Isolating Microplastics

In recent years, many techniques have been developed to detect microplastics in biota. Methods for extracting microplastics from biotic material include dissection, depuration, homogenization and digestion of tissues with chemicals or enzymes.


In larger animals, including squid [39], whales [40-41], turtles [42] and seabirds [43], dissection of the gastrointestinal tract and subsequent quantification of synthetic particles from the gut is the method of choice for assessing plastic consumption. In laboratory studies, it is more common for the whole organism (42% of studies) or the digestive tract (26% of studies) to be digested or analyzed. In comparison, 69% of field studies targeted the digestive tract, and 27% looked at the whole organism. In invertebrates and vertebrates and in pelagic and demersal fish, the excision of the intestinal tract can also be used to look for microplastics [6,7,23,32,44-68]. Investigation of stomachs and intestines is relevant for microplastics >0.5 mm in size. Microplastics larger than this do not readily pass through the gut wall without pre-existing damage, and the likelihood of translocation into tissues is too low to warrant regular investigation [69,70]. Localization of microplastics <0.5 mm can be determined by excising organs, such as the liver or gills [38,71,72], or, where the research question relates to risks of human consumption, edible tissues, for example, tail muscles of shrimp [73]. Microplastics present in dissected tissues can be isolated using saline washes, density flotation, visual inspection, or digestion.


Any externally adhered plastics can be removed prior to treatment by washing the study organism with water or saline water or using forceps [11,74]. A depuration step can be used to eliminate transient microplastics present in the intestinal tract. Depuration is facilitated by housing animals in microplastic-absent media (e.g., freshwater, seawater, sediment), with or without food, and leaving sufficient time for complete gut evacuation [75]. These media should be refreshed regularly to prevent consumption of egested microplastics [76]. Depuration ensures that only microplastics retained within tissues or entrapped in the intestinal tract are considered [15,76,78]. Depuration makes it also feasible to collect fecal matter, typically sampled via siphon, sieve or pipette. These feces can subsequently be digested, homogenized or directly visualized to assess and quantify egested microplastics. Fecal analysis has been used to determine microplastic consumption in a range of taxa, including sea cucumbers [79], copepods [34,80], isopods [16], amphipods [81], polychaetes [95] and mollusks [82-94].

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