Mechanisms influencing the impact of microplastics on freshwater benthic invertebrates: Uptake dynamics and adverse effects on Chironomus riparius

New insights into changes in phosphorus profile at sediment-water interface by microplastics: Role of benthic bioturbation

Microplastics (MPs) have attracted increasing attention due to their ubiquitous occurrence in freshwater sediments and the detrimental effects on benthic invertebrates. However, a clear understanding of their downstream impacts on ecosystem services is still lacking. This study examines the effects of bio-based polylactic acid (PLA), fuel-based polyethylene terephthalate (PET), and biofilm-covered PET (BPET) MPs on the bioturbator chironomid larvae (Tanypus chinensis), and the influence on phosphorus (P) profiles in microcosms. The changes in biochemical responses and metabolic pathways indicated that MPs disrupted energy synthesis by causing intestinal blockage and oxidative stress in T. chinensis, leading to energy depletion and impaired bioturbation activity. The impairment further resulted in enhanced sedimentary P immobilization. For larval treatments, the internal-P loadings were respectively 11.4%, 8.6%, and 9.0% higher in the PLA, PET, and BPET groups compared to the non-MP control. Furthermore, the influence of bioturbation on P profiles was MP-type dependent. Both BPET and PLA treatments displayed more obvious impacts on P profiles compared to PET due to the changes in MP bioavailability or sediment microenvironment. This study connects individual physiological responses to broader ecosystem services, showing that MPs alter P biogeochemical processes by disrupting the bioturbation activities of chironomid larvae.

Chronic exposure to polytetrafluoroethylene microplastics caused sex-specific effects in the model insect, Drosophila melanogaster (Diptera: Drosophilidae)

Microplastics (MPs) have become a prominent environmental concern due to their ubiquity in various ecosystems and widespread distribution through multiple channels. In this study, the oral effects of 2,000 mesh polytetrafluoroethylene (PTFE) microplastics were tested against Drosophila melanogaster (Meigen), at concentrations of 0, 0.1, 1, 10, and 20. After exposure to a microplastic-containing medium for 20 days, energy metabolism, fecundity, spontaneous movement, and sleeping time were measured. The study results showed that glucose levels in male flies were significantly reduced after exposure to PTFE-MPs. Measurement of lipid and protein levels indicated an increase in males but decrease in females, whereas these changes were not statistically significant. Reduction in sleep time was also observed, especially in males at the concentration of 20 g/l. Our study indicates that chronic exposure of PTFE-MPs can change energy metabolism and the amount of sleep on D. melanogaster in a sex dependent and dose dependent way. The results of our study are hoped to contribute to a better understanding of the effects of microplastics as new pollutants on insects.

Polyethylene microplastics induced lipidomic responses in Chironomus tepperi: A two-generational exploration

Microplastics (MPs) accumulating in freshwater sediment have raised concerns about potential risks to benthic dwelling organisms, yet few studies have examined the long-term impacts caused by MP exposure. This study investigated alterations to lipid profiles in an Australian freshwater invertebrate, Chironomus tepperi, induced by polyethylene MP fragments (1-45 μm) at environmentally relevant concentrations (125, 250, 500 and 1000 MPs/kg sediment), using a two-generational experimental design. In the parental generation, the relative abundance of triacylglycerols, total fatty acids and unsaturated fatty acids exhibited apparent hormetic patterns, with low-concentration stimulation and high-concentration inhibition observed. The overall trend in these lipid classes is consistent with previously observed changes to polar metabolite profiles, indicating that ingestion of MPs could inhibit nutrient assimilation from food leading to disruption of energy availability. In the first filial generation continuously exposed to MPs, however, abundance of cholesterol and total fatty acids increased with increasing exposure concentrations, suggesting different effects on energy metabolism between the parental generation and offspring. No differences in the lipidome were observed in first filial larvae that were not exposed, implying that MPs pose negligible carry-over effects. Overall, the combined results of this study together with a preceding metabolomics study provide evidence of a physical effect of MPs with subsequent impacts to bioenergetics. Nevertheless, future research is required to explore the potential long-term impacts caused by MPs, and to unravel the impacts of the surfactant control as a potential contributor to the observed hormetic response, particularly for studies exploring sub-lethal effects of MP exposure using sensitive omics techniques.

Microplastics from agricultural mulch films: Biodegradation and ecotoxicity in freshwater systems

The application of bio-based biodegradable mulch films in agriculture has raised environmental concerns regarding their potential impacts on adjacent freshwater ecosystems. This study investigated the biodegradation of microplastics derived from a bio-based biodegradable mulch (bio-MPs) and its acute and chronic ecotoxicity considering relevant scenarios (up to 200 and 250 mg/kg of sediment, using pristine and/or UV-aged particles), using the fungus Penicillium brevicompactum and the dipteran Chironomus riparius as model organisms, respectively, due to their ecological relevance in freshwater environments. Fourier-transform infrared spectroscopy analysis suggested changes in the fungus's carbohydrate reserves and bio-MP degradation through the appearance of low molecular weight esters throughout a 28 day biodegradation test. In a short-term exposure (48 h), C. riparius larvae exposed to pristine or UV-aged bio-MPs had up to 2 particles in their gut. Exposure to pristine bio-MPs decreased larval aerobic metabolism (<20 %) and increased neurotransmission (>15 %), whereas exposure to UV-aged bio-MPs activated larval aerobic metabolism (>20 %) and increased antioxidant defences (catalase activity by >30 % and glutathione-s-transferase by >20 %) and neurotransmission (>30 %). Longer-term (28-d) exposure to UV-aged bio-MPs did not affect larval survival and growth nor the dipteran's emergence but increased male numbers (>30 %) at higher concentrations. This study suggests that the selected agricultural bio-based mulch film is prone to biodegradation by a naturally occurring fungus. However, there is a potential for endocrine disruption in the case of prolonged exposures to UV-aged microplastics. This study emphasises the importance of further research to elucidate the potential ecological effects of these plastic products, to ensure effective management practices, and to establish new regulations governing their use.

Gene expression analysis of Chironomus riparius in response to acute exposure to tire rubber microparticles and leachates

Tire rubber microparticles (TRPs) entering aquatic ecosystems through stormwater runoffs is a significant challenge. TRPs are formed by the abrasion of tires with the road surface and include chemical additives that are an additional cause for concern. Currently, information on the molecular effects of TRPs, or especially its additives, in freshwater organisms is scarce. To address this problem, an array covering different cellular processes has been designed for the freshwater midge Chironomus riparius. Fourth-instar larvae were exposed to two concentrations of TRPs (1 mg L-1, 10 mg L-1) and tire rubber leachates (TRLs) (0,0125 %, 5 %) to evaluate the transcriptional activity by Real-Time PCR. To assess acute toxicity, larvae were exposed for 24 h and genes related to the endocrine system, stress response, DNA repair mechanisms, immune system, oxidative stress, and detoxification mechanisms were evaluated. The activity of the enzymes: glutathione S-transferase (GST) and catalase was also examined. The main pathway affected was the stress response showing overexpression of HSPs (HSC70.3, HSC70.4, HSC70.5, HSP60). Moreover, there was a reduction of the GSTd3 and catalase disrupting the antioxidant system. The upregulation of InR indicates a potential disturbance in the insulin pathway and ABCB6 activation only in TRPs exposure suggests its potential implication in their transport. However, most of these alterations are caused by TRLs, showing higher toxicity than TRPs. The results obtained in this work provide the first approach at the molecular and cellular levels to elucidate the impact of TRLs in freshwater organisms. To perform a realistic evaluation of the TR effects, additional research is required to assess the TR's long-term effects at the molecular level.

Source, transport, and toxicity of emerging contaminants in aquatic environments: A review on recent studies

Emerging contaminants (ECs) are gaining global attention owing to their widespread presence and adverse effects on human health. ECs comprise numerous composite types and pose a potential threat to the growth and functional traits of species and ecosystems. Although the occurrence and fate of ECs has been extensively studied, little is known about their long-term biological effects. This review attempts to gain insights into the unhindered connections and overlaps in aquatic ecosystems. Microplastics (MPs), one of the most representative ECs, are carriers of other pollutants because of their strong adsorption capacity. They form a complex of pollutants that can be transmitted to aquatic organisms and humans through the extended food chain, increasing the concentration of pollutants by tens of thousands of times. Adsorption, interaction and transport effects of emerging contaminants in the aquatic environment are also discussed. Furthermore, the current state of knowledge on the ecotoxicity of single- and two-pollutant models is presented. Herein, we discuss how aquatic organisms within complex food networks may be particularly vulnerable to harm from ECs in the presence of perturbations. This review provides an advanced understanding of the interactions and potential toxic effects of ECs on aquatic organisms.

Microplastics in marine invertebrates from the Red Sea Coast of Egypt: Abundance, composition, and risks

This study marked the first exploration of microplastics in marine invertebrates in the Red Sea Coast of Egypt. 110 individuals from 11 different species, including Bivalvia, Gastropoda, Echinoidea, and Holothuroidrea, were collected near a popular tourist destination. The average concentrations of microplastics varied among species, ranging from 8.2 to 136.5 items per individual or 0.2 to 18.1 items per gram of tissue wet weight, with 100 % occurrence. Bivalves had higher concentrations per gram of tissue compared to sediment dwellers and grazers, with Brachidontes pharaonis showing the highest levels. Actinopyga crassa, a sea cucumber, displayed the highest abundance per individual due to its large size and behavior. The identified plastic polymers suggested sources associated with tourism and maritime activities. The estimated human exposure to microplastics through bivalve consumption was minimal. Further research is needed to examine microplastics contamination in the Red Sea and its potential impacts on ecosystems and human well-being.

Metabolomic responses in freshwater benthic invertebrate, Chironomus tepperi, exposed to polyethylene microplastics: A two-generational investigation

The accumulation of microplastics (MPs) in sediments could pose risks to benthic organisms and their progeny. Here, we examined effects on traditional apical endpoints along with changes to whole body metabolite profiles induced by irregular shaped polyethylene MPs (1-45 µm) at environmentally relevant concentrations (125, 250, 500 and 1000 MPs/kg sediment) in Chironomus tepperi using a two-generation exposure regime. Survival and emergence of C. tepperi were negatively affected in the parental generation at the two highest concentrations, whereas endpoints associated with growth were only impacted at 1000 MPs/kg sediment. Metabolites associated with several amino acid and energy metabolism pathways were present at lower abundances at the highest exposure concentration suggesting an overall impact on bioenergetics which relates to the inhibition of food acquisition or nutrient assimilation caused by ingestion of MPs, rather than a traditional receptor-mediated toxicity response. In contrast, no significant effects on apical endpoints were observed in the continuous exposure of first filial generation, and lactic acid was the only metabolite that differed significantly between groups. Larvae in unexposed conditions showed no differences in survival or metabolite profiles suggesting that effects in the parental generation do not carry over to the next filial generation. The findings provide evidence on the underlying impacts of MP ingestion and potential adaption to MP exposure of C. tepperi.

Chironomus riparius Larval Gut Bacteriobiota and Its Potential in Microplastic Degradation

Chironomus riparius are sediment-dwelling invertebrates in freshwater ecosystems and are used as indicators of environmental pollution. Their habitat is threatened by high levels of contaminants such as microplastics and organic matter. A promising strategy for the eco-friendly degradation of pollutants is the use of bacteria and their enzymatic activity. The aim of this study was to characterize for the first time bacteriobiota associated with the gut of C. riparius larvae from nature and laboratory samples, to compare it with sediment and food as potential sources of gut microbiota, and to assess its ability to degrade cellulose, proteins, and three different types of microplastics (polyethylene, polyvinyl chloride, and polyamide). The metabarcoding approach highlighted Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota as most abundant in both gut samples. Culturable microbiota analysis revealed Metabacillus idriensis, Peribacillus simplex, Neobacillus cucumis, Bacillus thuringiensis/toyonensis, and Fictibacillus phosphorivorans as five common species for nature and laboratory samples. Two P. simplex and one P. frigoritolerans isolates showed the ability for intensive growth on polyethylene, polyvinyl chloride, and polyamide. Both cellulolytic and proteolytic activity was observed for Paenibacillus xylanexedens and P. amylolyticus isolates. The characterized strains are promising candidates for the development of environmentally friendly strategies to degrade organic pollution and microplastics in freshwater ecosystems.

Microplastics altered cellular responses, physiology, behaviour, and regeneration of planarians feeding on contaminated prey

Freshwater benthic environments are among the major sinks of microplastics (MPs, < 5 mm) sourced on inland anthropogenic activities. The ecotoxicological effects of MPs on benthic macroinvertebrates have been assessed preferably in collectors, shredders, and filter-feeders, but resulting in insufficient knowledge on the potential trophic transfer and its effects on macroinvertebrates with predator behaviour such as planarians. This work evaluated the behavioural (feeding, locomotion), physiological (regeneration) and biochemical responses (aerobic metabolism, energy reserves, oxidative damage) of the planarian Girardia tigrina after consuming contaminated live prey Chironomus riparius larvae previously exposed to microplastics of polyurethane (PU-MPs; 7-9 μm in size; 375 mg PU-MPs/kg). After the feeding period (3 h), planarians consumed 20 % more contaminated prey than uncontaminated prey, probably related to increased curling/uncurling movements of larvae (that might be more appellative to planarians). Histological analysis revealed planarians' limited intake of PU-MPs, mainly detected near the pharynx. The consumption of contaminated prey (and intake of PU-MPs) did not result in oxidative damage but slightly increased the aerobic metabolism and energy reserves which show that the consumption of more prey was sufficient to cope with the potential adverse effects of internalized MPs. Moreover, no effects were observed in the locomotion of planarians in good agreement with the hypothesis of sufficient energy acquired by the exposed planarians. Despite the previous, it seems that the energy acquired was not allocated for planarians' regeneration since a significant delay in the regeneration of the auricles was observed for planarians feeding on contaminated prey. Therefore, further studies should be performed considering the potential long-term effects (i.e., reproduction/fitness) and the effects of MPs that might result from continuous feeding on contaminated prey, representing a more realistic exposure scenario.

Exposure of the amphipod Hyalella azteca to microplastics. A study on subtoxic responses and particle biofragmentation

Microplastics are widespread pollutants in the environment and are considered a global pollution problem. Microplastics mostly originate from larger plastics and due to environmental conditions are undergoing constant fragmentation processes. It is important to understand the fragmentation pathways, since they play a key role in the fate of the particles, and also directly influence toxicity. Amphipods are potential inducers of plastic debris fragmentation. Here, Hyalella azteca was exposed to different concentrations (540, 2700, 5400 items/L) of 24.5 µm polystyrene microplastics (PS-MP) for 7 days. After exposure, oxidative stress, particle size reduction, and mortality were checked. No significant mortality was seen in any of the treatments, although changes were recorded in all enzymatic biomarkers analyzed. It was observed that throughout the ingestion and egestion of PS-MP by H. azteca, particles underwent intense fragmentation, presenting a final size up to 25.3% smaller than the initial size. The fragmentation over time (24, 72, 120, 168 h) was verified and the results showed a constant reduction in average particle size indicating that H. azteca are able to induce PS-MP fragmentation. This process may facilitate bioaccumulation and trophic particle transfer.