Some organic matter (OM) soil amendments derived from biowaste have been shown to reduce plant uptake of Cd, which presents them as an attractive option for mitigating potential health risks on some contaminated soils. However, recent studies have highlighted that dissolved organic matter (DOM) release from the amendments may increase the mobilization of metals in those soils. The provenance of the OM and the quality of the emergent DOM have been suggested as important determinants in the extent to which this occurs. However, these effects have not been systematically tested in different soil environments, where the amount of DOM released from the OM, and its affinity to form Cd-DOM complexes, may vary. Our aim in this work was to explore whether the type of OM soil amendment influences Cd mobility in contaminated soils at different pHs, and if DOM characteristics contribute to this effect.