Arctic Ocean sediments as important current and future sinks for marine microplastics missing in the global microplastic budget

Critical reassessment of microplastic abundances in the marine environment

Microplastics (MPs) pose a growing concern in the marine environment, but their global prevalence remains largely unknown due to the absence of precise and standardized detection methods. This review critically evaluates existing techniques for quantifying MP abundances in marine field studies, addressing inaccuracies resulting from the exclusion of particle sizes, polymer types, or limitations in identification methods. These traced inaccuracies were considered to recalculate MP abundances for particle sizes from 10 to 5000 μm, providing the first corrected global overview of MP distribution that enables quality assessment and reliable comparisons between adjusted data. The recalculations indicate that MP abundances are up to 15 times higher in marine waters (average (1.5 ± 36.2) × 105 items m-3) and up to 11 times higher in the marine sediments (average (2.7 ± 117.9) × 105 items kg-1) than previously reported in the literature. The Australasian Mediterranean Sea (average (1.2 ± 10.6) × 106 items m-3) and the North Atlantic (average (2.1 ± 37.6) × 105 items kg-1) emerged as the most polluted regions in marine waters and sediments, respectively, with primary contributors being the coasts of Southeast Asia and East America. This review demonstrates that previous field studies, global estimates, and models have significantly underestimated MP levels in marine environments in many cases, which could result in misinterpretations of both local and global pollution levels. This work highlights the critical need for precise handling of microplastic samples and urges future researchers to adopt standardized protocols for MP analysis to avoid inaccurate and misleading outcomes.

Diving into the Depths: Uncovering Microplastics in Norwegian Coastal Sediment Cores

High concentrations of microplastics (MPs) have been documented in the deep-sea surface sediments of the Arctic Ocean. However, studies investigating their high-resolution vertical distribution in sediments from the European waters to the Arctic remain limited. This study examines MPs in five sediment cores from the Norwegian Coastal Current (NCC), encompassing the water-sediment interface and sediment layers up to 19 cm depth. Advanced analytical methods for MP identification down to 11 μm in size were combined with radiometric dating and lithology observations. MPs were present across all sediment cores, including layers predating the introduction of plastics, with concentrations exhibiting significant variation (54-12,491 MP kg-1). The smallest size class (11 μm) predominated in most sediment layers (34-100%). A total of 18 different polymer types were identified across all sediment layers, with polymer diversity and depth correlations varying widely between stations. Our findings suggest that differences in seafloor topography and the impact of anthropogenic activities (e.g., fishing) lead to varying environmental conditions at the sampling sites, influencing the vertical distribution of MPs. This challenges the reliability of using environmental parameters to predict MP accumulation zones and questions the use of MPs in sediment cores as indicators of the Anthropocene.

Physiological and genetic responses of the benthic dinoflagellate Prorocentrum lima to polystyrene microplastics

Microplastics are well known as contaminants in marine environments. With the development of biofilms, most microplastics will eventually sink and deposit in benthic environment. However, little research has been done on benthic toxic dinoflagellates, and the effects of microplastics on benthic dinoflagellates are unknown. Prorocentrum lima is a cosmopolitan toxic benthic dinoflagellate, which can produce a range of polyether metabolites, such as diarrhetic shellfish poisoning (DSP) toxins. In order to explore the impact of microplastics on marine benthic dinoflagellates, in this paper, we studied the effects of polystyrene (PS) on the growth and toxin production of P. lima. The molecular response of P. lima to microplastic stress was analyzed by transcriptomics. We selected 100 nm, 10 μm and 100 μm PS, and set three concentrations of 1 mg L-1, 10 mg L-1 and 100 mg L-1. The results showed that PS exposure had limited effects on cell growth, but increased the OA and extracellular polysaccharide content at high concentrations. After exposure to PS MPs, genes associated with DSP toxins synthesis, carbohydrate synthesis and energy metabolism, such as glycolysis, TCA cycle and pyruvate metabolism, were significantly up-regulated. We speculated that after exposure to microplastics, P. lima may increase the synthesis of DSP toxins and extracellular polysaccharides, improve the level of energy metabolism and gene expression of ABC transporter, thereby protecting algal cells from damage. Our findings provide new insights into the effects of microplastics on toxic benthic dinoflagellates.

Do weathered microplastics impact the planktonic community? A mesocosm approach in the Baltic Sea

Microplastics (MPs) are ubiquitous pollutants of increasing concern in aquatic systems. However, little is still known about the impacts of weathered MPs on plankton at the community level after long-term exposure. In this study, we investigated the effects of weathered MPs on the structure and dynamics of a Baltic Sea planktonic community during ca. 5 weeks of exposure using a mesocosm approach (2 m3) mimicking natural conditions. MPs were obtained from micronized commercial materials of polyvinyl chloride, polypropylene, polystyrene, and polyamide (nylon) previously weathered by thermal ageing and sunlight exposure. The planktonic community was exposed to 2 μg L-1 and 2 mg L-1 of MPs corresponding to measured particle concentrations (10-120 μm) of 680 MPs L-1 and 680 MPs mL-1, respectively. The abundance and composition of all size classes and groups of plankton and chlorophyll concentrations were periodically analyzed throughout the experiment. The population dynamics of the studied groups showed some variations between treatments, with negative and positive effects of MPs exhibited depending on the group and exposure time. The abundance of heterotrophic bacteria, pico- and nanophytoplankton, cryptophytes, and ciliates was lower in the treatment with the higher MP concentration than in the control at the last weeks of the exposure. The chlorophyll concentration and the abundances of heterotrophic nanoflagellates, Astromoeba, dinoflagellate, diatom, and metazooplankton were not negatively affected by the exposure to MPs and, in some cases, some groups showed even higher abundances in the MP treatments. Despite these tendencies, statistical analyses indicate that in most cases there were no statistically significant differences between treatments over the exposure period, even at very high exposure concentrations. Our results show that weathered MPs of the studied conventional plastic materials have minimal or negligible impact on planktonic communities after long-term exposure to environmentally relevant concentrations.

Nanoplastic toxicity induces metabolic shifts in Populus × euramericana cv. '74/76' revealed by multi-omics analysis

There is increasing global concern regarding the pervasive issue of plastic pollution. We investigated the response of Populus × euramericana cv. '74/76' to nanoplastic toxicity via phenotypic, microanatomical, physiological, transcriptomic, and metabolomic approaches. Polystyrene nanoplastics (PS-NPs) were distributed throughout the test plants after the application of PS-NPs. Nanoplastics principally accumulated in the roots; minimal fractions were translocated to the leaves. In leaves, however, PS-NPs easily penetrated membranes and became concentrated in chloroplasts, causing thylakoid disintegration and chlorophyll degradation. Finally, oxidant damage from the influx of PS-NPs led to diminished photosynthesis, stunted growth, and etiolation and/or wilting. By integrating dual-omics data, we found that plants could counteract mild PS-NP-induced oxidative stress through the antioxidant enzyme system without initiating secondary metabolic defense mechanisms. In contrast, severe PS-NP treatments promoted a shift in metabolic pattern from primary metabolism to secondary metabolic defense mechanisms, an effect that was particularly pronounced during the upregulation of flavonoid biosynthesis. Our findings provide a useful framework from which to further clarify the roles of key biochemical pathways in plant responses to nanoplastic toxicity. Our work also supports the development of effective strategies to mitigate the environmental risks of nanoplastics by biologically immobilizing them in contaminated lands.

Intelligent classification and pollution characteristics analysis of microplastics in urban surface waters using YNet

Microplastics (MPs, ≤ 5 mm in size) are hazardous contaminants that pose threats to ecosystems and human health. YNet was developed to analyze MPs abundance and shape to gain insights into MPs pollution characteristics in urban surface waters. The study found that YNet achieved an accurate identification and intelligent classification performance, with a dice similarity coefficient (DSC) of 90.78%, precision of 94.17%, and recall of 89.14%. Analysis of initial MPs levels in wetlands and reservoirs revealed 127.3 items/L and 56.0 items/L. Additionally, the MPs in effluents were 27.0 items/L and 26.3 items/L, indicating the ability of wetlands and reservoirs to retain MPs. The concentration of MPs in the lower reaches of the river was higher (45.6 items/L) compared to the upper reaches (22.0 items/L). The majority of MPs detected in this study were fragments, accounting for 51.63%, 54.94%, and 74.74% in the river, wetland, and reservoir. Conversely, granules accounted for the smallest proportion of MPs in the river, wetland, and reservoir, representing only 11.43%, 10.38%, and 6.5%. The study proves that the trained YNet accurately identify and intelligently classify MPs. This tool is essential in comprehending the distribution of MPs in urban surface waters and researching their sources and fate.

Reshaping the plastisphere upon deposition: Promote N2O production through affecting sediment microbial communities in aquaculture pond

Microplastics (MPs) could provide vector for microorganisms to form biofilm (plastisphere), but the shaping process of MPs biofilm and its effects on the structure and function of sedimentary microbial communities especially in aquaculture environments are not reported. For this, we incubated MPs biofilm in situ in an aquaculture pond and established a sediment microcosm with plastisphere. We found that the formation of MPs biofilm in surface water was basically stable after 30 d incubation, but the biofilm communities were reshaped after deposition for another 30 d, because they were more similar to plastisphere communities incubated directly within sediment but not surface water. Moreover, microbial communities of MPs-contaminated sediment were altered, which was mainly driven by the biofilm communities present on MPs, because they but not sediment communities in proximity to MPs had a more pronounced separation from the control sediment communities. In the presence of MPs, increased sediment nitrification, denitrification and N2O production rates were observed. The K00371 (NO2-⇋NO3-) pathway and elevated abundance of nxrB and narH genes were screened by metagenomic analysis. Based on structural equation model, two key bacteria (Alphaproteobacteria bacterium and Rhodobacteraceae bacterium) associated with N2O production were further identified. Overall, the settling of MPs could reshape the original biofilm and promote N2O production by selectively elevating sedimental microorganisms and functional genes in aquaculture pond.