Effects of long-term exposure to microfibers on ecosystem services provided by coastal mussels

Ingestion and depuration of polyester microfibers by Crassostrea gasar (Adanson, 1757)

The study aimed to obtain environmentally relevant microfibers (MFs) from polyester fabric and assess their impact on the oyster Crassostrea gasar. MFs were obtained by grinding the fabric, and their accumulation in oysters gills and digestive glands was analyzed after exposure to 0.5 mg/L for 2 and 24 h. Additionally, a 48 h depuration was conducted on the oysters exposed for 24 h. Sublethal effects were assessed in oysters exposed for 24 h and depurated for 48 h, using biomarkers like Catalase (CAT), Glutathione S-transferase (GST), and Glutathione Peroxidase (GPx), along with histological analyses. Polyester fabric grinding produced significant MFs (average length: 570 μm) with degraded surface and increased malleability. Oysters showed increased MF accumulation in digestive glands post-exposure, with no impact on antioxidant enzymes. Depuration decreased MFs accumulation. Histological analysis revealed accumulation in the stomach and brown cells, possibly indicating inflammation. This raises concerns about MFs bioaccumulation in marine organisms, impacting the food chain and safety.

The effects of artificial light at night (ALAN) on the gaping activity and feeding of mussels

Artificial Light at Night (ALAN) is a common environmental pollutant which affects >22 % of the world's coastlines. However, the impact of ALAN wavelengths on coastal organisms is under-investigated. Here, we tested the impact of red, green, and white ALAN on the gaping activity and phytoplankton consumption of Mytilus edulis mussels and compared these to dark night. Mussels exhibited a semi-diel activity pattern. Although ALAN did not significantly affect the time open nor the phytoplankton consumption, it did have a colour-specific effect on the gaping frequency with red and white ALAN resulting in lower activity compared to the dark night. Green ALAN caused higher gaping frequency and a negative relationship between consumption and proportion of time open compared to the other treatments. Our findings suggest colour-specific ALAN effects on mussels and call for further investigation on the associated physiological mechanisms and potential ecological consequences.

First comparative assessment of contamination by plastics and non-synthetic particles in three bivalve species from an Italian sub-alpine lake

This study aimed to compare the contamination from plastics and non-synthetic particles in the three freshwater bivalve mollusks Unio elongatulus, (native) and Corbicula fluminea and Dreissena polymorpha (invasive), collected in Lake Maggiore, the second greatest Italian lake. Organisms were collected from eight sites located throughout the lake, during three years (2019-2021). The quali-quantitative characterization of particles has been carried out using a Fourier Transform Infrared Microscope System (μFT-IR). Results showed that both plastics and non-synthetic particles released in the water are taken up by bivalves, even though low intake-up to 6 particles/individuals-were measured for all the three species. Microfibers of both synthetic (polyester, polyamide) and natural (cellulose) origin represented the particles mostly ingested by bivalves. A significant decrease of particle loads was observed in 2020 with respect to 2019 and 2021, significantly different for D. polymorpha and U. elongatulus, suggesting a transient reduction of the particle release in the lake in this year. Our findings highlight the need to improve the understanding of the mechanisms of uptake and clearance of these contaminants by filter feeding organisms, and their adverse consequences in realistic environmental conditions.

A versatile approach to evaluate the occurrence of microfibers in mussels Mytilus galloprovincialis

Microplastics of fibrous shape are esteemed to be the most abundant micro-debris form present in the environment. Despite the occurrence of microfibers in fish may pose a risk to human health, the literature is scarce regarding studies on the contamination in commercial marine fish mostly due to methodological issues. In this study, a versatile approach, able to discriminate among natural and synthetic microfibers according to the evaluation of specific morphological features, is proposed in farmed mussels (Mytilus galloprovincialis). The approach was useful to determine that microfibers were present in 74% of mussel samples, with a mean number of 14.57 microfibers/individual, corresponding to 3.13 microfibers/g w.w. A negative correlation between the size of analysed mussels and the amount of microfibers/g w.w. was detected, showing that smaller specimens contained more microfibers than the larger ones. This work paves the way to further studies aimed to adequately assess the risk that microfibers may pose to marine biota, also considering the commercial value as seafood items of many species of the Mytilus genus and the potential implication for human exposure.

Long-term exposure of the Mediterranean mussels, Mytilus galloprovincialis to polyethylene terephthalate microfibers: Implication for reproductive and neurotoxic effects

As one of major types of microplastics (MPs), microfibers (MFs) are widely found in the marine ecosystem and can induce diverse impacts on various marine organisms. Sedentary species, such as mussels, can act as bioindicators for monitoring marine contamination. Hence, in this study, we used mussels (Mytilus galloprovincialis) to examine the toxicity of polyethylene terephthalate (PET) MFs of 100 μm size at concentrations of 0.0005, 0.1, 1, 10, and 100 mg/L for 32 days. PET MFs accumulated only in the stomachs and intestines of the mussels and caused digestive tubule atrophy. After exposure to PET MFs, no alteration in the mortality rate, shell height, length, and weight of the mussels was observed. However, the gonadal index decreased with increasing concentrations of PET MFs. This is because PET MFs decrease the sex hormones estradiol and testosterone in mussels, even at environmentally relevant concentrations. Furthermore, chronic exposure to PET MFs increased the activities of antioxidant-related (catalase and superoxide dismutase) and neurotoxicity-related (acetylcholine esterase) enzymes in the digestive gland and gill tissues of mussels. In addition, cellular immune parameters of apoptosis and DNA damage were observed in mussel hemocytes. Thus, this study demonstrates the risks of MPs in real marine environments by assessing how long-term exposure to low concentrations of PET MFs can cause potential sublethal impacts and reproductive failure in mussels.

A Paraffin Microtomy Method for Improved and Efficient Production of Standardized Plastic Microfibers

Microfibers are one of the most abundant microplastic particle types found in the environment, where they cause negative impacts on organisms and possibly on human health. Microfibers should be included in a wide range of laboratory studies; however, microfibers for scientific studies are not commercially available. Current methods to make microfibers generally create particles with large size ranges and poor precision, and efficient production of particles ≤100 µm is difficult. Laboratory studies of the biological and toxicological effects and chemical interactions of microfibers require uniform, small microfibers in sufficient numbers for environmentally relevant experiments. We developed a novel fiber embedding technique and modified a seminal cryomicrotomy method to produce precise microfibers in quantities suitable for environmentally relevant concentrations. Polyethylene terephthalate (PET) and nylon fibers were strategically wound onto a spindle, embedded in paraffin wax, and sectioned using a standard paraffin microtome. After processing with a suitable organic solvent to remove the wax, microfiber size distributions were assessed. The small microfibers (10-42 µm) were accurate to the target lengths with excellent precision and a production rate ≥13.5 times higher than previous methods. As a proof of application, three lengths of manufactured PET fibers were stained with Nile red and exposed to eastern oyster larvae (Crassostrea virginica) for 24 h. Larvae ingested the smaller fiber lengths (14 and 28 µm), and the Nile red-stained fibers were visible and distinguishable in the guts of the larvae. This experiment was the first to demonstrate ingestion of plastic particles other than microspheres by oyster larvae. The present method facilitates the use of small microfibers in laboratory experiments, allowing for a more complete understanding of microplastic effects in the environment. Environ Toxicol Chem 2022;41:944-953. © 2021 SETAC.

Effects of microplastics (PVC, PMMA) on the mussel Semimytilus algosus differ only at high concentrations from those of natural microparticles (clay, celite)

Laboratory exposure studies allow to investigate the impact of microplastics on marine biota, but commonly lack a procedural control, i.e. assessing the effects of natural microparticles. In two experiments with the mussel Semimytilus algosus, we compared the effects of clay vs. polyvinyl chloride (PVC) and celite vs. polymethyl-methacrylate (PMMA), respectively, at concentrations of 1.5, 15 and 150 mg l^-1. After more than 60 days, no effects on respiration and clearance rates, mortality and byssus strength were observed. However, in mussels exposed to PVC the Body Condition Index was 34% lower at 150 mg l^-1 than at 1.5 mg l^-1. Furthermore, at 15 mg l^-1, mussels exposed to microplastics produced over 40% less byssus than those exposed to natural microparticles. This suggests that mussels react differently to natural microparticles and to microplastics, but only at high particle loads that exceed current environmental microplastic concentrations by orders of magnitude.

Bivalves as Biological Sieves: Bioreactivity Pathways of Microplastics and Nanoplastics

AbstractOceanic and coastal sampling programs have indicated extensive plastic pollution of marine habitats and revealed the need for understanding the scope and potential impacts of plastics on marine organisms. Sampling regimes for macroplastics (>5 mm) that can be visually collected for quantification and characterization in marine habitats provide valuable environmental data for the larger plastics. But less is known about the scope or potential impacts of small micron- and nano-sized bits of plastic that result from weathering of macroplastics and inputs of manufactured particles that could profoundly affect marine invertebrates, especially suspension feeders. Essential fundamental information about bivalve biology along with current research and reviews on microplastics, nanoplastics, and engineered nanoparticles were integrated to discuss how filter-feeding bivalves can serve as valuable bioindicators of plastic pollution. Bivalves can serve as important bioaccumulators of plastic particles and exhibit processing pathways that serve as biological sieves. Mesoplastics (1-5 mm) and large microplastics (>25 µm) will have a relatively short transit time (hours to days) and will primarily be concentrated in biodeposits (pseudofeces and feces). Small microplastics (<25 µm) and nanoplastics (<1 µm) are more likely to be accumulated in digestive gland tissues and cells, and also hemocytes, and will have longer retention times. Lysosomes are a common target organelle for uptake and toxicity in both of these cell types. Therefore, bivalves can potentially act as biological sieves for characterizing relative environmental exposures and bioreactivity of microplastics and nanoplastics, based on critical particle capture and processing pathways. This framework highlights the importance of developing diagnostic approaches to characterize potential environmental risks associated with plastic particles as well as potential interactions with other anthropogenic pollutants.

Effects of microplastics on bivalves: Are experimental settings reflecting conditions in the field?

Bivalves are the focus of experimental research as they can filtrate a broad size range of microplastics (MPs) with negative consequences for their physiology. Studies use a range of MP shapes, materials, sizes and concentrations raising the question on whether these reflect environmental observations. We review experimental studies on the effects of MPs on marine bivalves and contrast the MP characteristics used with corresponding data from the environment. Mussels were the most common bivalve across experiments which reflect their high abundance and broad distribution in the field. Although fibres are the dominant shape of MPs in coastal systems, most studies focus on spherules and beads, and MP concentrations are often orders of magnitude higher than environmental levels. For higher relevance of experimental findings we recommend that maximum experimental concentrations of MPs are in the range of 100-1000 particles/L, that there is more focus on microfibers and that concentration is reported in particles/volume.