In the marine environment, most bivalve species base their reproduction on external fertilization. Hence, gametes and young stages face many threats, including exposure to plastic wastes which represent more than 80% of the debris in the oceans. Recently, evidence has been produced on the presence of nanoplastics in oceans, thus motivating new studies of their impacts on marine life. Because no information is available about their environmental concentrations, we performed dose-response exposure experiments with polystyrene particles to assess the extent of micro/nanoplastic toxicity. Effects of polystyrene with different sizes and functionalizations (plain 2-μm, 500-nm and 50-nm; COOH-50 nm and NH₂-50 nm) were assessed on three key reproductive steps (fertilization, embryogenesis and metamorphosis) of Pacific oysters (Crassostrea gigas). Nanoplastics induced a significant decrease in fertilization success and in embryo-larval development with numerous malformations up to total developmental arrest. The NH₂-50 beads had the strongest toxicity to both gametes (EC₅₀ = 4.9 μg/mL) and embryos (EC₅₀ = 0.15 μg/mL), showing functionalization-dependent toxicity. No effects of plain microplastics were recorded. These results highlight that exposures to nanoplastics may have deleterious effects on planktonic stages of oysters, presumably interacting with biological membranes and causing cyto/genotoxicity with potentially drastic consequences for their reproductive success.

During the Deepwater Horizon oil spill rapid natural weathering of Macondo crude oil occurred during the transport of oil to coastal areas. In response to the DWH incident, dispersant was applied to Macondo crude oil to reduce the movement of oil to coastal regions. This study aimed to assess the narcotic and phototoxicity of water-accommodated fractions (WAFs) of weathered Macondo crude oil, and chemically-enhanced WAFs of Corexit 9500 to Pacific (Crassostrea gigas) and eastern (Crassostrea virginica) oyster larvae. Phototoxic effects were observed for larval Pacific oysters exposed to combinations of oil and dispersant, but not for oil alone. Phototoxic effects were observed for larval eastern oysters exposed to oil alone and combinations of oil and dispersant. Corexit 9500 did not exhibit phototoxicity but resulted in significant narcotic toxicity for Pacific oysters. Oyster larvae may have experienced reduced survival and/or abnormal development if reproduction coincided with exposures to oil or dispersant.

Monitoring the presence of microplastics (MP) in marine organisms is currently of high importance. This paper presents the qualitative and quantitative MP contamination of two bivalves from the French Atlantic coasts: the blue mussel (Mytilus edulis) and the Pacific oyster (Crassostrea gigas). Three factors potentially influencing the contamination were investigated by collecting at different sampling sites and different seasons, organisms both wild and cultivated. Inter- and intra-species comparisons were also achieved. MP quantity in organisms was evaluated at 0.61±0.56 and 2.1±1.7MP per individual respectively for mussels and oysters. Eight different polymers were identified. Most of the MPs were fragments; about a half of MPs were grey colored and a half with a size ranging from 50 to 100μm for both studied species. Some inter-specific differences were found but no evidence for sampling site, season or mode of life effect was highlighted.

Following the discovery of potential chronic perfluoroalkyl substances (PFAS) contamination of Tilligerry Creek, Port Stephens (New South Wales Australia), sampling was undertaken to confirm the presence, extent and levels of contamination in commercial oyster crops of Sydney Rock Oyster (Saccostrea glomerata) and Pacific Oyster (Crassostrea gigas) grown within the estuary. Among a range of PFAS tested, only perfluorooctane sulfonate (PFOS) was detected. Concentrations of PFOS in oyster tissues for S. glomerata ranged from 1.6μgkg⁻¹ ww (wet weight) to below the limit of reporting of 0.3μgkg⁻¹ ww, with concentrations generally decreasing toward the lower reaches of the estuary. The sample of C. gigas tested had a PFOS concentration of 0.71μgkg⁻¹ ww that was consistent with concentrations observed in nearby S. glomerata. For harvest size (50–60g) S. glomerata, both holding contaminated oysters in a depuration system, and relocation to a non-contaminated area, saw significant reductions in the tissue PFOS concentrations. For oysters held in a depuration system, PFOS depurated at a rate of 0.008h⁻¹ (0.004–0.019h⁻¹; 90% CI), which corresponded with a depuration half-life of 87h (35–155h; 90%). A more conservative model (fitted to data that assumed concentrations<LOR were equal 0.5·LOR) predicted a depuration half-life of 131h. PFOS concentrations had fallen to below detectable limits within 162h. Similar decreases were observed in relocated oysters.

Despite a growing scientific attention on ecological impact of emerging pollutants (EPs) such as pharmaceuticals, personal care products, and pesticides, knowledge gaps remain regarding mixture toxicity and effects on aquatic organisms. Several EPs were screened in seawater (Normandy, France), and the ecotoxicity of five compounds, chosen on their occurrence in ecosystems and use worldwide, was assessed and were the biocides methylparaben (MP) and triclosan (TCS), a pesticide degradation product (AMPA), and the pharmaceuticals venlafaxine (VEN) and carbamazepine (CBZ). The acute or sub-chronic toxicity, alone or in binary/ternary mixtures of three of them (CBZ, AMPA, and MP), was assessed on one marine and two freshwater organisms: Crassostrea gigas, Pseudokirchneriella subcapitata, and Daphnia magna. TCS and AMPA were, respectively, the most (EC₅₀ < 1 mg L⁻¹) and the least (EC₅₀ > 50 mg L⁻¹) toxic chemicals for the four endpoints (algal growth inhibition, daphnia immobilization, oyster embryotoxicity, and metamorphosis). The anxiolytic VEN (EC₅₀ < 1 mg L⁻¹) was particularly toxic to oyster larvae showing sensitivity difference between freshwater and marine organisms. If all the mixtures appeared to be in the same range of toxicity, the joint-toxic effects mainly led to synergistic or antagonistic interactions compared to single-compound toxicity. The data also highlighted species-dependent differing models of toxicity and underscored the need for an awareness of cocktail effects for better ecological risk assessment.