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The PolDOC model has been developed in the VSoil platform to simulate transport processes of organic pollutants in subsoil horizons. A new module considering association of organic pollutants with dissolved organic matter (DOM) was created to describe the multiple roles of DOM in the transport of organic pollutants including co-transport, co-sorption and cumulative sorption.

Details of the work carried out under this theme are presented below.

The PolDOC model has been designed as a tool to test hypotheses put forward to explain how organic pollutants are transported in deep soil horizons. It was first developed during the PhD of Florian Chabauty (2016) and lately parameterized (Benoit et al., 2023). DOM is constituted by a mixture of organic molecules of different sizes and hydrophobic properties which explains why the role of DOM on the transport of organic pollutants through the soil profile remains controversial. Enhanced transport or little effect on sorption and desorption of the pollutants have been observed according to authors and studies. It is generally hypothesized that DOM modifies the sorption properties of the pollutants through co-sorption and/or cumulative sorption. Co-transport with DOM can also enhance the mobility of the pollutants. These three processes have been implemented in the PolDOC model by coupling an existing 1D water flow module based on the Richards equation (Richards PASTIS) and an existing 1D solute transport module (MIM-PASTIS). A new module of association of organic pollutants with DOM was developed (DOC_TOC_association_PolDOC) and hydrolysis of soil organic matter into DOM was included in the degradation module (DOC_TOC_degradation_PolDOC). Four species were considered to explain the transport of organic pollutants in the Bt horizon of an Albeluvisol: a generic molecule of aged DOM, produced by the hydrolysis of the organic matter of the Bt horizon ; a generic molecule of young DOM transported downward from the surface horizon ; a free organic pollutant molecule ; an association of the pollutant molecule with the more reactive young DOM molecule. Then the sink/source terms in the transport equation were used to describe co-sorption, cumulative sorption and co-transport. The PolDOC model has been parameterized on a published data set of the percolation of four organic pollutants through laboratory soil columns sampled in the Bt horizon of an Albeluvisol (Chabauty et al., 2016). Co-transport, cumulative sorption and increase of degradation were necessary processes to activate in order to correctly describe the transport of pollutants in the presence of DOM.

References:

Benoit P., Dollinger J., Lafolie F., Chabauty F., Pot V. (2023). Assessing the multiple effects of dissolved organic matter on the transport of organic pollutants in subsoil horizons through a modular modeling approach. EGU23-12446. EGU General Assembly 2023, Vienna. https://doi.org/10.5194/egusphere-egu23-12446

Chabauty F., Pot V., Bourdat-Deschamps M., Bernet N., Labat C., and Benoit P. (2016). Transport of organic contaminants in subsoil horizons and effects of dissolved organic mattter related to organic waste recycling practices. Environmental Science and Pollution Research, 23, 7, 6907-6918. https://doi.org/10.1007/s11356-015-5938-9

Chabauty, F., Lafolie, F., Benoit, P., Pot-Genty, V. (2016). Modelling of biogeochmical processes occuring during the transport of organic contaminants and dissolved organic matter in deep soil horizons in the context of agricultural soils receiving urban waste composts as organic amendments. Presented at 5th International EcoSummit 2016. Ecological Sustainability: Engineering Change, Montpellier, France (2016-08-29 - 2016-09-01). [Poster] https://hal.inrae.fr/hal-01605819

Chabauty F. (2015). Effets des matières organiques dissoutes sur le transport de différents contaminants organiques dans l’horizon illuvié (Bt) de sols limoneux profonds : approche expérimentale et modélisation. Thèse de Doctorat en Sciences de l’Environnement. École doctorale (ABIES) – AgroParisTech, Institut des Sciences et Industries du Vivant et de l’Environnement, 247pp.