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.

Is Zooplankton an Entry Point of Microplastics into the Marine Food Web?

Microplastics (MPs) overlap in size with phytoplankton and can be ingested by zooplankton, transferring them to higher trophic levels. Copepods are the most abundant metazoans among zooplankton and the main link between primary producers and higher trophic levels. Ingestion of MPs has been investigated in the laboratory, but we still know little about the ingestion of MPs by zooplankton in the natural environment. In this study, we determined the concentration and characteristics of MPs down to 10 µm in zooplankton samples, sorted calanoid copepods, and fecal pellets collected in the Kattegat/Skagerrak Sea (Denmark). We found a median concentration of 1.7 × 10-3 MPs ind-1 in the zooplankton samples, 2.9 × 10-3 MPs ind-1 in the sorted-copepods, and 3 × 10-3 MPs per fecal pellet. Most MPs in the zooplankton samples and fecal pellets were fragments smaller than 100 µm, whereas fibers dominated in the sorted copepods. Based on the collected data, we estimated a MP budget for the surface layer (0-18 m), where copepods contained only 3% of the MPs in the water, while 5% of the MPs were packed in fecal pellets. However, the number of MPs exported daily to the pycnocline via fecal pellets was estimated to be 1.4% of the total MPs in the surface layer. Our results indicate that zooplankton are an entry point of small MPs in the food web, but the number of MPs in zooplankton and their fecal pellets was low compared with the number of MPs found in the water column and the occurrence and/or ingestion of MPs reported for nekton. This suggests a low risk of MP transferring to higher trophic levels through zooplankton and a quantitatively low, but ecologically relevant, contribution of fecal pellets to the vertical exportation of MPs in the ocean.

A protocol for lixiviation of micronized plastics for aquatic toxicity testing.

Plastics contain various types and amounts of additives that can leach into the water column when entering aquatic ecosystems. Some leached plastic additives are hazardous to marine biota at environmentally relevant concentrations. Disparate methodological approaches have been adopted for toxicity testing of plastic leachates, making comparison difficult. Here we propose a protocol to standardize the methodology to obtain leachates from microplastics (MPs) for aquatic toxicity testing. Literature reviewing and toxicity tests using marine model organisms and different types of MPs were conducted to define the main methodological aspects of the protocol. Acute exposure to leachates from the studied plastics caused negative effects on the early life stages of sea urchins and marine bacteria. We provide recommendations of key factors influencing lixiviation of MPs , such as particle size (<250 µm), solid-to-liquid ratio (1-10 g/L), mixing conditions (1-60 rpm), and lixiviation time (72 h). The proposed methodology was successful to determine the toxicity of leachates from different micronized plastics on marine biota. Our recommendations balance sensitivity, feasibility and environmental relevance, and their use would help ensure comparability amongst studies for a better assessment of the toxicity of plastic leachates on aquatic biota.

Abundance and distribution of microplastics in surface waters of the Kattegat/ Skagerrak (Denmark).

Microplastics (MPs) are ubiquitous pollutants in the ocean, and there is a general concern about their persistence and potential effects on marine ecosystems. We still know little about the smaller size-fraction of marine MPs (MPs <300 µm), which are not collected with standard nets for MPs monitoring (e.g., Manta net). This study aims to determine the concentration, composition, and size distribution of MPs down to 10 µm in the Kattegat/Skagerrak area. Surface water samples were collected at fourteen stations using a plastic-free pump-filter device (UFO sampler) in October 2020. The samples were treated with an enzymatic-oxidative method and analyzed using FPA-µFTIR imaging. MPs concentrations ranged between 11 and 87 MP m-3, with 88% of the MPs being smaller than 300 µm. The most abundant shape of MPs were fragments (56%), and polyester, polypropylene, and polyethylene were the dominant synthetic polymer types. The concentration of MPs shows a significant positive correlation to the seawater density. Furthermore, there was a tendency towards higher MPs concentrations in the Northern and the Southern parts of the study area. The concentration of MPs collected with the UFO sampler was several orders of magnitude higher than those commonly found in samples collected with the Manta net due to the dominance of MP smaller size fractions. Despite the multiple potential sources of MPs in the study area, the level of MPs pollution in the surface waters was low compared (<100 MP m-3) to other regions. The concentrations of MPs found in the studied surface waters were six orders of magnitude lower than those causing negative effects on pelagic organisms based on laboratory exposure studies, thus is not expected to cause any impact on the pelagic food web.

The sub-lethal impact of plastic and tire rubber leachates on the Mediterranean mussel Mytilus galloprovincialis.

Ocean contamination by synthetic polymers can represent a risk for the fitness of marine species due to the leaching of chemical additives. This study evaluated the sub-lethal effects of plastic and rubber leachates on the mussel Mytilus galloprovincialis through a battery of biomarkers encompassing lysosomal endpoints, oxidative stress/detoxification parameters, and specific responses to metals/neurotoxicants. Mussels were exposed for 7 days to leachates from car tire rubber (CTR), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS) and polyvinyl chloride (PVC), containing organic additives and metals in the ng-µg/L range. The leachate exposure affected general stress parameters, including the neutral lipid content (all leachates), the lysosomal membrane stability (PS, PP, PVC and CTR leachates) and lysosomal volume (PP, PVC and TR leachates). An increased content of the lipid peroxidation products malondialdehyde and lipofuscin was observed in mussels exposed to PET, PS and PP leachates, and PP, PVC and CTR leachates, respectively. PET and PP leachates increased the activity of the phase-II metabolism enzyme glutathione S-transferase, while a decreased acetylcholinesterase activity was induced by PVC leachates. Data were integrated in the mussel expert system (MES), which categorizes the organisms' health status based on biomarker responses. The MES assigned healthy status to mussels exposed to PET leachates, low stress to PS leachates, and moderate stress to PP, CTR and PVC leachates. This study shows that additives leached from selected plastic/rubber polymers cause sub-lethal effects in mussels and that the magnitude of these effects may be higher for CTR, PVC and PP due to a higher content and release of metals and organic compounds.

The hidden threat of plastic leachates: A critical review on their impacts on aquatic organisms.

Plastic products are made from the essential polymer mixed with a complex blend of substances including catalyst remnants, polymerization solvents, and a wide range of other additives deliberately added to enhance the desirable characteristics of the final product. Additives include bisphenols, phthalates, flame retardants, and further emerging and legacy contaminants. With a few exceptions, additives are not chemically bound to the polymer, and potentially migrate within the material reaching its surface, then possibly leach out to the environment. Leachates are mixtures of additives, some of which belong to the list of emerging contaminants, i.e. substances that show the potential to pose risks to the environment and human health, while are not yet regulated. The review discusses the state of the art and gaps concerning the hidden threat of plastic leachates. The focus is on reports addressing the biological impacts of plastic leachates as a whole mixture. Degradation of plastics, including the weathering-driven fragmentation, and the release of additives, are analysed together with the techniques currently employed for chemically screening leachates. Because marine plastic litter is a major concern, the review mainly focuses on the effects of plastic leachates on marine flora and fauna. Moreover, it also addresses impacts on freshwater organisms. Finally, research needs and perspectives are examined, to promote better focused investigations, that may support developing different plastic materials and new regulations.