Impact of phthalates and microplastics on zebrafish: ingestion, bioaccumulation, and developmental effects

Abstract

Plastic pollution, especially the presence of microplastics and phthalates, has emerged as a critical global environmental issue with far-reaching consequences for ecosystems and human health. Microplastics, small plastic particles less than 5 mm in size, are now widely detected in aquatic environments, where they threaten biodiversity, water quality, and the health of aquatic organisms. Phthalates, commonly used as plasticizers to make plastics more flexible and durable, are chemical pollutants that easily leach into the environment, adding to the toxic burden. These contaminants, often co-occurring in aquatic ecosystems, pose serious risks due to their potential for bioaccumulation and biomagnification, affecting both wildlife and humans. Zebrafish (Danio rerio) have become a widely used model organism for toxicological studies, offering insights into how these pollutants affect development, physiology, and molecular pathways in aquatic species. This thesis investigates the combined effects of microplastics and phthalates on zebrafish larvae, focusing on ingestion patterns, bioaccumulation, molecular disruptions, and potential remediation strategies. A comprehensive review of the literature reveals that microplastics are a pervasive issue, with significant implications for ecosystems globally, including India. These small particles impact aquatic biota, disrupt food chains, and present potential health risks to humans through ingestion and accumulation. Phthalates, equally concerning, are persistent environmental contaminants that bioaccumulate in living organisms, leading to toxic effects on their development, reproduction, and overall health. Advanced detection techniques and more stringent regulations are necessary to address the rising concerns surrounding both microplastics and phthalates. The developmental toxicity of phthalates on zebrafish is a major focus of this research. Exposure to phthalates such as dibutyl phthalate (DBP), diethyl phthalate (DEP), and di-(2-ethylhexyl) phthalate (DEHP) leads to significant mortality and developmental defects in zebrafish larvae. These defects are linked to disruptions in critical genetic pathways involved in cardiovascular, dorsoventral axis, and bone development. The study highlights how phthalates interfere with bone morphogenesis through the BMP pathway, providing new insights into the long term effects of these plasticizers on aquatic vertebrates. Further, the research explores the impact of microplastics, both virgin and environmentally weathered, on zebrafish development. The findings demonstrate that weathered microplastics are more toxic than virgin particles, leading to higher mortality, oxidative stress, and DNA damage in zebrafish larvae. Molecular disruptions in key pathways such as oxidative stress response and DNA repair further underscore the heightened risks posed by microplastics that have undergone environmental aging. Lastly, the thesis examines potential remediation strategies to mitigate the harmful effects of these pollutants. The study highlights the protective role of humic acid and clay, which significantly reduce the bioavailability and toxicity of phthalates in zebrafish. These natural modulators decrease mortality and malformations, promoting normal growth and reducing oxidative stress in larvae exposed to phthalates. Additionally, microbial remediation techniques are explored, showing promising results in the degradation of phthalates in laboratory conditions. In conclusion, this thesis provides a comprehensive examination of the combined toxicological effects of microplastics and phthalates on zebrafish development. It offers valuable insights into the ecological risks posed by these pollutants and explores innovative strategies for mitigating their impact, contributing to the broader effort to address the global challenge of plastic pollution.