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. 2019 Dec 27;6(1):e03103.
doi: 10.1016/j.heliyon.2019.e03103. eCollection 2020 Jan.

The world is your oyster: low-dose, long-term microplastic exposure of juvenile oysters

Maes Thomas  1 , Barry Jon  1 , Stenton Craig  2   3   4 , Roberts Edward  2 , Hicks Ruth  2 , Bignell John  2 , Vethaak A Dick  5   6 , Leslie A Heather  5 , Sanders Matthew  2
Affiliations

The world is your oyster: low-dose, long-term microplastic exposure of juvenile oysters

Maes Thomas et al. Heliyon. .

Abstract

Bivalve filter feeders, such as oysters, filter large volumes of water and are particularly exposed to microplastics (MP). Consequently, these animals digest and assimilate high levels of MP in their bodies that may likely impact their physiology, and potentially affect shellfish stocks, benthic habitats and, indirectly, the health status of the marine ecosystem and human consumers. In this study we exposed juvenile oysters, Crassostrea gigas, to 3 different MP concentrations (104, 105 and 106 particles L-1), represented by 6μm Polystyrene (PS) microbeads, compared to a control treatment receiving no MP. The study ran for a period of 80 days to test for the impacts of MP on growth, Condition Index and Lysosomal Stability. From histological analysis, microbeads were detected in the intestines of exposed oysters and in the digestive tubules, but no cellular inflammatory features were observed over time. Weight and shell length remained comparable between the different treatments and control. We found that Condition Index in the highest concentration increased initially but significantly reduced over time. The oysters in the highest MP exposure also showed the lowest mean Lysosomal Stability score throughout the experiment. Lysosomes play a vital role in the cells defense mechanisms and breakdown of constituents, crucial for the oysters' wellbeing. Most importantly, we detected an increased mortality in those oysters who were chronically exposed to the highest loads of MP.

Keywords: Aquaculture; Aquatic ecology; Condition index; Ecological health; Environmental hazard; Environmental health; Environmental science; Environmental toxicology; Histology; Long term exposure; Lysosomal stability; Microplastics; Pacific oyster; Polystyrene microbeads; Wastewater management; Water pollution.

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Figures

Figure 1
Figure 1
a. Individual tank setup with 30 juvenile oysters. b. Experimental setup showing the 48 tanks and the PS microbead concentrations, the green tanks represent the stock preparation made daily for each exposure concentration (MP + Algae). All seawater was UV treated and ran through three sequential ceramic filtration units (20μm, 10μm, 0.2μm) before use.
Figure 2
Figure 2
Oyster number and sampling procedure, length and wet weight were measured for all oysters, before the experiment and at all sampling points. The abbreviations stand for: LMS = wet weight, shell length, flesh removed and cryopreserved for further lysosomal stability analysis. G- CI = Wet weight, length, dry shell weight, dry tissue weight for Condition Index determination. Histo = Wet weight, shell length, shell removed and tissue fixed in Davidsons for further histology analysis.
Figure 3
Figure 3
Histology slides of the oyster intestines (a) and digestive tubules (b) showing the fluorescent PS microbeads (yellow) excited at 491 & 512nm.
Figure 4
Figure 4
a. Plot of CI means by treatment and day; b. Plot of CI means of square root CI, by treatment and day.
Figure 5
Figure 5
a. Plot of means of shell length by treatment and day; b. Plot of means of weight by treatment and day (the figures are for survivors only).
Figure 6
Figure 6
a. Mean LMS score of survivors by day; b. Mean LMS of all oysters (dead & alive) by day.
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