An assessment of the biodistribution, persistence, and health impacts of microplastics and nanoplastics in fish

Abstract

Microplastics have been found in a diverse range of organisms across trophic levels. Although organisms are continuously exposed to microplastics (1 μm - 5 mm) and nanoplastics (< 1 μm), the risk of these exposures are not understood. A risk assessment for microplastics and nanoplastics is urgently needed, but first more information is required on the biodistribution, persistence, and subsequent health impacts of microplastics and nanoplastics in organisms. My thesis addresses these key knowledge gaps through a combination of environmental measurements and laboratory experiments. I first reviewed the microplastics literature to determine the state of knowledge regarding the trophic transfer, bioaccumulation, and biomagnification of microplastics and nanoplastics. I found that in most of the literature there was clear evidence of trophic transfer, equivocal evidence for bioaccumulation, and no evidence for biomagnification. I drew upon these noted knowledge gaps to guide my measurements of microplastic abundance in Atlantic killifish (Fundulus heteroclitus) captured near Falmouth, MA. I found that microplastics were both more abundant and diverse in the GI tract, compared to those in the muscle. Small microplastics, which are often not analyzed, were the most abundant, and I found evidence that these small microplastics may bioaccumulate. Following this, I compared the impact of the route of exposure on the biodistribution and persistence of polystyrene nanoplastic particles (50 nm and 500 nm) in zebrafish (Danio rerio). I found that exposure routes other than an oral exposure (i.e. dermal, respiratory) contribute to nanoplastic biodistribution, and that the nanoplastics were not persistent in tissues 2 days after exposure. I then examined the impact of a 50 nm polystyrene nanoplastic exposure on cardiovascular development and function in larval zebrafish. Larvae exposed to high concentrations of nanoplastics had significant defects in cardiovascular function. Altogether, my research indicates that nanoplastics and small microplastics might be slightly bioaccumulative in tissues, but that 50 nm polystyrene nanoparticles are not hazardous except in high concentrations; however, nanoplastics and microplastics are diverse. Future work should focus on expanding our knowledge of the toxicity of different types of plastic. This work lays the foundation for future risk assessments for microplastics and nanoplastics.