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