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 

Plasticrusts: A new potential threat in the Anthropocene's rocky shores

The new term 'plasticrusts' have been coined in a recent article published in Science of the Total Environment by Gestoso et al. (2019). This type of plastic pollution refers to plastic pieces of blends encrusting the texture of intertidal rocks forming crusts that could vary in color and forms.

Fig. 1. Pictures showing (A, B) a general overview of mid-upper intertidal rocky shore in Madeira Island encrusted by plastic; (C) detail of ‘plasticrusts’ on the surface of the rocks; and (D, E) view of ‘plasticrusts’ surrounded by the littorinid gastropod Tectarius striatus.

Plasticrusts could expose marine rock grazers, like gastropods, to plastic debris ingestion. This type of plastic pollution could be considered as a new litter category for monitoring guidelines.

Reference
Gestoso, I., Cacabelos, E., Ramalhosa, P., & Canning-Clode, Joao. (2019). Plasticrusts: A new potential threat in the Anthropocene's rocky shores. Science of The Total Environment, 687, 413-415. https://doi.org/10.1016/j.scitotenv.2019.06.123

Amberstripe scads ingest microplastics resembling their copepod prey

A research published in 2017 aimed to compare the size and color of microplastics and copepod species found in surface waters and in the digestive tract of Decapterus muroadsi captured along the coast of Rapa Nui. 

Although the majority of the microplastics in the medium (surface water) were orange, a high abundance of blue microplastic fragments were found in D. muroadsi digestive tracts. Statistical analysis indicated a significantly different selectivity among microplastics of the four colors found in the water samples. This confirmed a selectivity for blue microplastics.

Fig. 1. Size-frequency distribution (% of the total number) of microplastics (bars) of the four colors most frequently found in the 6 superficial water samples (195 microplastics in total; 6 black, 3 grey, 2 red, 2 yellow, 1 purple and 1 green particles are not shown here) and in the 16 fish that had ingested at least one microplastic (45 microplastics; 2 black and 1 green particles are not shown here). Size distributions of three blue-pigmented copepod species (scatter plots) found in the water samples and in the 20 fish that ingested copepods are shown. 

This study suggests that some fish could mistakenly ingest microplastics resembling their natural prey. 

Fig. 2. Examples of (a–f) blue microplastics in D. muroadsi digestive tracts, and (g) copepod prey Pontella sinica male, (h) Sapphirina sp. and (i) Corycaeus sp. in superficial water along the

coast of Rapa Nui (Easter Island). Scale bars represent 0.5 mm.

For further reading, check the references for the link to the full article.

References

Ory, N. C., Sobral, P., Ferreira, J. L., & Thiel, M. (2017). Amberstripe scad Decapterus muroadsi (Carangidae) fish ingest blue microplastics resembling their copepod prey along the coast of Rapa Nui (Easter Island) in the South Pacific subtropical gyre. Science of the Total Environment, 586, 430–437. https://doi.org/10.1016/j.scitotenv.2017.01.175

Are microplastics a threat to food security?

Last month I published a review article in the Journal of Food Science and Technology, entitled: Microplastics: an emerging threat to food security and human health. In this short review, I addressed the current state of art regarding microplastics contamination in food (mostly seafood and shellfish). I made an understanding of how microplastics could threat two of the four pillars of food security. Microplastic uptake pathways in humans (Fig. 1) are discussed and possible health implications are reviewed. 

Fig. 1. A model showing microplastics route from emission to human ingestion

I concluded that there is still knowledge gaps to be investigated in order to fully understand and quantify microplastic contamination impacts over food security and human health. 

I wanted to share my review with anyone that needed it, you can always request it from my ResearchGate account. 

References

De-la-Torre, G. E. (2019). Microplastics: an emerging threat to food security and human health. Journal of Food Science and Technology. https://link.springer.com/article/10.1007/s13197-019-04138-1

Marine macroinvertebrates inhabiting marine debris

During a sampling campaign, we found many stranded marine debris along the coast. In many cases, these items were inhabited by many marine macroinvertebrates, among sessile species and other species that seemed to be entangled.

Fig. 1. Stranded red fishing net inhabited by marine macroinvertebrates

In this example (Figure 1), we found a quite large fishing net, having bivalves, gastropods, a crustacean and even an echinoderm.

Fig. 2. Ocypode occidentalis

Fig. 3. Semimytilus algosus

Fig. 4. Tetrapygus niger

These findings suggest a potential invasion of non-native species and invasive species to foreign marine ecosystems due to rafting.

Microplastics in the marine environment

I've been researching microplastic (MP) presence and abundance for about two years now. It is interesting to see how these particles smaller than 5 mm in diameter or length are ubiquitous in the marine environment. After doing some research, we found MPs in different molluscs, fish and even in marine otter scats from the coast of Peru. Determining the exact sources is quite hard, but it is most likely that the poor waste water treatments promote the dispersal of microfibers (which are, by the way, the most common MP morphological type I've found here and many studies agree with this).

Fig. 1. Blue microfibers found in the stomach of Cheilodactylus variegatus from the coast of Lima, Peru

The MPs in figure 1 are about larger than 100um. I'm looking forward to investigate MP bioaccumulation in Peruvian bivalves through the correlation between MP content and valve length and wet weight of each individual. It sound very interesting to me.