This study investigates the feasibility of using expanded polystyrene (EPS) waste collected in coastal areas as a partial substitute for sand in cement mortars, without the need for pre-treatment. Two scenarios were evaluated: (i) direct collection from polluted coastlines and (ii) recovery from existing recycling stations. The environmental assessment was carried out through a life cycle assessment (LCA), while the economic performance was assessed through a life cycle costing (LCC). The results showed that second scenario had approximately 30 % lower environmental impact and significantly lower costs, mainly due to the elimination of the collection phase. Compared to sand, EPS had lower emissions per cubic meter due to its low density. The results confirm that the direct reuse of EPS waste from the coastal areas without pre-treatment is a technically feasible and economically viable solution for non-structural applications. This approach contributes to the reduction of plastic waste and supports the transition to a circular economy in the construction sector.