A call to evaluate Plastic's impacts on marine benthic ecosystem interaction networks

Polyester microfiber impacts on coastal sediment organic matter consumption

As plastic pollution continues to accumulate at the seafloor, concerns around benthic ecosystem functionality heightens. This research demonstrates the systematic effects of polyester microfibers on seafloor organic matter consumption rates, an important benthic ecosystem function connected to multiple reactions and processes. We used a field-based assay to measure the loss of organic matter, both with and without polyester microfiber contamination. We identified sediment organic matter content, mud content, and mean grain size as the main drivers of organic matter consumption, however, polyester microfiber contamination decoupled ecosystem relationships and altered observed organic matter cycling dynamics. Organic matter consumption rates varied across horizontal and vertical spaces, highlighting that consumption and associated plastic effects are dependent on environmental heterogeneity at both small (within sites) and larger (between sites) scales. Our results emphasize the important role habitat heterogeneity plays in seafloor organic matter consumption and the associated effects of plastic pollution on ecosystem function.

Using eRNA/eDNA metabarcoding to detect community-level impacts of nanoplastic exposure to benthic estuarine ecosystems

Plastic particles are ubiquitous in marine systems and fragment into smaller pieces, such as nanoplastics (NPs). The effects of NPs on marine organisms are of growing concern but are not well understood. Marine sediments act as a sink for many contaminants, like microplastics, and are rich habitats for benthic micro- and meiofauna which are ecologically-important components of marine food webs; however, little is known about the sensitivities of specific organisms to NPs or the effects on community diversity and composition. Utilizing molecular methods, such as metabarcoding of environmental DNA/RNA, allows for the rapid and comprehensive detection of microscopic organisms via high-throughput sequencing to assess adverse effects at the community level. The objective of this study was to use a metabarcoding approach to investigate the effects of NPs on benthic micro- and meiofaunal community diversity. Mesocosms were created with sediment cores collected from the Narrow River estuary (Rhode Island, USA) and exposed to 900 nm diameter weathered polystyrene beads at concentrations of 0.1, 1, 10, or 100 mg/kg dry weight in sediment for two weeks. Following exposure, RNA and DNA were co-extracted from the sediment, RNA was reverse-transcribed, 18S and COI markers were PCR-amplified, and amplicons were sequenced on an Illumina MiSeq. Using the 18S marker and eRNA template, increases to α-diversity and significant differences to β-diversity were observed in the highest NP exposures relative to the control. Observed differences in community composition were driven by the differential abundance of several types of protists and arthropods. Significant dose-dependent shifts in composition were observed in β-diversity Jaccard and Unweighted-Unifrac metrics with the 18S marker using the RNA template. To our knowledge, this is the first demonstration of a dose-response relationship for NPs at a community level, and it highlights the value of using community-level endpoints to assess environmental impacts of nanoparticles.

Nutrient enrichment mediates the effect of biodegradable and conventional microplastics on macroinvertebrate communities

There is growing concern regarding the lack of evidence on the effects bioplastics may have on natural ecosystems, whilst their production continues to increase as they are considered as a greener alternative to conventional plastics. Most research is limited to investigations of the response of individual taxa under laboratory conditions, with few experiments undertaken at the community or ecosystem scale, either investigating microplastics independently or in combination with other pollutants, such as nutrient enrichment. The aim of this study is to experimentally compare the effects of oil-based (high density polyethylene - HDPE) with those of bio-based biodegradable (polylactic acid - PLA) microplastics and their interaction with nutrient enrichment on freshwater macroinvertebrate communities under seminatural conditions. There were no significant differences in total abundance, alpha and beta diversities, or community composition attributable to the type of microplastics, their concentration, or nutrient enrichment compared with the control. However, there was a significant difference in macroinvertebrate alpha diversity between high concentrations of both microplastic types under ambient nutrient conditions, with lower diversity in communities exposed to HDPE compared with PLA. Nutrient enrichment mediated the effect of microplastic type, such that the diversity of macroinvertebrate communities exposed to HDPE were similar to those communities exposed to PLA. These findings suggest that the effects of microplastic pollution on macroinvertebrate communities are very weak at large-scale settings under seminatural conditions and that these effects might be mediated by the nutrient status of freshwater ecosystems. More research under large-scale, long-term, seminatural settings are needed in order to elucidate the impact of both conventional plastics and bioplastics on natural environments and their interactive effect with other occurring stressors and pollutants.

Modelled broad-scale shifts on seafloor ecosystem functioning due to microplastic impacts on bioturbation

Bioturbating species play an essential role in regulating nutrient cycling in marine sediments, but their interaction with microplastics (MP) remains poorly understood. Here we investigated the linkage between MP and ecosystem functioning using experimental observations of luminophore distribution in the sediment to parametrize bioturbation coefficients (Db). this information as fed into a simplified transport-reaction model, allowing us to upscale our experimental results. We found that the composition of bioturbators modulated shifts in the ecosystem functioning under microplastic stress. Maldanid worms (Macroclymenella stewartensis), functionally deep burrowing and upward-conveyor belt feeders, became less active. The Db of M. stewartensis reduced by 25% with the addition of 0.002 g MP cm-2 at surface sediment, causing accumulation of organic matter in the oxic sediment zone and stimulating aerobic respiration by 18%. In contract, the tellinid bivalve Macomona liliana, functionally a surface -deposit feeder that excretes at depth, maintained particle mixing behaviour in MP-contaminated systems. This study provides a mechanistic insight into the impacts of MP and indicates that the functional role of bioturbating species should be involved in assessing the global impact of MP. The model allowed us to understand the broad-scale impact of MP on seafloor habitat.

Real-world impacts of microplastic pollution on seafloor ecosystem function

Emerging research shows that microplastic pollution could be impacting seafloor ecosystem function, but this has been primarily demonstrated without environmental and ecological context. This causes uncertainty in the real-world effects of microplastic pollution and leaves out essential information guiding policy and mitigation. In this study, we take a well-supported sampling design and statistical approach commonly employed in benthic ecology to evaluate real-world effects of microplastic pollution on coastal, benthic ecosystem function. We utilised environmental gradients in the Waitemata Harbour of Auckland, New Zealand to evaluate the importance of commonly assessed biological, chemical, and geological sediment variables and the characteristics of microplastic contaminants in driving essential ecosystem functions. Our results showed that models including microplastic terms were more accurate and explained more variability than those without microplastic terms, highlighting that microplastics impact real-world seafloor ecosystem function. Specifically, microplastic fibers significantly influenced oxygen flux (p < 0.03) and the diverse forms of microplastics (i.e., richness) significantly influenced ammonium flux (p < 0.02). Additionally, interactions between microplastic fiber concentrations and mollusc abundances significantly contributed to oxygen flux (p < 0.02). These results provide the first evaluation of in situ relationships between microplastics and ecosystem function. Even more importantly, this study suggests the value of environmental and ecological context for addressing microplastic impacts on benthic ecosystems and argues for further field examination.

Priorities to inform research on marine plastic pollution in Southeast Asia

Southeast Asia is considered to have some of the highest levels of marine plastic pollution in the world. It is therefore vitally important to increase our understanding of the impacts and risks of plastic pollution to marine ecosystems and the essential services they provide to support the development of mitigation measures in the region. An interdisciplinary, international network of experts (Australia, Indonesia, Ireland, Malaysia, the Philippines, Singapore, Thailand, the United Kingdom, and Vietnam) set a research agenda for marine plastic pollution in the region, synthesizing current knowledge and highlighting areas for further research in Southeast Asia. Using an inductive method, 21 research questions emerged under five non-predefined key themes, grouping them according to which: (1) characterise marine plastic pollution in Southeast Asia; (2) explore its movement and fate across the region; (3) describe the biological and chemical modifications marine plastic pollution undergoes; (4) detail its environmental, social, and economic impacts; and, finally, (5) target regional policies and possible solutions. Questions relating to these research priority areas highlight the importance of better understanding the fate of marine plastic pollution, its degradation, and the impacts and risks it can generate across communities and different ecosystem services. Knowledge of these aspects will help support actions which currently suffer from transboundary problems, lack of responsibility, and inaction to tackle the issue from its point source in the region. Being profoundly affected by marine plastic pollution, Southeast Asian countries provide an opportunity to test the effectiveness of innovative and socially inclusive changes in marine plastic governance, as well as both high and low-tech solutions, which can offer insights and actionable models to the rest of the world.

The polymers and their additives in particulate plastics: What makes them hazardous to the fauna?

Due to the increasing concerns on global ecosystems and human health, the environmental risks posed by microplastics (MPs) and nanoplastics (NPs) have become an important topic of research. Their ecological impacts on various faunal species have been extensively researched and reviewed. However, the majority of those studies perceive these micro(nano)-plastics (MNPs) as a single entity rather than a collective term for a group of chemically distinct polymeric particulates. Each of the plastic polymers can possess unique physical and chemical behavior, which, in turn, can determine the possible environmental impacts. Furthermore, many studies explore the adsorption, absorption, and release of other environmental pollutants by MNPs. But only a handful of them explore the leaching of additives possessed by these polymers. Data on the environmental behavior and toxicity of individual additives associated with different polymer particulates are scarce. Knowledge about the leachability and ecotoxicity of the additives associated with environmental MNPs (unlike large plastic particles) remains limited. The ecological impacts of different MNPs together with their additives and the basis of their toxicity have not been explored yet. The present review systematically explores the potential implications of environmentally predominant polymers and their associated additives and discusses their physicochemical characteristics. The review ultimately aims to provide novel insights on what components precisely make MNPs hazardous to the fauna. The paper also discusses the major challenges proposed in the available literature along with recommendations for future research to throw light on possible solutions to overcome the hazards of MNPs.

Determination of nano and microplastic particles in hypersaline lakes by multiple methods

Microplastics and nanoplastics have a range of impacts on the aquatic environment and present major challenges to their mitigation and management. Their transport and fate depend on their composition, form, and the characteristics of the receiving environment. We explore the spatial and temporal dynamics of plastic particles in the world's second-largest hypersaline lake, combining information from microscopic, thermal gravimetric, and fractional methods. Studies on microplastic and nanoplastic pollution in these important environments are scarce, and there is limited understanding of their dynamics and fate. Our results for Urmia Lake (Iran) in 2016 and 2019 show a discrepancy in the composition and quantity of microplastics measured in river tributaries to the lake and the lake itself, suggesting an active microplastic sink. Potential sink mechanisms in hypersaline lakes are explored. The present study indicates that microplastics have different transport mechanisms and fate in these extreme environments, compared to lake and ocean environments.

Protocol for microplastic pollution monitoring in freshwater ecosystems: Towards a high-throughput sample processing - MICROPLASTREAM

Robust and reproducible quantification of microplastic pollution in freshwater ecosystems requires the processing of a large amount of samples collected in varying environmental conditions. Such samples are characterized by a high amount of organic matter compared to microplastics and are highly variable in terms of the quantity and the composition of matrices, requiring a standardized analytical protocol for sample treatment and analysis. However, two important and time-consuming steps for microplastic recovery are the elimination of organic matter and microscopic inspection of samples. Here, we developed and validated a protocol, targeting particles with length ranging from 700 µm to 5 mm, that includes a double-step digestion of organic matter, consisting of incubation with potassium hydroxide followed by hydrogen peroxide solutions, and two stereomicroscopic analyses. In addition, we developed several technical improvements allowing reducing the time needed to process samples, such as the design of an adapted filter-cap to improve the content transfer. The absence of physical and chemical alterations in the investigated microplastic pellets and the average reduction of 65.8% (± 9.59 SD) of organic matter in real samples demonstrated that our protocol is fit for purpose. We recommend a second stereomicroscopic analysis to avoid underestimating microplastic concentration and particle size distribution biased towards larger particles. When used for a large-scale monitoring of microplastic pollution, this protocol resulted in an estimated time of 38 h for one person for the treatment of a batch of 24 samples, allowing a higher throughput sample processing and reproducible quantification. • Protocol customization towards high-throughput sample processing • Double step digestion to improve organic matter elimination • Importance of stereomicroscopic analysis for microplastic recovery.