Microplastics in Freshwater Sediments Impact the Role of a Main Bioturbator in Ecosystem Functioning.

While microplastic transport, fate, and effects have been a focus of studies globally, the consequences of their presence on ecosystem functioning have not received the same attention. With increasing evidence of the accumulation of microplastics at sediment-water interfaces there is a need to assess their impacts on ecosystem engineers, also known as bioturbators, which have direct and indirect effects on ecosystem health. This study investigated the impact of microplastics on the bioturbator Tubifex tubifex alongside any effects on the biogeochemical processes at the sediment-water interface. Bioturbators were exposed to four sediment microplastic concentrations: 0, 700, 7000, and 70000 particles kg-1 sediment dry weight. Though no mortality was present, a significant response to oxidative stress was detected in tubificid worms after exposure to medium microplastic concentration (7000 particles kg-1 sediment dry weight). This was accompanied by a reduction in worm bioturbation activities assessed by their ability to rework sediment and to stimulate exchange water fluxes at the sediment-water interface. Consequently, the contributions of tubificid worms on organic matter mineralization and nutrient fluxes were significantly reduced in the presence of microplastics. This study demonstrated that environmentally realistic microplastic concentrations had an impact on biogeochemical processes at the sediment-water interface by reducing the bioturbation activities of tubificid worms.

Beyond microbeads: Examining the role of cosmetics in microplastic pollution and spotlighting unanswered questions.

The presence of microplastics in cosmetics and personal care products (C&PCPs) has been increasingly in the public eye since the early 2010s. Despite increasing research into the potential environmental and health effects of microplastics, most research to date on microplastics in C&PCPs has investigated "rinse-off" products, while the potential impacts of "leave-on" C&PCPs have been largely neglected, despite these products being purchased in greater volumes and often having two or more microplastic ingredients in their formulations(CosmeticsEurope, 2018b). This review aims to synthesize the current knowledge of microplastic in C&PCPs, assessing the potential environmental and human health impacts of C&PCPs and discussing the regulatory implications. The lack of studies on leave-on C&PCPs is significant, suggesting a severe knowledge gap regarding microplastic presence in, and emissions from, C&PCPs. There is a noticeable lack of studies on the (eco)toxicological consequences of microplastic exposure from C&PCPs. As a result, significant aspects of microplastic contamination may be overlooked in the microplastic legislations emerging globally (including from the European Commission), which intend to restrict microplastic use in C&PCPs but focus on rinse-off C&PCPs only. This review highlights the potential consequences of microplastics in leave-on C&PCPs for regulatory decision-making, particularly as alternatives to microplastics are considered during the phase-out periods and spotlights the need for sufficient monitoring and research on these alternatives, to avoid unforeseen consequences.

Snapshot Sampling May Not Be Enough to Obtain Robust Estimates for Riverine Microplastic Loads.

Wastewater treatment plants (WWTPs) have been described as key contributors of microplastics (MPs) to aquatic systems, yet temporal fluctuations in MP concentrations and loads downstream are underexplored. This study investigated how different sampling frequencies (hourly, weekly, and monthly) affect MP estimates in a stream linked to a single WWTP. Utilizing fluorescence microscopy and Raman spectroscopy, considerable hourly variations in MP concentrations were discovered, while the polymer composition remained consistent. This temporal variability in MP loads was influenced by MP concentration, discharge rates, or a mix of both. These results show a high uncertainty, as relying on sparse snapshot samples combined with annual discharge data led to significant uncertainties in MP load estimates (over- and/or underestimation of emissions by 3.8 billion MPs annually at this site). Our findings stress the necessity of higher-frequency sampling for better comprehending the hydrodynamic factors influencing MP transport. This improved understanding enables a more accurate quantification of MP dynamics, crucial for downstream impact assessments. Therefore, preliminary reconnaissance campaigns are essential for designing extended, representative site-monitoring programs and ensuring more precise trend predictions on a larger scale.

Easy and accessible way to calibrate a fluorescence microscope and to create a microplastic identification key.

We present here a technique for setting up detection limits on any fluorescent microscope in conjunction with the fluorophore Nile Red for microplastic identification. Our method also describes a rigorous morphology-specific identification key for microplastics to reduce subjectivity between researchers. The detection limits were established for nine common polymer types and five natural substrates which could result in false-positive signals when using Nile Red for microplastic identification. This method was then applied to real freshwater samples and identified particles were validated with micro-FTIR or Raman spectroscopy. This approach may reduce subjectivity in microplastic identification and counting and enhances transparency, repeatability and harmonization within microplastic research community.•Instructions for calibration of detection limits for microplastics on fluorescence microscope systems described•Microplastic identification key developed and tested to reduce false positive detection•Lower subjectivity for microplastic identification obtained using the detection limits & identification key.

Microplastic accumulation in endorheic river basins - The example of the Okavango Panhandle (Botswana).

The Okavango Panhandle is the main influent watercourse of the Okavango Delta, an inland sink of the entire sediment load of the Cubango-Okavango River Basin (CORB). The sources of pollution in the CORB, and other endorheic basins, are largely understudied when compared to exorheic systems and the world's oceans. We present the first study of the distribution of microplastic (MP) pollution in surface sediments of the Okavango Panhandle in Northern Botswana. MP concentrations (64 µm-5 mm size range) in sediment samples from the Panhandle range between 56.7 and 399.5 particles kg-1 (dry weight) when analysed with fluorescence microscopy. The concentrations of MP in the 20 µm to 5 mm grain size range (analysed with Raman spectroscopy) range between 1075.7 and 1756.3 particles kg-1. One shallow core (15 cm long) from an oxbow lake suggests that MP size decreases with depth while MP concentration increases downcore. Raman Spectroscopy revealed that the compositions of the MP are dominated by polyethene terephthalate (PET), polypropylene (PP), polyethene (PE), polystyrene (PS), and polyvinyl chloride (PVC). From this novel data set it was possible to estimate that 10.9-336.2 billion particles could be transported into the Okavango Delta annually, indicating that the region represents a significant sink for MP, raising concerns for the unique wetland ecosystem.

Prevailing impacts of river management on microplastic transport in contrasting US streams: Rethinking global microplastic flux estimations.

While microplastic inputs into rivers are assumed to be correlated with anthropogenic activities and to accumulate towards the sea, the impacts of water management on downstream microplastic transport are largely unexplored. A comparative study of microplastic abundance in Boulder Creek (BC), and its less urbanized tributary South Boulder Creek (SBC), (Colorado USA), characterized the downstream evolution of microplastics in surface water and sediments, evaluating the effects of urbanization and flow diversions on the up-to-downstream profiles of microplastic concentrations and loads. Water and sediment samples were collected from 21 locations along both rivers and microplastic properties determined by fluorescence microscopy and Raman spectroscopy. The degree of catchment urbanization affected microplastic patterns, as evidenced by greater water and sediment concentrations and loads in BC than the less densely populated SBC, which is consistent with the differences in the degree of urbanization between both catchments. Microplastic removal through flow diversions was quantified, showing that water diversions removed over 500 microplastic particles per second from the river, and caused stepwise reductions of downstream loads at diversion points. This redistribution of microplastics back into the catchment should be considered in large scale models quantifying plastic fate and transport to the oceans.

Nano and microplastic interactions with freshwater biota - Current knowledge, challenges and future solutions.

Current understanding of nano- and microplastic movement, propagation and potential effects on biota in freshwater environments is developing rapidly. Still, there are significant disconnects in the integration of knowledge derived from laboratory and field studies. This review synthesises the current understanding of nano- and microplastic impacts on freshwater biota from field studies and combines it with the more mechanistic insights derived from laboratory studies. Several discrepancies between the field and laboratory studies, impacting progress in process understanding, were identified including that the most prevalent plastic morphologies found in the field (fibres) are not those used in most of the laboratory studies (particles). Solutions to overcome these disparities are proposed to aid comparability of future studies. For example, environmental sampling and separation of biota into its constituents is encouraged when conducting field studies to map microplastic uptake preferences. In laboratory studies, recommendations include performing toxicity studies to systematically test possible factors affecting toxicity of nano- and microplastics, including morphology, chemical makeup (e.g., additives) and effects of plastic size. Consideration should be given to environmentally relevant exposure factors in laboratory studies, such as realistic exposure medium and effects of plastic ageing. Furthermore, based on this comprehensive review recommendations of principal toxicity endpoints for each of the main trophic levels (microbes, primary producers, primary consumers and secondary consumers) that should be reported to make toxicity studies more comparable in the future are given.

Gathering at the top? Environmental controls of microplastic uptake and biomagnification in freshwater food webs.

Microplastics are ubiquitous in the environment, with high concentrations being detected now also in river corridors and sediments globally. Whilst there has been increasing field evidence of microplastics accumulation in the guts and tissues of freshwater and marine aquatic species, the uptake mechanisms of microplastics into freshwater food webs, and the physical and geological controls on pathway-specific exposures to microplastics, are not well understood. This knowledge gap is hampering the assessment of exposure risks, and potential ecotoxicological and public health impacts from microplastics. This review provides a comprehensive synthesis of key research challenges in analysing the environmental fate and transport of microplastics in freshwater ecosystems, including the identification of hydrological, sedimentological and particle property controls on microplastic accumulation in aquatic ecosystems. This mechanistic analysis outlines the dominant pathways for exposure to microplastics in freshwater ecosystems and identifies potentially critical uptake mechanisms and entry pathways for microplastics and associated contaminants into aquatic food webs as well as their risk to accumulate and biomagnify. We identify seven key research challenges that, if overcome, will permit the advancement beyond current conceptual limitations and provide the mechanistic process understanding required to assess microplastic exposure, uptake, hazard, and overall risk to aquatic systems and humans, and provide key insights into the priority impact pathways in freshwater ecosystems to support environmental management decision making.