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Plastics are lightweight, inexpensive, and highly durable materials that are used in a wide variety of products, which have contributed to almost every aspect of modern life, displacing other materials and revolutionizing contemporary society. In 2016, global plastics production totaled around 335 million metric tons, around 40% of which was in single-use products that are discarded rapidly. (1) Consequently, considerable quantities of end-of-life plastics have accumulated as waste in managed systems and as litter in the environment. Once in the environment, exposure to ultraviolet light can cause plastics to become brittle and then fragment by mechanical action, leading to the formation of microscopic pieces, sometimes known as microplastics (MP). (2) It is estimated that up to 51 trillion microplastic fragments have accumulated at the sea surface and that quantities are increasing. (3) It has been widely suggested that this fragmentation will eventually result in the formation of plastic nanoparticles (NP). Current analytical approaches limit the ability to isolate and identify nanoparticles from environmental media. However, there is some experimental evidence to indicate the potential for nanoparticles to have accumulated in the environment. For example, Koelmans et al. (4) (2015) reported fragmentation of expanded polystyrene (EPS) to micro- and nanosize pieces in experiments involving a month of accelerated mechanical abrasion with glass beads and sand. Some other laboratory studies have also identified the presence of plastics at the nanoscale in water, after exposure of larger plastics pieces to UV and visible radiation. (5,6) Given the current rate of entry of plastic litter to the environment the potential for substantial long-term accumulation of nanoplastic fragments seems high. In addition, a range of nanoplastic particles are manufactured for commercial applications, including in paints, adhesives, coatings, biomedical products, electronics, (7) and cosmetics; (8) it seems likely that some of these manufactured nanoparticles will also be released to the environment.

–1 to 15 μg L–1 (μg L–1 = parts per billion, ppb) for ∼50 nm and below 0.5 μg L–1 for 5 μm plastic particles. A number of studies, all of which are laboratory based, have investigated either the uptake or effects of nanoplastics on a range of marine organisms. The majority have used concentrations exceeding by two to seven orders-of-magnitude, those predicted to occur in the environment (e.g., ref (3) SI Figure S1 and associated references). Predicted environmental concentrations, which are likely to increase exponentially as the particle size decreases are, for example, 1 pg Lto 15 μg L(μg L= parts per billion, ppb) for ∼50 nm and below 0.5 μg Lfor 5 μm plastic particles. (9) Concentrations are likely to be higher in environmental compartments where there is some degree of plastic particle accumulation.

–1), interferences from fluorescent background signals, the limited range of applicable organisms and rather weak resolution (e.g., due to internal light diffraction/reflection). The challenges of tracking plastic particles in biological or environmental media (including the need for lower limits of detection) have therefore impeded quantification of uptake and accumulation at environmentally realistic concentrations, thus far. A first step toward understanding the potential effects of nanoplastics on organisms is to describe the dynamics of ingestion and accumulation at predicted environmental concentrations in seawater (i.e., up to 15 ppb). (10) This has proven to be a difficult analytical challenge. Some studies have attempted to track fluorescent particles using commercially available, manufactured, surface-functionalized polystyrene nanoparticles, to produce qualitative characterization of the ingestion of MP or NP and tissue distributions in relatively transparent aquatic organisms. (11−13) However, the use of fluorescent particles has a number of disadvantages, including high limits of detection (often in the range mg L), interferences from fluorescent background signals, the limited range of applicable organisms and rather weak resolution (e.g., due to internal light diffraction/reflection). The challenges of tracking plastic particles in biological or environmental media (including the need for lower limits of detection) have therefore impeded quantification of uptake and accumulation at environmentally realistic concentrations, thus far.

nAg) were developed for quantifying and visualizing the distribution of particles in mollusks following exposures at concentrations as low as 100 ng L–1 by quantitative whole body autoradiography (QWBA). Stable and radioisotope techniques have recently been used successfully to study the fate of nonplastics nanoparticles at environmentally relevant concentrations. (14−16) In principle, this approach could also be used to study fundamental and largely unexplored questions concerning ingestion, depuration and tissue distributions (i.e., translocation) of nanoplastic particles by, and in, organisms. (17) Indeed, radiolabeled nonplastics nanoparticles have been used to overcome the significant limitations for quantifying nanomaterials in environmental and biological media (15,18−20) and to facilitate work at low limits of detection. For instance, radiolabeled silver nanoparticles (Ag) were developed for quantifying and visualizing the distribution of particles in mollusks following exposures at concentrations as low as 100 ng Lby quantitative whole body autoradiography (QWBA). (14) Such, techniques offer the possibility for direct visualization of intraorgan nanoparticle concentrations. Unfortunately, radiolabeled nanoplastics are not currently available, to our knowledge.

In the present study, we synthesized 14C-labeled nanopolystyrene particles (24 and 250 nm), and then exposed scallops to these particles, measured the biokinetics and quantified NP tissue distributions via QWBA. We used environmentally realistic NP concentrations (15 ppb) to test the hypothesis that this commercially important mollusk might uptake, absorb, and depurate, NP differently according to size. For each particle size, scallops were exposed to a single pulse (6 h) of radiolabeled NP in seawater in the presence of food. Exposed and control animals were sampled over time (i.e., during 48 days) to track NP and to quantify particle distribution.