The pervasive nature of microplastics (MP) throughout aquatic environments is of growing concern. Having been found to impact aquatic habitats in a myriad of ways, an increasing number of studies have been conducted in an effort to better understand their occurrences, distribution, and impact in nature. Due to a lack of standard monitoring approaches, however, existing data are largely incomparable and often sporadic in nature. Therefore, the work described in this thesis aims to address the existing need for comparable, long-term data on MP occurrences in aquatic systems as well as to investigate their impacts. This study focuses on freshwater and coastal environments, which have been identified as an important source and pathway for MP in aquatic ecosystems. To facilitate these aims, a novel rapid processing protocol was first designed to enable a routine monitoring of MP in surface seawaters. The protocol was then evaluated and applied to a time-series analysis of MP within coastal surface seawaters from March to November 2018, during which the abundance, composition, and temporal variability of MP were investigated. The rapid processing protocol designed successfully enabled the monitoring of MP to be conducted on surface seawaters on a weekly basis. The protocol was found to effectively minimize organic matrices present within surface seawater samples without imparting any degradative effects on the synthetic polymers tested. Additionally, recovery rates of 100% and 43 – 61% were achieved for larger (3 – 4 mm) and smaller MP (≈50 μm), respectively. Having applied the protocol to a routine monitoring of coastal surface seawaters, MP occurrences were investigated throughout a 9-month period and were found to vary in both composition and concentration. While no clear temporal trend was observed, the variability in MP occurrences was hypothesized to be driven by the hydrodynamic factors that mark the study area. Long term environmental data collected at the study site showed seasonal variability as subject to differing water masses and were found to share a statistically significant correlation to the occurrences of certain polymer types. The potential of MP to harbour and transport multidrug-resistant E. coli from freshwater to marine environments was additionally assessed through a sequential incubation experiment and culture-dependent approaches. Through this analysis, neither synthetic (HDPE and tyre wear) nor natural (wood) particles incubated at any of the sites along a salinity gradient were found to harbour extended-spectrum beta-lactamase (ESBL) producing E. coli. Coliforms and general E. coli communities, however, were detected on the surfaces of wood particles at all sites. ESBL-producing E. coli were found, on the contrary, in surrounding waters sampled from all incubation sites. From these findings, we speculated the absence of ESBL-producing E. coli on particle surfaces to be the product of the types of resistance markers carried, which have been shown to play an important role in their attachment mechanisms. Overall, the novel findings of this study collectively contribute to a broader understanding of the dynamics, distribution, and transport potential of MP within coastal environments and bridge the gap for prospective research in an effort to further our understanding of this emerging pollutant.