Soil organic carbon (SOC) and dissolved organic carbon (DOC) affect long-term heavy metal solubility in biosolids-amended soils, but their role needs to be further studied under Mediterranean climatic conditions. We investigated Zn solubility, as assessed by water extraction, in two typical Greek soils amended with biosolids at 0, 20, and 100 Mg ha(-1) during a 310-d incubation period. It was found that SOC decreased by nearly 30% over time in the 100 Mg ha(-1) treatment. There was evidence that DOC affected Zn solubility, because DOC increased significantly on Day 23, probably due to a flush in microbial activity, and water-extractable Zn followed the same trend. After that, both DOC and water-extractable Zn decreased back to values similar to those of the unamended soils. Although Zn solubility did not increase overall even at high biosolids application rates, this study shows that time-limited fluctuations in Zn solubility due to sudden DOC flushes, can be significant, and need to be further investigated.