Mobilisation of polycyclic aromatic hydrocarbons (PAHs) such as pyrene or phenanthrene by organic acids (citric, oxalic, tartaric, lactic, or acetic) U0126 solubility is dependent on the type of organic acid, pH, and soil organic matter content [8, 57]. For example, citric acid has been reported to be efficient in pyrene and phenanthrene extraction [8, 57]. Lower extractability of PAHs was found in soils of higher organic matter content, while adsorption of pyrene in the presence of organic acids decreased with increasing pH. Citric and malic acids inhibited adsorption of chemotherapeutics in soil. Soil pH, surface properties, and competitive adsorption of other cations affected this process [58].Introduction of Bacillus thuringiensis (Bt) to soil, as a result of rapid planting of Bt-transformed crops, may cause hazards for soil ecosystems; thus, the factors affecting its mobility need to be determined.

Organic acids (citric, oxalic, and acetic) are one of the factors affecting mobility of Bt toxin in soil. Fu et al. [59] reported decreased adsorption of Bt toxin by minerals such as kaolinite, goethite, and silicon dioxide due to low concentrations of organic acids, whereas high concentrations of these acids promoted adsorption of the toxin. Increasing concentrations of oxalate and citrate inhibited adsorption of Bt toxin by montmorillonite.Organic acids such as citric and tartaric acids were found to reduce Cr(VI) to Cr(III) in the soil [60] and to affect mobility of heavy metals due to their desorption, complexation, and precipitation.

Dissolution of minerals in fly ash from smelters allowed conversion of heavy metals to their mobile forms [61�C64]. Cu phytoextraction by Nicotiana tabacum L. was enhanced by citrate, whereas Pb phytoextraction was not stimulated by aliphatic organic acids, probably due to the rate of degradation of organic acids in soil, which is reported to be high for metals of low mobility and bioavailability [65].Generally, citric acid is the most effective in terms of desorption of different heavy metals, followed by malic > acetic > tartaric > oxalic acid (Cu, Hg, Pb, Cd, Zn, and 137Cs) [66�C73]. Schwab et al. [72] found citric acid to be the most efficient in desorption of Zn and Cd in sandy loam, but it had little impact on Pb movement. Desorption of heavy metals in soil by organic acids depends on the concentration and degradability of the organic acids, pH, and concentration of competing cations such as Ca2+ [61, 62, 74].

Effective mobilisation of Zn in soil due to formation Batimastat of citrate-Zn complexes was reported by Lombn?s et al. [62]. Citric acid rapidly degrades, even in heavy metal-polluted soils, with 20% degradation between 1 and 4 days being reported by Wen et al. [74]. Fast degradation of organic acids in soil leads to low migration [6, 54]. On the other hand, complexation of organic acids with Al slightly decreases their degradation [5].