To reduce environmental and human health risks of contaminated sites, having a comprehensive knowledge about the polycyclic aromatic hydrocarbon (PAH) removal processes is crucial. PAHs are contaminants which are highly recognized to pose threats to humans, animals, and plants. PAHs are hydrophobic and own two or more benzene rings, and hence are resistant to structural degradation. There are various techniques which have been developed to treat PAH-contaminated soil. Four distinct processes to remove PAHs in the contaminated soil, thought to be more effective techniques, are presented in this review: soil washing, chemical oxidation, electrokinetic, phytoremediation. In a surfactant-aided washing process, a removal rate of 90% was reported. Compost-amended phytoremediation treatment presented 58-99% removal of pyrene from the soil in 90 days. Chemical oxidation method was able to reach complete conversion for some PAHs. In electrokinetic treatment, researchers have achieved reliable results in removal of some specific PAHs. Researchers' innovations in novel studies and advantages/disadvantages of the techniques are also investigated throughout the paper. Finally, it should be noted that an exclusive method or a combination of methods by themselves are not the key to be employed for remediation of every contaminated site but the field characteristics are also essential in selection of the most appropriate decontamination technique(s). The remedy for selection criteria is based on PAH concentrations, site characteristics, costs, shortcomings, and advantages.

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The rate of metal transfer from the solid phase to solution is an important factor governing their concentration in the soil solution and its availability. In this research, the release rate of Zn in contaminated soils from Isfahan was studied using solutions citric acid, oxalic acid and malic acid 0/01 M during the period of 2-504 hours and its relationship with soil characteristics was investigated. The results showed that low molecular weight organic acids could release Zn in the contaminated soils. The Zn released by acids was in the order citric acid> oxalic acid> malic acid. Variation range of Zn released a solution of citric acid, oxalic acid and malic acid, which was 38/9-21173, 25/2-26761 and 25/5-20650 mg/kg of soil. Zn released in citric acid solution was higher than that of the two acids. Based on the determination coefficient and standard error estimates done by the kinetic equations, the release of Zn of the contaminated soils and three acid solution was described by the first order equation, elovich, parabolic diffusion and power function, with a high coefficient of determination and a low standard error. Correlation results showed that for the Zn release with the index of Zn usability, there was a significant correlation at 5% level. Showed Multivariate regression model showed that Calcium carbonate, pH and EC affected characteristics of Zn desorption.