The study, published in Advanced Biotechnology by a team at Sun Yat-sen University led by Jie Gao, Junzhe Zhang, and Junfeng Xie, was designed around environmentally realistic exposure levels. After a preliminary 14-day dose-finding trial, the researchers selected 10 micrograms per liter of green fluorescent polyethylene microplastic particles, roughly 5 micrometers in diameter, and 100 nanograms per liter of BPA. These concentrations caused negligible mortality but sit within ranges documented in freshwater systems worldwide. Microplastic abundances in natural waters span from tens of particles per cubic meter in remote regions such as the Tibetan Plateau to nearly 20,000 particles per cubic meter in urban rivers like the Pearl River, while BPA concentrations in surface waters across Asia range from a few nanograms to several hundred nanograms per liter.

Because BPA is hydrophobic and binds strongly to polymer surfaces, microplastics and BPA frequently co-occur, and the researchers suspected the particles might act as vectors that enhance BPA delivery into tissues. To test this, they exposed juvenile bass for 14 days in five groups: a blank control, a solvent control, microplastics alone, BPA alone, and the combined treatment. Fluorescent imaging confirmed that the particles accumulated progressively in liver tissue over the exposure period, and crucially, the co-exposed fish accumulated significantly more microplastics in their livers than fish receiving particles alone, supporting the vector hypothesis and hinting that the mixture was producing a toxicity greater than the sum of its parts.

The molecular story that emerged centers on NRF2, a transcription factor often described as the master regulator of antioxidant defense. Under normal conditions, NRF2 switches on genes encoding superoxide dismutase (SOD1), catalase (CAT), and glutathione peroxidase (GPx1), enzymes that neutralize reactive oxygen species before they damage cells. In the co-exposed fish, this system collapsed. Enzyme activity assays and quantitative PCR both showed that SOD1, CAT, and GPx activities and transcripts fell most sharply in the combined group, while NRF2 mRNA was downregulated and its cytoplasmic repressor Keap1 was upregulated, a pattern consistent with NRF2 being retained for degradation rather than allowed to activate antioxidant genes.

The downstream consequences were visible at every level the team examined. Malondialdehyde, a standard biomarker of lipid peroxidation, rose to its highest levels in co-exposed livers, and DCFH-DA fluorescence staining revealed intense reactive oxygen species accumulation in the same tissues. Histological sections stained with hematoxylin and eosin showed progressively worsening damage, from mild vacuolization in microplastic-treated fish to disorganized hepatic cords under BPA alone, and finally extensive vacuolization, hepatocellular necrosis, and nuclear pyknosis in the combined group. Liver function markers ALT and AST climbed in parallel, peaking under co-exposure, and the co-exposed livers were visibly hypertrophied.

Energy metabolism told an equally striking story. Hepatic ATP declined sharply in all treated fish, but the synergistic drop under co-exposure suggested that the mixture disrupted mitochondrial bioenergetics more severely than either contaminant individually. This energetic failure was accompanied by activation of the intrinsic apoptotic pathway: the pro-apoptotic genes Bax and Caspase-3 were upregulated, the anti-apoptotic gene Bcl-2 was downregulated, caspase-3 enzyme activity increased, and TUNEL staining revealed abundant apoptotic nuclei in co-exposed liver sections. Transmission electron microscopy extended the damage to the nervous system, showing swollen brain mitochondria with fragmented cristae and vacuolar degeneration in co-exposed fish, while control animals retained intact mitochondrial membranes and densely packed cristae.

To probe the mechanism, the team turned to computational tools. Molecular docking using an AlphaFold2-predicted structure of largemouth bass NRF2 showed that BPA binds stably within a hydrophobic pocket of the protein, with a calculated affinity of minus 6.2 kilocalories per mole. Key residues including Tyr33, Asn34, Gln37, and Arg36 form hydrogen bonds and van der Waals contacts that could destabilize NRF2’s conformation and impair its transcriptional activity. Network toxicology analysis identified 260 overlapping gene targets between BPA and polystyrene exposure, and enrichment analysis pointed to redox-related signaling cascades, including the PI3K-Akt, mTOR, and FoxO pathways, reinforcing the idea that both contaminants converge on NRF2-mediated redox control.

The most consequential experiment came last. After the 14-day exposure, fish were transferred to clean water and challenged with NNV by immersion at 2 times 10 to the 2 TCID50 per milliliter for six hours. NNV is a neurotropic pathogen that infects more than 120 marine and freshwater species, causing viral encephalopathy and retinopathy, with symptoms such as erratic swimming, anorexia, and lethargy, and it is known to exploit redox imbalance to evade immune defense. When the researchers measured viral capsid protein and RNA-dependent RNA polymerase transcripts in brain tissue at 0, 3, and 7 days post-infection, they found elevated viral gene expression in all exposed groups compared with controls, but the highest viral loads appeared exclusively in the co-exposed fish, peaking at both 3 and 7 days post-infection. Single exposures alone did not produce this enhancement, underscoring the synergistic nature of the effect.

The authors frame these findings within an adverse outcome pathway, positioning NRF2 inhibition as the molecular initiating event that cascades through oxidative stress, mitochondrial failure, and apoptosis to the organism-level outcome of heightened viral susceptibility. This mechanistic chain matters because most ecotoxicological risk assessments still evaluate chemicals one at a time, even though aquatic organisms in farmed and natural waters are bathed in complex mixtures. The results suggest that sublethal concentrations of two common contaminants, neither individually capable of compromising antiviral defense, can together push fish past a cellular tolerance threshold, with microplastics potentially amplifying BPA uptake and intracellular delivery.

For aquaculture, the implications are direct. Largemouth bass production in China has exceeded 100,000 tons annually since the species was introduced to Guangdong in the 1980s, but intensive farming has been associated with declining disease resistance, and NNV outbreaks cause high mortality with few treatment options. The researchers propose incorporating mixture-responsive biomarkers, such as NRF2 suppression, ATP depletion, and viral susceptibility, into environmental monitoring, and they call for extending this adverse outcome pathway framework across other species, developmental stages, and pollutant combinations. If the pattern holds broadly, the quiet synergy between plastic debris and its chemical passengers may represent an underappreciated driver of infectious disease in freshwater fish, one that single-compound toxicology has been structurally unable to see.

Subject of Research: Combined microplastic and bisphenol A exposure increases viral susceptibility in largemouth bass via NRF2-mediated oxidative stress

Article Title: Co-exposure to microplastics and bisphenol A increases viral susceptibility in largemouth bass (Micropterus salmoides) via oxidative stress

Article References: Gao, J., Zhang, J., Zheng, R., Jiang, J., Huang, S., Miao, Q., Wu, B., Tang, W., He, J., & Xie, J. (2025). Co-exposure to microplastics and bisphenol A increases viral susceptibility in largemouth bass (Micropterus salmoides) via oxidative stress. Advanced Biotechnology, 3(4), Article 31. https://doi.org/10.1007/s44307-025-00085-5

Image Credits: AI Generated

DOI: 10.1007/s44307-025-00085-5

Keywords: microplastics, bisphenol A, largemouth bass, oxidative stress, NRF2, nervous necrosis virus, aquaculture, ecotoxicology, apoptosis, mitochondrial dysfunction, freshwater pollution, mixture toxicity

The choice of concentration is central to the study’s significance. Rather than testing the high, often unrealistic doses that dominate laboratory toxicology, the researchers used 0.5 milligrams per liter, a level meant to reflect what fish actually encounter in polluted freshwater systems. This matters because regulatory decisions and risk assessments depend on knowing what happens at real-world exposures, not just at doses high enough to guarantee an effect. The team also chose a species with ecological and economic importance in South Asia, an air-breathing fish that inhabits ponds, lakes and slow-moving waters where plastic debris accumulates.

The hematological findings were stark. Fish exposed to either plastic showed declines in hemoglobin concentration and red blood cell counts, a pattern consistent with anemia, while their white blood cell counts climbed steadily across the three sampling points at days 7, 14 and 21. Rising leukocytes signal immune activation, an indication that the fish bodies were mounting a sustained defensive response to the particles. Crucially, these changes worsened over time and were most pronounced in the group receiving both plastics simultaneously, suggesting that the damage accumulates and that mixtures amplify the burden beyond what either polymer alone imposes.

Blood chemistry told a parallel story of physiological stress. The exposed fish showed significant elevations in liver and tissue damage markers, including SGOT, SGPT, alkaline phosphatase and lactate dehydrogenase, enzymes that leak into circulation when organs such as the liver, gills or kidneys are injured. Creatinine and blood urea nitrogen, both standard indicators of kidney function, also rose, pointing to renal strain. Meanwhile, glucose and cholesterol increased, hallmarks of a stress response that mobilizes energy reserves, while triglycerides and albumin fell, and the albumin-to-globulin ratio shifted in ways that reflect disturbed protein metabolism. Every one of these biochemical disturbances reached statistical significance, and the co-exposed group again fared worst.

Perhaps the most visually striking evidence came from the fish red blood cells themselves. Under the microscope, the researchers catalogued eight distinct types of nuclear abnormalities in erythrocytes: micronuclei, nuclear buds, binucleated cells, blebbed nuclei, tear-drop nuclei, kidney-shaped nuclei and notched nuclei. Each of these distortions is a recognized signature of genotoxic or cytotoxic stress, indicating damage to genetic material or to the machinery that divides cells. Micronuclei, for example, form when chromosome fragments or whole chromosomes fail to incorporate into the main nucleus during cell division. The frequency of every abnormality type rose significantly in all exposed groups, with the highest percentages appearing in fish that had swallowed both plastic types.

Growth, the ultimate integrator of an animal’s health, deteriorated as well. Over the three weeks of exposure, plastic-treated fish gained less weight than controls, and the standard metrics of aquaculture and ecology all declined: percentage weight gain, specific growth rate, feed intake ratio and condition factor, a measure comparing a fish’s weight to its length. The combined-exposure group recorded the lowest values across most of these parameters. Because growth reflects the net outcome of feeding, digestion, metabolism and energy allocation, its suppression suggests that the physiological costs of dealing with microplastics, from immune activation to tissue repair, were draining resources that would otherwise fuel development.

The polymer identities likely explain part of the difference in toxicity. Polyethylene, the material of shopping bags and packaging film, is chemically inert but can still physically interact with membranes and tissues. Polyvinyl chloride, by contrast, is a more problematic polymer in the environment because it carries chlorine in its backbone and is formulated with plasticizers and other additives that can leach out over time. In this study, PVC microplastics proved more toxic than PE microplastics on their own, and the mixture outstripped both. The particles themselves were characterized by scanning electron microscopy and dynamic light scattering, revealing irregular fragments and spherical aggregates with an average hydrodynamic diameter of roughly 1,128 nanometers and a polydispersity index of 1.426, meaning the fish were ingesting a heterogeneous soup of particle sizes rather than uniform beads.

To tie the whole dataset together, the researchers ran a Pearson correlation analysis across all hematological, biochemical, nuclear and growth parameters. The matrix revealed strong positive associations among the nuclear abnormality categories, among the metabolic markers such as glucose, cholesterol and triglycerides, and among the growth indicators, alongside negative correlations linking blood parameters to growth metrics. Statistically significant correlations, marked at p less than 0.05, wove the separate strands of evidence into a coherent picture: the same fish that carried damaged red cell nuclei were the ones with deranged blood chemistry and stunted growth. This internal coherence strengthens the argument that these biomarkers can serve as a diagnostic panel for microplastic toxicity in sentinel fish species.

Why should mixtures matter so much? Aquatic environments are never contaminated by a single polymer. Wastewater effluent, urban runoff and degrading debris deliver a shifting cocktail of polyethylene, polyvinyl chloride, polystyrene and other plastics simultaneously, yet most laboratory studies test one material at a time. The present work adds to a growing body of evidence, including earlier studies of microplastics combined with pesticides, herbicides and heavy metals, that co-exposure can intensify harm. Possible mechanisms include additive tissue burden, complementary modes of action between particle types, and the physical and chemical differences between a hydrocarbon polymer and a chlorinated one carrying leachable additives. The study is, according to its authors, the first to evaluate PE and PVC microplastic toxicity in Channa punctatus, filling a gap for a species widely used in Indian toxicology research.

The broader implications reach beyond one fish species in one laboratory. Channa punctatus serves as a sentinel, an organism whose responses warn of conditions that may eventually affect entire food webs, including commercially important fish and, by extension, the humans who eat them. Microplastics have already been documented in wild fish, in packaged foods and in human blood, and research continues into what chronic low-dose exposure means for human health. The Indian team’s findings sound what they describe as an urgent call to recognize the silent, combined threat of mixed microplastic pollution in freshwater ecosystems. As global plastic production continues to climb, the study suggests that risk assessments built on single polymers may systematically underestimate the damage occurring in rivers, ponds and lakes where the plastic soup is the norm, not the exception.

Subject of Research: Toxic effects of polyethylene and polyvinyl chloride microplastics on fish blood, metabolism and growth

Article Title: From plastic to pathophysiology: polyethylene (PE) and polyvinyl chloride (PVC) microplastics disrupt fish blood, metabolism, and growth

Article References: Arya, N., Bakhasha, J., Saxena, V., Kumar, G., Saran, K., Priya, N., Khan, M., Verma, P., Raza, I., Yadav, K. K., & Trivedi, A. (2026). From plastic to pathophysiology: polyethylene (PE) and polyvinyl chloride (PVC) microplastics disrupt fish blood, metabolism, and growth. Ecotoxicology, 35(8), Article 177. https://doi.org/10.1007/s10646-026-03175-9

Image Credits: AI Generated

DOI: 10.1007/s10646-026-03175-9

Keywords: microplastics, polyethylene, polyvinyl chloride, Channa punctatus, ecotoxicology, hematology, genotoxicity, nuclear abnormalities, fish growth, freshwater pollution, mixture toxicity, biomarkers

The research team, led by Ahmeed Olalekan Ashade of Lagos State University of Science and Technology together with colleagues at Lagos State University and Elizade University, set out to isolate bacteria capable of degrading hydrocarbons while tolerating heavy metals and producing surface-active biomolecules. Such a combination of traits has been sparsely reported in the literature, particularly for West African freshwater systems, even though co-contamination by petroleum and metals is the norm rather than the exception in polluted industrial waterways. The work builds on the group’s earlier metagenomic surveys, which showed that Ologe Lagoon harbors a diverse array of prokaryotic phylotypes with potential biotechnological value.

To capture these hardy microbes, the researchers identified three sampling points reflecting different levels of human disturbance: an industrial-contaminated site, a human-activities site, and a presumed-undisturbed reference site. Surface water was collected in sterile flasks and sediments were retrieved from the lagoon floor using an Ekman grab, yielding composites of 1,500 milliliters of water and 600 grams of sediment. Physicochemical profiling of the samples confirmed measurable burdens of nickel, cadmium, lead, mercury, and cobalt in both water and sediment, with sediment nickel reaching 5.21 milligrams per kilogram at the reference site and water nickel peaking at 1.18 milligrams per kilogram at the industrial site.

The isolation strategy relied on continuous enrichment, a technique that applies strong selective pressure to favor organisms with the desired traits. Samples were incubated aerobically for 30 days in mineral salt medium containing 1 percent Escravos light crude oil as the sole carbon and energy source, fortified with filter-sterilized solutions of nickel chloride, cadmium chloride, and lead acetate at concentrations of 0.5, 0.1, and 1.0 millimolar respectively. Flasks were shaken at 150 revolutions per minute in the dark at 27 degrees Celsius, and after three consecutive transfers onto fresh medium, pure bacterial colonies were obtained. Control flasks containing heat-killed cells confirmed that the observed changes were biological rather than abiotic.

Molecular identification using 16S rDNA Sanger sequencing and phylogenetic analysis with the Neighbor Joining algorithm revealed three standout strains. Strain OLW3 was identified as Alcaligenes aquatilis with 99.86 percent sequence similarity, strain OLW6 as Alcaligenes faecalis with 99.45 percent similarity, and strain OLW15 as Rossellomorea marisflavi with 98.28 percent similarity. The 16S rRNA sequences were deposited in GenBank under accession numbers OP626095, OP626097, and OP626099. The genus Alcaligenes, belonging to the phylum Pseudomonadota, is renowned for its metabolic versatility, with members documented in impacted sediments from Charleston Harbor in the United States to Quintero Bay in Chile, where they degrade hydrocarbons, synthetic dyes, and pharmaceutical compounds. Rossellomorea marisflavi, a Gram-positive, spore-forming, moderately halophilic bacterium formerly classified among the bacilli, contributes to organic matter decomposition and nutrient cycling in sediments.

When the three strains were grown on crude oil-heavy metal mineral salt medium over a 30-day time course, their degradation performance was striking. Strain OLW3, after a six-day lag phase likely reflecting the time needed to induce catabolic enzymes such as dioxygenases for these complex hydrophobic substrates, achieved a degradation rate of 0.056 milligrams per liter per day, a degradation rate constant of 6.43 per day, a half-life of 12.49 days, and an overall percentage degradation of 81.06 percent. Strain OLW15 proved the most efficient, with a degradation rate of 0.065 milligrams per liter per day, a rate constant of 7.16 per day, a half-life of 10.58 days, and 85.67 percent degradation. Strain OLW6, after a seven-day acclimatization period, degraded 54.27 percent of the hydrocarbons, a figure the authors suggest could be improved through optimization of growth conditions.

Gas chromatography with flame ionization detection provided molecular-level confirmation of biodegradation. Chromatograms taken at day 0, day 15, and day 30 showed progressive reductions in the peak areas of hydrocarbon fractions across all three enrichment systems. Strain OLW3 completely removed nC5 pentane and nC6 hexane by day 30 and reduced nC4 isobutane from 43.66 to 10.04 milligrams per kilogram, consistent with aerobic oxidation of straight-chain alkanes into alcohols and organic acids that feed into central metabolic pathways and beta-oxidation. Strain OLW6 cut m,p-xylene from 175.11 to 32.78 milligrams per kilogram and nC13 tridecane from 128.16 to 47.64 milligrams per kilogram, while strain OLW15 halved anthraquinone and reduced propyl-benzene from 125.47 to 36.27 milligrams per kilogram. Declining ratios of nC17 to pristane and nC18 to phytane, classic biomarkers of biodegradation, further documented preferential consumption of readily degradable aliphatics over recalcitrant isoprenoids.

Equally important was the demonstration that these bacteria tolerated the metals present in their enrichment medium. In tolerance assays on Luria Bertani media fortified with metal concentrations ranging from 0.5 to 20 millimolar, strain OLW3 tolerated up to 2.5 millimolar lead, strain OLW6 resisted cadmium concentrations in the same range, and strain OLW15 withstood 1.5 millimolar nickel. The authors note that bacteria deploy diverse detoxification strategies, including efflux pumps that expel metal ions, extracellular sequestration via exopolysaccharides, biosorption and bioprecipitation, and intracellular binding by metallothioneins. Exopolysaccharide production carries a double benefit, decreasing cell surface hydrophobicity to aid adhesion to hydrophobic hydrocarbons while simultaneously binding lead outside the cell, thereby reducing metal bioavailability and protecting the wider food web from uptake.

The biosurfactant credentials of the isolates were assessed through hemolytic, oil spread, and cetyltrimethylammonium bromide blue agar assays, along with measurements of the emulsification index after 24 hours. Strains OLW3 and OLW6 showed complete beta-hemolysis on blood agar, a presumptive indicator of biosurfactant production, while OLW15 tested positive on the blue agar plate assay used to detect anionic biosurfactants such as rhamnolipids. Emulsification indices reached 50 to 58.9 percent on crude oil and kerosene for OLW3, and 58.3 and 50 percent on crude oil for OLW6 and OLW15 respectively, with all isolates emulsifying vegetable oil at 36 to 58 percent. Statistical analysis using one-way analysis of variance with Friedman multiple test comparison confirmed significant differences among the emulsification datasets, with post-hoc Dunn’s testing showing the greatest divergence between OLW6 and OLW15.

Perhaps most compelling from an applied perspective is the robustness of the biosurfactants under harsh conditions. Near-neutral pH favored production for all isolates, but OLW3 and OLW6 remained active at pH 10, and OLW6 continued producing biosurfactant at 80 degrees Celsius while OLW3 and OLW15 functioned at 50 degrees Celsius. All three tolerated 10 percent sodium chloride, suggesting utility in coastal and saline environments where salt stress often undermines bioremediation. These properties point toward applications ranging from in-situ cleanup in hot climates to microbial enhanced oil recovery, where biosurfactants reduce oil viscosity and improve mobility, and to refinery and petrochemical wastewater treatment. The authors propose that whole-genome sequencing, characterization of metal resistance mechanisms, and high-performance liquid chromatography profiling of the biosurfactants represent the next steps. For now, the message from Ologe Lagoon is clear: even ecosystems degraded by unchecked pollution can yield microbial resources capable of healing environments like their own home.

Subject of Research: Hydrocarbon-degrading, heavy metal-tolerant, biosurfactant-producing bacteria isolated from Ologe Lagoon water and sediments in Lagos State, Nigeria

Article Title: Hydrocarbon degradation and heavy metal tolerance of bacterial isolates from Ologe lagoon water and sediments

Article References: Ashade, A. O., Obayori, O. S., Fashola, M. O., Salam, L. B., & Oso, S. O. (2026). Hydrocarbon degradation and heavy metal tolerance of bacterial isolates from Ologe lagoon water and sediments. BMC Environmental Science, 3(1), Article 8. https://doi.org/10.1186/s44329-026-00051-z

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00051-z

Keywords: bioremediation, hydrocarbon degradation, heavy metal tolerance, biosurfactant, Ologe Lagoon, Alcaligenes, Rossellomorea marisflavi, crude oil pollution, 16S rRNA sequencing, gas chromatography, freshwater pollution, Nigeria