Particular attention is being paid to the presence of heavy metals—especially mercury—because of their tendency to accumulate in water. These toxic and persistent substances in the environment continuously accumulate and increase as a result of anthropogenic activity (Sonthalia et al., 2004). This paper presents the detection and measurement of the amount of dissolved mercury in young and mature leachates of a sanitary landfill, where the young leachates have had a technical environmental treatment compared with the mature leachates, using differential pulse anodic stripping voltammetry as an instrumental technique. The results showed significant differences in mercury content in both leachates.