Microplastic uptake and retention in Perna perna (L.);

Tripneustes gratilla (L.) and Stomopneustes variolaris (Lamarck).

Gerber. G., Mkhize, T., Robertson–Andersson, D.V. & Moodley, G. K. University of KwaZulu–Natal; School of Life Sciences

INTRODUCTION

Microplastics particles (< 5 mm) are ubiquitous throughout the marine environment making them bioavailable to organisms in lower trophic levels such as filter-feeders that are likely to ingest these particles

1.

Once ingested, microplastics may pose several physiological threats such as starvation, malnutrition, stunted growth as well as death in some organisms

2.

Additionally, the surfaces of microplastic particles may readily adsorb toxins (e.g. persistent organic pollutants (POP’s) and heavy metals), which may then be absorbed by the organism,

bioaccumulate and be transferred through the food web3.

RESULTS AND DISCUSSION

REFERENCES

http://i.ytimg.com/vi/2oQeXhURTgY/maxresdefault.jpg http://www.engineering.com/portals/0/BlogFiles/composting-bottle_large.jpg

http://dynamicco.com/wp-content/uploads/Sand-blasting-of-container-ship.jpg http://www.citizenscampaign.org/images/petition/slideshow/microbead-products.jpg https://encounterswithwildlife.files.wordpress.com/2014/08/wetland_ecology_group_university_of_helsinki_mytilus_edulis_microplastic.jpg http://www.ramepbc.org/uploads/site_page_images/436_0_l.jpg

1. Andrady, A. L. 2011. Microplastics in the marine environment. Marine Pollution Bulletin, 62(8), 1596-1605 2. Van Cauwenberghe, L., Claessens, M., Vandegehuchte, M. B., & Janssen, C. R. 2015. Microplastics are taken up by mussels (Mytilus edulis) and lugworms (Arenicola marina) living in natural habitats. Environmental Pollution, 199, 10-17. 3. Bakir, A., Rowland, S. J., & Thompson, R. C. 2014. Enhanced desorption of persistent organic pollutants from microplastics under simulated physio-logical conditions. Environmental Pollution, 185, 16-23. Claessens, M., Van Cauwenberghe, L., Vandegehuchte, M. B., & Janssen, C. R. (2013). New techniques for the detection of microplastics in sediments

AIMS

1. Investigate filtration rates of microplastic fibres by P. Perna over a one hour and a 24 hour period.

2. Determine madreporite pore size in T. gratilla and S. variolaris to assess sizes of microplastics

potentially taken up into the water vascular system (WVS).

3. Determine whether microplastic uptake occurs via the water vascular system of T. gratilla

and S. variolaris.

METHODOLOGY

Perna perna, T. gratilla and S. variolaris were collected and maintained in 50 L of

recirculating artificial seawater (Red Sea Salt™) (22°C and 30 psu) for 24 hours to allow for depuration.

Filtration of microplastics in P. perna

Sixteen dead mussels were evenly distributed between four glass tanks each containing 8 L of artificial seawater. 1 mg/L UV fluorescent microplastics fibres (10 – 100 µm) were dispensed into each tank. Fifty ml water samples were initially taken from each tank and again after one hour, thereafter each sample was filtered and

photographed at 40 X magnification using UV light microscopy. Percentage differences in particle numbers before and after one hour were calculated. The procedure was repeated with

live mussels. The percentage difference in particle numbers for dead mussels was subtracted from the percentage difference in particle numbers of live mussels as a correction factor.

The experiment was repeated using microplastic fiber concentrations of 2 mg/L and 5 mg/L.

Microplastic ingestion in P. perna

Ten live mussels were distributed into ten 5 L containers containing aerated, recirculating artificial seawater. 1 mg/L of microplastic fibres were dispensed into each container and mussels were allowed 24 hours to feed. The gut and visceral mass were dissected and digested following methods described by Claessens et al. (2013). Each sample was filtered and photographed at 40 X magnification using UV-light microscopy. Microplastic particle counts

for each mussel were calculated. This procedure was repeated using microplastic fiber concentrations of 2 mg/L and 5 mg/L.

Madreporite pore-size of T. gratilla and S. variolaris

The madreporite was removed from each specimen and placed into a 25 % bleach-deionized water solution to dissolve the soft tissue and spines.

The samples were gold-coated using a sputter coater (Quorum QI50R-ES) and observed with an SEM (LEO 1450 VP). Ten random madreporite pores were measured per individual at 220 X magnification.

Uptake of microplastics into the WVS of T. gratilla and S. variolaris

Five live individuals of T. gratilla and S. variolaris were individually distributed among 10 tanks each containing 5 L artificial

seawater.

2 mg/L of microplastic fibres were dispensed into each tank and the experiment was run for 48 hours.

The WVS was removed from each specimen and digested following methods described by Claessens et al. (2013).

The samples were filtered and the residue viewed under UV-light to check for presence of microplastics.

Figure 1b: Microplastic fibres magnified under UV fluorescence

(40 X)

Figure 3: Log-transformed particle number present in gut and

visceral mass of P. perna (One-way ANOVA:

p < 0.000; F value = 31.98)

Figure 2: Particle number difference (%) filtered over one hour by

P. perna (One-Way ANOVA: p = 0.004; F value = 10.83)

Gerber, G. (2015)

Gerber, G. (2015)

Differences in microplastic quantities before and after one hour were 32.8 ± 20.4 %, 21.2 ± 9.6 % and < 1 ± 0 % for microplastic

concentrations of [1 mg/L], [2 mg/L] and [5 mg/L], respectively (Figure 2). Filtration rates of P. perna decreased with

increasing concentrations of microplastics within the first hour of microplastic introduction.

However, P. perna ingests more microplastic fibres with increasing concentrations of microplastics in 24 hours (Figure 3). Mean

particle numbers present in the gut and visceral mass of the mussels are 95 ± 83 particles, 204 ± 90 particles

and 994 ± 459 particles for [1 mg/L], [2 mg/L] and [5 mg/L], respectively.

Figure 1a: UV fluorescent microplastics inside the visceral

mass of P. perna.

Figure 4: SEM image of S. variolaris madreporite pores (220 X) Figure 5: SEM image of T. gratilla madreporite pores (220 X)

There is a significant difference in mean madreporite pore diameter between T. gratilla (70.2 ± 4.3 µm) (Figure 5) and

S. variolaris (63.3 ± 5.5 µm) (Figure 4) (Mann Whitney U= 577.0; p=0.005).

This study confirms for the first time that both T. gratilla and S. variolaris take up microplastics into their water-vascular

system via madreporite pores.

The investigation highlights the vulnerability of sea urchins to microplastic pollution via dual uptake mechanisms

(Gastric ingestion and madreporite uptake).

Mkhize, T. (2015) Mkhize, T. (2015)

CONCLUSIONS

Although higher microplastic concentrations result in an initial depression in filtration rates,

P. perna adapt within 24 hours and are able to cope with the highest

concentration tested [5 mg/L].

This data suggests that mussels are able to filter greater loads of microplastics in natural

systems, which has the potential to facilitate an increased uptake of toxins

(e.g. heavy metals and POP’s) to the mussels.

As mussels are an important subsistence food source for a large social sector, these

results highlight the potential impacts of microplastic pollution on human food sources

and emphasizes the need for further research on toxin transfer mechanisms.

The dual mechanisms of microplastic uptake in sea urchins are a cause for concern, since

sea urchins, including other Echinoderms, are potentially vulnerable to increased

microplastic retention and transfer of toxins.

This is problematic as Echinoderms are important marine ecosystem engineers and changes

in their abundance may result in cascade effects.

The authors would like thank

the NRF for research funds.