Polar PAC (Polycyclic Aromatic Compound) mobilization and transfer in water in coal tar contaminated soils

Abstract : Due to the coal transformation activities occurring between the 18th and 20th centuries, about 200 000 sites in Europe have been diagnosed nowadays as polluted by polycyclic aromatic hydrocarbons (PAHs). Because of their toxicity, mutagenic and carcinogenic properties, 16 PAHs, listed as priority pollutants by the US EPA, are regulated and measured for site diagnosis or monitoring during remediation treatment. However, associated to PAHs, polar PACs (OPACs and N-PACs) occur and could induce a risk for water resources. O-PACs and N-PACs are present in the initial pollution (coal tars) as PAHs but can also be produced during remediation treatments or during natural attenuation processes. Moreover, recent studies revealed that O-PACs and N-PACs (i) are leached in higher proportion than PAHs and (ii) can be equally or more toxic than corresponding parent PAHs. All these reasons imply increasing of our knowledge on the mechanisms involved in polar PAC mobilization and transfer to water, especially by comparison to PAHs. In fine, should polar PACs be included in coal tar contaminated site diagnosis in order to improve risk evaluation? In this project, the mobilization and transfer of polar PACs and PAHs were assessed via leaching experiments of aged contaminated soils from two former coking plants (Lorraine, France), which have undergone aging processes. A multiscale approach was used: batch (50 g), laboratory column (2 kg) and pilot scale column (2 m3 lysimeter). In a first step, PAC mobilization was investigated at laboratory scale under various conditions of temperature, ionic strength, PAC availability and water flow rate. PAC transfer was also assessed in situ with a lysimeter column. Dissolved Organic Carbon (DOC) and dissolved PAC concentrations (including 16 PAHs, 11 O-PACs and 5 N-PACs) were measured. Batch experiments, carried out on soils with a high available contamination, revealed that PAC (LMW PAH and polar PAC) mobilization was mainly controlled by dissolution processes according to the Raoult law. For aged soils (low pollutant availability), the mobilization of PACs was lower, especially for LMW-PAHs and polar PACs. In both case, HMWPAHs were mainly released in association with colloids. The temperature increased the mobilization of all PACs while an increase in ionic strength caused a decrease in all PAC mobilization, with a lower impact on polar PACs compared to PAHs. Whatever the column scale (laboratory and field lysimeter), results tend to show a higher release of polar PACs. Polar PACs exhibited intermediate behavior between PAHs (hydrophobic compounds) and DOC. These first results showed that (i) the pollution availability is a fundamental parameter for PAC transfer, and (ii) that polar PACs seem to behave similarly to PAHs but with a higher mobilization and transfer rate. All these findings underline the need to include polar PACs in diagnosis and monitoring of potentially contaminated sites.
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Marine Boulange, Catherine Lorgeoux, Julien Michel, Raymond Michels, Pierre Faure. Polar PAC (Polycyclic Aromatic Compound) mobilization and transfer in water in coal tar contaminated soils. 14. International Conference on Sustainable Use and Management of Soil, Sediment and Water Resources (AquaConSoil 2017), Jun 2017, Lyon, France. pp.331. ⟨ineris-01853494⟩

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