Contamination of aquatic environments by microplastics (MPs) and plastic additives, such as plasticizers, is becoming an increasingly serious ecological concern. In particular, polyvinyl chloride (PVC)-based polymeric materials, widely used in industry, may represent a potential source of these substances in aquatic environments. The aim of this study was to assess the release of phthalates (the most commonly used plasticizers) from two types of PVC materials under varying environmental conditions. Laboratory tests were conducted under controlled conditions, analyzing the effects of temperature and contact time on the migration of phthalates into water. It was found that four phthalates such as DEHP (bis(2-ethylhexyl) phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), and DMP (dimethyl phthalate) were released from the tested polymer materials into the water. These compounds are known for their potential toxicity, including endocrine-disrupting effects, raising concerns about their presence in aquatic environments and their possible impact on aquatic organisms. Multiple regression models demonstrated that temperature and contact time significantly influence the emission rate of plasticizers from the polymer matrix. Elevated water temperature substantially accelerates the migration process of phthalic acid esters into the aquatic environment. The results of this study confirm that PVC-based materials can serve as a relevant source of chemical pollution in aquatic ecosystems, particularly during prolonged water exposure under changing environmental conditions.