World Aquaculture December 2020

WWW.WA S.ORG • WORLD AQUACULTURE • DECEMBER 2020 29 Data is starting to emerge and recent publications have reported that microplastics have been found in fishmeals. On a global scale, this would be a substantial number and therefore many aquafeed companies are actively looking at measures to prevent the occurrence of plastics in fishmeals. However, existing methods may only help to detect a limited size range (e.g. microplastics but not nanoplastics), complicated by the fact that different methods will generate different results for the same product. It is not clear today whether some of these microplastic particles are, in addition to deriving from forage fish biomass, are also emerging from the rawmaterial used for extruding the feed or from degradation of feed bags. With an estimated 1.2 billion feed bags generated per year for the Asian market alone, this could introduce a significant risk. Nevertheless, the risk may be completely controlled as soon as the feed industry is aware of it. In a recent report from the FAO (Technical Paper 615), 7 μg of plastic particles is estimated to be present in every portion (225 g) of mussels reaching a consumer’s table. At present, accumulation of microplastics not passing through the gut membrane in filter feeders is seen more as a consumer perception issue rather than a significant health risk. The accumulation of plastic particles in filter feeders and communication of the associated risks may hinder the development of molluscan aquaculture in areas where high exposure to plastic particles may occur. On this point, it is generally accepted that the presence of plastics in the aquatic environment is going to remain, even if the production of plastics upstreamwas immediately stopped and management of plastic waste was immediately started. Therefore, understanding oceanographic conditions, mapping the sources of microplastics, coupling particle tracking models with adequate monitoring plans and understanding howwaste may accumulate in areas where filter feeders are produced is of interest for selection of production sites. What to test: Tests should be carried out on a minimum of five aggregated samples of 5-7 shucked individuals. All body tissues (record the weight of the shelled animals). Repeat at 6-month intervals. What to test: Tests should be carried out on the stomachs of a minimum of five individuals for animals above 10 cm maximum length, or aggregate samples 5-7 of whole individuals in animals below 10 cm in maximum length. Repeat at 6-month intervals. What to test: Soft-bodied invertebrates should be tested in the same manner as aggregated crustaceans (above). Repeat at 6-month intervals. What to test: Tests should be carried out on the fillets of at least five individuals, as well as on the stomachs of a minimum of five individuals for animals above 10 cm maximum length, or aggregate samples 5-7 of whole individuals in animals below 10 cm in maximum length. How to extract plastic: Digestion* with acids, bases, oxidizing agents or enzymes, followed by filtering of the supernatant (see below). Vacuum filtration should be used to draw the sample through glass-fibre filter papers (pore size 2µm / 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 spectros How to report your findings: Where possible, the number and weight of plastic items per individual should be reported, in addition to the average length and weight of the animals tested. Additional information regarding the maximum, minimum and mean length and differing morphologies of recovered plastics should also be recorded. The presence of plastic in the fish fillet should be reported as size and number of particles per 100 g. TABLE 2. A simplified model for establishing the uptake of meso and microplastics. How is microplastic uptake measured? The uptake of meso, micro and nanoplastics can vary between individuals, dependent on species, sex and size classes. Despite determination of nanoplastics level still representing a problem, the level of microplastics present within an animal may be determined as follows. At all stages, exposure of the sample to air should be limited to prevent contamination. Mollusks Crustaceans Other invertebrates Fish * Cold digestion processes are preferred to limit potential damage to any plastics in the sample. + Filters should be changed regularly to prevent clogging/bursting. ( C O N T I N U E D O N P A G E 3 0 )