Study On The PAHs Aging Behavior In The Soil With Different Character And The Efficiency Of Different Extraction Methods

The Persistent Organic Pollutants (POPs), as a new type of pollutant, had attracted extensive attention because of its long time residues and high lipophilicity in the soil, which would bring grater security risks on crop quality and human health. The mobility, transformation and ultimate fate of POPs in the environment are strongly dependent on the aging and sequestration effect of the contaminants in soil. In this study, we used three kinds of polycyclic aromatic hydrocarbons (PAHs), phenanthrene, pyrene and benzopyrene, as the model compounds to study the adsorption and the adsorption trends over time in seven different soils, as well as the relationship between sorption and soil character. Meanwhile we compared the efficiency of different extraction methods which were used to extract the PAHs from soil. The following results were obtained by the experiments:I) This study added three kinds of PAHs into seven soils and found with the extension of aging time, the pollutants entered into the slow process after a short-term rapid adsorption, and then migrated slowly to the condensed OM and the microporous internal. The SOM of soil existed non-homogeneous and had different binding sites to the PAHs. The two-compartment first order kinetic model could fit the migration perfectly.II) The study compared different extraction methods by using 0.01% CaCl₂ solution, butanol, 1:1 DCM/actone, and the soxhlet extraction (1:1 n-hexane/DCM) and found the butanol was most suitable for the bioavailability evaluation of organic pollutions, and the 1:1 DCM/actone could replace the soxhlet to extraction the total amount of pollutants.III) The extractable PAHs in the soil were positively correlated to dissolved organic carbon (DOC) and negatively correlated to clay. The increase of DOC could increase the mobility of PAHs and avoid them to be bounded in the soil internal, and the clay could prevent the PAHs desorption to some extent because of its large adsorption capacity. IV) The "hard carbon" in soil determined the slow migration behavior of PAHs, and the slow migration ratio increased with the increase of hard carbon. The hard carbon had great significance to the adsorption and final fate of organic pollutants in the soil. In addition, the soil particle size and the molecular bulk of pollutants had an appreciable effect to the pollutants aging in the soil.