The main goal is to progress in the understanding and modeling of biophysical processes and their coupling involved in the fate, bioavailability and transport of organic contaminants in soil. In our former project, one challenge was to better consider the hydric status of soil in the modeling of pesticide and organic contaminant fate. Especially we had identified several retroaction loops between water dynamics and fresh organic matter decomposition, dissolved organic carbon production, microbial degradation and transformation of contaminants and their diffusive and convective transport in soil. During the last 5-year period:

• we developed a new model - Pastis_Mulch - able to simulate herbicide losses by wash-off and leaching in conservation agriculture (see Highlight 3: S. Aslam PhD, 2014). The model offers the possibility to describe the effect of water content of the mulch-soil interface and in the whole soil on mulch decomposition and pesticide behavior. Working with different cover crop species also demonstrated that the decomposition of mulch has a strong impact on the persistence of pesticides at the soil surface (Cassigneul et al., 2015; 2016; 2018). Such persistence is critical for further emission to atmosphere as it was shown for a compound such as S-metalochlor (collaboration with C. Bedos – Eco&Phy team - Bedos et al., 2017);
• we developed a new model – Pol-DOC- accounting for the complex interactions between dissolved organic matter and the reactive transport of organic contaminant (Chabauty, PhD, 2015). This model was tested on an experimental dataset obtained in displacement experiments of pesticides and pharmaceuticals in undisturbed soil columns. Results show that DOM behaved as a highly reactive solute, which was continuously generated within the soil columns during flow and increased after flow interruption. DOM significantly increased the mobility of all compounds, but the effects differed according the hydrophobic and the ionic character of the molecules (Chabauty et al., 2016).

Another challenge was to better assess the bioavailability of organic contaminants in soil, especially the ones entering soil through organic waste application (see previous topic). At the time of ECOSYS launching, it was strategic to contribute to the ambition in matter of soil ecotoxicology through collaborations with the Ecotox Team. Concerning this objective:

• we developed analytical methods to approach the availability of antibiotics potentially present in sludge and manure (see Highlight 4: Goulas PhD, 2016). In collaboration with O. Crouzet- Ecotox team - these methods have been tested to explain the observed effect of such antibiotics on microbial transformation of nitrogen
• we studied the fate of cocktails of contaminants (antibiotics and trace elements) and their impacts on soil microorganisms (PhD A. Andriamalala; CEMABS project)
• we developed a new model able to simulate the long-term effect of organic waste compost application on PAH fate in cropped soil (V-Soil HAP model - Brimo et al., 2018). This model can simulate the exposure of several contaminant in the context of organic waste application (PAH but also emerging contaminant –Geng et al., 2015; 2016).

Beside cognitive objectives, another objective concerned the use of different modeling approaches at the plot scale - partially derived from process-based models shortly described above - in order to assess the performances of different cropping systems in the reduction of pesticide dispersion. A particular effort in the last period has concerned the assessment of the impacts of innovative systems designed to reduce pesticide use (Ecophyto plan):

• we compared the performances of several pesticide fate models MACRO-PEARL-PRZM for simulating the S- metolachlor and mesotrione vertical fluxes in different irrigated maize cropping systems (Marin-Benito et al., 2014; 2018);
• we developed new modeling approaches to assess and compare the impacts of newly designed cropping systems (Lammoglia et al., 2017a; Lammoglia et al., 2017b). A main conclusion was that conservation tillage systems would lead to increased impacts (due to increase in herbicide applications and susceptibility to macropore flow) while systems such as low inputs or no herbicide systems would reduce the impacts on environment and human health (Mamy et al., 2017);
• we used Hydrus-2D to correctly simulate over a 6-year period, the dynamics of water and isoproturon in a heterogeneous soil profile under different urban waste compost applications (Filipovic et al., 2014; 2016). Modeling results indicated that spatial and temporal variations in pesticide degradation rate due to tillage and compost application play a major role in the dynamics of isoproturon leaching. Both types of compost were found to reduce isoproturon leaching.

All the previous activities have benefited also from an ongoing reflection based on the possibility to extrapolate knowledge obtained on certain organic contaminants used as a model compound to other contaminants and to find a way to overcome the difficulty that only a very small proportion of chemicals can be studied in laboratory tests or monitoring studies because it is time-consuming and/or cost prohibitive. In the recent period, we developed TyPol to classify organic compounds, and their degradation products, according to both their behavior in the environment and their molecular properties. The strategy relies on partial least squares analysis and hierarchical clustering (Servien et al., 2014). This tool was tested and progressively improved:

• we used it in complement of suspect screening approach to assess the risk posed by potential transformation products of tebuconazole (Storck et al., 2016) and chlordecone (Benoit et al., 2017)
• we implemented new parameters related to ecotoxicological effects of pesticides (Traore et al., 2018) and started to extend to database to emerging contaminants

Scientific stategy and project

Our major research questions still concern the understanding and modeling of processes and their coupling involved in the fate, bioavailability and transport of organic contaminants in soil. We will pursue our efforts to better consider the hydric status in relation to soil intrinsic properties (texture, composition) but also to drivers such as crop successions and associations, intercropping, agroforestry which have a great influence on soil structure, organic matter (quality, distribution) and biological activity. Recent development of models such as PASTIS-Mulch (Aslam et al., 2018) or Pol- DOC (Chabauty, PhD, 2015) could be tested in different field situations and benefits from their implementation on platforms such as V-Soil (BAGAGE’s WP, DIGESTATE project). Accounting explicitly for the spatial organization at the pore scale in models describing both physical and biological processes has been identified as a lever for understanding the retroactions between water dynamics and organic contaminant biodegradation and transport. This will be initiated in the frame of new projects concerning pharmaceuticals potentially present in reused waters (SIMUPORE and related projects).

The recent work on bioavailability of emerging contaminant in organic waste products will be detailed by considering both treatment and application. Their evolution and distribution within organic fractions will be assessed during representative treatment chains including anaerobic digestion and composting for urban and agricultural wastes. Additionally, the interactions with mineral and organic phases during treatments will be considered (N. Sertillanges’s PhD, DIGESTATE project collaboration with CIRAD Recyclage et Risque, LBE and EMMAH, CEREGE). We also plan in collaboration with CIRAD (UR 78 Recyclage et Risques) and the start-up MetRHIZLab to start new activities on the plant uptake of organic molecules by temperate and tropical crops. We will adapt the RHIZOtest Bioassay (Bravin et al.,2010) to organic contaminants and use field data obtained in the SOERE-PRO field experiments to validate the bioassay results. In continuation with recent projects at the landscape level, we wish to continue the collaboration with the soil biologists (Ecotox team) to progress in the exposure of soil organisms (earthworms, carabids) to pesticides. For instance, recent bioaccumulation data obtained in different agricultural landscapes will be analyzed using the TyPol clustering approach to analyze a posteriori the links between lateral atmospheric dispersion, soil persistence and bioaccumulation. This will provide some responses for the “phytopharmacovigilance” program of ANSES. Concerning pesticides and other contaminants, the question of contaminant mixtures in soils will be targeted in order to progress in multi-exposure assessment. Several projects will use TyPol approach with the following objectives : (i) to improve the tool for analyzing the biodegradation of pharmaceuticals (PhD 2018-2021 with INRAE LBE), (ii) to explore the environmental fate and ecotoxicological effects of antitumor drugs analogs (PhD 2018-2021, EDIFIS project), (iii) to help in choosing model tracers to conduct experimentation in volcanic soils in the West Indies context (PHYLODISPO project 2017-2020 in collaboration with INRAE ASTRO), (iv) to support suspect screening approaches looking for pesticide and pharmaceutical transformation products in aquatic ecosystems (JPI INSPECT 2019-2021).

Concerning the assessment of the performances of cropping systems in the reduction of pesticide dispersion, progressing in mechanistic models and bringing new modules (e.g. PASTIS-Mulch, POLDOC, sorption equilibria at the solid-gas interface) on platforms such as V-Soil and OpenFluid (Collab. with INRAE LISAH, EMMAH) remain the best option to fill the gaps we recently evidenced on pesticide fate models. This will contribute to simulate the effects of pluriannual crop successions, intercropping, agroforestry, no till and mulch effect. In the continuation of the MIPP project, this will allow accounting for the diversity of cropping systems at the landscape scale. The effect of climate change on pesticide flows, considering change in cropping systems design and in pesticide use, will also be studied.