Comparative evaluation of the toxicity of compostable, conventional and environmental microplastics on zebrafish larvae co-exposed to Aeromonas hydrophila

Abstract

Microplastic pollution poses increasing ecological risks, but the effects of different types and their interactions with aquatic pathogens remain poorly understood. Understanding the complex interactions between microplastics, pathogens and aquatic organisms is crucial for developing comprehensive environmental protection strategies. This study assesses the effects of different microplastics - compostable, conventional and environmental - and their co-exposure with the bacteria Aeromonas hydrophila on zebrafish (Danio rerio) larvae. The microplastics used in the thesis were derived from conventional and compostable plastic bags purchased in local supermarkets in Namur (Belgium) and from environmental bags collected in the Sambre river. Starting from the fifth day after fertilisation, the larvae were exposed to three types of microplastics (1-50 µm) and the bacteria (LD20) for 3 days. The microplastics affected bacterial colonisation, promoted biofilm formation and altered the elemental composition of the bacteria, showing significant differences for every element tested except phosphorus. Behavioural analyses revealed a reduction in locomotor activity during microplastic exposure, particularly with conventional microplastics, which was enhanced by bacterial co-exposure. Physiological assessments showed an increase in heart rate under all stress conditions, although body length and eye size remained unchanged. Transcriptomic analysis revealed the overexpression of genes coding for immune (interleukin 6 (il6), interleukin 1 beta (il1β)) and oxidative stress (glutathione peroxidase 1a (gpx1a), heat shock protein 70 (hsp70) and myeloid-specific peroxidase (mpx)), particularly under the influence of combined stressors. The results highlight the urgent need to limit plastic pollution and to continue research into the ecological effects of the plastisphere phenomenon.

Date of Award	2024
Original language	English
Awarding Institution	University of Namur Université Catholique de Louvain
Supervisor	Patrick Kestemont (Supervisor) & Omayma Missawi (Co-Supervisor)