Purpose Organic acids in the soil can alter the effectiveness of stabilizers used in contaminated soil remediation. Methods The influence of the aluminum oxide ( Al2O3) and titanium dioxide ( TiO2) nanoparticles at the rate of 2% on the adsorption of Cd, Cu, Ni, and Zn with and without the co-existence of organic acids (10 mmol citric and malic acids) was investigated under single (containing only one potentially toxic element (PTE)) and competitive (containing all studied PTE) systems. Results In the absence of organic acids and in both systems and all treatments Cu was more strongly adsorbed, while the Ni was the least adsorbed PTE in all treatments and in presence and absence of organic acids. In general, the application of both organic acids separately decreased the adsorption capacity of the control (untreated soil having no nanoparticles) and nanoparticles-treated soils for PTEs in both systems, whereas this reduction was more pronounced with citric acid treatment. Based on the Freundlich distribution coefficients, in the presence of both citric and malic acids and especially malic acid, Cd had higher adsorption in TiO2- treated soils, while other PTEs had differed in different treatments in both systems. This suggests that Cd might be more stabilized in presence of organic acids and TiO2 nanoparticles and that poses a less ecotoxicological threat. The results of speciation at calculated equilibrium pH indicated low adsorption of Cd, Ni, Zn, and Cu in single and Ni in the competitive systems from the control soils in presence of citric acid. Conclusion These findings highlight the importance of determining the fate and interactions of organic and PTEs coexisting in agricultural soils amended with nanoparticles.
