Phytotoxicity of landfill leachate after treatment – assessment using seed germination bioassays

Landfill leachate (LL), generated primarily by rainwater seepage through waste layers, poses a significant environmental threat owing to its complex composition. LL assessment is typically based on physicochemical analyses, which may not be sufficient for drawing reliable conclusions. Comprehensive LL characterization is crucial for monitoring the environmental impact of leachate and assessing the effectiveness of the treatment. Therefore, this study aimed to assess the relationship between leachate toxicity to three plant species, Sinapis alba, Lepidium sativum, and Sorghum saccharatum , and its physicochemical properties. Furthermore, the polycyclic aromatic hydrocarbon (PAHs) removal efficiency from leachate was assessed. Systems without vegetation were more effective in removing PAHs than those with vegetation, achieving a concentration reduction exceeding 90%. The difference in PAH removal between the unvegetated and vegetated systems with biochar was greater than 60%. The longer retention time yielded the best results in leachate treatment, including a reduction of 3- and 4-ring PAHs by 57.71% and 26.7%, respectively, and a stimulating effect was demonstrated regardless of the system variant used. Our results indicated that raw LL inhibited plant growth and caused high phytotoxicity (Germination Index (GI) < 50%) in all plant species analyzed. However, LL after treatment at 14-day HRT did not cause phytotoxic effects, as the GI in all cases exceeded 100%. Clear differences in the sensitivity of individual plant species to LL were observed, with L. sativum being the most sensitive species under the majority of experimental conditions. These results provide additional reference data for risk assessment and leachate management.