Microplastics are often found in the greatest quantities in terrestrial environments, in addition to those found along coasts and in oceans. They may get into water bodies from a variety of different sources such as deposition from the atmosphere, runoff from polluted land, and effluent from municipal treatment plants. The objective of this study is to conduct a comprehensive evaluation of the existing scientific literature related to microplastics in wastewater. Specifically, the focus is on investigating the possible impacts of wastewater containing microplastics on both aquatic and terrestrial biota. Additionally, this study attempts to identify any gaps in the current research, with the intention of informing future research priorities in this field. A comprehensive selection of over 200 scientific papers on the subject of microplastic pollution, covering the years 2000–2023, has been selected from a prominent scientific database. These papers encompass a wide range of topics, including recent advancements in the study of microplastics in wastewater, their origins, behaviour in aquatic and terrestrial environments, and their potential adverse impacts on various organisms such as aquatic and terrestrial animals, soil microbial communities, plants, and finally humans. The results showed that using wastewater for irrigation can lead to the presence of microplastics in terrestrial ecosystems and can facilitate the transmission of contaminants in both terrestrial and aquatic ecosystems by interacting with a wide range of pollutants. The findings also indicate that although there has been significant scientific investigation into marine microplastics, research on the prevalence of microplastic contamination in freshwater and terrestrial environments is comparatively limited and requires greater attention for a better understanding of the fate, transport, and consequences of microplastics in relation to water, soil qualities, polymer composition, forms, and various types of land use.