Uptake and Retention of Nanoplastics in Quagga Mussels

Abstract

Here, a set of experiments to assess the feasibility of using an invasive and widespread freshwater mussel (Dreissena rostrformis bugensis) as a sentinel species for nanoplastic detection is reported. Under laboratory experimental conditions, mussels ingest and retain fluorescent polystyrene (PS) beads with carboxylic acid (-COOH) termination over a size range of 200-2000 nm. The number of beads the mussels ingested is quantified using fluorescence spectroscopy and the location of the beads in the mussels is imaged using fluorescence microscopy. PS beads of similar size (1000-2000 nm) to mussels' preferred food are trafficked in the ciliated food grooves of the gills. Beads of all sizes are observed in the mussels' digestive tracts, indicating that the mussels do not efficiently reject the beads as unwanted foreign material, regardless of size. Fluorescence microscopy shows all sizes of beads are concentrated in the siphons and are retained there for longer than one month postexposure. Combined atomic force microscopy-infrared spectroscopy and photothermal infrared spectroscopy are used to locate, image, and chemically identify the beads in the mussel siphons. In sum, these experiments demonstrate the potential for using mussels, specifically their siphons, to monitor environmental accumulation of aquatic nanoplastics.

Keywords: AFM‐IR; PT‐IR; microplastics; mussels; nanoplastics.

Figure 1

Exemplar fluorescence images of isolated tissues (gills, rectums, siphons) from quagga mussels dosed with 200 nm (a–c), 1000 nm (d–f), and 2000 nm (g–i) carboxylate‐modified PS beads containing a red dye (excitation/emission 580/605). All images were acquired with the same microscope settings, leading to some images appearing overexposed. The images demonstrate the substantial accumulation of beads of all three sizes in the rectums and of the 1000 and 2000 nm beads in the siphons. Mussels were dosed with 200 and 1000 nm beads at 1 × 10⁻¹² m and 2000 nm beads at 0.01 × 10⁻¹² m for 24 h.

Figure 2

Box plots of the mean fluorescence intensity of mussel feces following dosing with PS beads containing a red dye. Mussels were dosed with a) 200 nm beads at 1 × 10⁻¹² m and allowed to clear for 21 d; b) 1000 nm beads at 1 × 10⁻¹² m and allowed to clear for 44 d; and c) 2000 nm beads at 0.01 × 10⁻¹² m and allowed to clear for 20 d. The boxes labeled “c” are the control.

Figure 3

Fluorescence images of quagga mussel siphons after mussels were dosed with a) 200 nm (1 × 10–12 m); b) 1000 nm (1 × 10–12 m); and c) 2000 nm (0.01 × 10–12 m) carboxylic‐acid‐terminated PS beads with a red dye and allowed to clear until their feces were no longer fluorescent (see Figure 2 for clearance times).

Figure 4

a) AFM deflection image of 1000 nm PS beads in a siphon from a quagga mussel dosed with beads at 1 × 10⁻¹² m (see Figure S7, Supporting Information, for AFM images of undosed mussel siphons). The small yellow square indicates where the AFM‐IR spectrum was acquired. Dotted red circles highlight representative PS beads; b) AFM‐IR spectra comparing mussel siphon with PS beads and control siphon. Distinctive PS peaks at 1452 and 1492 cm⁻¹ are evident in the spectrum of the dosed mussel (indicated with arrows); c) mIRage IR spectrum of a mussel siphon embedded with PS beads. The solid line corresponds to a region of the siphon with PS beads. The distinctive PS signals at 1452 and 1492 cm⁻¹ are obvious. The dashed line corresponds to a region of the siphon with no PS beads.