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Turning Microplastics Into Nanoplastics Through Digestive Fragmentation by Antarctic Krill

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Turning Microplastics Into Nanoplastics Through Digestive Fragmentation by Antarctic Krill

Amanda L Dawson et al. Nat Commun.

Abstract

Microplastics (plastics <5 mm diameter) are at the forefront of current environmental pollution research, however, little is known about the degradation of microplastics through ingestion. Here, by exposing Antarctic krill (Euphausia superba) to microplastics under acute static renewal conditions, we present evidence of physical size alteration of microplastics ingested by a planktonic crustacean. Ingested microplastics (31.5 µm) are fragmented into pieces less than 1 µm in diameter. Previous feeding studies have shown spherical microplastics either; pass unaffected through an organism and are excreted, or are sufficiently small for translocation to occur. We identify a new pathway; microplastics are fragmented into sizes small enough to cross physical barriers, or are egested as a mixture of triturated particles. These findings suggest that current laboratory-based feeding studies may be oversimplifying interactions between zooplankton and microplastics but also introduces a new role of Antarctic krill, and potentially other species, in the biogeochemical cycling and fate of plastic.

Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Polyethylene particle size and proportion fragmented. a Microplastic particle size (mean ± S.D) in all sample types: whole krill homogenates, egested faecal pellets, and in the exposure stock suspension, letters denote statistically significant differences (p < 0.05, two-sample Kolmogorov–Smirnov Test). b Proportion of whole beads (blue) and fragments (orange) isolated from Antarctic krill (Euphausia superba) exposed to a Low (20%) (n = 9 krill with 16,308 particles detected) and High (80%) (n = 9 with 51,168 particles detected) plastic concentrations. Letters denote statistically significant differences (p < 0.05, Χ2 test)
Fig. 2
Fig. 2
Proportions of egested fragmented and whole beads over time. Frequency of whole (blue) and fragmented (orange) particles isolated from faecal pellets of Antarctic krill exposed to Low (20%; n = 3 beakers) (dark) and high (80%; n = 3 beakers) (light) concentrations at: a 24 h on Day 1 (n = 6) and Day 4 (n = 6), b 4 (n = 6) and 24 h (n = 6) on Day 4 only. All faecal material per beaker (containing five krill) was pooled to form a single sample per time point per dose. Letters denote statistically significance differences in the proportion of whole beads excreted over time (p < 0.05, X2 test)
Fig. 3
Fig. 3
Fate of polyethylene beads and fragments after ingestion by Antarctic krill. Krill (n = 17) were used for histological analysis. a Beads on a filter paper isolated from digested krill with autofluorescent mandible, b Digestive gland tissue, c Midgut and digestive gland tissue, d Mandible with polyethylene fragments embedded in the surface, e and f Faecal pellet with polyethylene beads under bright field and fluorescence microscopy. WB: whole bead, FB: fragmented bead, M: mandible, DG: digestive gland, MG: midgut
Fig. 4
Fig. 4
The proportion of PE plastic fragments to whole beads isolated from Antarctic krill. Faecal material (from n = 15 krill) was collected over 5 days, after switching from 10 days of low dose microplastic exposure, with daily static renewal, to an uncontaminated algae diet. Total refers to the total number of particles measured in each 24 h period of faecal material. Fragments are shown in orange, while whole beads are shown in blue

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