The review’s methodology was deliberately rigorous. The team searched Web of Science and Scopus from 1970 all the way to August 2025, using predefined combinations of terms covering microplastics, marine microalgae, toxicity, and marine pollution. After removing duplicates and screening titles, abstracts, and keywords, 59 publications addressing microplastic–microalgae interactions were retained for bibliometric characterization. Of these, 43 original studies reporting direct experimental exposure of marine microalgae to plastic particles qualified for the comparative ecotoxicological synthesis. Strikingly, no eligible publications predate 2016, indicating that this research field is barely a decade old. Publication output grew from a single paper in 2016 to a peak of fourteen in 2024, a trajectory that mirrors the broader explosion of microplastic science but also reveals how young and incomplete the evidence base for marine primary producers remains compared with the meta-analyses already available for fish and aquatic invertebrates.

Geographically, the field is strikingly concentrated. China accounted for 54.24 percent of the 59 selected publications, followed by Spain and South Korea at 6.78 percent each, with Portugal, France, Italy, Belgium, and Brazil contributing smaller shares. Sixteen countries appeared in total, yet only seven publications involved international co-authorship, a mere 11.86 percent. The authors suggest this insularity may contribute to the methodological heterogeneity that pervades the literature, since research groups working in isolation tend to adopt different experimental designs, particle characteristics, and exposure conditions. The dominance of Chinese output aligns with global bibliometric trends in aquatic ecotoxicology and has been linked to expanded research funding, notably through the National Natural Science Foundation of China since 2015.

When it comes to what is being tested, one polymer dominates the experimental record. Polystyrene appeared in 25 of the 43 studies, followed by polyethylene in 10, polyvinyl chloride in 5, and polymethyl methacrylate in 3. Polyamide, polylactic acid, polybutylene succinate, polyethylene terephthalate, tire wear particles, and gear-derived microplastics each featured in a single study. The review’s authors point out an important disconnect here: polystyrene’s laboratory ubiquity likely reflects the commercial availability of standardized fluorescent spheres and microbeads rather than its environmental prevalence, since polyethylene and polypropylene are often more abundant in surface waters. This mismatch between what scientists test and what organisms actually encounter in the ocean has significant implications for extrapolating laboratory findings to real-world risk assessment.

The organisms under scrutiny show a similar taxonomic skew. Diatoms, the glass-walled phytoplankton that underpin much of coastal and oceanic productivity, were investigated in 22 studies, or 51.2 percent of the experimental dataset. Chlorophyta, the green algae, featured in 10 studies, and dinoflagellates in 8. Other groups, including haptophytes, raphidophytes, cryptophytes, cyanobacteria, and red algae, were barely represented. The authors highlight this as a critical gap, noting that coccolithophores, for example, play a central role in the marine calcium carbonate cycle yet remain almost entirely unstudied in the microplastic context. Because microplastic toxicity is increasingly recognized as species-specific, expanding taxonomic diversity is essential for predicting how entire phytoplankton communities, not just a handful of laboratory workhorses, might respond to chronic plastic exposure.

So what do the experiments actually show? The most frequently evaluated endpoints were grouped into six functional categories, and growth and population parameters led by a wide margin, assessed in 40 of the 43 studies. Growth inhibition, growth rate, cell density, and cell viability were the workhorse measurements. Cellular stress and damage indicators, particularly oxidative stress driven by overproduction of reactive oxygen species, appeared in 29 studies, with documented consequences including lipid peroxidation, membrane damage, organelle injury, and reduced esterase activity. Photosynthetic physiology, encompassing photosynthetic rate, efficiency, photochemistry, and chlorophyll fluorescence, was examined in 20 studies, while structural and interaction parameters such as aggregation appeared in 25, photosynthetic biochemistry in 14, and broader biochemical or metabolic responses in 13.

The mechanisms of toxicity emerging from this literature are multifaceted. Smaller particles appear to exert greater toxicity through enhanced surface interactions with algal cells, whereas larger particles can inhibit growth indirectly through shading, physically blocking the light that photosynthetic cells depend on. Direct physical interference has been demonstrated in the diatom Skeletonema costatum, where cell–particle contact disrupts normal function. Microplastics can also act as vectors for other contaminants: work by Prata and colleagues showed that the presence of microplastics can alter the toxicity of pharmaceuticals such as procainamide and doxycycline in the microalga Tetraselmis chuii. Meanwhile, species-specific hetero-aggregation between plastic particles and phytoplankton, first characterized by Long and colleagues, can reshape particle dynamics in the water column, modifying light availability and nutrient exchange in ways that ripple through entire microbial communities.

Perhaps the most conceptually important section of the review concerns what the authors call the dynamic nature of microplastics. Particles in the ocean are not static objects. Aging and weathering alter surface chemistry, charge, roughness, and functional groups, changing how particles aggregate, adsorb contaminants, leach additives, and interact with cells. Dissolved organic matter and algal extracellular polymeric substances can coat particles in an eco-corona; one study showed that this coating actually reduced the toxicity of polystyrene nanoplastics to marine Chlorella by decreasing particle–cell interactions and oxidative stress. Biofilms growing on plastic surfaces can modify particle density, transport, and bioavailability, while weathering may enhance the release of polymer additives that contribute chemical toxicity of their own. Yet these environmentally transformed particles remain severely underrepresented in experimental work, meaning most laboratory findings rest on pristine, commercially manufactured plastics that bear little resemblance to weathered marine debris.

The review is refreshingly candid about the limits of the evidence. Most experiments rely on short-term laboratory assays with simplified exposure scenarios, often using concentrations exceeding those typically found in nature. Indeed, studies employing environmentally relevant concentrations and particle-size distributions have reported limited or no effects on microalgal growth under the conditions tested. The authors therefore argue that current evidence supports the identification of potential toxicity mechanisms far more strongly than it supports quantitative ecological risk prediction. They also flag transient effects, in which initial physiological vulnerability gives way to adaptive recovery, as a phenomenon that complicates interpretation and underscores the need to quantify actual particle bioavailability in exposure media.

Critical endpoints remain almost entirely unexplored: aggregate formation, particle sinking dynamics, DNA damage, relative electron transfer rates, and long-term exposure under realistic conditions all fall into this category. These are not academic omissions. Because microalgae sit at the base of marine food webs, alterations in their growth, lipid composition, and photosynthetic performance could propagate upward, influencing trophic transfer of both energy and plastic particles themselves. The review proposes a practical path forward: pairing robust apical endpoints such as growth inhibition, already standardized in OECD algal testing guidelines, with complementary photosynthetic physiology measures, while deploying biochemical biomarkers for mechanistic interpretation. The authors stop short of claiming laboratory responses translate directly into ecological harm. Instead, their synthesis delivers something arguably more valuable: a clear-eyed map of what we know, what we have merely assumed, and what the next decade of microplastic ecotoxicology must urgently address if science is to keep pace with one of the planet’s most pervasive pollutants.

Subject of Research: Ecotoxicological effects of microplastic exposure on marine microalgae

Article Title: Microplastic toxicity in marine microalgae: an ecotoxicological synthesis of experimental biological responses

Article References: Santos, N. G. R., Pinho, K. F. B., Reis, I. D. C. S., Luvizotto-Santos, R., & Jorge, M. B. (2026). Microplastic toxicity in marine microalgae: an ecotoxicological synthesis of experimental biological responses. Ecotoxicology, 35(8), Article 178. https://doi.org/10.1007/s10646-026-03181-x

Image Credits: AI Generated

DOI: 10.1007/s10646-026-03181-x

Keywords: microplastics, marine microalgae, ecotoxicology, oxidative stress, photosynthesis, phytoplankton, polystyrene, polyethylene, primary productivity, eco-corona, marine pollution, systematic review

The review followed the PRISMA-ScR reporting guidelines for scoping reviews, searching five databases between January 2010 and February 2026 for studies that exposed freshwater fish to silver nanoparticles through water and compared at least two surface conditions under equivalent circumstances. Twenty-one studies met those strict criteria, and together they paint a picture of a field dominated by a handful of model organisms. Zebrafish, Danio rerio, appears in virtually every endpoint category examined, from lethality and malformations to oxidative stress, DNA damage, neurobehavioral changes, histopathology and gene expression. Japanese medaka, Oryzias latipes, is the second most represented species, while rainbow trout and a few neotropical fish round out the dataset. Across all of these species, oxidative stress and silver bioaccumulation were the most broadly assessed endpoints, while genotoxicity and behavioral effects remained largely confined to the two main laboratory models.

To understand why surface chemistry matters so much, it helps to grasp what happens to a silver nanoparticle the moment it enters freshwater. Unlike seawater, where high ionic strength screens the electrostatic repulsion between particles and triggers almost instant agglomeration, freshwater allows nanosilver to remain colloidally stable for longer periods. That stability keeps the particles suspended in the water column where pelagic fish encounter them, but it also means the particles continue to oxidize and release silver ions, the single most important driver of nanosilver toxicity. Over time, agglomeration and sedimentation progressively shift the particles toward the benthic compartment, transferring the exposure burden from open-water fish to bottom-dwelling organisms. Temperature, fluctuating water levels and algal exudates have all been shown to accelerate ion release, while sulfidation and chlorination in natural waters lock silver into far less soluble compounds such as silver sulfide and silver chloride.

Manufacturers fight this instability by wrapping particles in capping agents, and the choice of wrapper turns out to be a decisive toxicological variable. The most common coatings in chemically synthesized nanosilver are citrate, polyvinylpyrrolidone, polyethylene glycol, gum arabic, silicate and polyethyleneimine, with citrate, PVP and PEI dominating the fish literature. The comparative evidence reveals a striking lack of consistency about which coating is worst. In zebrafish embryos, one study of five differently stabilized formulations concluded that the toxicity mechanism depends entirely on the stabilizer: in some cases the coating itself was the poison, in others the nanoparticle, and in others a combination of both. Another zebrafish study found that adding a coating actually increased toxicity compared with naked particles, because a positively charged hydroxyethylcellulose shell reacted more strongly with the negatively charged chorion surrounding the embryo. A third investigation of fourteen different preparations ranked PVP-coated particles as the most toxic, largely because PVP and thiol coatings released the most silver ions.

Rainbow trout told a different story. When researchers compared citrate, branched PEI, PVP and silicate coatings at an environmentally realistic concentration of 50 micrograms per liter, PVP proved the most bioavailable but not the most toxic. Instead, citrate and branched PEI, both charged coatings, produced the greatest genotoxicity and inflammation, reinforcing surface charge as a primary driver of biological damage. In Japanese medaka, gum arabic-coated particles were the most lethal despite releasing little ionic silver, pointing to a genuinely particle-specific toxicity pathway. A follow-up study with ten formulations confirmed gum arabic as the most dangerous coating and traced the mechanism to disruption of sodium regulation through inhibition of the Na+/K+-ATPase pump at the ionocytes of the gill epithelium, rather than to oxidative stress. The same coating can therefore occupy entirely different positions in a toxicity ranking depending on the species, life stage and endpoint being measured.

Particle size compounds the picture. In adult zebrafish exposed to citrate- or PVP-coated particles of 20 and 100 nanometers, size contributed more to toxicity than coating type, with smaller particles consistently more damaging. Yet even here the coating mattered: at equivalent sizes, citrate-coated particles outperformed PVP-coated ones across oxidative stress, DNA damage and apoptosis endpoints, even though PVP-exposed fish accumulated more silver in their tissues. That dissociation between internalized silver and harm is one of the review’s most important insights, because it demonstrates that total tissue burden is a poor proxy for toxicological risk. What matters is not how much silver enters the fish but in what chemical form, released where, and at what rate, a conclusion that challenges the assumptions underlying many standard hazard assessments.

Once nanosilver enters a natural water body, its synthetic coating is almost immediately overlaid by a second layer of adsorbed molecules, the eco-corona, composed of humic and fulvic substances, proteins, carbohydrates and extracellular polymeric substances. This environmental corona resets the particle’s biological interface, typically increasing its hydrodynamic diameter, rendering its surface more negative and blocking the oxidation sites where silver ions are generated. The review found that natural organic matter, especially humic acid, consistently mitigates nanosilver toxicity in fish. In zebrafish larvae, humic acid reduced mortality in a concentration-dependent manner by acting as a barrier to ion release. In adult zebrafish, humic acid actually increased dissolved silver over time by complexing ions through its carboxylic groups, yet mortality and behavioral impairments were still alleviated, showing that toxicity mechanisms extend well beyond simple ion release. An ex vivo gill model in two neotropical species confirmed reduced bioaccumulation, oxidative stress and ion release in the presence of humic acids, extending the protective effect beyond standard laboratory models.

Environmental transformations over time add further layers of complexity. Aged silver nanoparticles proved significantly more toxic than freshly prepared ones in medaka embryos, because ten days of aging increased ionic silver release in linear proportion to mortality. Humic acid counteracted this effect, but only when it had been pre-incubated with the particles, highlighting that contact time is essential for eco-corona formation and its protective action. Sulfidation, the natural conversion of particle surfaces to silver sulfide, acted as what one research team called a natural antidote: mortality in zebrafish embryos decreased progressively with increasing sulfidation levels, and sulfidated particles alleviated hepatic oxidative stress and brain acetylcholinesterase suppression in adult fish. Even the absence of a coating proved informative, as uncoated particles aggregated on the outer chorion surface without penetrating the embryo, yet still caused harm through ions generated at the chorion surface, confirming that the embryonic envelope functions as a filter for particles but not for dissolved silver.

The review closes with a candid assessment of the field’s blind spots. Most studies employed concentrations in the milligram-per-liter range, far above reported environmental levels, and only one included study used a genuinely environmentally relevant concentration of 20 micrograms per liter. The assumption that green-synthesized nanoparticles, made with plant extracts as reducing and capping agents, are inherently safer was directly contradicted by a zebrafish study in which green-synthesized particles were markedly more toxic than PVP-coated counterparts, releasing more ionic silver despite similar sizes, while a comparison in silver carp was confounded by lead contamination in the chemical reference material. Taxonomic coverage remains narrow, dominated by zebrafish and medaka, and endpoints skew toward embryo lethality rather than reproduction, neurobehavior or histopathology. The author argues that hazard assessments based solely on pristine, as-synthesized nanoparticles likely overestimate environmental risk, and that future experiments must track surface transformations dynamically, use realistic exposure levels and broaden both species and endpoints if protective water quality criteria for this emerging nanopollutant are to rest on solid ground.

Subject of Research: How surface coatings, eco-corona formation and environmental transformations modulate silver nanoparticle toxicity in freshwater fish

Article Title: Surface coatings and eco-corona as modulators of silver nanoparticle toxicity in freshwater fish

Article References: Ale, A. (2026). Surface coatings and eco-corona as modulators of silver nanoparticle toxicity in freshwater fish. Discover Toxicology, 3(1), Article 14. https://doi.org/10.1007/s44339-026-00060-2

Image Credits: AI Generated

DOI: 10.1007/s44339-026-00060-2

Keywords: silver nanoparticles, nanotoxicology, freshwater fish, eco-corona, surface coatings, zebrafish, humic acid, sulfidation, oxidative stress, silver ion release, green synthesis, ecotoxicology