Periglacial morphogenesis in the Paris Basin: insight from geophysical survey and consequences for the fate of soil pollution.

International audienceGeophysical survey by of the Pierrelaye-Bessancourt area revealed conductive polygon patterns of 20-30 m diameter detected between 0.5 and 1.7 m depth. The patterns are formed by greenish glauconite and carbonated sand hollows where clay-rich pedological horizons bend downward, forming narrow tongs extending up to 2-3 m depth. Such structures were interpreted as a buried polygonal ice-wedge network. Geometrical relationships between the lithological units allowed the identification of successive landscape events and a landscape chronology. The sequence started during the Saalian glaciation with (1) development of patterned grounds by thermokarstic cryoturbation; (2) consecutive deflation/erosion during post-permafrost aridity; (3) loess and eolian sand deposits; (4) weathering of the former deposits with development of pedogenic horizons during the Eemian interglacial; (5) recurrent cryoturbation and thermal cracking leading to infolding of the pedogenic horizons during the Pleniglacial optimum (Weichselian); (5) finally erosion that levelled the periglacial microreliefs, leading to the modern landscape. In this agricultural area, urban waste water has been spread and has led to high levels of metal pollution in the surface horizons of the soils. The polygonal cryogenic structures have major impacts on soil hydrology and dispersion/distribution of heavy metals toward the geological substrate

Etude d'évaluation du risque de mobilité des métaux dans l'agrosystème contaminé de Pierrelaye-Bessancourt : prospections du site, fonctionnement des sols et tests de lixiviation.

Ce sont les mécanismes de fixation et de libération des métaux dans ces sols pollués qui ont été approchés. Dans ce sens, l'étude se veut un outil d'aide à la décision pour les aménagements futurs du territoire. 1- Les de structures polygonales reconnues par géophysique conditionnent les modes et lieux d'infiltration des eaux. 2- L'irrigation a conduit à la déstabilisation des argiles des sols qui de ce fait ne jouent plus le rôle de rétention. Toutes les phases porteuses de métaux sont plus ou moins directement liées aux anciennes conditions d'hydromorphie (irrigation). L'arrêt de l'irrigation va déstabiliser progressivement ces complexes porteurs et libérer métaux retenus. 3- Des antibiotiques ont été mis en évidence dans les sols. Ils sont susceptibles d'agir sur les microorganismes des sols, et de ce fait présenter des risques environnementaux. 4- Les tests de lixiviation (lessivage/mobilisation) montrent la sensibilité des métaux à l'acidification du milieu et à l'oxydation de la matière organique. En raison de l'arrêt de l'irrigation il y aura accélération de la migration des métaux. 5- Les options de réaménagement sont discutées sous le regard sols/paysages : (1) en cas de boisement, l'acidification entraînera leur évacuation ; (2) les sols en place génèrent des poussières (dispersion dans l'environnement et inhalation humaine) ; (3) La dispersion incontrôlée des terres lors de terrassements est certainement un risque majeur

Assessing antibiotic contamination in metal contaminated soils four years after cessation of long-term waste water irrigation.

International audienceSpreading of urban wastewater on agricultural land may lead to concomitant input of organic and inorganic pollutants. Such multiple pollution sites offer unique opportunities to study the fate of both heavy metals and pharmaceuticals. We examined the occurrence and fate of selected antibiotics in sandy-textured soils, sampled four years after cessation of 100 years irrigation with urban wastewater from the Paris agglomeration. Previous studies on heavy metal contamination of these soils guided our sampling strategy. Six antibiotics were studied, including quinolones, with a strong affinity for organic and mineral soil components, and sulfonamides, a group of more mobile molecules. Bulk samples were collected from surface horizons in different irrigation fields, but also in subsurface horizons in two selected profiles. In surface horizons, three quinolones (oxolinic acid, nalidixic acid, and flumequine) were present in eight samples out of nine. Their contents varied spatially, but were well-correlated one to another. Their distributions showed great similarities regarding spatial distribution of total organic carbon and heavy metal contents, consistent with a common origin by wastewater irrigation. Highest concentrations were observed for sampling sites close to irrigation water outlets, reaching 22 μgkg−1 for nalidixic acid.Within soil profiles, the two antibiotic groups demonstrated an opposite behavior: quinolones, found only in surface horizons; sulfamethoxazole, detected in clay-rich subsurface horizons, concomitant with Zn accumulation. Such distribution patterns are consistent with chemical adsorption properties of the two antibiotic groups: immobilization of quinolones in the surface horizons ascribed to strong affinity for organicmatter (OM),migration of sulfamethoxazole due to a lower affinity for OM and its interception and retention in electronegative charged clay-rich horizons. Our work suggests that antibiotics may represent a durable contamination of soils, and risks for groundwater contamination, depending on the physicochemical characteristics both of the organic molecules and of soil constituents