Characterization of Landfill Leachate and their Toxic Effects on Germination and Seedling Growth of Various Plant Species – A Case Study

Leachate generated from landfills contains many toxic contaminants, such as dissolved organics, inorganic salts, ammonia, and heavy metals, which impact the surrounding environmental systems. This study characterized the AL-Mufarrihat Sanitary Landfill (MSL) leachate in Al-Medinah Al-Munawwarh (MM) province, Saudi Arabia, by analyzing important physicochemical parameters. Phytotoxicity was assessed using various higher plant bioassays, namely, Cucumber (Cucumis sativus L.), Tomato (Lycopersicum esculentum L.), Cabbage (Brassica oleracea var. capitata L.), and Corn (Zea mays L.). The effective concentration of seed germination represented by EC50 was calculated using a USEPA computer program based on Finney's Probit Analysis Method. Selected phytotoxicity test endpoint parameters, namely relative seed germination (RSG), relative root elongation (RRE), and germination index (GI) were determined. The tested leachate exhibited low concentrations of heavy metals, whereas high levels of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) were recorded. The mean EC50 values for MSL leachate exposed to B. oleracea, L. esculentum, C. sativus, and Z. mays were 2.66%, 3.12%, 4.27%, and 5.22%, respectively. These values indicate that B. oleracea was the most sensitive bioassay, whereas Z. mays was the least sensitive. All tested bioassays showed severe phytotoxic responses to the exposed higher leachate concentrations, represented by complete inhibition for RSG, RRE, and GI. Lower leachate concentrations exhibited stimulatory effects on RSG, whereas RRE and GI were hindered, even at these lower concentrations. The results revealed that although RSG and RRE were effective and promising parameters in phytotoxicity evaluation, GI was the most responsive parameter for phytotoxicity assessment. The high levels of organic and inorganic compounds in the leachate are likely the primary cause of the phytotoxicity observed in the bioassays. The results of this study highlight the pollution potential of landfill leachate in Saudi Arabia and will furnish supplementary reference information for hazard assessment and future leachate management.