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Polar PAC (Polycyclic Aromatic Compound) Mobilization And Transfer In Water From Coal Tar Contaminated Soils: From Batch To Lysimeter Column Expériments

Abstract : Due to past coal transformation activities, about 200 000 sites have been diagnosed as polluted by polycyclic aromatic hydrocarbons (PAHs) in Europe. Because of their toxic, mutagenic and carcinogenic properties, 16 PAHs are regulated and measured for site diagnosis and monitoring during remediation treatment. Associated to PAHs, polar PACs (O-PACs and N-PACs) occur and could induce a risk for water resources. Polar PACs are present in the initial pollution (coal-tars) and can be produced during remediation treatments or natural attenuation. Moreover, recent studies revealed that polar PACs (i) are leached in higher proportions than PAHs and (ii) can be as toxic as corresponding PAHs. Consequently, the mechanisms involved in polar PAC mobilization and transfer to water, especially compared with PAHs, need to be elucidated. 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. A multi-scale 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 in laboratory batch experiments under various conditions of temperature, ionic strength, PAC availability. For laboratory column, different conditions were applied on a column with raw coking plant soil and a column with the same soil with its contaminant availability increased. Different nature (ionic strength, organic matter concentration) and flow of the percolating solutions were tested to evaluate their impact on PAC mobilization. On the field scale, leaching tests were performed with artificial rain applied on a lysimeter column (2 m3) filled with a contaminated soil sampled on a former coking plant site. Dissolved Organic Carbon (DOC) and dissolved PAC concentrations were measured. The results from batch experiments show a release of low molecular weight PAHs and polar PACs mainly by dissolution (Raoult’s law), while higher molecular weight PAHs were mainly released in association with colloids. Aging mainly controls the former mechanism and ionic strength mainly controls the latter one. The Raoult’s law predicts the PAC equilibrium concentration at high level of pollution availability but it overestimates PAC concentration at low availability. This is mainly due to limitation of PAC diffusion within coal-tar particles with aging. The most soluble PACs (especially polar PACs) were the most sensitive to aging. Column experiments confirm a preferential release of polar PACs compared with PAHs. For laboratory column tests, satisfactory predictions are obtained for polar PAC release when the pollution is available, it is not the case for the raw soil, suggesting that availability is a major parameter that needs to be taken into account for historical contamination impacted by aging. Leaching tests performed on the lysimeter column confirm a release of PACs according to a coal-tar dissolution mechanism, although PAC concentrations are much lower compared to those predicted by the Raoult’s law. These findings underline the need to include polar PACs in diagnosis and monitoring of potentially contaminated sites.
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Submitted on : Tuesday, March 23, 2021 - 3:56:27 PM
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  • HAL Id : hal-03178167, version 1


Marine Boulangé, Catherine Lorgeoux, Coralie Biache, Pierre Faure, Julien Michel, et al.. Polar PAC (Polycyclic Aromatic Compound) Mobilization And Transfer In Water From Coal Tar Contaminated Soils: From Batch To Lysimeter Column Expériments. Contaminated Site Management in Europe (CSME), Oct 2018, Nancy, France. ⟨hal-03178167⟩



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