# Co-Exposure of Microplastics and Avermectin at Environmental-Related Concentrations Caused Severe Heart Damage Through ROS-Mediated MAPK Signaling in Larval and Adult Zebrafish

## TL;DR

Exposure to microplastics and a pesticide together harms zebrafish hearts by triggering harmful chemical reactions and signaling pathways.

## Contribution

This study reveals a new mechanism of heart damage in zebrafish from combined microplastic and pesticide exposure.

## Key findings

- Co-exposure to microplastics and avermectin reduced survival, hatching, and myocardial cell counts in zebrafish larvae.
- In adult zebrafish, co-exposure caused heart tissue disorganization and increased inflammation and oxidative stress.
- Blocking ROS and MAPK pathways partially reversed heart damage, indicating their role in toxicity.

## Abstract

The widespread presence of polystyrene microplastics (PS-MPs) and agricultural pollutants such as avermectin (AVM) in aquatic environments poses a significant threat to aquatic organisms. However, the combined toxic effect of PS-MPs and AVM on cardiac development remains poorly understood. This study aimed to investigate the cardiac toxicity of AVM co-exposed with two sizes of MPs (large MPs, LMPs, 20 µm; small MPs, SMPs, 80 nm) in both larval and adult zebrafish. Firstly, under the co-exposure conditions of MPs and AVM, we observed significant cardiac developmental toxicity, including decreased survival rate, body length, and hatching rate, as well as a significant reduction in the number of myocardial cells. Secondly, the number of neutrophils and antioxidant enzyme activities such as CAT and SOD were greatly decreased, while inflammatory cytokines such as TNF-α and IL8 were significantly increased after co-exposure in larval zebrafish. Thirdly, there was severe disorganization of cardiomyocytes and interstitial edema in adult zebrafish hearts under the co-exposure by histopathological examination. Our results suggest that cardiomyocyte proliferation was suppressed, but heart apoptosis level and anti-apoptotic genes were significantly increased in the AVM+MPs co-exposure. Additionally, transcriptome sequencing and bioinformatics analysis revealed that significant changes in differentially expressed genes in the AVM+SMPs co-exposure group, particularly in the processes related to oxidation–reduction, inflammatory response, and the MAPK signaling pathway in the adult zebrafish heart. Furthermore, our pharmacological experiments demonstrated that inhibiting ROS and blocking the MAPK signaling pathway could partially rescue the heart injury induced by AVM and MPs co-exposure in both larval and adult zebrafish. In summary, this study suggested that co-exposure to AVM and MPs could induce heart toxicity mainly via the ROS-mediated MAPK signaling pathway in zebrafish. The information provided important insights into the potential environmental risk of microplastic and pesticide co-exposure on aquatic ecosystems.