Food availability is crucial for effects of 1-μm polystyrene beads on the nematode Caenorhabditis elegans in freshwater sediments

Impact of microplastic concentration on soil nematode communities on the Qinghai-Tibet Plateau: Evidence from a field-based microcosms experiment

Microplastics are an emerging pollutant that poses a threat to local ecosystems. Recent studies have revealed that microplastics have penetrated the Qinghai-Tibetan Plateau. While previous studies have investigated the migration and distribution of microplastics and their effects on soil properties, their effects on soil fauna communities remain underexplored. Here, we conducted a 1-year microplastic addition experiment to evaluate the responses of soil nematode communities and employed piecewise structural equation modeling to disentangle the direct and indirect effects of microplastics on these communities. We found that: (1) nematode abundance, diversity, and metabolic footprints exhibited a hump-shaped response to microplastic treatments, peaking at the 0.1 % treatment; (2) nematode biomass was significantly affected by microplastics, with the lowest biomass observed at the 10 % treatment; (3) the direct effects of microplastics on nematode abundance outweighed indirect effects, particularly influencing fungivores and omnivorous nematodes; (4) although microplastics did not significantly alter energy flow within nematode communities, the relationship between the energy flow of fungivores and omnivorous was stronger than those among other trophic groups. Our study offers insights on microplastics' impact on nematode communities and their varied responses to microplastic concentrations, crucial for understanding ecological effects on soil ecosystems.

Interactions between nanoplastics and Tetrahymena thermophila: Low toxicity vs. potential biodegradation

Nanoplastics (NPs) are prevalent throughout the environment and have raised growing environmental concerns. Although numerous studies have examined the toxicological aspects of NPs, few have investigated their environmental fate and behavior when affected by organisms other than bacteria or fungi. Planktonic ciliates are essential components of aquatic ecosystems and play important roles in decomposing organic matter and transferring energy from the microbial food web to higher trophic levels. To investigate the interplay between NPs and the ciliate Tetrahymena thermophila, we executed a sequence of feeding experiments utilizing 50 nm polystyrene nanoplastics (PS-NPs). In the presence of sufficient nutrition, exposure to PS-NPs (even at concentrations up to 500 mg/L) did not significantly inhibit growth in Tetrahymena thermophila, indicating only a mild toxic effect of PS-NPs. When ingested by T. thermophila, the PS-NPs are repackaged into aggregates with lysosomal components in the food vacuole and finally expelled as compacted "fecal pellets". This process modifies the physical attributes of PS-NPs, including their hydrophilicity, aggregability, and buoyancy, influencing their transportation, retention, deposition dynamics, and ultimately their bioavailability within the environment. A total of 73 proteins were identified from the fecal pellets, containing various hydrolases. Gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA) were used to identify changes in molecular weights, functional groups, and thermal stabilities of PS-NP residues in fecal pellets. The results verified the degradation of PS-NPs during the passage through the T. thermophila cell.

Benefits and costs: Understanding the influence of heavy metal pollution on environmental adaptability in Strauchbufo raddei tadpoles through an energy budget perspective

Understanding the impact of environmental pollution on organismal energy budgets is crucial for predicting adaptive responses and potential maladaptation to stressors. However, the regulatory mechanism governing the trade-off between energy intake and consumption remains largely unknown, particularly considering the diverse adaptations influenced by exposure history in realistic field conditions. In the present study, we conducted a simulated field reciprocal transplant experiment to compare the energy budget strategies of Strauchbufo raddei tadpoles exposed to heavy metal. The simulated heavy metal concentrations (0.29 mg/L Cu, 1.17 mg/L Zn, 0.47 mg/L Pb, 0.16 mg/L Cd) mirrored the actual environmental exposure concentrations observed in the field habitat. This allowed for a comparison between tadpoles with parental chronic exposure to heavy metal pollutants in their habitat and those without such exposure. Results revealed that under heavy metal exposure, tadpoles originating from unpolluted areas exhibited heightened vulnerability, characterized by reduced food intake, diminished nutrient absorption, increased metabolism cost, reduced energy reserves, and increased mortality rates. In contrast, tadpoles originating from areas with long-term heavy metal pollution demonstrated adaptive strategies, manifested through adjustments in liver and small intestine phenotypes, optimizing energy allocation, and reducing energy consumption to preserve energy, thus sustaining survival. However, tadpoles from polluted areas exhibited certain maladaptive such as growth inhibition, metabolic suppression, and immune compromise due to heavy metal exposure. In conclusion, while conserving energy consumption has proven to be an effective way to deal with long-term heavy metal stress, it poses a threat to individual survival and population development in the long run.

Do functional traits and biochemical biomarkers of the nematode Oncholaimus campylocercoides De Coninck and Schuurmans Stekhoven, 1933 affected by fluoranthene and polystyrene microplastics? Results from a microcosm bioassay and molecular modeling

The current experiment measured the multifaceted effects of polystyrene and fluoranthene, acting alone or in a mixture, on the meiobenthic nematode species Oncholaimus campylocercoides. This Oncholaimid was first experimentally selected from an entire nematode assemblage taken from the Jeddah coasts (Saudi Arabia). Several discernible changes were found in morphometry and functional traits after exposure to single and combined treatments. An increase in the activity of the biochemical biomarkers catalase and glutathione S-transferase was also observed following the exposure of males and gravid females of O. campylocercoides to 37.5 ng fluoranthene·g-1 dry weight (DW) and 62.5 mg polystyrene·kg-1 DW paralleled by a higher vulnerability of females. Moreover, the reproduction and feeding of this species were impaired, starting from 37.5 ng fluoranthene·g-1 and 62.5 mg polystyrene·kg-1, respectively. These results have been confirmed by good binding affinities and molecular interactions of fluoranthene and polystyrene with both GLD-3 and SDP receptors.

The multifaceted effects of fluoranthene and polystyrene on the taxonomic composition and associated functional traits of marine meiofauna, by using single and mixture applications

The current experiment measured the multifaceted effects of polystyrene and fluoranthene, acting alone or in a mixture on marine meiofauna, but with a special focus on nematodes' morphological and functional traits. The results showed changes in the abundances for all tested concentrations of both compounds. The nematode communities exposed to the highest concentrations of fluoranthene (30 ng.g-1 Dry Weight (DW)) and polystyrene (100 mg.kg-1 DW) alone or in a mixture, were significantly less diverse compared to control and were associated with significant changes in the percentage of taxonomic composition and feeding-guilds. The most sensitive taxa to fluoranthene comprised epistratum feeders, whereas the nematodes mostly affected by polystyrene were omnivores-carnivores. A new functional tool, the Index of Sensitivity (IOS), proved to be reliable in depicting the changes that occurred in the taxonomic and functional features of the nematofauna.

Multigenerational effects of co-exposure to dimethylarsinic acid and polystyrene microplastics on the nematode Caenorhabditis elegans

In the current study, we assessed the impact of DMA (dimethylarsinic acid) and MPs (microplastics) interactions in C. elegans over the course of five generations. We found that the redox state of the organisms changed over generations as a result of exposure to both pollutants. From the third generation onward, exposure to MPs reduced GST activity, indicating reduced detoxifying abilities of these organisms. Additionally, dimethylarsinic exposure decreased the growth of organisms in the second, fourth, and fifth generations. In comparison to isolated pollutants, the cumulative effects of co-exposure to DMA and MPs seem to have been more harmful to the organisms, as demonstrated by correlation analysis. These findings demonstrate that DMA, despite being considered less hazardous than its inorganic equivalents, can still have toxic effects on species at low concentrations and the presence of MPs, can worsen these effects.

A framework for systematic microplastic ecological risk assessment at a national scale

Microplastic pollution is widespread in terrestrial and aquatic environments; however, a systematic assessment of the ecological risks of microplastics is lacking. This study collected research studies on microplastics in soil, aquatic and sediment environments, and screened 128 articles including 3459 sites to assess the ecological risks posed by microplastics in China following a literature quality assessment. We developed a systematic ecological risk assessment framework for microplastics in terms of spatial characterization, biotoxicity and anthropogenic impacts. The results of the pollution load index indicated that 74% and 47% of the soil and aquatic environments studied, respectively, faced a medium or higher level of pollution. Comparing predicted no effect concentrations (PNEC) and measured environmental concentrations (MECs), revealed that soil (97.70%) and aquatic (50.77%) environmental studies were at serious ecological risk from microplastics. The results of the pressure-state-response model showed that the microplastic pollution in Pearl River Delta was in a high-risk state. In addition, we found that ultraviolet radiation and rainfall exacerbate soil microplastic pollution, and higher river runoff may carry large amounts of microplastic from the source. The framework developed in this study will help assess the ecological risks of microplastics in the region to promote the mitigation of plastic pollution.

Reproductive toxicity of micro- and nanoplastics

Large-scale plastic pollution occurs in terrestrial and marine environments and degrades into microparticles (MP) and nanoparticles (NP) of plastic. Micro/nanoplastics (MP/NPs) are found throughout the environment and different kinds of marine organisms and can enter the human body through inhalation or ingestion, particularly through the food chain. MPs/NPs can enter different organisms, and affect different body systems, including the reproductive, digestive, and nervous systems via the induction of different stresses such as oxidative stress and endoplasmic reticulum stress. This paper summarizes the effects of MPs/NPs of different sizes on the reproduction of different organisms including terrestrial and marine invertebrates and vertebrates, the amplification of toxic effects between them through the food chain, the serious threat to biodiversity, and, more importantly, the imminent challenge to human reproductive health. There is a need to strengthen international communication and cooperation on the remediation of plastic pollution and the protection of biodiversity to build a sustainable association between humans and other organisms.

Biochemical and physiological effects of multigenerational exposure to spheric polystyrene microplastics in Caenorhabditis elegans

Although studies have already shown the effects of exposure to microplastics (MP) in different species, the effects over generations in these individuals remain poorly understood. Therefore, the present study aimed to evaluate the effect of polystyrene MP (spherical, 1 μm) on the responses of the free-living nematode Caenorhabditis elegans in a multigenerational approach over five subsequent generations. MP concentrations of both 5 and 50 μg/L induced a detoxification response, increasing glutathione S-transferase (GST) activity and inducing the generation of reactive oxygen species (ROS) and lipid peroxidation (TBARS). MP also demonstrated the ability to accumulate in the animal's body during the 96 h of each generational exposure, and possibly, this constant interaction was the main reason for the decreased response in physiological parameters as in the exploratory behavior (body bending) of nematodes, and in the reproduction, being this last parameter most negatively affected during the five exposed generations, with a reduction of almost 50% in the last generation. These results emphasize the importance of multigenerational approaches, highlighting their advantage in the assessment of environmental contaminants.

Long-Term Toxicity of 50-nm and 1-μm Surface-Charged Polystyrene Microbeads in the Brine Shrimp Artemia parthenogenetica and Role of Food Availability

Micro and nanoplastics (MNPs) as emerging contaminants have become a global environmental issue due to their small size and high bioavailability. However, very little information is available regarding their impact on zooplankton, especially when food availability is a limiting factor. Therefore, the present study aims at evaluating the long-term effects of two different sizes (50 nm and 1 μm) of amnio-modified polystyrene (PS-NH₂) particles on brine shrimp, Artemia parthenogenetica, by providing different levels of food (microalgae) supply. Larvae were exposed to three environmentally relevant concentrations (5.5, 55, and 550 μg/L) of MNPs over a 14-days of exposure with two food levels, high (3 × 10⁵~1 × 10⁷ cells/mL), and low (1 × 10⁵ cells/mL) food conditions. When exposed to high food levels, the survival, growth, and development of A. parthenogenetica were not negatively affected at the studied exposure concentrations. By comparison, when exposed to a low food level, a U shape trend was observed for the three measured effects (survival rate, body length, and instar). Significant interactions between food level and exposure concentration were found for all three measured effects (three-way ANOVA, p < 0.05). The activities of additives extracted from 50 nm PS-NH₂ suspensions were below toxic levels, while those from 1-μm PS-NH₂ showed an impact on artemia growth and development. Our results demonstrate the long-term risks posed by MNPs when zooplankton have low levels of food intake.

Risk assessment of microplastics in freshwater sediments guided by strict quality criteria and data alignment methods

Determining the risks of microplastics is difficult because data is of variable quality and cannot be compared. Although sediments are important sinks for microplastics, no holistic risk assessment framework is available for this compartment. Here we assess the risks of microplastics in freshwater sediments worldwide, using strict quality criteria and alignment methods. Published exposure data were screened for quality using new criteria for microplastics in sediment and were rescaled to the standard 1-5000 µm microplastic size range. Threshold effect data were also screened for quality and were aligned to account for the polydispersity of environmental microplastics and for their bioaccessible fraction. Risks were characterized for effects triggered by food dilution or translocation, using ingested particle volume and surface area as ecologically relevant metrics, respectively. Based on species sensitivity distributions, we determined Hazardous Concentrations for 5% of the species (HC₅, with 95% CI) of 4.9 × 10⁹ (6.6 × 10⁷ - 1.9 × 10¹¹) and 1.1 × 10¹⁰ (3.2 × 10⁸ - 4.0 × 10¹¹) particles / kg sediment dry weight, for food dilution and translocation, respectively. For all locations considered, exposure concentrations were either below or in the margin of uncertainty of the HC₅ values. We conclude that risks from microplastics to benthic communities cannot be excluded at current concentrations in sediments worldwide.

Long-term exposure of a free-living freshwater micro- and meiobenthos community to microplastic mixtures in microcosms

Microplastics in a wide range of shapes and polymer types (MPs; <5 mm) accumulate in freshwater sediments, where they may pose an environmental threat to sediment-dwelling micro- and meiobenthos. To date, the effects of MPs on those organisms have mostly been studied in single-species experiments exposed to high particle concentrations. By contrast, there have been few investigations of the effects resulting from the long-term exposure of natural communities to environmental relevant MPs. This research gap was addressed in the present study. A microcosm experiment was conducted to examine the impact of a mixture of MPs of varying polymer composition, shape, and size (50% polystyrene (PS) beads: 1-μm diameter; 37% polyethylene terephthalate (PET) fragments: 32 × 21 μm in size, and 13% polyamide (PA) fibers 104 × 15 μm in size; % based on the total particle number) provided at two concentrations (low: 4.11 × 10⁵ MPs/kg sediment dw and high: 4.11 × 10⁷ MPs/kg sediment dw) and two exposure durations (4 and 12 weeks) on a micro- and meiobenthic community collected from a freshwater sediment. MPs exposure did not alter the abundance of protozoa (ciliates and flagellates) as well as the abundance and biomass of meiobenthic organisms (nematodes, rotifers, oligochaetes, gastrotrichs, nauplii), whereas the abundance and biomass of harpacticoid copepods was affected. Neither nematode species diversity (species richness, Shannon-Wiener index, and evenness) nor the NemaSPEAR[%]-index (pollution-sensitive index based on freshwater nematodes) changed in response to the MPs. However, changes in the structure of the meiobenthic and nematode community in the presence of environmentally relevant MPs mixtures cannot be excluded, such that microcosms experiments may be of value in detecting subtle, indirect effects of MPs.