Microplastic dispersal behavior in a novel overhead stirring aqueous exposure system

Iurgi Salaberria,Colette Nadvornik-Vincent,Giovanna Monticelli,Dag Altin,Andy M Booth

doi:10.1016/j.marpolbul.2020.111328

Abstract

Using nominal dose metrics to describe exposure conditions in laboratory-based microplastic uptake and effects studies may not adequately represent the true exposure to the organisms in the test system, making data interpretation challenging. In the current study, a novel overhead stirring method using flocculators was assessed for maintaining polystyrene (PS) microbeads (Ø10.4 μm; 1.05 g cm−3) in suspension in seawater during 24 h and then compared with static and rotational exposure setups. Under optimized conditions, the system was able to maintain 59% of the initial PS microbeads in suspension after 24 h, compared to 6% using a static system and 100% using a rotating plankton wheel. Our findings document for the first time that overhead stirring as well as other, commonly used exposure systems (static) are unable to maintain constant microplastic exposure conditions in laboratory setups whereas rotation is very effective. This suggests toxicological studies employing either static or overhead stirring systems may be greatly overestimating the true microplastic exposure conditions.

Highlights

While there is an increasing quantity of data reporting microplastic concentrations in different marine environmental compartments, a comparable amount of microplastic effects data for marine organisms is currently lacking (Barboza et al, 2019; Botterell et al, 2019; Prata et al, 2019). This is evidenced by the first study attempting to evaluate the risk of microplastic pollution being conducted only in 2018 (Everaert et al, 2018), and where the scarcity of effects data was highlighted as a critical limitation
A stainless steel beaker was tested to include a material with a different microstructure than glass, but should not be used in a microalgae toxicity test as it is impermeable for light required for algae growth
The results show that glass, the most commonly used exposure vessel material in laboratory studies, performed best and that less conventional exposure vessels appear to offer no advantage in terms of maintaining a constant microplastic exposure concentration

Summary

Introduction

While there is an increasing quantity of data reporting microplastic concentrations in different marine environmental compartments, a comparable amount of microplastic effects data for marine organisms is currently lacking (Barboza et al, 2019; Botterell et al, 2019; Prata et al, 2019). Most toxicological studies with microplastic employ nominal dose metrics with the assumption that exposure is 100% and constant over time It is doubtful this reflects the true exposure conditions as microplastic particles are unlikely to remain homogenously dispersed in the aqueous phase due to aggregation, settling and sedimentation processes (Alimi et al, 2018; Choi et al, 2019; Gambardella et al, 2017; Karami, 2017; Kowalski et al, 2016). Many polymers are inherently hydrophobic and exhibit surface charges in water that can reduce microplastic bioavailability due to homo-aggregation and adhesion to exposure vessel surfaces and analytical equipment (Fotopoulou and Karapanagioti, 2012; Kim et al, 2015)

Methods

Results

Conclusion