Pearl Farming Micro-Nanoplastics Affect Oyster Physiology and Pearl Quality.

Pearl farming is crucial for the economy of French Polynesia. However, rearing structures contribute significantly to plastic waste, and the widespread contamination of pearl farming lagoons by microplastics has raised concerns about risks to the pearl industry. This study aimed to evaluate the effects of micro-nanoplastics (MNPs, 0.4-200 µm) on the pearl oyster (Pinctada margaritifera) over a 5-month pearl production cycle by closely mimicking ecological scenarios. MNPs were produced from weathered plastic pearl farming gear and tested at environmentally relevant concentrations (0.025 and 1 µg L-1) to decipher biological and functional responses through integrative approaches. The significant findings highlighted the impacts of MNPs on oyster physiology and pearl quality, even at remarkably low concentrations. Exposure to MNPs induced changes in energy metabolism, predominantly driven by reduced assimilation efficiency of microalgae, leading to an alteration in gene expression patterns. A distinct gene expression module exhibited a strong correlation with physiological parameters affected by MNP conditions, identifying key genes as potential environmental indicators of nutritional-MNP stress in cultured oysters. The alteration in pearl biomineralization, evidenced by thinner aragonite crystals and the presence of abnormal biomineral concretions, known as keshi pearls, raises concerns about the potential long-term impact on the Polynesian pearl industry.

A critical review on the evaluation of toxicity and ecological risk assessment of plastics in the marine environment.

The increasing production of plastics together with the insufficient waste management has led to massive pollution by plastic debris in the marine environment. Contrary to other known pollutants, plastic has the potential to induce three types of toxic effects: physical (e.g intestinal injuries), chemical (e.g leaching of toxic additives) and biological (e.g transfer of pathogenic microorganisms). This critical review questions our capability to give an effective ecological risk assessment, based on an ever-growing number of scientific articles in the last two decades acknowledging toxic effects at all levels of biological integration, from the molecular to the population level. Numerous biases in terms of concentration, size, shape, composition and microbial colonization revealed how toxicity and ecotoxicity tests are still not adapted to this peculiar pollutant. Suggestions to improve the relevance of plastic toxicity studies and standards are disclosed with a view to support future appropriate legislation.

On the horns of a dilemma: Evaluation of synthetic and natural textile microfibre effects on the physiology of the pacific oyster Crassostrea gigas.

Fast fashion and our daily use of fibrous materials cause a massive release of microfibres (MF) into the oceans. Although MF pollution is commonly linked to plastics, the vast majority of collected MF are made from natural materials (e.g. cellulose). We investigated the effects of 96-h exposure to natural (wool, cotton, organic cotton) and synthetic (acrylic, nylon, polyester) textile MF and their associated chemical additives on the capacity of Pacific oysters Crassostrea gigas to ingest MF and the effects of MF and their leachates on key molecular and cellular endpoints. Digestive and glycolytic enzyme activities and immune and detoxification responses were determined at cellular (haemocyte viability, ROS production, ABC pump activity) and molecular (Ikb1, Ikb2, caspase 1 and EcSOD expression) levels, considering environmentally relevant (10 MF L-1) and worst-case scenarios (10 000 MF L-1). Ingestion of natural MF perturbed oyster digestive and immune functions, but synthetic MF had few effects, supposedly related with fibers weaving rather than the material itself. No concentration effects were found, suggesting that an environmental dose of MF is sufficient to trigger these responses. Leachate exposure had minimal effects on oyster physiology. These results suggest that the manufacture of the fibres and their characteristics could be the major factors of MF toxicity and stress the need to consider both natural and synthetic particles and their leachates to thoroughly evaluate the impact of anthropogenic debris. Environmental Implication. Microfibres (MF) are omnipresent in the world oceans with around 2 million tons released every year, resulting in their ingestion by a wide array of marine organisms. In the ocean, a domination of natural MF- representing more than 80% of collected fibres-over synthetic ones was observed. Despite MF pervasiveness, research on their impact on marine organisms, is still in its infancy. The current study aims to investigate the effects of environmental concentrations of both synthetic and natural textile MF and their associated leachates on a model filter feeder.

Mission Tara Microplastics: a holistic set of protocols and data resources for the field investigation of plastic pollution along the land-sea continuum in Europe.

The Tara Microplastics mission was conducted for 7 months to investigate plastic pollution along nine major rivers in Europe-Thames, Elbe, Rhine, Seine, Loire, Garonne, Ebro, Rhone, and Tiber. An extensive suite of sampling protocols was applied at four to five sites on each river along a salinity gradient from the sea and the outer estuary to downstream and upstream of the first heavily populated city. Biophysicochemical parameters including salinity, temperature, irradiance, particulate matter, large and small microplastics (MPs) concentration and composition, prokaryote and microeukaryote richness, and diversity on MPs and in the surrounding waters were routinely measured onboard the French research vessel Tara or from a semi-rigid boat in shallow waters. In addition, macroplastic and microplastic concentrations and composition were determined on river banks and beaches. Finally, cages containing either pristine pieces of plastics in the form of films or granules, and others containing mussels were immersed at each sampling site, 1 month prior to sampling in order to study the metabolic activity of the plastisphere by meta-OMICS and to run toxicity tests and pollutants analyses. Here, we fully described the holistic set of protocols designed for the Mission Tara Microplastics and promoted standard procedures to achieve its ambitious goals: (1) compare traits of plastic pollution among European rivers, (2) provide a baseline of the state of plastic pollution in the Anthropocene, (3) predict their evolution in the frame of the current European initiatives, (4) shed light on the toxicological effects of plastic on aquatic life, (5) model the transport of microplastics from land towards the sea, and (6) investigate the potential impact of pathogen or invasive species rafting on drifting plastics from the land to the sea through riverine systems.

Discussion about suitable applications for biodegradable plastics regarding their sources, uses and end of life.

This opinion paper offers a scientific view on the current debate of the place of biodegradable plastics as part of the solution to deal with the growing plastic pollution in the world's soil, aquatic, and marine compartments. Based on the current scientific literature, we focus on the current limits to prove plastic biodegradability and to assess the toxicity of commercially used biobased and biodegradable plastics in natural environments. We also discuss the relevance of biodegradable plastics for selected applications with respect to their use and end of life. In particular, we underlined that there is no universal biodegradability of plastics in any ecosystem, that considering the environment as a waste treatment system is not acceptable, and that the use of compostable plastics requires adaptation of existing organic waste collection and treatment channels.

Additives in polypropylene and polylactic acid food packaging: Chemical analysis and bioassays provide complementary tools for risk assessment.

Plastic food packaging represents 40 % of the plastic production worldwide and belongs to the 10 most commonly found items in aquatic environments. They are characterized by high additives contents with >4000 formulations available on the market. Thus they can release their constitutive chemicals (i.e. additives) into the surrounding environment, contributing to chemical pollution in aquatic systems and to contamination of marine organism up to the point of questioning the health of the consumer. In this context, the chemical and toxicological profiles of two types of polypropylene (PP) and polylactic acid (PLA) food packaging were investigated, using in vitro bioassays and target gas chromatography mass spectrometry analyses. Plastic additives quantification was performed both on the raw materials, and on the material leachates after 5 days of lixiviation in filtered natural seawater. The results showed that all samples (raw materials and leachates) contained additive compounds (e.g. phthalates plasticizers, phosphorous flame retardants, antioxidants and UV-stabilizers). Differences in the number and concentration of additives between polymers and suppliers were also pointed out, indicating that the chemical signature cannot be generalized to a polymer and is rather product dependent. Nevertheless, no significant toxic effects was observed upon exposure to the leachates in two short-term bioassays targeting baseline toxicity (Microtox® test) and Pacific oyster Crassostrea gigas fertilization success and embryo-larval development. Overall, this study demonstrates that both petrochemical and bio-based food containers contain harmful additives and that it is not possible to predict material toxicity solely based on chemical analysis. Additionally, it highlights the complexity to assess and comprehend the additive content of plastic packaging due to the variability of their composition, suggesting that more transparency in polymer formulations is required to properly address the risk associated with such materials during their use and end of life.

Diversity and molecular epidemiology of Ostreid herpesvirus 1 in farmed Crassostrea gigas in Australia: Geographic clusters and implications for "microvariants" in global mortality events.

Since 2010, mass mortality events known as Pacific oyster mortality syndrome (POMS) have occurred in Crassostrea gigas in Australia associated with Ostreid herpesvirus 1. The virus was thought to be an OsHV-1 µVar or "microvariant", i.e. one of the dominant variants associated with POMS in Europe, but there are few data to characterize the genotype in Australia. Consequently, the genetic identity and diversity of the virus was determined to understand the epidemiology of the disease in Australia. Samples were analysed from diseased C. gigas over five summer seasons between 2011 and 2016 in POMS-affected estuaries: Georges River in New South Wales (NSW), Hawkesbury River (NSW) and Pitt Water in Tasmania. Sequencing was attempted for six genomic regions. Numerous variants were identified among these regions (n = 100 isolates) while twelve variants were identified from concatenated nucleotide sequences (n = 61 isolates). Nucleotide diversity of the seven genotypes of C region among Australian isolates (Pi 0.99 × 10-3) was the lowest globally. All Australian isolates grouped in a cluster distinct from other OsHV-1 isolates worldwide. This is the first report that Australian outbreaks of POMS were associated with OsHV-1 distinct from OsHV-1 reference genotype, µVar and other microvariants from other countries. The findings illustrate that microvariants are not the only variants of OsHV-1 associated with mass mortality events in C. gigas. In addition, there was mutually exclusive spatial clustering of viral genomic and amino acid sequence variants between estuaries, and a possible association between genotype/amino acid sequence and the prevalence and severity of POMS, as this differed between these estuaries. The sequencing findings supported prior epidemiological evidence for environmental reservoirs of OsHV-1 for POMS outbreaks in Australia.

Cryogrinding and sieving techniques as challenges towards producing controlled size range microplastics for relevant ecotoxicological tests.

The impact of microplastics (MP) has attracted much attention from the scientific community and many laboratory assessments have been made of their effects on aquatic organisms. To produce MP from real environmental plastic waste, which would enable more realistic experiments, we used plastic pearl farming equipment from French Polynesian lagoons. Here, the pearl oyster Pinctada margaritifera could encounter MP coming from their breakdown in its surrounding environment. We tested an established method based on mechanical cryogenic grinding and liquid sieving. Our desired size range was 20-60 µm, corresponding to the optimal particle size ingested by P. margaritifera. The protocol was effective, generating MP particles of 20-60 µm (∼17,000-28,000 MP µg-1), but also produced too many smaller particles. The peak in the desired size range was thus flattened by the many small particles <3 µm (∼82,000-333,000 MP µg-1; 53-70% of total analysed particles), visible at the limit of Coulter counter analysis (cut-off point: 2 µm). Laser diffraction analysis (cut-off point: 0.4 µm) provided greater detail, showing that ∼80-90% of the total analysed particles were <1 µm. Diverging particle size distributions between those expected based on sieving range and those really observed, highlight the need to perform fine-scaled particle size distribution analyses to avoid underestimating the number of small micro- and nanoplastics (MNP) and to obtain an exact estimation of the fractions produced. Size and microstructure characterization by scanning electron microscopy suggested spontaneous particle self-assembly into crystal superstructures, which is the supposed cause of the divergence we observed. Overall, our results emphasize that particle self-assembly is a technical hurdle requiring further work and highlight the specific need to finely characterize the size distribution of MNP used in ecotoxicological experiments to avoid overestimating effects.

Tire rubber chemicals reduce juvenile oyster (Crassostrea gigas) filtration and respiration under experimental conditions.

Tires can release a large number of chemical compounds that are potentially hazardous for aquatic organisms. An ecophysiological system was used to do high-frequency monitoring of individual clearance, respiration rates, and absorption efficiency of juvenile oysters (8 months old) gradually exposed to four concentrations of tire leachates (equivalent masses: 0, 1, 10, and 100 µg tire mL-1). Leachates significantly reduced clearance (52 %) and respiration (16 %) rates from 1 µg mL-1, while no effect was observed on the absorption efficiency. These results suggest that tire leachates affect oyster gills, which are the organ of respiration and food retention as well as the first barrier against contaminants. Calculations of scope for growth suggested a disruption of the energy balance with a significant reduction of 57 %. Because energy balance directs whole-organism functions (e.g., growth, reproductive outputs), the present study calls for an investigation of the long-term consequences of chemicals released by tires.

Chemical effects of different types of rubber-based products on early life stages of Pacific oyster, Crassostrea gigas.

Rubber products and debris with specific chemical signatures can release their constitutive compounds into the surrounding environment. We investigated the chemical toxicity of different types of new and used rubber products (tires, crumb rubber granulates, aquaculture rubber bands) on early life stages of a model marine organism, Pacific oyster Crassostrea gigas. Leachates obtained from used products were generally less toxic than those from new ones. Leachates from new products induced embryotoxicity at different concentrations: oyster-farming rubber bands (lowest observed effect concentration, LOEC = 1 g L-1) and crumb rubber granulates (LOEC = 1 g L-1) > tires (LOEC = 10 g L-1). Moreover, new oyster-farming rubber bands induced spermiotoxicity at 10 g L-1 (-29% survival) resulting in decreased oyster reproductive output (-17% fertilization yield). Targeted chemical analyses revealed some compounds (2 mineral contaminants, 15 PAHs, 2 PCBs) in leachates, which may have played a role. Rubber used in marine aquaculture (rubber bands) or present at sea as waste (tire, crumb rubber granulates) therefore release hazardous chemical molecules under realistic conditions, which may affect oyster development. Aquaculture development work is necessary to improve practices for eco-safety, as efforts to limit the contamination of marine environments by terrestrial rubber debris.

Microplastics contamination in pearl-farming lagoons of French Polynesia.

Pearl-farming is the second most important source of income in French Polynesia. However, tropical lagoons are fragile ecosystems with regard to anthropogenic pressures like plastic pollution, which threaten marine life and the pearl oyster-related economy. Here, we investigated the spatial distribution of microplastics (MP) and concentrations in surface water (SW), water column (WC) and cultivated pearl oyster (PO) from three pearl-farming atolls with low population and tourism. Microplastics were categorized by their size class, shape, colour and polymer type identified using FTIR spectroscopy. Widespread MP contamination was observed in every study site (SW, 0.2-8.4 MP m-3; WC, 14.0-716.2 MP m-3; PO, 2.1-125.0 MP g-1 dry weight), with high contamination in the WC highlighting the need to study the vertical distribution of MP, especially as this compartment where PO are reared. A large presence of small (< 200 µm) and fragment-shaped (> 70%) MP suggests that they result from the breakdown of larger plastic debris. The most abundant polymer type was polyethylene in SW (34-39%), WC (24-32%), while in PO, polypropylene (14-20%) and polyethylene were more evenly distributed (9-21%). The most common MP identified as black-grey polyethylene and polypropylene matches the polymer and colour of ropes and collectors questioning a pearl-farming origin.

Identification and quantification of plastic additives using pyrolysis-GC/MS: A review.

Analysis of organic plastic additives (OPAs) associated to plastic polymers is growing. The current review outlines the characteristics and the development of (multi-step) pyrolysis coupled with a gas chromatography mass spectrometer (Py-GC/MS) for the identification and semi-quantification of OPAs. Compared to traditional methods, Py-GC/MS offers advantages like suppressing extensive steps of preparation, limiting contamination due to solvents and the possibility to analyse minute particles. Its key advantage is the successive analysis of OPAs and the polymeric matrix of the same sample. Based on the studied articles, numerous methods have been described allowing identification and, in some case, semi-quantification of OPAs. There is nevertheless no gold standard method, especially given the huge diversity of OPAs and the risks of interferences with polymers or other additives, but, among other parameters, a consensus temperature seems to arise from studies. More broadly, this review also explores many aspects on the sample preparation like weight and size of particles and calibration strategies. After studying the various works, some development prospects emerge and it appears that methodological developments should focus on better characterizing the limits of the methods in order to consider which OPAs can be quantified and in which polymers this is feasible.

An Irgafos® 168 story: When the ubiquity of an additive prevents studying its leaching from plastics.

Plastic pollution is a source of chemical to the environment and wildlife. Despite the ubiquity of plastic pollution and thus plastic additive in the environment, plastic additives have been studied to a limited extend. As a prerequisite to a study aiming to evaluate the leaching of a common additive used as an antioxidant (Irgafos® 168) from polyethylene microparticles, an inventory of the potential background contamination of the laboratory workplace was done. In this study, Irgafos® 168 (tris(2,4-ditert-butylphenyl) phosphite) and its oxidized form (tris (2,4-ditert-butylphenyl) phosphate) were quantified in different laboratory reagents, including the plastic packaging and the powders, using Pyrolysis-GC/MS. At least one form of Irgafos® 168 was detected in all tested laboratory reagents with higher concentrations in caps and bottles as compared to the powders. Additionally, oxidized Irgafos® 168 was also found in the reverse osmosed and deionized water container used in the laboratory. The same profile of contamination, i.e. higher concentration of the oxidized form and higher concentrations in acidic reagents, was observed when comparing the reagent and their respective containers suggesting that the additive is leaching from the container into the powder. Overall, this study demonstrates that the antioxidant additive Irgafos® 168 is ubiquitous in the laboratory workplace. Plastic additives such as Irgafos® 168 can therefore largely interfere and biased ecotoxicological and toxicological studies especially using environmentally relevant concentrations of microplastics. The source, fate and effects of plastic additive from plastic debris should be carefully considered in future studies that require setting up methods to overcome these contaminations.

Toxic effects of leachates from plastic pearl-farming gear on embryo-larval development in the pearl oyster Pinctada margaritifera.

Pearl-farming leads to significant plastic pollution in French Polynesia (FP) as the end of life of most farming gear is currently poorly managed. Plastic debris released into the aquatic environment accumulates, with potentially detrimental effects on the lagoon ecosystem and pearl oyster Pinctada margaritifera, a species of ecological, commercial and social value. Here, we tested the effects of leachates from new (N) and aged (A) plastic pearl-farming gear (spat collector and synthetic rope) obtained after 24 h and 120 h incubation, on the embryo-larval development of the pearl oyster using an in-vitro assay. Embryos were exposed for 24 h and 48 h to a negative control (0) and the leachate from 0.1, 1, 10 and 100 g of plastic. L-1. After 24 h exposure to leachate at 100 g.L-1, effects were observed on embryo development (-38% to -60% of formed larvae) and mortality (+72% to +82%). Chemical analyses of plastic gear indicated the presence of 26 compounds, consisting of organic contaminants (PAHs) and additives (mainly phthalates). Screening of leachates demonstrated that these compounds leach into the surrounding seawater with an additional detection of pesticides. Higher levels of phthalates were measured in leachates obtained from new (6.7-9.1 µg.L-1) than from aged (0.4-0.5 µg.L-1) plastics, which could be part of the explanation of the clear difference in toxicity observed after 48 h exposure at lower concentrations (0.1-10 g.L-1), associated with mortality ranging from 26 to 86% and 17-28%, respectively. Overall, this study suggests that plastic gear used in the pearl-farming industry releases significant amounts of hazardous chemicals over their lifetime, which may affect pearl oyster development that call for in-situ exploration.

Detection of ostreid herpesvirus-1 in plankton and seawater samples at an estuary scale.

Ostreid herpesvirus-1 (OsHV-1) is known to associate with particles in seawater, leading to infection and disease in the Pacific oyster Crassostrea gigas. The estuarine environment is highly complex and changeable, and this needs to be considered when collecting environmental samples for pathogen detection. The aims of this study were to (1) compare different aspects of collecting natural seawater and plankton samples for detection of OsHV-1 DNA and (2) determine whether detection of OsHV-1 DNA in such environmental samples has merit for disease risk prediction. The results of one experiment suggest that sampling on the outgoing tide may improve the detection of OsHV-1 DNA in seawater and plankton tow samples (odds ratio 2.71). This statistical comparison was not possible in 2 other experiments. The method (plankton tow or beta bottle) and depth of collection (range: 250-1250 mm) had no effect on the likelihood of detection of OsHV-1. OsHV-1 DNA was found at low concentrations in plankton tow and seawater samples, and only when outbreaks of mortality associated with OsHV-1 were observed in nearby experimental or farmed populations of C. gigas. This suggests that single point in time environmental samples of seawater or plankton are not sufficient to rule out the presence of OsHV-1 in an estuary. The association of OsHV-1 with particles in seawater needs to be better understood in order to determine whether more selective and sensitive methods can be devised to detect it, before environmental samples can be reliably used in disease risk prediction.

Nanoplastics exposure modulate lipid and pigment compositions in diatoms.

The impact of nanoplastics (NP) using model polystyrene nanoparticles amine functionalized (PS-NH2) has been investigated on pigment and lipid compositions of the marine diatom Chaetoceros neogracile, at two growth phases using a low (0.05 µg mL-1) and a high (5 µg mL-1) concentrations for 96 h. Results evidenced an impact on pigment composition associated to the light-harvesting function and photoprotection mainly at exponential phase. NP also impacted lipid composition of diatoms with a re-adjustment of lipid classes and fatty acids noteworthy. Main changes upon NP exposure were observed in galactolipids and triacylglycerol's at both growth phases affecting the thylakoids membrane structure and cellular energy reserve of diatoms. Particularly, exponential cultures exposed to high NP concentration showed an impairment of long chain fatty acids synthesis. Changes in pigment and lipid content of diatom' cells revealed that algae physiology is determinant in the way cells adjust their thylakoid membrane composition to cope with NP contamination stress. Compositions of reserve and membrane lipids are proposed as sensitive markers to assess the impact of NP exposure, including at potential predicted environmental doses, on marine organisms.

Microplastic contamination and pollutant levels in mussels and cockles collected along the channel coasts.

Nowadays, environmental pollution by microplastics (<5 mm; MP) is a major issue. MP are contaminating marine organisms consumed by humans. This work studied MP contamination in two bivalve species of commercial interest: blue mussel (Mytilus edulis) and common cockle (Cerastoderma edule) sampled on the Channel coastlines (France). In parallel, 13 plastic additives and 27 hydrophobic organic compounds (HOC) were quantified in bivalves flesh using SBSE-TD-GS-MS/MS to explore a possible relationship between their concentrations and MP contamination levels. MP were extracted using a 10% potassium hydroxide digestion method then identified by µ-Raman spectroscopy. The proportion of contaminated bivalves by MP ranged from 34 to 58%. Blue mussels and common cockles exhibited 0.76 ±â€¯0.40 and 2.46 ±â€¯1.16 MP/individual and between 0.15 ±â€¯0.06 and 0.74 ±â€¯0.35 MP/g of tissue wet weight. Some HOC and plastic additives were detected in bivalves. However, no significant Pearson or Spearman correlation was found between MP loads and plastic additives or HOC concentrations in bivalve tissues for the two species.

Do transparent exopolymeric particles (TEP) affect the toxicity of nanoplastics on Chaetoceros neogracile?

The potential presence of nanoplastics (NP) in aquatic environments represents a growing concern regarding their possible effects on aquatic organisms. The objective of this study was to assess the impact of polystyrene (PS) amino-modified particles (50  nm PSNH2) on the cellular and metabolic responses of the diatom Chaetoceros neogracile cultures at two essential phases of the growth cycle, i.e. exponential (division) and stationary (storage) phases. Both cultures were exposed for 4 days to low (0.05 µg mL-1) and high (5 µg mL-1) concentrations of PS-NH2. Exposure to NP impaired more drastically the major cellular and physiological parameters during exponential phase than during the stationary phase. Only an increase in ROS production was observed at both culture phases following NP exposures. In exponential phase cultures, large decreases in chlorophyll content, esterase activity, cellular growth and photosynthetic efficiency were recorded upon NP exposure, which could have consequences on the diatoms life cycle and higher food-web levels. The observed differential responses to NP exposure according to culture phase could reflect i) the higher concentration of Transparent Exopolymer Particles (TEP) at stationary phase leading to NP aggregation and thus, probably minimizing NP effects, and/or ii) the fact that dividing cells during exponential phase may be intrinsically more sensitive to stress. This work evidenced the importance of algae physiological state for assessing the NP impacts with interactions between NP and TEP being one key factor affecting the fate of NP in algal media and their impact to algal' cells.

Polystyrene microbeads modulate the energy metabolism of the marine diatom Chaetoceros neogracile.

Due to the growing concern about the presence of microplastics (MP) in the environment, the number of studies evaluating the toxicity of these small persistent particles on different marine species has increased in recent years. Few studies have addressed their impact on marine phytoplankton, a subject of great concern since they are primary producers of the aquatic food web. The aim of this study is to unravel the cytotoxicity of 2.5 µg mL-1 unlabelled amino-modified polystyrene beads of different sizes (0.5 and 2 µm) on the marine diatom Chaetoceros neogracile. In addition to traditional growth and photosynthesis endpoints, several physiological and biochemical parameters were monitored every 24 h in C. neogracile cells by flow cytometry during their exponential growth (72 h). Dynamic Light Scattering measurements revealed the strong aggregation and the negative charge of the beads assayed in the culture medium, which seemed to minimize particle interaction with cells and potentially associated impacts. Indeed, MP were not attached to the microalgal cell wall, as evidenced by scanning electron micrographs. Cell growth, morphology, photosynthesis, reactive oxygen species levels and membrane potential remained unaltered. However, exposure to MP significantly decreased the cellular esterase activity and the neutral lipid content. Microalgal oil bodies could serve as an energy source for maintaining a healthy cellular status. Thus, MP-exposed cells modulate their energy metabolism to properly acclimate to the stress conditions.

Surface functionalization determines behavior of nanoplastic solutions in model aquatic environments.

Plastic debris are classified as a function of their size and recently a new class was proposed, the nanoplastics. Nano-sized plastics have a much greater surface area to volume ratio than larger particles, which increases their reactivity in aquatic environment, making them potentially more toxic. Only little information is available about their behavior whereas it crucially influences their toxicity. Here, we used dynamic light scattering (DLS) to explore the influence of environmental factors (fresh- and saltwater, dissolved organic matter) on the behavior (surface charge and aggregation state) of three different nano-polystyrene beads (50 nm), with (i) no surface functionalization (plain), (ii) a carboxylic or (iii) an amine functionalization. Overall, the positive amine particles were very mildly affected by changes in environmental factors with no effect of the salinity gradient (from 0 to 653 mM) and of a range 1-30 µg.L-1 and 1-10 µg.L-1 of organic matter in artificial seawater and ultrapure water, respectively. These observations are supposedly linked to a coating specificity leading to repulsive mechanisms. In contrast, the stability of the negatively charged carboxylic and plain nanobeads was lost under an increasing ionic strength, resulting in homo-aggregation (up to 10 µm). The increase in organic matter content had negligible effect on these two nanobeads. Analysis performed over several days demonstrated that nanoplastics formed evolving dynamic structures detected mainly with an increase of the homo-aggregation level. Thus, surface properties of given polymers/particles are expected to influence their fate in complex and dynamic aquatic environments.