Effects of a pre-incubation period on the photoinduced toxicity of polycyclic aromatic hydrocarbons to the luminescent bacterium Vibrio fischeri

Photocatalytic removal of benzo[a]pyrene and antibacterial efficacy of Graphitic Carbon Nitride-silver-nickel (g-C3N4-Ag-Ni) mediated nanocomposites

A few PAHs (polycyclic aromatic hydrocarbons) which are known to be pervasive and are of high priority are found to be detrimental pollutants having high potential in the destruction of the network. Hence, photocatalytic disintegration of these PAHs, namely benzo [a]pyrene, found in water is explored. A novel nanocomposite of Ag-Ni on g-C3N4 was fabricated. The prepared nanocomposites were characterized by techniques like UV, XRD, SEM-EDAX, FTIR, and DLS to understand their nature. The activity of the same as a catalyst in the deterioration of the benzopyrene molecule in water was investigated under different conditions including change in the concentration of the PAH, dosage of the catalyst prepared, pH of the reaction mixture, and by changing the source of irradiation. In addition, antibacterial analysis of the prepared nanocomposite material was conducted to determine whether it could be applied to environmental cleanup strategies of high quality.

Impact of Reactive Oxygen Species Scavenging on the Intermediate Production of Anthracene and Anthraquinone in Fresh versus Saltwater Environments

While salinity can alter the photodegradation of hydrophobic organic compounds (HOCs), the cause of their altered kinetics in seawater is not well understood. Because HOC intermediate photoproducts are often more toxic than their parent compounds, characterizing the generation of intermediates in saline environments is needed to accurately predict their health effects. The present study investigated the influence of salinity on the generation of anthraquinone through the photolysis of anthracene and the generation of anthrone and 1-hydroxyanthraquinone from the photolysis of anthraquinone as well as their reactivities with hydroxyl radicals. This was conducted by measuring the photolysis rates of anthracene and anthraquinone and characterizing their product formation in buffered deionized water, artificial seawater, individual seawater halides (bromide, chloride, and iodide), dimethyl sulfoxide, furfuryl alcohol, and solutions of hydrogen peroxide. Salinity enhanced the persistence of anthraquinone by a factor >10 and altered its product formation, including the generation of the suspected carcinogen 1-hydroxyanthraquinone. In part, this was attributed to reactive oxygen species (ROS) scavenging by the seawater constituents chloride and bromide. In addition, anthraquinone and its hydroxylated products were found to be moderately to highly reactive with hydroxyl radicals, further illustrating their tendency to react with ROS in aqueous environments. The present study emphasizes the importance of considering the effects of salinity on organic contaminant degradation; it can significantly enhance the persistence of HOCs and alter their intermediate formation, subsequently impacting chemical exposure times and potential toxic effects on estuarine/marine organisms. Environ Toxicol Chem 2023;42:1721-1729. © 2023 SETAC.

Comparative analysis on the photolysis kinetics of four neonicotinoid pesticides and their photo-induced toxicity to Vibrio Fischeri: Pathway and toxic mechanism

Neonicotinoids are widely used pesticides all over the world and pose severe water pollution. Although they can be degraded via absorbing sunlight, few attentions have been paid to the environmental risks of their photolysis products. In this paper, the photo-toxicity was investigated for four neonicotinoids (dinotefuran, nitenpyram, thiamethoxam and clothianidin) based on a series of experiments (i.e., photolysis kinetics, radical scavenging, bioluminescent inhibition test to Vibrio Fischeri and intermediate identification) and in-silico calculation of photolysis pathway. The results show that direct photolysis dominates the photolysis of the four neonicotinoids under simulated sunlight radiation. The bioluminescent inhibition kinetics shows that all four neonicotinoids have photo-induced toxicity to V. fischeri, but with different light-induced responses. Scavenging radicals (·OH and ¹O₂) will decrease the photo-induced toxicity of all the four neonicotinoids, indicating radicals play important roles to the photo-chemical reactions of intermediates. Dissolved organic matters exhibit slightly shading effect to the photolysis rates of four parent compounds. However, the ROSs generated by DOM can accelerate the photo-chemical reactions of intermediates, leading to different photo-induced toxicity in present of DOM. According to the detected intermediates and Gaussian calculations, there are different photolysis pathways and mechanisms for the four neonicotinoids. The calculation for photo-sensitization reactions with ³O₂ indicates that both energy transfer reactions and electron transfer reactions can be produced under simulated sunlight radiation, which further consolidate that reactive oxygen species are involved in the photolysis process. A theoretical model has been developed to explain the toxicity variations of four neonicotinoids in different aqueous conditions.

Effects of crude oil and aromatic compounds on growth and bioluminescence of Vibrio campbellii FS5

Fifteen native luminescent bacteria were isolated from the Gulf of Thailand, and their sensitivity for the detection of toxicity of crude oil and its aromatic components was investigated. Of these isolates, Vibrio campbellii strain FS5 was one of the two most highly inhibited bacteria at all crude oil concentrations. This bacterium showed a decrease in luminescence intensity of between 10.7 and 80.2% after a 15-min exposure to 0.0001-10 mg/L of crude oil. The degree of bioluminescence inhibition increased with increasing concentrations of crude oil. The presence of crude oil at all concentrations had negative effects on the log bioluminescence per log number of viable cells after 15- to 105-min exposure. About 10 to 100 times, lower half maximal effective concentration (EC₅₀) values were observed for polycyclic aromatic hydrocarbons (PAHs) than those for benzene, toluene, ethylbenzene, and xylene (BTEX). In the presence of each individual BTEX and PAH, the bioluminescence inhibition increased with increasing exposure time (1-32 h). This indigenous bacterium can be used as a simple and general indicator of oil contamination and its impact on coastal waters as well as for assessing potential toxicity during oil bioremediation.

Photolysis and photo-induced toxicity of pyraclostrobin to Vibrio fischeri: Pathway and toxic mechanism

Pyraclostrobin is a fungicide used widely across the world. However, its photolysis pathway and toxic mechanism is unclear. In this study, photolysis and photo-induced toxicity of pyraclostrobin to Vibrio fischeri were determined. The results showed that direct photolysis dominated the degradation of pyraclostrobin. Gas Chromatography-Mass spectrometry and quantum chemical calculation revealed that the pyraclostrobin was firstly photo-degraded into Methyl N-phenyl-carbamate and 1-(4-chlorophenyl)-3-hydroxy-1H-pyrzole, synthetic intermediates of pyraclostrobin, then into aniline, benzoquinone and acids. Toxicity assay showed that bioluminescent inhibition rate to V. fischeri fluctuated with radiation/illumination time and the toxicity curve can be classified into three phases (Phase I: 0-10 min, incline; Phase II: 10-60 min, decline; Phase III: 60-120 min, incline). The up-and-down curve indicates the change of parent compound during the photolysis. Simulation of molecular docking showed that the CDOCKER interaction energy of pyraclostrobin (-44.71) lower than other intermediate products (>-30.00), indicating that the parent compound is more toxic than its intermediates. An increased toxicity observed in the toxicity curve was attributed to the generation of benzoquinone with log1/EC₅₀ of 6.73, which can greatly change structure of target luciferase in Vibrio fischeri. In addition, the addition of radical scavengers can inhibit the bioluminescence of the tested solutions, indicating the involvement of radicals in the transformation of intermediates. This paper reveals that one of photochemical transformation products of pyraclostrobin can cause more toxic than its parent compound to bacteria. Environmental risk assessment should consider not only the parent compound, but also its metabolites.

Aqueous photochemical degradation of hydroxylated PAHs: Kinetics, pathways, and multivariate effects of main water constituents

Hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) are contaminants of emerging concern in the aquatic environment, so it is of great significance to understand their environmental transformation and toxicity. This study investigated the aqueous photochemical behavior of four OH-PAHs, 9-Hydroxyfluorene (9-OHFL), 2-Hydroxyfluorene, 9-Hydroxyphenanthrene and 1-Hydroxypyrene, under simulated sunlight irradiation (λ>290 nm). It was observed that their photodegradation followed the pseudo-first-order kinetics. Based on the determined quantum yields, their calculated solar apparent photodegradation half-lives in surface waters at 45° N latitude ranged from 0.4min for 9-Hydroxyphenanthrene to 7.5 × 10(3)min for 9-OHFL, indicating that the OH-PAHs would intrinsically photodegrade fast in sunlit surface waters. Furthermore, 9-OHFL as an example was found to undergo direct photolysis, and self-sensitized photooxidation via OH rather than (1)O2 in pure water. The potential photoreactions involved photoinduced hydroxylation, dehydrogenation and isomerization based on product identification by GC-MS/MS. 9-OHFL photodegraded slower in natural waters than in pure water, which was attributed to the integrative effects of the most photoreactive species, such as Fe(III), NO3(-), Cl(-) and humic acid. The photomodified toxicity was further examined using Vibrio fischeri, and it was found that the toxicity of photolyzed 9-OHFL did not decrease significantly (p>0.05) either in pure water or in seawater, implying the comparable or higher toxicity of some intermediates. These results are important for assessing the fate and risks of OH-PAHs in surface waters.

Spectroscopic and molecular docking studies on the charge transfer complex of bovine serum albumin with quinone in aqueous medium and its influence on the ligand binding property of the protein

The spectral techniques such as UV-Vis, (1)H NMR and fluorescence and electrochemical experiments have been employed to investigate the interaction between 2-methoxy-3,5,6-trichloro-1,4-benzoquinone (MQ; a water soluble quinone) and bovine serum albumin (BSA) in aqueous medium. The fluorescence of BSA was quenched by MQ via formation of a 1:1 BSA-MQ charge transfer adduct with a formation constant of 3.3×10(8) L mol(-1). Based on the Forster's theory the binding distance between them is calculated as 2.65 nm indicating high probability of binding. For the first time, influence of quinone on the binding property of various types of ligands such as aspirin, ascorbic acid, nicotinimide and sodium stearate has also been investigated. The results indicated that the strong and spontaneous binding existing between BSA and MQ, decreased the intensity of binding of these ligands with BSA. Since Tryptophan (Trp) is the basic residue present in BSA, a comparison between binding property of Trp-MQ adduct with that of BSA-MQ with these ligands has also been attempted. 1H NMR titration study indicated that the Trp forms a charge transfer complex with MQ, which reduces the interaction of Trp with the ligands. Molecular docking study supported the fact that the quinone interacts with the Trp212 unit of the BSA and the free energy change of binding (ΔG) for the BSA-MQ complex was found to be -46 kJ mol(-1), which is comparable to our experimental free energy of binding (-49 kJ mol(-1)) obtained from fluorescence study.

Microbial community responses to bioremediation treatments for the mitigation of low-dose anthracene in marine coastal sediments of Bizerte lagoon (Tunisia)

PURPOSE

The main goals of this study were to investigate (1) the behavior of microbial communities in response to low-dose bioavailable anthracene addition in lightly contaminated sediment from Bizerte Lagoon and (2) the effects of bioremediation treatments on microbial biomass, activity, and community structure.

METHODS

Sediment microcosms amended with 1 ppm anthracene were incubated in triplicate during 30 days. Biostimulation (addition of nitrogen and phosphorus fertilizer) and bioaugmentation (inoculation of a hydrocarbonoclastic bacterium) were used as bioremediation treatments. Bacterial biomass was estimated using flow cytometry. Sediment oxygen consumption was measured with oxygen microelectrodes. Bacterial community structure was assessed by molecular fingerprints (terminal restriction fragment length polymorphism; T-RFLP) analysis.

RESULTS

Anthracene contamination resulted in a significant reduction of bacterial abundance with an impact on cell integrity. Concomitantly, sediment oxygen consumption was strongly inhibited. Correspondence analysis on T-RFLP data indicated that bacterial community structures from anthracene-contaminated microcosms were different from that of the control. Interestingly, the changes observed in microbial biomass, structure, and activities as a result of anthracene contamination were not alleviated even with the use of biostimulation and combination of biostimulation and bioaugmentation strategy for anthracene bioremediation. Nevertheless, both treatment methods resulted in different community structures relative to the contaminated and control microcosms with the appearance of distinct populations.

CONCLUSION

Anthracene spiking severely affected microbial communities, suggesting dominance of nontolerant populations in this lightly-contaminated sediment. Although biostimulation and/or bioaugmentation treatments did not alleviate the anthracene toxic effects, the changes observed in microbial population and structure suggest that the proposed treatments might be promising to promote bacterial growth. Further works are still required to propose a more efficient strategy to stimulate biodegradation that takes into account the complex interactions between species for resource access.

Oxidation of anthracene by immobilized laccase from Trametes versicolor

The laccase of Trametes versicolor was immobilized on the functionalized nanoparticles SBA-15 with the average diameter less than 10 nm. Laccase mediated oxidations of anthracene (ANT) were investigated in the presence of two mediators, 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) and 1-hydroxybenzotriazole (HBT). Oxidation of ANT was more efficiently enhanced by adding 1 mM of HBT than that by adding ABTS. After 48 h oxidation HBT group significantly oxidized ANT with residue 58% relative to 88% in the ABTS group. HPLC and GC/MS analyses indicated the main product of ANT oxidation was anthraquinone (ANQ). The fluorescein diacetate (FDA) uptake of two human cell lines was used to assess the cytotoxicity and genotoxicity of ANT and ANQ. Treatments with ANT and ANQ at 5 and 10 microM exhibited significant cytotoxicity to the HaCaT cells and the A3 lymphocytes and no significant genotoxicity was observed. The results illustrated that ANQ is less toxic than ANT as well.

Assessment of mixture toxicity of copper, cadmium, and phenanthrenequinone to the marine bacterium Vibrio fischeri

Transition metals and polycyclic aromatic hydrocarbons (PAHs) are cocontaminants at many sites. Contaminants in mixtures are known to interact with biological systems in ways that can greatly alter the toxicity of individual compounds. The toxicities (individually and as mixtures) of copper (Cu), a redox-active metal; cadmium (Cd), a nonredox active metal; and phenanthrenequinone (PHQ), a redox-active oxygenated PAH, were examined using the bioluminescent bacterium Vibrio fischeri. We found that the cotoxicity of Cu/PHQ was dependent on the ratio of concentrations of each chemical in the mixture. Different interaction types (synergism, antagonism, and additivity) were observed with different combinations of these toxicants. The interaction types changed from antagonism at a low Cu to PHQ ratio (1:4), to additive at an intermediate Cu to PHQ ratio (2:3), to synergistic at higher Cu to PHQ ratios (3:2 and 4:1). In contrast to Cu/PHQ mixtures, the cotoxicity of Cd/PHQ did not change at different mixture ratios and was found for the most part to be additive. For the individual chemicals and their mixtures, reactive oxygen species (ROS) production was observed in V. fischeri, suggesting that individual and mixture toxicity of Cu, Cd, and PHQ to V. fischeri involves ROS-related mechanisms. This study shows that mixture ratios can alter individual chemical toxicity, and should be taken into account in risk assessment.

Phototoxicity of pyrene affects benthic algae and bacteria from the Arctic

Phototoxicity of polycyclic aromatic hydrocarbons (PAHs) in the Arctic is important to study since the future PAH load is likely to increase. In combination with the increased UV-light penetration due to ozone layer thinning, phototoxicity may be a potential problem for arctic areas. The aim of this study was to evaluate effects of pyrene and phototoxicity of pyrene on natural algae and bacteria from arctic sediments. Sediments from a shallow-water marine baywere spiked with different pyrene concentrations. Microcosms containing the sediment were incubated under three light regimes, natural sunlight with UV-light, natural sunlight without UV-light, and dark. Significant effects were evident at low pyrene concentrations, particularly in presence of UV-light, indicating phototoxicity. The microalgae were especially sensitive to the phototoxicity of pyrene. Already atthe lowest pyrene concentration (Cfree: 4 nM) algal 14C-incorporation and chlorophyll a content were reduced. The toxic effects of pyrene on the microalgae probably led to the release of organic matter. In agreement with this, bacterial activity increased at high pyrene concentrations indicated by increased oxygen consumption and increased release of inorganic N and P from the sediment. This study indicates that phototoxicity of PAHs may be relevant for sediment communities from shallow marine arctic areas at environmentally relevant pyrene concentrations.

Combined effects of pyrene and UV-light on algae and bacteria in an arctic sediment

The phototoxicity potential of pyrene on natural algae and bacteria in an arctic sediment was evaluated and compared to that of pyrene treatment alone based on some functional and structural endpoints. Microcosms with arctic sediment from a shallow-water marine bay were incubated with pyrene under three different light regimes, natural sunlight with UV-light (Light(UV)), natural sunlight without UV-light (Light) and dark.Presence of pyrene directly affected the algal community measured as decreased (14)C-incorporation and decreased ammonium, nitrate and silicate uptake. These direct toxic effects from pyrene on the algae eventually led to indirect effects on the bacterial community observed as increased oxygen consumption. Besides the direct toxicity of pyrene to the benthic microbial community, indications of phototoxicity were found on the bacterial community detected as decreased oxygen consumption and increased bacterial diversity under Light(UV) compared to Light. No indication of phototoxicity of pyrene was found on the algae, which might be due to the high direct toxicity of pyrene. Our results indicate that shallow arctic marine areas might be affected by phototoxicity if concentrations of oil components in the sediments increase.

Photoinduced toxicity of selected PAHs to the marine microalga Phaeodactylum tricornutum

In this study, the effects of different concentrations of pyrene, phenanthrene, fluoranthene, and chrysene within the solubility limits of the chemicals on marine microalgal species of Phaeodactylum tricornutum were examined under UV-A and UV-B lights by application of batch toxicity tests. The algal species were also exposed to the individual PAHs under cool-white fluorescent bulbs in the same laboratory conditions in order to compare the results with the responses of UV-exposed organisms. EC50 values calculated with the trimmed Spearman Karber method demonstrate that the UV light dramatically enhances the toxicity of the selected model PAHs. In most cases, the magnitude of increase in PAH toxicity was directly related to the concentration of individual PAHs and the duration of UV-lighting.

Ecotoxicological Effects of Combined UVB and Organic Contaminants in Coastal Waters: A Review

Organisms living in coastal waters are exposed to anthropogenic contaminants from terrestrial drainage, ice melting and maritime traffic and to enhanced UVB radiation (UVBR; 280-320 nm) caused by decreased concentrations of ozone in the stratosphere. This article reviews available information about the combined effects of UVBR and selected hydrosoluble contaminants potentially present in surface waters on marine species and especially on plankton community structure in high-latitude coastal zones. Effects of UVBR on three selected pesticides (Atrazine, carbaryl and Acifluorfen) and possible induction of phototoxicity are reviewed. Most toxicological studies have been conducted under laboratory conditions with questionable relevance for coastal marine ecosystems. Similarly, photoactivation of polycyclic aromatic hydrocarbons (PAHs) has been closely examined and reported effects on aquatic species summarized. Experiments with field-sampled communities demonstrated the complexity and the difficulty in determining the impact of multiple stressors on an aquatic ecosystem, even for ecosystems simplified by eliminating large grazers and fish. Nutrient status, specific composition and light history have influenced the different responses of planktonic assemblages exposed to enhanced UVBR and water-soluble fraction (WSF) from crude oil or to tributyltin. Plankton assemblages subjected to changes in the ozone hole were physiologically stressed and more susceptible to WSF toxicity than communities from less enhanced UVBR-impacted sites. A close relationship between phytoplankton assemblages and bacteria was observed in all experiments in mesocosms. A contaminant-induced phytoplankton crash after a bloom event may release important carbon and nutrient sources for bacteria. The magnitude of phytoplanktonic mortality induced by a contaminant probably influenced how rapidly bacteria grew over time. The transition from a herbivorous food web to a microbial food web has significant ecological implications for carbon cycling and energy flow in pelagic systems. A high phytoplankton mortality implies a situation in which the potential for downward carbon export from surface waters is high. In contrast, high bacterial enrichment implies that the phytoplankton carbon is largely recycled in surface waters through a microbial loop and does not contribute significantly to sinking particle flux. The most ecologically relevant results were obtained with mesocosm studies using field-collected communities. The enhancement of hydrocarbon toxicity in the presence of a high level of UVBR cannot be described as being a synergistic or an additive effect, because the WSF alone is not toxic and may even be beneficial by increasing bacterial activity. This is a case in which one stressor has the ability to modify another stressor to cause it to be toxic to target organisms. These abiotically induced interactions may be important for biological communities exposed to extreme conditions when physical, chemical or photochemical reactions modify the nature of environmental stressors before they interact with biological functions. The need for models on the impacts of multiple stressors on biodiversity and ecosystem functioning is emphasized.

Use of spent mushroom compost to bioremediate PAH-contaminated samples

Spent mushroom compost (SMC) is a bulky waste byproduct of mushroom industry and produced abundantly. The SMC of Pleurotus pulmonarius immobilized laccase (0.88 mmoles min(-1) g(-1)) and manganese peroxidase (0.58 mmoles min(-1) g(-1)) of which the optimal temperatures were 45 and 75 degrees C, respectively. In laboratory test, complete degradative removal of individual naphthalene, phenanthrene, benzo[a]pyrene and benzo[g,h,i]perylene (200 mg PAH kg(-1) sandy-loam soil) by 5% SMC was obtained in two days under continuous shaking at 80 degrees C. The SMC-treated PAH samples had significantly reduced or removed their toxicities as revealed by the Microtox bioassay. These results were confirmed by gas chromatography-mass spectrometry analysis on the breakdown products. A phthalic derivative which is reported as a degradative product of PAHs by ozonation or ligninolysis was also detected in the SMC-treated samples. The results demonstrate the potential in employing SMC in ex situ bioremediation.

Measurement of short- and long-term toxicity of polycyclic aromatic hydrocarbons using luminescent bacteria

Growing concern over environmental contamination has stimulated rigorous efforts to establish reliable biological monitoring assays. Methodology was developed for measuring photoinduced short- and long-term toxicity of an important group of contaminants, polycyclic aromatic hydrocarbons (PAHs), using the luminescent bacterium Vibrio fischeri. The toxicity of most PAHs can be greatly enhanced on exposure of a living organism and/or the chemicals to ultraviolet (UV) radiation. There are two major mechanisms involved in photoinduced toxicity of PAHs: photosensitization and photomodification. In the former, production of singlet oxygen leads to cellular damage. In the latter, photooxidation of PAHs results in new compounds (usually oxygenated PAHs) that are often more toxic than their parent PAHs. Microbial toxicity assays were developed to measure short- and long-term photoinduced toxicity of PAHs. The bioassays were based on inhibition of luminescence and growth of V. fischeri. The short-term assay should detect toxicity of chemicals that are taken up rapidly and/or whose photosensitization activity is immediate. The long-term assay should identify chemicals where the rate of assimilation is slow and/or time is required for photoinduced effects to be realized. The assays were tested with 12 different PAHs. The short-term assay did not reveal photoinduced toxicity for any of the test chemicals. However, photoinduced toxicity was apparent in the long-term assay, indicating that short-term assays may be opaque to this key mechanism of PAH toxicity.