"Groundbreaking study: Combined effect of marine heatwaves and polyethylene microplastics on Pacific oysters, Crassostrea gigas".

Microplastics (MPs) and rising marine seawater temperatures are one of the major environmental problems threatening the survival of marine organisms and biodiversity. However, interactions between such multiple stressors are virtually unexplored. This study aimed to assess the combined effect of two temperatures and polyethylene MPs on the Pacific oyster Crassostrea gigas, one of the most globalized mollusc species for aquaculture. Our work highlights the potential ecological risk posed by these two factors on marine bivalve molluscs. The experimental design was carried out following a 14-day exposure of oysters to environmental concentrations of polyethylene MPs (0.01 mg.L-1), and to two temperatures (15 °C and 22 °C). Sampling was performed on days 0, 7, and 14. The µ-FTIR analysis was applied to quantify MPs of interest and to check a potential environmental contamination. Tissue samples of digestive glands were collected from the oysters to evaluate the activity of biomarkers including superoxide dismutase, glutathione-s-transferase, malondialdehyde and laccase through protein levels. We note that the combination of MPs and high water temperature (HWT, 22 °C) had a significant impact both on the survival of animals and on stress markers, by modifying lipid peroxidation and immune responses. This original study gave the first innovative results on this topic and provides us with knowledge of the combined effects of MPs pollution and HWT (simulating marine heatwaves situation) on C. gigas. There remains a lack of information on the toxicity and the potential environmental hazard of plastics in the marine environment.

Artificial weathering of plastics used in oyster farming.

With the omnipresence of plastic litter from oyster farming in marine coastal areas, the objective of this work was to better understand the weathering of plastics used in this field, focusing on oyster spat collectors. During their use, around fifteen years, collectors made of polypropylene (PP) undergo numerous degradations, alternatively submerged, emerged in seawater, and stored outdoor until the next cycle. They weaken, crack, break, end up fragmenting and disseminated in the environment as microplastics associated to persistent organic pollutants. In this work, a comparison of 55 months of in situ weathering with five months of artificial weathering in air or in artificial seawater in a homemade UV chamber was conducted to better understand the mechanisms involved. Chemical, thermal and surface characterizations of virgin and weathered samples were conducted using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Environmental Scanning Electron Microscopy (ESEM). After 55 months of in situ weathering, collectors were notably damaged with large fissures and loss of microplastics (MPs) associated with an increase of carbonyl index values and a decrease of melting temperatures and crystallinity rates. Considering only UV irradiation, five months of artificial weathering at 30 °C under continuous irradiation of 6.9 W/m2 under UV lamps (295-400 nm) reproduced approximately 4.4 months of natural sunlight. Artificial weathering confirmed that photooxidation by combined effects of UV rays and oxygen was the main weathering mechanism and was reduced in seawater. These results help to understand the mechanisms involved in the weathering of these collectors in the marine environment and provide valuable information for industrials and professionals. Our study suggests a better storage away from UV rays and a reduction of the duration of use compared to current practices.

Intergenerational effects of environmentally-aged microplastics on the Crassostrea gigas.

This study focused on the impacts of aged aquaculture microplastics (MPs) on oysters (Crassostrea gigas). Adult oysters were exposed for two months to a cocktail of MPs representative of the contamination of the Pertuis Charentais area (Bay of Biscay, France) and issuing from oyster framing material. The MPs mixture included 28% of polyethylene, 40% of polypropylene and 32% of PVC (polyvinyl chloride). During the exposure, tissues were sampled for various analyzes (MP quantification, toxicity biomarkers). Although no effect on the growth of adult oysters was noted, the mortality rate of bivalves exposed to MPs (0.1 and 10 mg. L-1 MP) increased significantly (respectively 13.3 and 23.3% of mortalities cumulative). On the one hand, the responses of biomarkers revealed impacts on oxidative stress, lipid peroxidation and environmental stress. At 56 days of exposure, significant increases were noted for Glutathione S-Transferase (GST, 10 mg. L-1 MP), Malondialdehyde (MDA, 10 mg. L-1 MP) and Laccase (LAC, 0.1 and 10 mg. L-1 MP). No variations were observed for Superoxyde Dismutase (SOD). Besides, ingestion of MPs in oyster tissues and the presence in biodeposits was highlighted. In addition, in vitro fertilisations were performed to characterize MPs effects on the offspring. Swimming behavior, development and growth of D-larvae were analysed at 24-, 48- and 72-h after fertilisation. D-larvae, from exposed parents, demonstrated reduced locomotor activity. Developmental abnormalities and arrest as well as growth retardation were also noted. This study highlighted direct and intergenerational effects of MPs from aged plastic materials on Pacific oysters.

Coastal ecosystem inventory with characterization and identification of plastic contamination and additives from aquaculture materials.

In the early 1970s, studies of marine litter first appeared in the scientific literature. Fifty years later, knowledge of several coastal areas of the Atlantic, the driving forces of oyster farmers and aquaculture, is lacking. This work documents a pilot study on an Atlantic coastal area (France). This study aims to (i) characterize the abundance of macroplastics related to aquaculture tools; (ii) microplastics present in beach sediments and (iii) characterization of pollutants present on aquaculture plastics collected. First, it was observed that 70% of the plastics collected on the beach were characteristic of aquaculture materials. In sediments, MPs most found were Polyamide between 10 and 20 µm, with a total MP concentration of 397-457 MPs.kg-1. Pipes collectors (PVC), frequently used in aquaculture, have been shown to have concentrations of dimethylphthalates and naphthalene. Waste management and support policies can then base their actions on such studies, in order to improve their knowledge.

Evidence of deleterious effects of microplastics from aquaculture materials on pediveliger larva settlement and oyster spat growth of Pacific oyster, Crassostrea gigas.

Plastic is currently used in aquaculture as a material for settlement and magnification of oyster spats. Plastic weathering and fragmentation under natural conditions can lead to the production of micro and nanoparticles and additive leakage, with potential toxic effects on marine life. This study investigates the effects of the exposure to microplastic (MPs) cocktail derived from aged aquaculture material on oyster pediveliger larvae (Crassostrea gigas). The cocktail was made of high-density polyethylene (HDPE), polypropylene (PP) and polyvinyl chloride (PVC). The concentrations tested were 0, 0.1, and 10 mg MP·L-1. During the 7-day fixation phase, pediveliger larvae (17 days) were exposed to the MP cocktail in laboratory-controlled conditions. After exposure, the success of settlement was significantly lower for larvae exposed to 10 mg MP·L-1 (49 ± 0.9%) compared to control ones (61.8 ± 1.6%). No malformations or metamorphosis abnormalities were observed. Growth of pediveliger and spat stages was monitored up to 11 months. During the first twenty-eight days of development, spat growth was significantly lower for the two MPs exposure conditions (0.1 and 10 mg MP·L-1; respectively -51.8% and -44.4%) compared to control group. Subsequently, the previously exposed oysters grew faster than the control condition, resulting in a significantly greater growth (0.1 and 10 mg MP·L-1: +18.3% and +19.7%) than the control group at the end of follow-up. The nearly one-year follow-up highlighted the potential effects of MPs from aquaculture on larvae and spat of C. gigas.

Toxicity and risk assessment of six widely used pesticides on embryo-larval development of the Pacific oyster, Crassostrea gigas.

This study aims to assess the toxic effects and the potential risk of widely used agricultural pesticides on the development (malformations and developmental arrest), growth and swimming activity of oyster D-larvae (Crassostrea gigas). Freshly fertilized oyster embryos were exposed for 24 h at 24 °C to different concentrations (0, 0.01, 0.1, 1 and 10 µg.L-1) of six different pesticides: Glyphosate and its commercial solution (Roundup), Isoproturon, Nicosulfuron, Chlortoluron and Boscalid. The six pesticides tested induced a significant increase in larval malformations and developmental arrests. All pesticides except Glyphosate and Isoproturon affected larval growth. Roundup, Nicosulfuron, Chlortoluron and Boscalid also affected the swimming behaviour of the D-larvae, with a significant decrease recorded in their maximum swimming speed. Comparison of the LOEC (Lowest-Observed-Effect Concentration) of each compound led to the following toxicity classification: Boscalid > Chlortoluron = Nicosulfuron > Glyphosate > Roundup > Isoproturon, with respectively LOEC of 0.0028; 0.015; 0.017; 0.11; 0.3 and 0.78 µg.L-1. By comparison of the maximum concentrations in the Pertuis Charentais (South West, France) and LOEC of each pesticide, the following risk scale was obtained: Chlortoluron > Boscalid > Glyphosate > Roundup > Nicosulfuron > Isoproturon. Our results revealed that Chlortoluron, Boscalid and to a lesser extent Glyphosate represent a potential threat to early life stages of oyster living in the Pertuis Charentais marine area.

Subchronic exposure to high-density polyethylene microplastics alone or in combination with chlortoluron significantly affected valve activity and daily growth of the Pacific oyster, Crassostrea gigas.

Nowadays, pesticides and microplastics (MPs) are commonly found in coastal waters worldwide. Due to their widespread use, their persistence and toxicity, they may induce adverse effects on physiology and behaviour of marine organisms such as the Pacific oyster (Crassostrea gigas). This study explored the growth and valve activity of juvenile oysters exposed for 24 days to two frequently detected pollutants in the Pertuis Charentais (South West, France): a herbicide (chlortoluron, 85 µg.L-1) and high-density polyethylene microparticles (HDPE 20-25 µm, 112 MP.mL-1) alone or in combination (cocktail condition; 97 µg.L-1 of chlortoluron + 108 MP. mL-1). The valve activity of juvenile oysters recorded by using a High Frequency and Non-Invasive valvometer (HFNI) was characterized by three parameters: the number of valve micro-closures (VMC), the Valve Opening Amplitude (VOA), and the Valve Opening Duration (VOD). Additionally, daily shell growth and the oyster daily rhythm were assessed. The exposure to MPs of oysters led to a significant increase of VMC and a decrease of VOD and shell growth. The exposure to chlortoluron showed a significant increase of VOA and a decrease of VMC. In combination with MPs, chlortoluron still increased VOA and decreased VMC but also reduced the shell growth. Chronobiological analysis did not reveal any effects on the daily rhythm of both contaminants. This work highlighted significant effects of high environmental concentrations of MPs and Chlortoluron on the behaviour and growth of the Pacific oyster.

Experimental ingestion of fluorescent microplastics by pacific oysters, Crassostrea gigas, and their effects on the behaviour and development at early stages.

Plastics are persistent synthetic polymers that accumulate as waste in the marine environment. Microplastics (MPs, <5 mm) can be found either as microbeads in body care and some industrial products or as plastic debris through degradation. Plastic microbeads (1-5 µm, fluorescent, Cospheric) were used to characterise the MP ingestion and determine their potential harmful effects on both the swimming behaviour and development of oyster D-larvae (Crassostrea gigas). For 24 h, embryos were first exposed to MPs at a temperature of 24 °C. In addition, 3 day-old D-larvae were exposed to the same temperature for 1, 3 and 5 h. Three concentrations of MPs were used: 0.1, 1 and 10 mg MP. L-1. After a 24-h period of embryonic exposure, we noted that MP agglomerates were stuck to the D-larvae coat and locomotor eyelashes. We also observed a significant increase in severe malformations and developmental arrests for larvae exposed to MPs ranging from 1 mg MP. L-1. In terms of swimming behaviour, the maximum speed recorded was lower for larvae exposed at 0.1 and 1 mg MP. L-1. After an acute exposure to MPs, particles were found in the digestive tract of 3 dpf (days post fertilisation) D-larvae. After 1-h exposure, the concentrations tested (0.1, 1 and 10 mg MP. L-1) resulted in respectively 38%, 86% and 98%. The larvae swimming behaviour was recorded and analysed. Unlike the results observed at the embryo-larval stage, 3-dpf larvae showed significant impacts with no dose-response effect.

Microplastics and sorbed contaminants - Trophic exposure in fish sensitive early life stages.

The present study evaluated very small microplastic particle (MPs) transfer to zebrafish and marine medaka larvae via prey experimentally exposed to MPs from the onset of feeding. Larvae were fed Paramecium or Artemia nauplii loaded with fluorescent 1-5 or 10-20 µm MP. Pollutant accumulation was analyzed by optically tracking of benzo[a]pyrene (BaP) and recording cyp1a transcription. Paramecium transferred 1-5 µm particles only, whereas Artemia efficiently transferred both MPs. Although zebrafish and medaka larvae fed from the onset of active food intake (2-3 dph, respectively) on Paramecium and from days 6-7 post-hatch on Artemia nauplii, neither MP accumulation nor translocation to tissues was detected. MP egestion started within few hours after ingestion. Cyp1a induction and fluorescent analyses proved BaP bioavailability after transfer via Paramecium and Artemia. Unicellular or plankton organisms ingest contaminants via MPS and transfer effectively these to sensitive early life-stages of vertebrates, giving rise to whole-life exposure.

High density polyethylene (HDPE) microplastics impair development and swimming activity of Pacific oyster D-larvae, Crassostrea gigas, depending on particle size.

Understanding the effects of plastic debris on marine ecosystems is essential in encouraging decision-makers to take action. The present study investigates the effect of a 24 h experimental exposure to high density polyethylene (HDPE) microplastics (MPs) of different sizes (4-6, 11-13 and 20-25 µm) and at three concentrations (0.1, 1 and 10 mg MP.L-1) on the development and locomotor activity of early stages of Pacific oyster, Crassostrea gigas. The bivalve embryo-larval assay (NF ISO 17244, 2015) was used in this study but with additional toxicity criteria: developmental arrests, abnormal D-larvae, maximum speed and swimming trajectory. Copper (Cu), was used as a positive control. Our results show that smaller MPs (4-6 and 11-13 µm) induced higher rates of malformations and developmental arrests than the larger ones (20-25 µm). In addition, a dose-dependent decrease of maximum swimming speed was observed for larvae exposed to MPs of 4-6 and 11-13 µm. On the other hand, there was no significant difference in swimming speed with the largest MPs size tested (20-25 µm). For all three sizes of MPs, there was a decrease in straight-line swimming trajectories, and an increase in circular trajectories. This abnormal swimming behaviour could affect larvae survival as well as colonization of new habitats.