Effects of microplastics mixed with natural particles on Daphnia magna populations

Alteration to organismal behavior due to microplastic exposure

Influx of plastics into the biosphere has faced increased public scrutiny in the last twenty years. Plastics fragment into particles at the microscale which can lead them to interact with organisms in unanticipated ways. Research has focused on hazards linked to ingestion of microplastics with little research focused on how secondary effects influence organismal behavior and interspecies relationships. Plastics do not establish homogenous test suspensions; they either float or sink. The present study investigated how the presence of microplastics influenced the behavior of Daphnia magna, and two planktivorous fish, Pimephales promelas and Gambusia affinis. The study investigated two plastic types: fluorescent microspheres and microplastic fragments. The results demonstrated that microplastics influenced the behavior of the organisms with effects dependent on species and plastic type. Microplastics attracted D. magna and decreased their mobility and total swimming distance. Both fish species were more often found at the bottom of the chamber and their behavior was linked to D. magna location. Some changes in fish mobility were observed with fluorescent microspheres. Coloration of microplastics may have influenced the organism's responses results and further research is needed. Results of the present study reveal a potential effect of microplastics on communal distribution of aquatic organisms in natural ecosystems.

Toxicity of microplastics polystyrene to freshwater planarians and the alleviative effects of anthocyanins

It is impossible to overlook the effects of microplastics (MPs) on aquatic organisms as they continuously accumulate in water environment. Freshwater planarians, which exist in the benthic zone of water bodies and come into contact with the deposited MPs particles, provide a highly representative model for studying the effects of MPs on aquatic organisms. Anthocyanins (ANTs) have gained significant popularity in recent years for their diverse health benefits. In the current study, the median lethal concentration (LC50) of polystyrene (PS) to planarian Dugesia japonica was determined for the first time. Based on this, multiple toxic effects of single PS and PS in combination with ANTs on planarians were explored. The results showed that PS exposure disrupted the redox homeostasis and induced oxidative damage in planarians. Also, PS stress affected the neuromorphology, aggravated cell apoptosis in planarians probably by altering neural gene expressions as well as promoting the expression of apoptosis-related genes while inhibiting stem cell marker genes. In addition, the results also suggested that co-exposure of ANTs could effectively alleviate the toxicity of PS on planarians. Particularly, long-term environmentally relevant concentration PS exposure exhibited a higher propensity for inducing toxicity on planarians than short-term high concentration acute exposure, indicating that the harm of environmental MPs to humans and wildlife exposed to them should not be underestimated. Therefore, considering the recently rising and rapid development of ecotoxicomics, more in-depth research on the toxicity mechanism of environmentally relevant concentration PS-MPs to freshwater planarians from multi-omics levels will be our future work.

Microplastic Passage through the Fish and Crayfish Digestive Tract Alters Particle Surface Properties

Most studies on the effects of organisms on microplastic characteristics have focused on microorganisms, while the impact of animal feeding behavior, particularly in aquatic species like fish and decapod crustaceans, has been less explored. This study examines how polyethylene spherical microplastics (275 μm in diameter) passing through the digestive tracts of crucian carp (Carassius carassius) and Australian crayfish (Cherax quadricarinatus) affect surface properties, particle size, and bacterial colonization. The species were fed diets with or without microplastics. The particles underwent two rounds of passage through the digestive tracts and were then exposed to known bacterial densities. Surface damage, size, and biofilm coverage were analyzed using scanning electron microscopy, while alterations in surface chemical composition were assessed through Fourier transform infrared spectroscopy with attenuated total reflectance, and the formation and penetration of nanoplastics in gut tissues and glands were determined using Py-GC/MS. Results show that the passage significantly altered surface properties and reduced microplastic size, without affecting chemical composition or nanoplastic penetration into tissues. These changes promoted bacterial colonization compared to controls. The findings suggest that animal feeding activity may play an important role in the mechanical fragmentation of microplastics in aquatic environments, potentially leading to their faster degradation.

Multigenerational toxic effects in Daphnia pulex are induced by environmental concentrations of tire wear particle leachate

Microplastic pollution has emerged as the second most significant scientific issue in environmental science and ecology. Similarly, the biological effects of tire wear particles (TWPs) have garnered considerable research attention; however, studies on chronic TWP leachate toxicity at environmentally relevant concentrations remain sparse. Here, we investigated the effects of TWP leachate at environmentally relevant concentrations (0.3 mg/L and 3 mg/L) on multigenerational and transgenerational Daphnia pulex for 21 days/generation, spanning three generations (F0-F2). Growth and reproductive indices (body length, growth rate, time to first clutch, number of clutches, and total offspring/female) across generations were analyzed. Multigenerational exposure to TWP leachate did not cause D. pulex death, but impaired growth and development, prolonged sexual maturity time, and reduced reproductive capacity. The transgenerational exposure group (3 mg/L) also exhibited some sub-lethal effects, such as delayed reproduction, suggesting a transgenerational impact. Gene transcription analyses and weighted gene co-expression network analysis showed that the most impacted pathways were associated with lysosome function, apoptosis, and glutathione metabolism, indicating that TWP leachate exposure compromised immune defense mechanisms and disrupted APs, CTSB, GST, DUSP1, and ERN1 gene expression. These findings underscore multigenerational toxicity effects and TWP leachate transmission patterns on aquatic organisms at realistic environmental concentrations.

Distinct Effect of Benzophenone-3 Additive Leaching from Polyethylene Microplastics on Daphnia magna Population Dynamics

The adverse effect of chemical additives leaching from microplastics (MPs) on Daphnia magna populations is not fully understood. In this study, D. magna populations were exposed to polyethylene (PE) MP fragments (5.0 mg/L), PE MP fragments containing the ultraviolet stabilizer benzophenone-3 (MP/BP-3 fragments, 5.0 mg/L), and BP-3 leachate (79 ± 10 µg/L) from PE MP/BP-3 fragments. The test duration was 42 days to observe the population dynamics of D. magna. BP-3 leachate delayed the development and somatic growth of D. magna, resulting in a significantly lower (p < 0.05) population size (number of organisms) compared with the control group. For instance, the population size was 7.7 ± 8.1 and 115 ± 3.5 (n = 3), respectively, at 18 d. However, both MP and MP/BP-3 fragments did not significantly decrease (p > 0.05) the population size of D. magna until day 18. These findings suggest that chemical additive leachates from MPs may have a distinct adverse effect on aquatic organisms, requiring further comprehensive investigation.

Combined toxicity of perfluoroalkyl substances and microplastics on the sentinel species Daphnia magna: Implications for freshwater ecosystems

Persistent chemicals from industrial processes, particularly perfluoroalkyl substances (PFAS), have become pervasive in the environment due to their persistence, long half-lives, and bioaccumulative properties. Used globally for their thermal resistance and repellence to water and oil, PFAS have led to widespread environmental contamination. These compounds pose significant health risks with exposure through food, water, and dermal contact. Aquatic wildlife is particularly vulnerable as water bodies act as major transport and transformation mediums for PFAS. Their co-occurrence with microplastics may intensify the impact on aquatic species by influencing PFAS sorption and transport. Despite progress in understanding the occurrence and fate of PFAS and microplastics in aquatic ecosystems, the toxicity of PFAS mixtures and their co-occurrence with other high-concern compounds remains poorly understood, especially over organisms' life cycles. Our study investigates the chronic toxicity of PFAS and microplastics on the sentinel species Daphnia, a species central to aquatic foodwebs and an ecotoxicology model. We examined the effects of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and polyethylene terephthalate microplastics (PET) both individually and in mixtures on Daphnia ecological endpoints. Unlike conventional studies, we used two Daphnia genotypes with distinct histories of chemical exposure. This approach revealed that PFAS and microplastics cause developmental failures, delayed sexual maturity and reduced somatic growth, with historical exposure to environmental pollution reducing tolerance to these persistent chemicals due to cumulative fitness costs. We also observed that the combined effect of the persistent chemicals analysed was 59% additive and 41% synergistic, whereas no antagonistic interactions were observed. The genotype-specific responses observed highlight the complex interplay between genetic background and pollutant exposure, emphasizing the importance of incorporating multiple genotypes in environmental risk assessments to more accurately predict the ecological impact of chemical pollutants.

Role of benzophenone-3 additive in the effect of polyethylene microplastics on Daphnia magna population dynamics

The adverse effects of microplastics (MPs) on Daphnia magna have been extensively studied; however, their population-level effects are relatively unknown. This study investigated the effect of polyethylene MP fragments (33.90 ± 17.44 μm) and benzophenone-3 (BP-3), which is a widely used plastic additive (2.91 ± 0.02% w/w), on D. magna population dynamics in a 34-day microcosm experiment. In the growth phase, neither MP nor MP/BP-3 fragments changed the population size of D. magna compared with the control. However, MP/BP-3 fragments significantly reduced (p < 0.05) the population biomass compared to that of the control, whereas MP fragments did not induce a significant reduction. The MP/BP-3 group had a significantly higher (p < 0.05) neonate proportion than that in the control and MP groups. MP/BP-3 fragments upregulated usp and downregulated ecrb, ftz-f1, and hr3, altering gene expression in the ecdysone signaling pathway linked to D. magna growth and development. These findings suggested that BP-3 in MP/BP-3 fragments may disrupt neonatal growth, thereby decreasing population biomass. In the decline phase, MP fragments significantly decreased (p < 0.05) the population size and biomass of D. magna compared with the control and MP/BP-3 fragments. This study highlights the importance of plastic additives in the population-level ecotoxicity of MPs.