Short- and long-term single and combined effects of microplastics and chromium on the freshwater water flea Daphnia magna

Microplastics and nanoplastics co-exposure modulates chromium bioaccumulation and physiological responses in rats

The environmental fragmentation of plastics generates a mixture of plastic particles of various sizes, which frequently co-occur with other mobile and persistent environmental pollutants. Despite the prevalence of such scenarios, the interaction between micro- and nanoplastics (MNPs) and their combined effects with environmental pollutants, such as highly toxic hexavalent chromium (Cr(VI)), remain almost entirely unexplored in mammalian species. This study demonstrated that nanoplastic and microplastic particles co-aggregate and together influence Cr bioaccumulation patterns and related physiological alterations in rats. Following a four-week repeated intragastric exposure of Wistar rats to MNPs and Cr(VI), either alone or in combination, MNPs significantly enhanced Cr bioaccumulation in the liver, heart, brain, and skin. Under co-exposure conditions, Cr(VI) was the primary driver of cellular effects observed in the blood, including shifts in immune cell subpopulations (e.g., neutrophils, lymphocytes) and alterations in red blood cell indices, while serum biochemistry reflected limited physiological stress. MNPs per se decreased creatine kinase activity and increased cholesterol levels. In summary, polystyrene MNPs increase Cr(VI) distribution and bioavailability, but co-exposure does not uniformly exacerbate toxicity. Instead, their interaction may selectively alter physiological responses, emphasizing the need for a deeper understanding of their combined effects and potential health risks.

Toxicity comparison of polylactic acid and polyethylene microplastics co-exposed with methylmercury on Daphnia magna

The prevalence of microplastics (MPs) in aquatic ecosystems has become a significant environmental concern due to their persistence and potential toxicity. Although bioplastics, such as polylactic acid (PLA), are promoted as eco-friendly alternatives to conventional plastics, their toxicity remains poorly understood. This study compares the toxicity and pollutant vector roles of polar PLA-derived bio-microplastics (bio-MPs) with apolar low-density polyethylene (LDPE) MPs, both individually and in combination with methylmercury (MeHg), in Daphnia magna. PLA bio-MPs, both alone and in combination with MeHg, significantly reduced survival rates and reproduction while inducing oxidative stress. Additionally, PLA bio-MPs increased Hg accumulation and negatively impacted acetylcholinesterase activity and vitellogenin gene expression compared to LDPE MPs. The findings of this study suggest that PLA bio-MPs, despite being in vivo biodegradable, may pose similar or even greater environmental risks than fossil fuel-based MPs, particularly due to their potential to enhance the bioaccumulation and toxicity of coexisting pollutants.

Short-term and long-term effects of microplastics and organic UV-filters on the invertebrate model species Daphnia magna

There is an ongoing debate regarding the role of microplastics (MPs) in enhancing the effects of various chemical compounds, highlighting the need for more detailed analyses. In this study, neonates of the water flea (Daphnia magna) were exposed to polystyrene MPs (PS-MPs; 3 µm; exposure concentration, 1.25 mg/L), a mixture of seven organic UV-filters (avobenzone, ethylhexyl triazone, homosalate, iscotrizinol, octinoxate, octisalate, and octocrylene; each at a low environmental concentration of 200 ng/L), or the combination of both pollutants for 3, 7, or 21 days. Results showed that PS-MPs alone decreased the body size of daphnids, while all treatments increased heart rate by the end of the 21-day exposure. On days 3 and 21, both PS-MPs and PS-MPs + UV-filters reduced swimming speed and total distance travelled. Additionally, PS-MPs increased the time of the first egg production, but decreased the egg number in the first production, total egg number, maximum egg number, and total neonate number during the 21-day treatment. Similarly, UV-filters or the combined pollutants increased the time of the first egg production and decreased the total neonate number. All treatments increased multixenobiotic resistance activity on days 3 and 7, while only UV-filters elevated CYP450 activity on day 3. PS-MPs or combined pollutants increased GST activity during early exposure but showed no effect on day 21. CAT activity was also affected by treatments in a time-dependent manner. These findings demonstrate that chronic exposure to PS-MPs and UV-filters, applied individually or in combination at a low environmental concentration, moderately impacts development, heart rate, and swimming activity in D. magna, while significantly altering reproduction and key cellular functions such as membrane transport activity, metabolism, and antioxidant defense. Co-exposure did not reveal a clear pattern of synergism or antagonism, suggesting that joint toxicity risks of these xenobiotics typically emerge at concentrations higher than low environmental levels. Future studies should explore potential interactions more thoroughly and assess transgenerational effects on reproduction and cellular defense pathways.

Phenotypic and Gene Expression Alterations in Aquatic Organisms Exposed to Microplastics

The use of plastics, valued for its affordability, durability, and convenience, has grown significantly with the advancement of industry. Paradoxically, these very properties of plastics have also led to significant environmental challenges. Plastics are highly resistant to decomposition, resulting in their accumulation on land, where they eventually enter aquatic environments, due to natural processes or human activities. Among these plastics, microplastics, which are tiny plastic particles, are particularly concerning when they enter aquatic ecosystems, including rivers and seas. Their small size makes them easily ingestible by aquatic organisms, either by mistake or through natural feeding behaviors, which poses serious risks. Moreover, microplastics readily adsorb other pollutants present in aquatic environments, creating pollutant complexes that can have a synergistic impact, magnifying their harmful effects compared to microplastics or pollutants acting alone. As a result, extensive research has focused on understanding the effects of microplastics on aquatic organisms. Numerous studies have demonstrated that aquatic organisms exposed to microplastics, either alone or in combination with other pollutants, exhibit abnormal hatching, development, and growth. Additionally, many genes, particularly those associated with the antioxidant system, display abnormal expression patterns in these conditions. In this review, we examine these impacts, by discussing specific studies that explore changes in phenotype and gene expression in aquatic organisms exposed to microplastics, both independently and in combination with adsorbed pollutants.

Adverse effects of environmentally relevant microplastics on in vivo endpoints, oxidative stress, and mitogen-activated protein kinase signaling pathway and multixenobiotic resistance system in the marine rotifer Brachionus plicatilis

This study compared the toxicological effects of environmentally relevant microplastics (MPs) on the marine rotifer Brachionus plicatilis, focusing on MPs derived from various sources, including fossil fuel-based low-density polyethylene, bio-based polylactic acid (PLA), biodegradable poly(butylene adipate-co-terephthalate), and a novel PLA modified with β-cyclodextrin. We assessed in vivo effects such as reproductive output and mortality, alongside in vitro oxidative stress responses, including oxidative stress, antioxidant enzyme activities, and activation of the mitogen-activated protein kinase (MAPK) signaling pathway and the multixenobiotic resistance (MXR) system. Reproductive output and lifespan reduced significantly across all MP types, ranging from 0.5 to 10 mg L-1, indicating compromised reproductive fitness and life maintenance. At an environmentally relevant concentration of 0.5 mg L-1, in vitro assessments revealed differential modulation of reactive oxygen species levels and antioxidant enzyme activities, contingent upon the specific MP type. Moreover, MAPK signaling pathway and MXR assays showed changes in phosphorylation and detoxification proteins depending on the type of MPs. This study highlights the ecological risks that various MPs, including bio-based, biodegradable, and petrochemical-based MPs, could pose in marine environments.

Water acidification aggravates lithium-induced toxicity represented by energy supply, oxidative stress, and cell fate in Daphnia magna neonates

Lithium is extensively utilized in industrial energy production, particularly in lithium-ion batteries, and in pharmaceuticals for the treating clinical mood disorders. Consequently, lithium is frequently detected in various environmental matrices. It has been reported to cause a range of toxic effects on aquatic organisms including oxidative stress, neurological disorders, and reproductive suppression. Water acidification is a global issue with numerous negative impacts on aquatic organisms. It can alter the physio-chemical properties and bioavailability of metal ions. The acidic leaching process during lithium battery treatment and global water acidification both suggest that lithium contamination often occurs in acidic environments. In the present study, Daphnia magna neonates were exposed to four treatments (control, lithium alone, low pH, and combined) to investigate whether an acidic environment exacerbates the toxic effects of lithium on aquatic organisms and to explore potential toxic action mechanisms. The results indicated that low pH posed a significant threat to the growth and reproduction of D. magna. When exposed to both lithium and low pH, there was increased lithium accumulation and an energy trade-off response, leading to increased energy allocation to reproduction and reduced energy for growth. Lithium exposure stimulated D. magna activity, while low pH inhibited it, suggesting that an imbalance in energy consumption and supply. Combined exposure to lithium and low pH resulted in severe oxidative stress due to mitochondrial dysfunction, under-utilization of energy substances, and increased ionic homeostasis disturbances. Consequently, the exposed organism altered apoptosis and autophagy processes to maintain homeostasis. The present study demonstrated that lithium and water acidification posed a population-level threat to D. magna, and their combined exposure significantly largely exacerbated the toxic effects.

Sight of Aged Microplastics Adsorbing Heavy Metal Exacerbated Intestinal Injury: A Mechanistic Study of Autophagy-Mediated Toxicity Response

Contaminant-bearing polystyrene microplastics (PSMPs) may exert significantly different toxicity profiles from their contaminant-free counterparts, with the role of PSMPs in promoting contaminant uptake being recognized. However, studies investigating the environmentally relevant exposure and toxic mechanisms of aged PSMPs binding to Cr are limited. Here, we show that loading of chromium (Cr) markedly alters the physicochemical properties and toxicological profiles of aged PSMPs. Specifically, Cr-bearing aged PSMPs induced severe body weight loss, oxidative stress (OS), autophagy, intestinal barrier injury, inflammation-pyroptosis response, and enteropathogen invasion in mice. Mechanistic investigations revealed that PSMPs@Cr exacerbated the OS, resulting in intestinal barrier damage and inflammation-pyroptosis response via overactivated Notch signaling and autophagy/cathepsin B/IL-1β pathway, respectively, which ultimately elevated mortality related to bacterial pathogen infection. In vitro experiments confirmed that autophagy-mediated reactive oxygen species (ROS) overproduction resulted in severe pyroptosis and impaired intestinal stem cells differentiation alongside the overactivation of Notch signaling in PSMPs@Cr-exposed organoids. Overall, our findings provide an insight into autophagy-modulated ROS overproduction within the acidic environment of autophagosomes, accelerating the release of free Cr from PSMPs@Cr and inducing secondary OS, revealing that PSMPs@Cr is a stable hazard material that induces intestinal injury. These findings provided a potential therapeutic target for environmental MPs pollution caused intestinal disease in patients.

Stressful Effects of Individual and Combined Exposure to Low-Concentration Polylactic Acid Microplastics and Chromium on Marine Medaka Larvae (Oryzias melastigma)

Microplastics and heavy metal pollution frequently co-occur in the marine environment, raising concerns about their potentially harmful impacts on marine fish. This study undertook a comprehensive evaluation of the individual and combined stress effects of polylactide microplastics (PLA-MPs) and chromium (Cr) on marine medaka larvae. Following a 14-day exposure to PLA-MPs (100 μg/L) and Cr (50 μg/L), both individually and in combination, significant increases in heart rate and body length were observed. Notably, the combined exposure to PLA-MPs and Cr caused marked histopathological alterations, including shedding, atrophy, and lysis of the intestinal tissues. Furthermore, both individual and combined exposure induced oxidative stress in fish larvae, leading to changes in various enzyme activity indices. Individual exposure to either PLA-MPs or Cr led to anxious behavior in the larvae, whereas combined exposure not only caused anxious behavior but also altered swimming patterns. These findings suggest that combined exposure to PLA-MPs and Cr can exacerbate the toxic effects on marine medaka larvae.

Colonization characteristics and surface effects of microplastic biofilms: Implications for environmental behavior of typical pollutants

This paper summarizes the colonization dynamics of biofilms on microplastics (MPs) surfaces in aquatic environments, encompassing bacterial characteristics, environmental factors affecting biofilm formation, and matrix types and characteristics. The interaction between biofilm and MPs was also discussed. Through summarizing recent literatures, it was found that MPs surfaces offer numerous benefits to microorganisms, including nutrient enrichment and enhanced resistance to environmental stress. Biofilm colonization changes the surface physical and chemical properties as well as the transport behavior of MPs. At the same time, biofilms also play an important role in the fragmentation and degradation of MPs. In addition, we also investigated the coexistence level, adsorption mechanism, enrichment, and transformation of MPs by environmental pollutants mediated by biofilms. Moreover, an interesting aspect about the colonization of biofilms was discussed. Biofilm colonization not only had a great effect on the accumulation of heavy metals by MPs, but also affects the interaction between particles and environmental pollutants, thereby changing their toxic effects and increasing the difficulty of MPs treatment. Consequently, further attention and research are warranted to delve into the internal mechanisms, environmental risks, and the control of the coexistence of MPs and biofilms.

Single and combined effects of increased temperature and methylmercury on different stages of the marine rotifer Brachionus plicatilis

Rapid, anthropogenic activity-induced global warming is a severe problem that not only raises water temperatures but also shifts aquatic environments by increasing the bioavailability of heavy metals (HMs), with potentially complicated effects on aquatic organisms, including small aquatic invertebrates. For this paper, we investigated the combined effects of temperature (23 and 28 °C) and methylmercury (MeHg) by measuring physiological changes, bioaccumulation, oxidative stress, antioxidants, and the mitogen-activated protein kinase signaling pathway in the marine rotifer Brachionus plicatilis. High temperature and MeHg adversely affected the survival rate, lifespan, and population of rotifers, and bioaccumulation, oxidative stress, and biochemical reactions depended on the developmental stage, with neonates showing higher susceptibility than adults. These findings demonstrate that increased temperature enhances potentially toxic effects from MeHg, and susceptibility differs with the developmental stage. This study provides a comprehensive understanding of the combined effects of elevated temperature and MeHg on rotifers. ENVIRONMENTAL IMPLICATION: Methylmercury (MeHg) is a widespread and harmful heavy metal that can induce lethal effects on aquatic organisms in even trace amounts. The toxicity of metals can vary depending on various environmental conditions. In particular, rising temperatures are considered a major factor affecting bioavailability and toxicity by changing the sensitivity of organisms. However, there are few studies on the combinational effects of high temperatures and MeHg on aquatic animals, especially invertebrates. Our research would contribute to understanding the actual responses of aquatic organisms to complex aquatic environments.

Combined effects of nanoplastics and elevated temperature in the freshwater water flea Daphnia magna

Global warming and nanoplastics (NPs) are critical global issues. Among NPs, one of the most hazardous types of plastics, polystyrene (PS), poses ecotoxicological threats to several freshwater organisms. The degree of toxicity of PS-NPs is strongly influenced by various environmental factors. This study illustrates the combined effects of temperature and PS-NPs on the water flea Daphnia magna. The sensitivity of D. magna to PS-NPs was tested under control (23 °C) and elevated temperatures (28 °C). As a result, increased temperatures influenced the uptake and accumulation of PS-NPs. Co-exposure to both higher temperatures and PS-NPs resulted in a drastic decrease in reproductive performance. The level of oxidative stress was found to have increased in a temperature-dependent manner. Oxidative stress was stimulated by both stressors, leading to increased levels of reactive oxygen species and antioxidant enzyme activity supported by upregulation of antioxidant enzyme-related genes under combined PS-NPs exposure and elevated temperature. In the imbalanced status of intracellular redox, activation of the p38 mitogen-activated protein kinase signaling pathway was induced by exposure to PS-NPs at high temperatures, which supported the decline of the reproductive capacity of D. magna. Therefore, our results suggest that PS-NPs exposure along with an increase in temperature significantly affects physiological processes triggered by damage from oxidative stress, leading to severely inhibited reproduction of D. magna.

Synergistic toxic mechanisms of microplastics and triclosan via multixenobiotic resistance (MXR) inhibition-mediated autophagy in the freshwater water flea Daphnia magna

Since a mixed state of environmental contaminants, including microplastics (MPs), heavy metals, pharmaceuticals, and personal care products (PPCPs), exists in aquatic ecosystems, it is necessary to evaluate not only the adverse effects of exposure to a single stressor but to combined stressors. In this study, we exposed the freshwater water flea Daphnia magna to 2 μm MPs and triclosan (TCS), one of PPCPs, for 48 h to investigate the synergistic toxic consequences of simultaneous exposure to both pollutants. We measured in vivo endpoints, antioxidant responses, multixenobiotic resistance (MXR) activity, and autophagy-related protein expression via the PI3K/Akt/mTOR and MAPK signaling pathways. While MPs single exposure did not show toxic effects in water fleas, simultaneous exposure to TCS and MPs was associated with significantly greater deleterious effects in the form of increased mortality and alterations in antioxidant enzymatic activities compared with water fleas exposed to TCS alone. In addition, MXR inhibition was confirmed by measurement of the expression of P-glycoproteins and multidrug-resistance proteins in MPs-exposed groups, which led to the accumulation of TCS. Overall, these results suggest that simultaneous exposure to MPs and TCS resulted in higher TCS accumulation via MXR inhibition, leading to synergistic toxic effects such as autophagy in D. magna.

Impact of food matrices on the characteristics and cellular toxicities of ingested nanoplastics in a simulated digestive tract

Microplastic and nanoplastic (MNP) pollution has become a major global food safety concern. MNPs can interact with food matrices, and their passage through the gastrointestinal tract can modify their properties. To explore whether and how food matrices influence MNP toxicity, we investigated the interactions between polystyrene nanoplastics (PS-NPs) and food matrices, using an in vitro gastrointestinal digestion model. Then, we tested cell viability, particle uptake and cellular toxicities induced by PS-NPs with food matrices in Caco-2 cells. The results showed that PS-NPs were aggregated, both with and without food matrices, after in vitro gastrointestinal digestion. Glyceryl trioleate exerted greater ability to stabilize digestas and to disperse PS-NPs than starch and bovine serum albumin. The protein corona's protein composition on PS-NPs varied when it interacted with different food matrices. Moreover, when combined with food matrices, the PS-NPs' uptake was enhanced, thus aggravating cellular inflammation, stress, and apoptosis levels. Finally, through co-exposure to a mixture of food matrices, we found a combined negative effect of PS-NPs and cadmium on cellular inflammation, stress, and apoptosis levels. This is the first study to compare the impact of various food matrices on the characteristics and cellular toxicities of ingested NPs in a simulated digestive tract.

Physiological effects and molecular response in the marine rotifer Brachionus plicatilis after combined exposure to nanoplastics and copper

Because nanoplastics (NPs) can transport pollutants, the absorption of surrounding pollutants into NPs and their effects are important environmental issues. This study shows a combined effect of high concentrations of NPs and copper (Cu) in the marine rotifer Brachionus plicatilis. Co-exposure decreased the growth rate, reproduction, and lifespan. The highest level of NP ingestion was detected in the co-treated group, but the Cu concentration was higher in the Cu single-exposure group. ERK activation played a key role in the downstream cell signaling pathway activated by the interaction of NPs and Cu. The increased sensitivity of B. plicatilis to Cu could be due to the impairment of MXR function caused by a high concentration of NPs, which supports our in vivo experiment results. Our results show that exposure to NPs could induce the dysfunction of several critical molecular responses, weakening resistance to Cu and thereby increasing its physiological toxicity in B. plicatilis.

Temperature related toxicity features of acute acetamiprid and thiacloprid exposure in Daphnia magna and implications on reproductive performance

This study investigated the potential for elevated temperature to alter the toxicity of acetamiprid (ACE) and thiacloprid (Thia) in the ecotoxicity model Daphnia magna. The modulation of CYP450 monooxygenases (ECOD), ABC transporter activity (MXR) and incident cellular reactive oxygen species (ROS) overproduction was screened in premature daphnids following acute (48 h) exposure to sublethal concentrations of ACE and Thia (0.1-, 1.0 μM) at standard 21 °C and elevated 26 °C temperatures. Delayed outcomes of acute exposures were further evaluated based on the reproduction performance of daphnids monitored over 14 days of recovery. Exposures to ACE and Thia at 21^o C elicited moderate induction of ECOD activity, pronounced inhibition of MXR activity and severe ROS overproduction in daphnids. In the high thermal regime, treatments resulted in significantly lower induction of ECOD activity and inhibition of MXR activity, suggesting a suppressed metabolism of neonicotinoids and less impaired membrane transport activity in daphnids. Elevated temperature on its own, caused a three-fold rise in ROS levels in control daphnids, while ROS overproduction upon neonicotinoid exposure was less accentuated. Acute exposures to ACE and Thia caused significant decreases also in the reproduction of daphnids, indicating delayed outcomes even at environmentally relevant concentrations. Both the cellular alterations in exposed daphnids and decreases in their reproductive output post exposures evidenced closely similar toxicity patterns and potentials for the two neonicotinoids. While elevated temperature elicited only a shift in baseline cellular alterations evoked by neonicotinoids, it significantly worsened the reproductive performance of daphnids following neonicotinoid exposures.

Recent analytical techniques, and potential eco-toxicological impacts of textile fibrous microplastics (FMPs) and associated contaminates: A review

Despite of our growing understanding of microplastic's implications, research on the effects of fibrous microplastic (FMPs) on the environment is still in its infancy. Some scientists have hypothesized the possibility of natural textile fibres, which may act as one of the emerging environmental pollutants prevalent among microplastic pollutants in the environment. Therefore, this review aims to critically evaluate the toxic effects of emerging FMPs, the presence, and sources of FMPs in the environment, identification and analytical techniques, and the potential impact or toxicity of the FMPs on the environment and human health. About175 publications (2011-2023) based on FMPs were identified and critically reviewed for transportation, analysis and ecotoxicological behaviours of FMPs in the environment. Textile industries, wastewater treatment plants, and household washing of clothes are significant sources of FMPs. In addition, various characterization techniques (e.g., FTIR, SEM, RAMAN, TGA, microscope, and X-Ray Fluorescence Spectroscopy) commonly used for the identification and analysis of FMPs are also discussed, which justifies the novelty aspects of this review. FMPs are pollutants of emerging concern due to their prevalence and persistence in the environment. FMPs are also found in the food chain, which is an alarming situation for living organisms, including effects on the nervous system, digestive system, circulatory system, and genetic alteration. This review will provide readers with a comparison of different analytical techniques, which will be helpful for researchers to select the appropriate analytical techniques for their study and enhance their knowledge about the harmful effects of FMPs.

Heavy metals and metalloid in aquatic invertebrates: A review of single/mixed forms, combination with other pollutants, and environmental factors

Heavy metals (HMs) and metalloid occur naturally and are found throughout the Earth's crust but they are discharged into aquatic environments at high concentrations by human activities, increasing heavy metal pollution. HMs can bioaccumulate in higher organisms through the food web and consequently affect humans. In an aquatic environment, various HMs mixtures can be present. Furthermore, HMs adsorb on other environmental pollutants, such as microplastics and persistent organic pollutants, causing a synergistic or antagonistic effect on aquatic organisms. Therefore, to understand the biological and physiological effects of HMs on aquatic organisms, it is important to evaluate the effects of exposure to combinations of complex HM mixtures and/or pollutants and other environmental factors. Aquatic invertebrates occupy an important niche in the aquatic food chain as the main energy link between higher and lower organisms. The distribution of heavy metals and the resulting toxic effects in aquatic invertebrates have been extensively studied, but few reports have dealt with the relationship between HMs, pollutants, and environmental factors in biological systems with regard to biological availability and toxicity. This review describes the overall properties of individual HM and their effects on aquatic invertebrates and comprehensively reviews physiological and biochemical endpoints in aquatic invertebrates depending on interactions among HMs, other pollutants, and environmental factors.

Presence, variation, and potential ecological impact of microplastics in the largest shallow lake of Central Europe

The presence of microplastics (MPs) in the global ecosystem has generated a rapidly growing concern worldwide. Although their presence in the marine environment has been well-studied, much less data are available on their abundance in freshwaters. MPs alone and in combination with different chemicals has been shown to cause acute and chronic effects on algae and aquatic invertebrate and vertebrate species at different biological levels. However, the combined ecotoxicological effects of MPs with different chemicals on aquatic organisms are still understudied in many species and the reported data are often controversial. In the present study, we investigated, for the first time, the presence of MPs in Lake Balaton, which is the largest shallow lake of Central Europe and an important summer holiday destination. Moreover, we exposed neonates of the well-established ecotoxicological model organism Daphnia magna to different MPs (polystyrene [3 μm] or polyethylene [≤ 100 μm]) alone and in combination with three progestogen compounds (progesterone, drospirenone, levonorgestrel) at an environmentally relevant concentration (10 ng L^-1) for 21 days. The presence of 7 polymer types of MPs in the size range of 50-100 μm was detected in Lake Balaton. Similarly to the global trends, polypropylene and polyethylene MPs were the most common types of polymer. The calculated polymer-independent average particle number was 5.5 particles m^-3 (size range: 50 μm - 100 μm) which represents the values detected in other European lakes. Our ecotoxicological experiments confirmed that MPs and progestogens can affect D. magna at the behavioral (body size and reproduction) and biochemical (detoxification-related enzyme activity) levels. The joint effects were negligible. The presence of MPs may lead to reduced fitness in the aquatic biota in freshwaters such as Lake Balaton, however, the potential threat of MPs as vectors for progestogens may be limited.

Polystyrene microplastics reduce Cr(VI) and decrease its aquatic toxicity under simulated sunlight

Microplastics (MPs) serve as vectors for chromium (Cr), influencing its fate and toxicity in aquatic environments, and have attracted much attention recently. However, it is still unknown whether MPs mediate Cr species transformation under sunlight irradiation. This study confirmed that polystyrene (PS) MPs could reduce Cr(VI) to Cr(III) under sunlight irradiation, with a photoreduction rate constant of 0.0023 h^-1. PS MPs-mediated Cr(VI) reduction was predominantly dependent on O₂^•- and simultaneously suppressed by ¹O₂, •OH and ³PS* . Aged PS MPs were exposed to simulated sunlight irradiation for 0, 200, 500, and 800 h, and Cr(VI) reduction was hindered by increased ¹O₂ and •OH formation and light-screening effects (decreased photon absorption). The size, functional groups and concentration of PS MPs and environmental factors (e.g., humic acid, pH, Mg²⁺, Fe³⁺ and O₂) strongly affected Cr(VI) reduction. Furthermore, Cr(VI) reduction induced by PS MPs could occur in reservoir water, and the reduction rate was faster than that in double distilled (DD) water. Correspondingly, PS MPs (1 mg/L) decreased the oxidative stress induced by Cr(VI) to Lemna minor in reservoir water after 96 h of sunlight irradiation. This study provided deep insight into how PS MPs affect Cr species transformations and hazardous effects in realistic aquatic environments under sunlight conditions.