World Aquaculture December 2020

34 DECEMBER 2020 • WORLD AQUACULTURE • WWW.WA S.ORG the administered dose, plastics below 150 μm in size have been found in the portal and lymphatic systems of mammals, although it is unlikely that larger particles can be absorbed. Only microplastic particles ≤20 μm have been reported in adjoining internal organs, generally resulting in kidney and liver accumulation (FAO 2017). Nevertheless, once nanoplastics have been absorbed, they may be distributed to all internal organs and it cannot be excluded that they might also cross the blood-brain barrier. The negative effects observed in both vertebrates and invertebrates include the immune response (Pazzaglia et al. 1987, Brandts et al. 2018) and oxidative stress in the central nervous system (Oberdörster 2004, Brown et al. 2001). In addition to other negative effects on human health (Galloway et al. 2015), a signi cant inverse association between exposure to 38.9-nm polystyrene nanoplastics and serum concentrations of testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) was found in male rats (Amereh et al. 2020), thus indicating potential risk for human reproductive physiology as well. Effects of Microplastics on Fish Effects of MNP on fish growth, diseases and mortality have also been reported (Manabe et al. 2011, Pedà et al. 2016). In zebrafish, exposure to 1 mg/L of 47-nm polystyrene particles for 48 to 72 h was toxic, causing embryo mortality (Chenetal et al. 2017). Necrosis, infiltrations and liver lipid drops have been observed in zebrafish after 21 days of exposure to 2 mg/L of MNP 5 μm and 0.07 μm in size (Lu et al. 2016). The effects of MNP change in relation to their size, molecular structure and interaction with plasma proteins (Waring et al. 2018, Cederwall et al. 2012). An interaction with proteins, creating a “protein corona” effect was reviewed by Nguyen and Lee (2017). MNPs may accumulate in fish tissues (Karami et al. 2017), affecting lipid metabolism (Cedervall et al. 2012) and fish feeding behavior (Mattson et al. 2017). Inflammatory responses have also been reported (Brown et al. 2001, Greven 2016). Damage in the distal intestine of 50-83 percent of European seabass Dicentrarchus labrax was observed after 30 days of feeding with polyvinyl chloride (PVC, 0.1 percent w/w) (Pedà et al. 2016). Even more serious intestinal damage occurred when PVCmicroplastics were collected from marine water polluted by hydrocarbon compounds. Effects on different trophic levels in aquatic invertebrates suggest that 55-110 nmMNPs cause acute toxicity at 0.4-416.5 μg/ mL (Casado et al. 2013). Survival and reproduction are reduced in Daphnia galeata after 5 days of exposure to 52-nm polystyrene particles (Cui et al. 2017). Safe Levels of MNPs: Complexity and Uncertainty Our knowledge is still in its infancy, although some of the recent literature may help to address the problem and suggest conditions potentially harmful for some aquatic animal species. Therefore, we clearly cannot afford not to manage the risk. No rules and policies regulating safety levels of MNP in food exist, whereas in feeds for animals, a contamination level up to 0.15 percent of plastics is generally tolerated, more for opportunistic reasons than a decision based on science. Although a number of challenges on utilizing standardized MNPs were recently reported in the literature, this is not sufficient for a risk management approach. Indeed, a risk threshold for standardized MNPs that is reasonable is needed. Different risks of harmmay be due to the chemical nature, shape and size as well as from interactions with other pollutants. The fact that additives such as bisphenol, phthalates and heavy metals are found in commercial plastics, allied with their ability to adsorb hydrophobic contaminant pollutants, can no longer be ignored. Therefore, defining safe/tolerable levels to establish a reference target for a risk management approach, developing a database of fish responses to the MNPs present in the environment, and conducting experiments on rodents and collecting observations in humans could represent first steps in this process. It is necessary to find appropriate bioindicators and identify target organs and physiological interferences to develop accurate monitoring and management protocols; fish species may also represent good animal models for such studies. Nevertheless, accurately standardized experimental protocols should be developed, also allowing the comparison of the results produced by different research groups. Microplastics as Food Contaminants Today, no legislation exists for microplastics and nanoplastics as contaminants in food. Following a request from the German Federal Institute for Risk Assessment (BfR), the Panel for Contaminants in the Food Chain of the European Food Safety Authority (EFSA) delivered a statement on the presence of microplastics and nanoplastics in food, with a particular focus on seafood. Nevertheless, this report (EFSA 2016) does not include recommendations for a possible risk threshold because toxicity and toxicokinetic data are lacking for both microplastics and nanoplastics for a human risk assessment. At the same time, it was recommended that an analytical method be further developed for microplastics and nanoplastics to assess their presence and to identify and quantify the amounts in food. Furthermore, a database should be generated documenting their occurrence in food, in particular for smaller-sized particles (<150 μm). Limited data are available concerning microplastics in food, including agriculture foods, seafood species such as fish, shrimp and bivalves, as well as for other foods, including honey, beer, table salt and tap water. In honey, 0.166 microplastic fibers/g have been reported, in beer 0.017-0.033 particles/g, and in table salt 0.007- 0.680 particles/g. In seafood, microplastics in marine species are concentrated mainly in the digestive tract (Fig. 2). The average number of particles was 1-7/g in fish, 0.75 particles/g in shrimp and 0.2-4/g FIGURE 2. Micro- and nanoplastics accumulate in different fish tissues and organs to varying degrees, but mainly in the gut. Fish samples represent 13 species collected from coastal estuaries of China (Source: Su et al . 2019).