Particle Size and Pre-Treatment Effects on Polystyrene Microplastic Settlement in Water: Implications for Environmental Behavior and Ecotoxicological Tests

Lars Eitzen,Aki Sebastian Ruhl,Martin Jekel

doi:10.3390/w12123436

Lars Eitzen, Aki Sebastian Ruhl + Show 1 more

Open Access

https://doi.org/10.3390/w12123436

Copy DOI

Abstract

Microplastic (MP) particle dispersions used in many recent publications covering adsorption or toxicological studies are not characterized very well. The size distribution of polydisperse dispersions is highly dependent on the agglomeration processes and influences experimental outcomes. Therefore, pre-treatment is a prerequisite for reproducibility. In this study, manual/automated shaking and ultrasonic treatment as different mechanical dispersion techniques were applied for the dispersion of cryomilled polystyrene (PS). Particle numbers and size distribution of dispersions were analyzed by a light extinction particle counter and the dispersion efficiency (ED) as the ratio between calculated volume and theoretical volume of suspended particles was used to compare techniques. PS dispersions (20 mg/L) treated for 90 min in an ultrasonic bath (120 W, 35 kHz) were evenly dispersed with a particle concentration of 140,000 particles/mL and a high reproducibility (rel. SD = 2.1%, n = 6). Automated horizontal shaking for 754 h (250 rpm) reached similar particle numbers (122,000/mL) but with a lower reproducibility (rel. SD = 9.1%, n = 6). Manual shaking by hand dispersed the lowest number of particles (55,000/mL) and was therefore found to be unsuitable to counteract homo-agglomeration. ED was calculated as 127%, 104% and 69% for ultrasonic treatment, horizontal shaking and manual shaking, respectively, showing an overestimation of volume assuming spherical shaped particles.

Highlights

A great emphasis in microplastic (MP) research is put on the spatial distribution, transport and behavior of microplastics in water
After h the batches were treated with increased to a plateau of about 102,000–134,000 1/mL after 410 h
Primary MP particles released into the environment most likely start out as a hardly dispersible material, as with the model particles used in this study, and the dispersion of these is still unknown

Summary

Introduction

A great emphasis in microplastic (MP) research is put on the spatial distribution, transport and behavior of microplastics in water. All these studies use artificial MP dispersions to extrapolate laboratory findings to environmental behavior. For this reason, meaningful results require attention during the preparation of MP dispersions. MP exposure experiments conducted with only a few details on applied mass, particle size distribution and concentration are hard to compare [1]. Prerequisites have been formulated for particle characterization used in toxicology studies regarding surface area or size distribution and homogeneity of dispersion [2,3]. Stable dispersions with most particles existing separately allow for correct extrapolations of mass/number concentration effects. Dispersion stability is linked to particle size and specific surface area.

Objectives

Methods

Results

Conclusion