation are largely unknown, despite the fact that thermal disintegration methods are widely used. In contrast to physical and chemical methods, biological degradation of PFAS has been regarded as efficient method. However, PFAS are difficult to instantly and completely metabolize through biological methods due to the limitations of biocatalytic mechanisms. Nevertheless, cost, easy-to-operate and environmentally safe are some of the advantages over its counterpart. The present review comprehensively discusses the occurrence of PFAS, the state-of-the science of remediation technologies and approaches applied, and the remediation challenges. The article also focuses on the future research directions toward the development of effective methods for PFAS-contaminated site in-situ treatment.

Comparative Evaluation of Chlorella vulgaris and Anabaena variabilis for Phycoremediation of Polluted River Water: Spotlighting Heavy Metals Detoxification.

This study investigated the phycoremediation abilities of Chlorella vulgaris (microalga) and Anabaena variabilis (cyanobacterium) for the detoxification of polluted river water. Lab-scale phycoremediation experiments were conducted for 20 days at 30 °C using the microalgal and cyanobacterial strains and water samples collected from the Dhaleswari river in Bangladesh. The physicochemical properties such as electrical conductivity (EC), total dissolved solids (TDS), biological oxygen demand (BOD), hardness ions, and heavy metals of the collected water samples indicated that the river water is highly polluted. The results of the phycoremediation experiments demonstrated that both microalgal and cyanobacterial species significantly reduced the pollutant load and heavy metal concentrations of the river water. The pH of the river water was significantly raised from 6.97 to 8.07 and 8.28 by C. vulgaris and A. variabilis, respectively. A. variabilis demonstrated higher efficacy than C. vulgaris in reducing the EC, TDS, and BOD of the polluted river water and was more effective at reducing the pollutant load of SO42- and Zn. In regard to hardness ions and heavy metal detoxification, C. vulgaris performed better at removing Ca2+, Mg2+, Cr, and Mn. These findings indicate that both microalgae and cyanobacteria have great potential to remove various pollutants, especially heavy metals, from the polluted river water as part of a low-cost, easily controllable, environmentally friendly remediation strategy. Nevertheless, the composition of polluted water should be assessed prior to the designing of microalgae- or cyanobacteria-based remediation technology, since the pollutant removal efficiency is found to be species dependent.

A microbial consortium led by a novel Pseudomonas species enables degradation of carbon tetrachloride under aerobic conditions.

Carbon tetrachloride (CT) is a recalcitrant and high priority pollutant known for its toxicity, environmental prevalence, and inhibitory activities. Although much is known about anaerobic CT biodegradation, microbial degradation of CT under aerobic conditions has not yet been reported. This study reports for the first time the enrichment of a stable aerobic CT-degrading bacterial consortium, from a CT-contaminated groundwater sample, capable of co-metabolically degrading 30 µM of CT within a week. A Pseudomonas strain (designated as Stari2) that is the predominant bacterium in this consortium was isolated, and further characterization showed that this bacterium can tolerate and co-metabolically degrade up to 5 mM of CT under aerobic conditions in the presence of different carbon/energy sources. The CT biodegradation profiles of strain Stari2 and the consortium were found to be identical, while no significant positive correlation between strain Stari2 and other bacteria was observed in the consortium during the period of higher CT biodegradation. These results confirmed that the isolated Pseudomonas strain Stari2 is the key player in the consortium catalyzing the biodegradation of CT. No chloroform (CF) or other chlorinated compound was detected during the cometabolism of CT. The whole genome sequencing of strain Stari2 showed that it is a novel Pseudomonas species. The findings demonstrated that biodegradation of CT under aerobic conditions is feasible, and the isolated CT-degrader Pseudomonas sp. strain Stari2 has a great potential for in-situ bioremediation of CT-contaminated environments.

Efficient biodegradation of 1,4-dioxane commingled with additional organic compound: Role of interspecies interactions within consortia.

Microbial consortia-mediated biodegradation of 1,4-dioxane (1,4-D), an emerging water contaminant, is always a superior choice over axenic cultures. Thus, better understanding of the functions of coexisting microbes and their interspecies interactions within the consortia is crucial for predicting biodegradation efficiency and designing efficient 1,4-D-degrading microbial consortia. This study evaluated how microbial community compositions and interspecies interactions govern the microbial consortia-mediated 1,4-D biodegradation by investigating the biodegradability and microbial community dynamics of both enriched (N112) and synthetic (SCDs and SCDNs) microbial consortia in the absence or presence of additional organic compound (AOC). In the absence of AOC, N112 exhibited 100% 1,4-D biodegradation efficiency at a rate of 12.5 mg/L/d, whereas the co-occurrence of AOC resulted in substrate-dependent biodegradation inhibition and thereby reduced the biodegradation efficiency and activity (2.0-10.0 mg/L/d). The coexistence and negative influence of certain low-abundant non-degraders on both 1,4-D-degraders and key non-degraders in N112 was identified as the prime cause behind such biodegradation inhibition. Comparing with N112, SCDN-1 composed of 1,4-D-degraders and key non-degraders significantly improved the 1,4-D biodegradation efficiency in the presence of AOC, confirming the absence of negative influence of low-abundant non-degraders and cooperative interactions between 1,4-D-degraders and key non-degraders in SCDN-1. On the contrary, both two-species and three-species SCDs comprised of only 1,4-D-degraders resulted in lower 1,4-D biodegradation efficiency as compared to SCDN-1 under all treatment conditions, while max. 91% 1,4-D biodegradation occurred by SCDs in the absence of AOC. These results were attributed to the negative interaction among 1,4-D-degraders and the absence of complementary roles of key non-degraders in SCDs. The findings improve our understanding of how interspecies interactions can regulate the intrinsic abilities and functions of coexisting microbes during biodegradation in complex environments and provide valuable guidelines for designing highly efficient and robust microbial consortia for practical bioremediation of 1,4-D like emerging organic contaminants.

Presence of toxic metals in rice with human health hazards in Tangail district of Bangladesh.

Rice is the staple food of Bangladeshi people and is consumed at least twice a day. Thus, the presence of toxic metals in rice grains has become a major public health concern in Bangladesh. The present research was conducted to investigate the concentrations of toxic metals in rice grains and their possible human health risks in the Tangail district of Bangladesh. Toxic metals were measured by using an inductively coupled plasma mass spectrometer (ICP-MS), and the mean concentrations of toxic metals in rice samples were found in order of Cr > Pb > Ni > As > Cu > Cd. The concentrations of Cr, Pb, As, and Cd in the studied rice grain samples exceeded the FAO/WHO standard values for food samples by 100%, whereas the Ni concentrations by 10%. The principal component analysis (PCA) revealed significant anthropogenic contributions of Cr, Ni, As, and Pb concentrations in rice grains. The metal concentrations in rice grain samples showed strong significant correlations by forming primary clusters with each other. The estimated daily intake (EDI) values of Cr, Ni, As, Cd, and Pb from all samples were higher than the maximum tolerable daily intake (MTDI) allowed. The total targeted hazard quotient (TTHQ) values of Cu, Ni, As, Cd, and Pb also exceeded the threshold value of 1.00, indicating a potential non-carcinogenic risk. The estimated target carcinogenic risk of As was higher than the USEPA threshold level 10-4 (0.0001) indicating increased risk of cancer for adults and children in the study area.

Potentially toxic elements in street dust from an urban city of a developing country: ecological and probabilistic health risks assessment.

Anthropogenic activities in and around the urban highways followed by aerodynamic processing generate street dusts, which can cause adverse health effects through different exposure pathways. Hence, considering the high degree of industrialization, concomitant unplanned urbanization, and rapid demographic augmentation, street dust samples from an urban city (Gazipur, Bangladesh) were investigated in terms of potentially toxic elements (using ICP-MS) to evaluate their ecological and health risks. Mean concentrations (± SD) of lead (Pb), copper (Cu), chromium (Cr), cadmium (Cd), zinc (Zn), nickel (Ni), and arsenic (As) in the analyzed air-dried samples were 40.9 ± 13.6, 44.9 ± 15.4, 83.3 ± 19.0, 9.1 ± 5.4, 239.1 ± 34.7, 33.5 ± 10.4, and 2.1 ± 0.8 mg/kg, respectively with heterogeneous distribution which were 0.2 (As) to 82.7 (Cd) times higher than the available internationally recommended limits. Element-specific environmental indices revealed that contamination levels followed the descending order as Cd > Zn > Cu > Pb > Cr > Ni > As, whereas individual ecological risks followed the descending order as Cd > Cu > Pb > Ni > Zn > Cr > As. Sampling site-specific composite indices indicated that sampling sites with high loadings of traffic, population, industrialization, and urbanization were mostly polluted. Multivariate statistical approaches also deduced the similar origins of the studied elements. In terms of the investigated elements, the study site possessed high potential ecological risks, although non-carcinogenic and carcinogenic risks through different pathway's exposures seem insignificant, where children are more vulnerable than adults.

Isolation and Characterization of Novel Bacteria Capable of Degrading 1,4-Dioxane in the Presence of Diverse Co-Occurring Compounds.

Biodegradation is found to be a promising, cost-effective and eco-friendly option for the treatment of industrial wastewater contaminated by 1,4-dioxane (1,4-D), a highly stable synthetic chemical and probable human carcinogen. This study aimed to isolate, identify, and characterize metabolic 1,4-D-degrading bacteria from a stable 1,4-D-degrading microbial consortium. Three bacterial strains (designated as strains TS28, TS32, and TS43) capable of degrading 1,4-D as a sole carbon and energy source were isolated and identified as Gram-positive Pseudonocardia sp. (TS28) and Gram-negative Dokdonella sp. (TS32) and Afipia sp. (TS43). This study, for the first time, confirmed that the genus Dokdonella is involved in the biodegradation of 1,4-D. The results reveal that all of the isolated strains possess inducible 1,4-D-degrading enzymes and also confirm the presence of a gene encoding tetrahydrofuran/dioxane monooxygenase (thmA/dxmA) belonging to group 5 soluble di-iron monooxygenases (SDIMOs) in both genomic and plasmid DNA of each of the strains, which is possibly responsible for the initial oxidation of 1,4-D. Moreover, the isolated strains showed a broad substrate range and are capable of degrading 1,4-D in the presence of additional substrates, including easy-to-degrade compounds, 1,4-D biodegradation intermediates, structural analogs, and co-contaminants of 1,4-D. This indicates the potential of the isolated strains, especially strain TS32, in removing 1,4-D from contaminated industrial wastewater containing additional organic load. Additionally, the results will help to improve our understanding of how multiple 1,4-D-degraders stably co-exist and interact in the consortium, relying on a single carbon source (1,4-D) in order to develop an efficient biological 1,4-D treatment system.

Cadmium contamination in agricultural soils of Bangladesh and management by application of organic amendments: evaluation of field assessment and pot experiments.

In recent years, cadmium (Cd) contamination in agricultural soils and its subsequent transfer to crops is one of the high-priority environmental and public health issues of global concern, especially in densely populated developing countries like Bangladesh. However, no effective strategy has been introduced or implemented yet to manage Cd-contaminated soils in order to sustain agricultural production with no human health risks. In this study, agricultural soil samples were collected from 60 locations of 10 upazilas from Tangail district to assess the extent of soil Cd contamination. The Cd concentration ranged from 0.83 to 4.08 mg kg-1 with a mean of 2.17 mg kg-1 in topsoil (0-15 cm), and from 0.67 to 3.74 mg kg-1 with a mean of 2.10 mg kg-1 in subsoil (16-30 cm). The values of contamination factor (CF) indicated that all the sampling locations were found to be highly contaminated with Cd. Pot trials with the application of different doses of biochar and vermicompost in Cd-contaminated soil (0.8 mg kg-1 Cd) revealed that integrated application of biochar (5 t ha-1) and vermicompost (5 t ha-1) was the best treatment that significantly (p < 0.05) reduced plant Cd concentration (72%) and increased the biomass of experimental crop, Red amaranth (Amaranthus cruentus). This combined treatment also significantly reduced the uptake of Cr (37%) when co-contamination was present. The study suggests the application of biochar (5 t ha-1) in combination with vermicompost (5 t ha-1) to reduce human health risk and increase crop production when the soil is loamy sand in texture.

Impacts of nationwide lockdown due to COVID-19 outbreak on air quality in Bangladesh: a spatiotemporal analysis.

In Bangladesh, a nationwide lockdown was imposed on 26 March 2020, due to the COVID-19 pandemic. Due to restricted emissions, it was hypothesized that the air quality has been improved during lockdown throughout the country. The study is intended to assess the impact of nationwide lockdown measures on air quality in Bangladesh. We analyzed satellite data for four different air pollutants (NO2, SO2, CO, and O3) to assess the changes in the atmospheric concentrations of pollutants in major cities as well as across the country. In this study, the concentrations of NO2, SO2, CO, and O3 from 1 February to 30 May of the year 2019 and 2020 were analyzed. The average SO2 and NO2 concentrations were decreased by 43 and 40%, respectively, while tropospheric O3 were found to be increased with a maximum of > 7%. Among the major cities, Dhaka, Gazipur, Chattogram, and Narayanganj were found to be more influenced by the restricted emissions. In Dhaka, NO2 and SO2 concentrations were decreased approximately by 69 and 67%, respectively. Our analysis reveals that NO2 concentrations are highly correlated with the regional COVID-19 cases (r = 0.74). The study concludes that the lockdown measures significantly reduced air pollution because of reduced vehicular and industrial emissions in Bangladesh.

Enrichment and Analysis of Stable 1,4-dioxane-Degrading Microbial Consortia Consisting of Novel Dioxane-Degraders.

Biodegradation of 1,4-dioxane, a water contaminant of emerging concern, has drawn substantial attention over the last two decades. A number of dioxane-degraders have been identified, though many of them are unable to metabolically utilize 1,4-dioxane. Moreover, it is considered more preferable to use microbial consortia rather than the pure strains, especially in conventional bioreactors for industrial wastewater treatment. In the present study, a stable 1,4-dioxane-degrading microbial consortium was enriched, namely 112, from industrial wastewater by nitrate mineral salt medium (NMSM). The consortium 112 is capable of utilizing 1,4-dioxane as a sole carbon and energy source, and can completely degrade 1,4-dioxane up to 100 mg/l. From the consortium 112, two 1,4-dioxane-degrading bacterial strains were isolated and identified, in which the Variovorax sp. TS13 was found to be a novel 1,4-dioxane-degrader that can utilize 100 mg/l of 1,4-dioxane. The efficacy of the consortium 112 was increased significantly when we cultured the consortium with mineral salt medium (MSM). The new consortium, N112, could utilize 1,4-dioxane at a rate of 1.67 mg/l·h. The results of the ribosomal RNA intergenic spacer analysis (RISA) depicted that changes in the microbial community structure of consortium 112 was the reason behind the improved degradation efficiency of consortium N112, which was exhibited as a stable and effective microbial consortium with a high potential for bioremediation of the dioxane-impacted sites and contaminated industrial wastewater.