How to extract microplastics from fish guts

Some months ago we investigated the microplastic concentration in three commercial fish from the coast of Lima, Peru (De-la-Torre et al., 2019). In general terms, our results indicated that carnivore fish accumulate more microplastics than planktivore fish. This suggests that microplastics could biomagnify along the food chain, as previous results researching the common prey of these species, like chitons and intertidal bivalves, contained microplastics in their soft tissues. 

Indeed, some interesting results, although more and broader research is needed.

The method used to assess microplastic abundance in fish guts followed a simple procedure, as described in Fig. 1. 

Fig. 1. Procedural steps for extracting microplastics from fish guts

Stomach and intestines were extracted and placed in 25 ml glass screw cab test tubes and filled with 10% (w/v) potassium hydroxide (KOH), shaken for a few seconds and heated at 60 °C over 24 h. Following digestion, the supernatant solution was vacuum filtrated through a 20 – 25 µm pore glass fiber filter paper (Whatman) in an 8 cm in diameter porcelain Büchner funnel. Finally, filters must be observed under a stereomicroscope. 

It is absolutely necessary to conduct quality control measures. In this case, all glass and other materias must be rinsed twice or thrice with distillated/Ultrapura/deionized water. Cotton lab coats and gloves must be worn at all times and surfaces must be wiped clean. If possible, conducting the procedure under a fumehood. Quality assurance by having an airborne procedural blank by placing a wet filter on a petri dish for as long as the duration of the laboratory analysis and scan it under a stereomicrospe. The number of airborne microfibers contaminating the blank must not exceed 2 MP/blank. Also, 10% KOH alone must be vacuum filtrated and scanned to determine external contamination reached the KOH. 

References

De-la-Torre, G.E., Dioses-Salinas, D.C., Pérez-Baca, B.L. & Santillán, L. (2019). Microplastic abundance in three commercial fish from the coast of Lima, Peru. Brazilian Journal of Natural Sciences, 2(3), 171-177. https://doi.org/10.31415/bjns.v2i3.67