The increasing global concern over plastic pollution has prompted extensive research into the fragmentation of plastics into smaller particles, particularly at the sub-micrometer scale. While the term nanoplastics (NPs) remains under debate, this study proposes a working definition describing NPs as unintentionally produced plastic particles within the 1–1000 nm size range that exhibit colloidal behaviour. Both microplastics (MPs) and NPs are now recognized as pervasive anthropogenic contaminants in diverse environmental matrices, originating from primary sources (such as microbeads, glitters, and industrial abrasives) and secondary sources (including tire wear, textile fibers, and degradation of larger plastic debris). Fragmentation and aging processes enhance their surface area and hydrophilicity, promoting interactions with other pollutants. Consequently, MPs and NPs act as vectors for hazardous substances like heavy metals, polycyclic aromatic hydrocarbons, and persistent organic pollutants, posing serious ecological and human health risks. The combined effects of plastic pollution, ocean warming, and acidification exacerbate the vulnerability of marine environments. Overall, this research contributes to a deeper understanding of nanoplastic pollution dynamics and their role in heavy metal transport, thereby emphasizing the need for improved global monitoring and management strategies.