Morocco faces a growing waste issue due to population growth, economic expansion, and industrialization, leading to environmental concerns, especially regarding leachate. Casablanca’s main landfill, which is operational from 1986 to 2022, produces more than 800,000 m3/year of leachate, posing significant environmental risks. Our research not only concentrates on traditional chemical analyses for leachate assessments but also emphasizes ecosystem interactions. Phytotoxicity tests assess the impact of contaminants, particularly heavy metals, complementing traditional chemical analyses. Our study investigated the accumulation of these contaminants in the soil and their subsequent transfer to plant tissues. This research aimed to examine the accumulation of heavy metals, including Pb, Cd, and Hg, in soils irrigated with varying leachate concentrations (C0: control; C1: 5%; C2: 7%; C3: 10%; and C4: 15%). The experiments involved the cultivation of M. sativa plants under open-field conditions. To assess the transfer of metals from soil to plant tissues, the transfer factor (TF) index was calculated. Our findings revealed that Pb, Cd, and Hg exhibited transfer factor ranges of 0.55-0.93, 0.07 to 0.21, and 0.1 to 0.37, respectively. The accumulation of heavy metals at the different leachate concentrations followed the order Pb > Hg > Cd.