Toward Safe Urban Food Systems and Soil Health: A Comparison of Organic and Mineral Amendments for Controlling Cadmium (Cd) Levels in Leafy Vegetable Crops

Urban soils are often contaminated with potentially toxic elements (PTEs), which may enter the food chain through crop uptake and pose risks to human health. At the same time, composting of organic waste represents an important circular economy strategy, providing organic amendments that can improve soil quality and potentially reduce contaminant bioavailability. This study evaluated the effectiveness of amendments in reducing cadmium (Cd) mobility and plant uptake under controlled conditions. A pot experiment was conducted using soils artificially contaminated with Cd at concentrations of 2, 5, 10, 100, and 300 mg kg−1. Granulated plant-based compost was compared with granulated cattle manure and gabbro meal. Lettuce (Lactuca sativa L.) cv. ‘Omerga’ and pak choi (Brassica chinensis L.) cv. ‘Bopak F1’ were selected as test crops due to their high Cd accumulation. Compost application significantly decreased the soluble Cd fraction, determined by 1 mol L−1 NH4NO3 extraction. At the highest contamination level, soluble Cd concentrations decreased from 9.5 to approximately 2.0 mg kg−1. Compost amendments also reduced Cd accumulation in edible plant tissues, particularly in lettuce, while improving plant growth and biomass production. These findings demonstrate that composted organic materials can effectively mitigate Cd bioavailability, enhance soil health, and support more sustainable urban food production systems.