Phytoremediation of Pb and Cd Contaminated Soils Using Medicago Sativa

Heavy metal contamination of soils represents a significant environmental and public health concern due to the inherent toxicity, persistence, and non-biodegradable nature of metals such as lead (Pb) and cadmium (Cd). These elements accumulate in terrestrial ecosystems, disrupt soil biochemical processes, and pose serious risks to food safety through plant uptake and trophic transfer. In this context, phytoremediation has emerged as an environmentally sustainable and cost-effective approach for the management of metal-contaminated soils. The present study investigated the phytoremediation potential of Medicago sativa for soils co-contaminated with Pb and Cd, with particular emphasis on the role of soil chemical modification, nutrient amendments, and chelating agent application in regulating metal bioavailability and plant uptake. Controlled pot experiments, complemented by field trials, were conducted using Pb-contaminated soil amended with cadmium to simulate multi-metal contamination scenarios. Soil pH was adjusted to 5.5, 6.5, and 7.0, while nitrogen, phosphorus, and potassium were applied at agronomically relevant rates to assess their influence on plant growth and metal accumulation. To enhance metal mobility, chelating agents including ethylenediaminetetraacetic acid (EDTA) and citric acid were applied. Bioavailable fractions of Pb and Cd were quantified using diethylenetriaminepentaacetic acid (DTPA) extraction, and metal concentrations in plant tissues were determined by atomic absorption spectrometry. The results revealed a pronounced influence of soil pH on metal uptake, with acidic conditions (pH 5.5) significantly enhancing the bioavailability and accumulation of Pb and Cd by approximately 30% and 45%, respectively. Nitrogen supplementation promoted vegetative growth and biomass production, resulting in increased total metal uptake despite relatively modest changes in tissue metal concentrations. Among the chelating agents, EDTA induced the greatest enhancement of Pb and Cd uptake, although its application was associated with observable phytotoxic effects, likely due to excessive metal mobilization. In contrast, citric acid produced moderate increases in metal uptake while maintaining normal plant growth, highlighting its potential as a more environmentally benign chelating agent. Across all treatments, Cd uptake consistently exceeded Pb uptake, reflecting its greater mobility and weaker sorption to soil constituents. This study provides a robust scientific basis for the development of effective and environmentally sustainable phytoremediation strategies targeting multi-metal contaminated soils.