Sorption, uptake, trophic transfer and immunotoxicity of microplastics and nanoplastics in the aquatic environment

Plastic pollution is one of the biggest emerging issues that the world faces today. Microplastics (100 nm - 5 mm) and nanoplastics (1nm - 100 nm), are small pieces of plastics that mainly result from environmental degradation of plastic debris. Their ubiquitous presence, resistance to aging, small size, diverse physicochemical characteristics, and lack of analytical methods for their detection and quantification, have raised the concern of their potential impact on the environment and human health. Studies have shown their potential roll as vectors of pollutants in the environment through the sorption of water pollutants onto plastic particles. Studies have also shown the potential for accumulation and toxicity of microplastics and nanoplastics in aquatic organisms. However, it is uncertain how microplastics and nanoplastics interact specifically with different types of pollutants, how much and for how long they can be taken up, accumulate and transfer in the trophic chain. In addition, the mechanism of toxicity in aquatic organisms remains unclear. Research from this dissertation will investigate the sorption behavior, uptake, trophic transfer, accumulation, depuration, and immunotoxicity of microplastics and nanoplastics in the aquatic environment and freshwater aquatic organisms. The sorption behavior of three non-steroidal anti-inflammatory drugs (NSAIDs) was examined with four types of microplastics under varying water conditions. Low sorption occurred between NSAIDs and microplastics under environmentally relevant conditions. The sorption process exhibited a pronounced pH dependency due to the effect of pH on the speciation of the compounds and the surface charge of the particles. Only under acidic conditions (pH 2) in which NSAIDs are non-ionized, NSAIDs were highly sorbed onto microplastics mainly ruled by hydrophobic interactions. Among NSAIDs tested, diclofenac exhibited the highest sorption coefficients to microplastics. Polyethylene microplastic particles exhibited the highest affinity for NSAIDs. The uptake, tissue translocation, trophic transfer, and depuration of polystyrene (PS) microplastics were assessed between Daphnia magna and Pimephales promelas, fathead minnow (FHM). Bioconcentration factors (BCF) and bioaccumulation factors (BAF) were also determined. Throughout the five days of exposure, PS particles were only found within the gastrointestinal (GI) tract of both species. The BCF for Daphnia was 0.034 ± 0.005 for the low concentration and 0.026 ± 0.006 for the high concentration. The BAF for FHM was 0.094 ± 0.037 for the low concentration and 0.205 ± 0.051 for the high concentration. Between 72 and 96 h after exposure all microplastic particles were depurated from both species. The presence of food had a significant effect on the depuration of microplastic particles from Daphnia, but not for FHM. The immunotoxicity of nanoplastics was assessed in vivo in adult male FHM after their exposure (ingestion of contaminated prey and intraperitoneal injection) to PS nanoplastics. Gene expression of specific genes related to innate immune response in liver and kidney was measured. After 48 hours of exposure, PS nanoplastics were encountered in liver and kidney of FHM, which supports the idea that nanoplastics particles move along the food chain and may translocate from the gut to other organs. PS nanoplastics significantly affect the innate immune system of FHM, in general suppressing the synthesis and function of neutrophils, macrophages, and complement, in principal hematopoietic tissues. This research provides valuable information regarding the fate and toxicity of microplastics and nanoplastics in the environment and will aid in the ecological risk assessment and future regulation of plastic pollution.

This dissertation won 2nd Place in the Texas Tech University Outstanding Thesis and Dissertation Award, Biological Life Sciences, 2021.