This study aims to review the effects of microplastics (MPs) with and without adsorbed organic pollutants or heavy metals on marine animals and the associated risks. First, the sources, composition, migration, and distribution of MPs in the marine environment is presented. Second, the effects of the abovementioned MPs were summarized, revealing that MPs alone affect the behavior and physiology of marine animals, whereas MPs adsorbed with pollutants exhibit either synergistic or antagonistic effects (increasing or decreasing bioaccumulation and toxicity, respectively). The impacts pose risks to marine animals at both the individual and population levels. Moreover, the migration of MPs within the food chain introduces additional threats to marine ecosystems. Meanwhile, by consuming contaminated marine animals, MPs can enter and accumulate in the human body, damaging human health. This review provides a reference for similar studies investigating the marine environment and a scientific basis for the protection and management of marine ecosystems.