Microplastics are a highly concerning pollutant that have gained attention from the scientific community and other regulatory authorities due to their potential risks to organisms and ecosystems. Microplastics are widespread in both terrestrial and aquatic ecosystems and can be found even in Antarctica and deep-sea sediments. The ability to survive for long periods in the environment and their aptitude of inter- and intra-environmental translocation can prompt poor environmental outcomes. The adsorption of heavy metals and other toxic persistent organic pollutants is a further cause for concern. Furthermore, microplastics enable the development of a distinct microbial niche within an ecosystem, which could potentially impair ecosystem function by promoting the growth of selective microbial communities. The acquisition of metal-resistant, antibiotic-resistant genes, and the enrichment of antibiotic-resistant bacteria on microplastic surfaces have recently been reported. Moreover, some studies have also reported the colonization of pathogenic bacterial strains such as Vibrio spp. on microplastic surfaces. This review aims to address the sources of microplastic pollution in the freshwater and marine environments and to discuss their potential functions in the environment.