Toxicity of hydroxylated polychlorinated biphenyls (HO-PCBs) using the bioluminescent assay Microtox(®)

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge. The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Transformation of hydroxylated polychlorinated biphenyls by bacterial 2-hydroxybiphenyl 3-monooxygenase

Monohydroxylated PCBs (OH-PCBs) are an (eco)toxicologically significant group of compounds, as they arise from the oxidation of polychlorinated biphenyls (PCBs) and, at the same time, may exert even more severe toxic effects than their parent PCB molecules. Despite having been widely detected in environmental samples, plants, and animals, information on the fate of OH-PCBs in the environment is scarce, including on the enzymatic machinery behind their degradation. To date, only a few bacterial taxa capable of OH-PCB transformation have been reported. In this study, we aimed to obtain a deeper insight into the transformation of OH-PCBs in soil bacteria and isolated a Pseudomonas sp. strain P1B16 based on its ability to use o-phenylphenol (2-PP) which, when exposed to the Delor 103-derived OH-PCB mixture, depleted a wide spectrum of mono-, di, and trichlorinated OH-PCBs. In the P1B16 genome, a region designated as hbp was identified, which bears a set of putative genes involved in the transformation of OH-PCBs, namely hbpA encoding for a putative flavin-dependent 2-hydroxybiphenyl monooxygenase, hbpC (2,3-dihydroxybiphenyl-1,2-dioxygenase), hbpD (2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase), and the transcriptional activator-encoding gene hbpR. The hbpA coding sequence was heterologously expressed, purified, and its substrate specificity was investigated towards the Delor 103-derived OH-PCB mixture, individual OH-PCBs, and multiple (chlorinated) phenolics. Apart from 2-PP and 2-chlorophenol, HbpA was also demonstrated to transform a range of OH-PCBs, including a 3-hydroxy-2,2',4',5,5'-pentachlorobiphenyl. Importantly, this is the first direct evidence of HbpA homologs being involved in the degradation of OH-PCBs. Moreover, using a P1B16-based biosensor strain, the specific induction of hbp genes by 2-PP, 3-phenylphenol, 4-phenylphenol, and the OH-PCB mixture was demonstrated. This study provides direct evidence on the specific enzymatic machinery responsible for the transformation of OH-PCBs in bacteria, with many implications in ecotoxicology, environmental restoration, and microbial ecology in habitats burdened with PCB contamination.

Laccases—Versatile Enzymes Used to Reduce Environmental Pollution

The accumulation of waste and toxic compounds has become increasingly harmful to the environment and human health. In this context, the use of laccases has become a focus of interest, due to the properties of these versatile enzymes: low substrate specificity, and water formation as a non-toxic end product. Thus, we begin our study with a general overview of the importance of laccase for the environment and industry, starting with the sources of laccases (plant, bacterial and fungal laccases), the structure and mechanism of laccases, microbial biosynthesis, and the immobilization of laccases. Then, we continue with an overview of agro-waste treatment by laccases wherein we observe the importance of laccases for the biodisponibilization of substrates and the biodegradation of agro-industrial byproducts; we then show some aspects regarding the degradation of xenobiotic compounds, dyes, and pharmaceutical products. The objective of this research is to emphasize and fully investigate the effects of laccase action on the decomposition of lignocellulosic materials and on the removal of harmful compounds from soil and water, in order to provide a sustainable solution to reducing environmental pollution.

Biodegradation of trichlorobiphenyls and their hydroxylated derivatives by Rhodococcus-strains

A possibility of using a complex approach is considered to explain features of biodestruction of polychlorinated biphenyls (PCBs), which are known to be persistent organic pollutants. The approach comprises the following main stages: (i) chemical modification of chloroarenes by hydroxylation and (ii) bacterial degradation of the hydroxylated derivatives. This approach is applicable to individual trichlorobiphenyls (PCB 29, PCB 30) and to a widespread mixture Trikhlorbifenil (analog of Aroclor 1242 and Delor 103). As bacterial strain destructors, the Rhodococcus-strains (КТ112-7, СН628, P25) were used. It was established that the main metabolites of microbial biodegradation of both polychlorobiphenyls and their hydroxy derivatives are polychloro- and hydroxy(polychloro)benzoic acids, which allows an assumption to be made about possible further biodegradation of these compounds down to the products of the base exchange reaction in a cell: water, carbon dioxide and chlorine compounds. The study discusses the effect that the structure of PCBs congeners causes on the conversion by hydroxylation, on the biodegradation rate of both PCBs and their hydroxy derivatives, and on the metabolite formation levels.

Comparative toxicity reduction potential of UV/sodium percarbonate and UV/hydrogen peroxide treatments for bisphenol A in water: An integrated analysis using chemical, computational, biological, and metabolomic approaches

Bisphenol A (BPA) is a common industrial chemical with significant adverse impacts on biological systems as an environmental contaminant. UV/hydrogen peroxide (UV/H₂O₂) is a well-established technology for BPA treatment in water while UV/sodium percarbonate (UV/SPC) is an emerging technology with unclear biological impacts of treated effluent. Therefore, in this study, the toxicity evaluation of BPA solution treated with UV/H₂O₂ and UV/SPC was preformed and compared based on transformation products (TPs) profile, quantitative structure-activity relationship (QSAR), Escherichia coli (E. coli) toxicity assays, and metabolomic analysis. TPs with hydroxylation, double-ring split, and single-ring cleavage were generated from BPA during the treatments with both technologies, but TPs with quinonation were specifically detected in UV/H₂O₂ treated solution at the UV dose of 1470 mJ cm^-2. QSAR prediction based on TPs profile (excluding benzoquinone TPs) suggested that UV/H₂O₂ and UV/SPC treatments of BPA may increase matrix toxicity due to the formation of multi-hydroxylated TPs; however decreased bioaccumulation potential of all TPs may mitigate the increase of toxicity by reducing the chance of TPs to reach the concentration of toxicity threshold. In vivo assays with E. coli showed inhibited cell growth, arrested cell cycle, and increased cell death in BPA solution treated with UV/H₂O₂ at the UV dose of 1470 mJ cm^-2. Metabolomic analysis indicated that BPA solution treated with UV/H₂O₂ at UV dose of 1470 mJ cm^-2 impacted E. coli metabolism differently than other solutions with unique inhibition on glycerolipid metabolism. Moreover, BPA interfered in various metabolic pathways including alanine, aspartate and glutamate metabolism, starch and sucrose metabolism, pentose phosphate pathway, and lysine degradation, which were mitigated after the treatments. UV/SPC showed advantage over UV/H₂O₂ of attenuated impact on butanoate metabolism with UV irradiation. This study has generated valuable data for better understanding of biological impacts of BPA and its solutions treated with UV/H₂O₂ or UV/SPC, thus providing insights for their application prospect for water and wastewater treatment.

Screening and metabolic potential of fungal strains isolated from contaminated soil and sediment in the polychlorinated biphenyl degradation

Polychlorinated biphenyls (PCBs) are widespread persistent pollutants deleterious for environment and very dangerous for human kind. As the bioremediation of PCB polluted sites by model white-rot fungi is still unsatisfactory, the use of efficient native strains which have the natural capacity to develop on polluted sites may constitute a relevant alternative strategy. In this study, we isolated 12 fungal strains from PCB contaminated soil and sediment, improved the screening method to obtain the most efficient ones in biodegradation and detoxification of PCBs and characterized potential underlying enzymatic activities. Four strains Penicillium chrysogenum, P. citreosulfuratum, P. canescens and Aspergillus jensenii, showed remarkable biodegradation capacities, greater than 70%. The remaining PCB-toxicity of their culture, including that of Trametes versicolor and Acremonium sclerotigenum, which present interesting ecological and metabolic properties, was studied. Only P. canescens was able to significantly reduce the toxicity related to PCBs and their metabolites. The enzymatic activities induced by PCBs were different according to the strains, namely laccases in T. versicolor and peroxidases in Ac. sclerotigenum. Our promising results show that the use of native fungal strains can constitute an effective strategy in the depollution of PCB polluted sites.

Biodegradability of hydroxylated derivatives of commercial polychlorobiphenyls mixtures by Rhodococcus-strains

For the first time, investigations are is carried out for the interactions of hydroxylated polychlorobiphenyls (HO-PCBs) mixtures, which were obtained from PCBs commercially available under the trade name Sovol, with the Rhodococcus (R.) strains. It is established that the HO-PCBs mixtures containing basic products within the range of 83.2-95.8% cause a toxic effect on the growth of R. wratislaviensis KT112-7, R. wratislaviensis CH628, R. ruber P25 strains. The inhibitory concentration (IC50) was varied within the range of 30-490 mg/l. For the first time, it is found that the bacterial strains can use HO-PCBs as a source of carbon with no co-substrate added. The strains are shown to degrade 95.5-100% of the HO-PCBs mixtures at a concentration of 0.1 g/l during 14 days. It is demonstrated that HO-PCBs degrading occurs following the classical bacterial pathway of transforming biphenyl/PCB. However, the HO-PCBs metabolites, which are substituted benzoic acids, are not the final products of the transformation and are subjected to further degrading by the strains. Therefore, the R. wratislaviensis KT112-7, R. wratislaviensis CH628, and R. ruber P25 strains are shown to degrade the HO-PCBs mixtures efficiently and are found to be stable to their toxic action.

An unexpected discovery of 1,4-benzoquinone as a lipophilic mediator for toxicity detection in water

Since most toxicological risk assessments are based on individual single-species tests, there is uncertainty in extrapolating these results to ecosystem assessments. Herein, we successfully developed a mediated microbial electrochemical biosensor with mixed microorganisms for toxicity detection by microelectrode array (MEA). In order to fully mobilize all the mixed microorganisms to participate in electron transfer to amplify the current signal, 1,4-benzoquinone (BQ) was used as the lipophilic mediator to mediate the intracellular metabolic activities. Hydrophilic K₃[Fe(CN)₆] was employed as an extracellular electron acceptor to transport electrons from hydroquinone (HQ) to the working electrode. Under the optimal conditions of 50 mM phosphate buffer solution (PBS), 0.4 mM BQ, 10 mM K₃[Fe(CN)₆] and OD₆₀₀ = 0.5 bacteria concentration, the half-maximal inhibitory concentration (IC₅₀) values measured with the composite-mediated respiration (CM-RES) of BQ-K₃[Fe(CN)₆] for Cu²⁺, Cd²⁺ and Zn²⁺ were 5.95, 7.12 and 8.86 mg L^-1, respectively. IC₅₀ values obtained with the single mediator K₃[Fe(CN)₆] were 2.34, 5.88 and 2.42 mg L^-1 for the same samples. The results indicate that the biosensor with the single mediator K₃[Fe(CN)₆] had higher sensitivity to heavy metal ions than the biosensor with composite mediators. After verification, we found that the addition of BQ cannot amplify the current. The IC₅₀ value of 0.89 mg L^-1 for BQ was obtained using K₃[Fe(CN)₆] as the single mediator. This suggests that BQ is highly toxic, which explained why the sensitivity of the biosensor with the combined mediator BQ-K₃[Fe(CN)₆] was lower than that of the biosensor with the single mediator K₃[Fe(CN)₆]. At the same time, this also implies that toxicity itself cannot be ignored when it is used as an electronic mediator in a mediated microbial electrochemical biosensor.

Removal of persistent organic pollutants (POPs) from waters and wastewaters by the use of ionizing radiation

The most important advantages of the use of ionizing radiation over other AOPs are exceptionally efficient in situ generation of very reactive oxidizing free radicals ^•OH from water radiolysis and very unique simultaneous generation of strongly reducing hydrated electrons. They allow to carry out Advanced Oxidation and Reduction Processes (AO/RPs) simultaneously. Carrying out only oxidative or reductive processes is also possible by the use of appropriate scavengers of free radicals in irradiated solutions. For the application of these processes for environmental protection purposes gamma-rays from radioisotope sources or beams of accelerated electrons are most commonly used. In the case of particularly resistant POPs some chemical additives to the irradiated solutions may enhance the yield of decomposition. This review based on 125 references reported so far presents the applications of the discussed technology in removing POPs from waters and wastewaters, including pesticides listed among POPs, dioxins, polychlorinated biphenyls, polycyclic aromatic hydrocarbons and selected perfluorinated surfactants.

Autophagy role in environmental pollutants exposure

During the last decades, the potential harmfulness derived from the exposure to environmental pollutants has been largely demonstrated, with associated damages ranging from geno- and cyto-toxicity to tissue malfunction and alterations in organism physiology. Autophagy is an evolutionarily-conserved cellular mechanism essential for cellular homeostasis, which contributes to protect cells from a wide variety of intracellular and extracellular stressors. Due to its pivotal importance, its correct functioning is directly linked to cell, tissue and organismal fitness. Environmental pollutants, particularly industrial compounds, are able to impact autophagic flux, either by increasing it as a protective response, by blocking it, or by switching its protective role toward a pro-cell death mechanism. Thus, the understanding of the effects of chemicals exposure on autophagy has become highly relevant, offering new potential approaches for risk assessment, protection and preventive measures to counteract the detrimental effects of environmental pollutants on human health.

Polychlorinated biphenyl quinone-induced signaling transition from autophagy to apoptosis is regulated by HMGB1 and p53 in human hepatoma HepG2 cells

Autophagy, which works to remove stress and maintain cellular homeostasis, is usually considered a "pro-survival" signal. Contrarily, apoptosis is programmed "pro-death" machinery. Polychlorinated biphenyls (PCBs) are a group of ubiquitous industrial pollutants. Our previous studies illustrated that a PCB quinone metabolite, PCB29-pQ, elicited both autophagy and apoptosis. However, the signaling underlying the autophagy and apoptosis cross-talk has not been characterized. Here, we found that PCB29-pQ-induced autophagy mainly occurred at a lower concentration (5 μM), while apoptosis mostly arose at a higher concentration (15 μM) in HepG2 cells. Next, we demonstrated the elevation of intracellular calcium levels and calpain activity with PCB29-pQ treatment; however, the unaffected subcellular location of truncated ATG5 and Beclin1 suggested the irrelevance of calpain towards the autophagy-to-apoptosis signaling shift. HMGB1 and p53 both serve as transcription factors that play crucial roles in the regulation of PCB29-pQ-induced autophagy and apoptosis. PCB29-pQ not only enhanced the expression of HMGB1 and p53 but also promoted their binding and cytosolic translocation. Interestingly, HMGB1 rather than p53 plays a primary role in 5 μM of PCB29-pQ-induced autophagy in the nucleus; however, p53 promoted apoptosis to a great extent in the cytosol at the dose of 15 μM PCB29-pQ. Together, HMGB1 and p53 provided a subtle balance between autophagy and apoptosis, thus determining the fate of PCB29-pQ-treated cells.

Transcriptomic response of Arabidopsis thaliana exposed to hydroxylated polychlorinated biphenyls (OH-PCBs)

Hydroxylated polychlorinated biphenyls (OH-PCBs) are toxic contaminants produced by biotic or abiotic transformation of PCBs. In this study, we have tested the toxicity of 2,5-dichlorobiphenyl (2,5-DCB) and three of its OH-derivatives, 2'-OH-, 3'-OH-, and 4'-OH-2,5-DCB toward the model plant, Arabidopsis thaliana. Toxicity tests showed that the parent 2,5-DCB (5 mg L^-1) had little effect on the plants, while all three OH-metabolites (5 mg L^-1) exhibited a significant toxicity, with 4'-OH-2,5-DCB being the most potent (inhibition concentration 50%-IC₅₀ in germination tests = 9.8 mg L^-1 for 2'-OH-2,5-DCB, 9.5 mg L^-1 for 3'-OH-2,5-DCB, and 4.8 mg L^-1 for 4'-OH-2,5-DCB). Whole-genome expression microarrays (Affymetrix) showed that exposure to the three OH-PCBs resulted in rather similar expression patterns, which were distinct from the one developing in response to 2,5-DCB. Searching an Arabidopsis microarray database (Genevestigator) revealed that, unlike the parent compound, the three OH-derivatives induced expression profiles similar to inhibitors of brassinosteroid synthesis (i.e., brassinazole, propiconazole, and uniconazole), resulting in severe iron deficiency in exposed plants. Our results suggest that the higher phytotoxicity of OH-derivatives as compared to 2,5-DCB is at least partly explained by the inhibition of the brassinosteroid pathway.

Airborne PCBs and OH-PCBs Inside and Outside Urban and Rural U.S. Schools

PCBs appear in school air because many school buildings were built when PCBs were still intentionally added to building materials and because PCBs are also present through inadvertent production in modern pigment. This is of concern because children are especially vulnerable to the toxic effects of PCBs. Here we report indoor and outdoor air concentrations of PCBs and OH-PCBs from two rural schools and four urban schools, the latter near a PCB-contaminated waterway of Lake Michigan in the United States. Samples (n = 108) were collected as in/out pairs using polyurethane foam passive air samplers (PUF-PAS) from January 2012 to November 2015. Samples were analyzed using GC/MS-MS for all 209 PCBs and 72 OH-PCBs. Concentrations inside schools were 1-2 orders of magnitude higher than outdoors and ranged from 0.5 to 194 ng/m³ (PCBs) and from 4 to 665 pg/m³ (OH-PCBs). Congener profiles were similar within each sampling location across season but different between schools and indicated the sources as Aroclors from building materials and individual PCBs associated with modern pigment. This study is the first cohort-specific analysis to show that some children's PCB inhalation exposure may be equal to or higher than their exposure through diet.

Effects of Polychlorinated Biphenyls (PCBs) and Their Hydroxylated Metabolites (OH-PCBs) on Arabidopsis thaliana

Plants metabolize polychlorinated biphenyls (PCBs) into hydroxylated derivatives (OH-PCBs), which are sometimes more toxic than the parent PCBs. The objective of this research was to compare the toxicity of a suite of PCBs and OH-PCBs toward the model plant, Arabidopsis thaliana. While parent PCBs and higher-chlorinated OH-PCBs exhibited a low or nondetectable toxicity, lower-chlorinated OH-PCBs significantly inhibited the germination rate and plant growth, with inhibition concentration 50% (IC₅₀) ranging from 1.6 to 12.0 mg L^-1. The transcriptomic response of A. thaliana to 2,5-dichlorobiphenyl (2,5-DCB), and its OH metabolite, 4'-OH-2,5-DCB, was then examined using whole-genome expression microarrays (Affymetrix). Exposure to 2,5-DCB and 4'-OH-2,5-DCB resulted in different expression patterns, with the former leading to enrichment of genes involved in response to toxic stress and detoxification functions. Exposure to 2,5-DCB induced multiple xenobiotic response genes, such as cytochrome P-450 and glutathione S-transferases, potentially involved in the PCB metabolism. On the contrary, exposure to both compounds resulted in the down-regulation of genes involved in stresses not directly related to toxicity. Unlike its OH derivative, 2,5-DCB was shown to induce a transcriptomic profile similar to plant safeners, which are nontoxic chemicals stimulating detoxification pathways in plants. The differentiated induction of detoxification enzymes by 2,5-DCB may explain its lower phytotoxicity compared to 4'-OH-2,5-DCB.