World Aquaculture December 2020

28 DECEMBER 2020 • WORLD AQUACULTURE • WWW.WA S.ORG present in the gut, the levels of these chemicals already inside the organisms and exposure from the same chemicals in food and the surrounding water. Despite the level of uncertainty, potential impacts on the profitability of farms, whether from a direct impact on the product or indirectly from consumer perception of the product, must be established and mitigated where possible. Routes by which micro- and nanoplastics may affect aquaculture production and the value of the resulting product include environmental exposure from airborne, waterborne or sediment plastics, and that originating from the exposure of other organisms subsequently processed into feed. The potential for exposure and uptake has been explored in many recent studies focusing on microplastics (0.1 μm to 5 mm) and nanoplastics (<0.1 μm) in the environment and in feed. The size limit between microplastics and nanoplastics is being discussed intensively. During the roundtable, nanoplastics were defined as plastics capable of passing intestinal epithelia (~0.1 μm). The rationale behind this decision was to organize discussions around what can be measured, separating impacts by the biological (at the organism level) or physiological (at the cellular level) effects. Nevertheless, where microplastics are found, nanoplastics are likely to be present as well. There are currently no standardized methodologies for sampling and analysis of plastics from established authoritative sources (e.g. ISO, EPA, APHA, AFNOR) due to the varied requirements for sampling methods in different aquatic environments such as extractions from sediments or water, and a lack of standardized terminology in this emerging field (e.g. nano- vs microplastics). The requirement for an understanding of plastics input to the environment fromwear and tear of common aquaculture infrastructure and products (tanks, pipes, liners, etc.), as well as the plastics found in feeds, requires serious investigations from the research community and feed manufacturers. What to test: A minimum of five replicate samples of feed (250 g). What to test: A minimum of five samples of sediment (volume 500 mL), taken from a depth of no more than 5 cm below the sediment surface. Repeat at 6-month intervals. What to test: Flow-through systems: A minimum of five samples of water (volume 500 mL) collected at the facility inflow (pre- and post-filtering is applicable). Repeat at 6-month intervals. Extractive operations: A minimum of ten samples of water (volume 500 mL) collected from the surface 5 cm. Repeat at 6-month intervals. How to extract plastic: Digestion* with acids, bases, oxidizing agents or enzymes, followed by filtering of the supernatant (see below). How to extract plastic: Density separation with hypersaturated salt (NaCl) solution, followed by filtering of the supernatant (see below). How to extract plastic: Vacuum filtration should be used to draw the sample through glass fibre filter papers (pore size 2 µm / 0.45 µm)+. An additional digestion or settlement step may be necessary in the presence of high concentrations of sediment or organic matter. How to characterize plastic: Filter papers should be observed under a microscope. Plastics should be counted and, where possible, weighed and the longest axis measured. The morphology of plastics may be categorized in the manner outlined in Lusher et al. 2020. The identity of suspected plastics may be determined by lithophilic stains and fluorescent microscopy, or by FTIR or Raman spectroscopy. How to report your findings: Where possible, plastic concentrations should be reported as the number and weight of plastic items per liter of sediment or water or per kilogram of feed. Additional information regarding the maximum, minimum and mean length, and differing morphologies of recovered plastics should also be recorded. TABLE 1. A simplified model for establishing the environmental prevalence of meso and microplastics. 1 Where might plastic contamination come from? Operational plastics Meso and microplastics may enter the farm from an array of different sources. These may be identified and quantified using the measures below. At all stages, exposure of the sample to air should be limited to prevent contamination. Undertake an inventory of plastics used in the system and its supporting operations. Feed Sediments Water 1 Nanoplastics are not reasonably detected at the moment because of missing or inadequate procedures. * Cold digestion processes are preferred to limit potential damage to any plastics in the sample. + Filters should be changed regularly to prevent clogging/bursting.