Isabelle Lamy

Structure and affinity towards Cd2+, Cu2+, Pb2+ of synthetic colloidal amorphous aluminosilicates and their precursors

Abstract Amorphous aluminosilicates were synthesised at two different initial reagent concentrations. Depending on the concentration used, the final reaction products were identified as either imogolite or allophane. In millimolar medium (millimolar Al initial concentration and Al/Si=2), imogolite precursors are synthesised during hydrolysis and condensed by heating to build up imogolite tubes. In decimolar medium, precursors with varying local structures are synthesised and condense upon heating to build up allophanes spheroids aggregates. In each medium, silica gel coprecipitated in proportions less than 10% in mass, which seems to have only a weak influence on aluminosilicate synthesis. The zero point of salt effect of suspensions of imogolite, allophane and their respective precursors were determined, and the affinity of these four products towards Cd2+ , Cu2+ and Pb2+ was studied. For imogolite and for both precursors, Cu2+ and Pb2+ adsorption can be described as specific, whereas Cd2+ adsorption is only electrostatic. The three metallic cations display specific adsorption towards allophane suspensions.

Colloidal facilitated transfer of metals in soils under different land use

In order to assess the importance of colloids in the metal transfer in soils under varying land use (a podzol under a forest, a cultivated luvisol and a luvisol under a metallophyte grassland), gravitational waters were collected in situ by zero-tension lysimeters. Dissolved and colloidal fractions of metals were separated by ultracentrifugation and colloids were studied by transmission electron microscopy (TEM) coupled with energy dispersive X-ray analysis (EDS). The stability of metal complexes in the collected solutions was operationally defined by an ion exchange method. The results show that in the two luvisols about 75% of Pb was always present in colloidal forms and a substantial fraction of Pb in solution was present as stable complexes and labile complexes with slow dissociation kinetics. Zn and Cd were found mostly in dissolved forms and mainly as free ions or labile complexes in solution. In the podzol, all metals were found in dissolved forms and as free ions or labile complexes. The Zn-bearing colloids were organic (biocolloids) or mineral (smectites, Fe-oxyhydroxides, Ca- or Al-rich phosphates) depending on soil type and land use. The results are discussed in terms of metal mobility to explain the different vertical metal distributions observed in the soil profiles.

Assessing the fate of antibiotic contaminants in metal contaminated soils four years after cessation of long-term waste water irrigation

Spreading 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 μg kg(-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 organic matter (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.

Functional traits of soil invertebrates as indicators for exposure to soil disturbance.

We tested a trait-based approach to link a soil disturbance to changes in invertebrate communities. Soils and macro-invertebrates were sampled in sandy soils contaminated by long-term wastewater irrigation, adding notably organic matter and trace metals (TM). We hypothesized that functional traits of invertebrates depict ways of exposure and that exposure routes relate to specific TM pools. Geophages and soft-body invertebrates were chosen to inform on exposure by ingestion or contact, respectively. Trait-based indices depicted more accurately effects of pollution than community density and diversity did. Exposure by ingestion had more deleterious effects than by contact. Both types of exposed invertebrates were influenced by TM, but geophages mainly responded to changes in soil organic matter contents. The trait-based approach requires to be applied in various conditions to uncorrelate specific TM impacts from those of other environmental factors.

Is there a relationship between earthworm energy reserves and metal availability after exposure to field-contaminated soils?

Generic biomarkers are needed to assess environmental risks in metal polluted soils. We assessed the strength of the relationship between earthworm energy reserves and metal availability under conditions of cocktail of metals at low doses and large range of soil parameters. Aporrectodea caliginosa was exposed in laboratory to a panel of soils differing in Cd, Pb and Zn total and available (CaCl2 and EDTA-extractable) concentrations, and in soil texture, pH, CEC and organic-C. Glycogen, protein and lipid contents were recorded in exposed worms. Glycogen contents were not linked to the explaining variables considered. Variable selection identified CaCl2 extractable metals concentrations and soil texture as the main factors affecting protein and lipid contents. The results showed opposite effects of Pb and Zn, high inter-individual variability of biomarkers and weak relationships with easily extractable metals. Our results support the lack of genericity of energy reserves in earthworms exposed to field-contaminated soils.

Impact of miscanthus cultivation on trace metal availability in contaminated agricultural soils: complementary insights from kinetic extraction and physical fractionation.

In order to assess the impact of in situ energy crop cultivation on Cu, Pb, Zn and Cd availabilities in an area contaminated by atmospheric fallout, a parcel divided in two parts was sampled: one under perennial miscanthus since three years and the other staying under annual crops used as reference. Metal availability parameters determined using EDTA extractions at equilibrium and kinetic extractions were related to metal localization in size fractions after physical fractionation. Extraction at equilibrium as well as kinetically defined labile pools highlighted significantly lower Cu and Pb availabilities in the soil under miscanthus compared to the annual crop reference while physical fractionations highlighted an increased localization of these metals in the fine size fractions. For Zn and Cd, changes in metal availability were highlighted only through the kinetic parameters of extraction rate constants while localization in size fractions changed for Cd only. Indeed for these metals extraction at equilibrium and kinetically defined labile and slowly labile pools failed to show some changes. Organic carbon percentage was significantly higher in the 20-50μm and 200-2000μm fractions for the miscanthus sample underlying the importance of no-tillage and organic carbon inputs. Pearson correlations among metal availability parameters and metal and organic carbon localizations were used to identify the more important fractions involved in the metal availability. Results revealed that available metal pools were related to metal localization in the finer soil fractions (<50μm) and to the organic carbon localization in the 20-50μm and 200-2000μm fractions.

Using a two site-reactive model for simulating one century changes of Zn and Pb concentration profiles in soils affected by metallurgical fallout.

Predicting the transfer of contaminants in soils is often hampered by lacking validation of mathematical models. Here, we applied Hydrus-2D software to three agricultural soils for simulating the 1900-2005 changes of zinc and lead concentration profiles derived from industrial atmospheric deposition, to validate the tested models with plausible assumptions on past metal inputs to reach the 2005 situation. The models were set with data from previous studies on the geochemical background, estimated temporal metal deposition, and the 2005 metal distributions. Different hypotheses of chemical reactions of metals with the soil solution were examined: 100% equilibrium or partial equilibrium, parameterized following kinetic chemical extractions. Finally, a two-site model with kinetic constant values adjusted at 1% of EDTA extraction parameters satisfactory predicted changes in metal concentration profiles for two arable soils. For a grassland soil however, this model showed limited applicability by ignoring the role of earthworm activity in metal incorporation.

Subcellular partitioning of metals in Aporrectodea caliginosa along a gradient of metal exposure in 31 field-contaminated soils.

Subcellular fractionation of metals in organisms was proposed as a better way to characterize metal bioaccumulation. Here we report the impact of a laboratory exposure to a wide range of field-metal contaminated soils on the subcellular partitioning of metals in the earthworm Aporrectodea caliginosa. Soils moderately contaminated were chosen to create a gradient of soil metal availability; covering ranges of both soil metal contents and of several soil parameters. Following exposure, Cd, Pb and Zn concentrations were determined both in total earthworm body and in three subcellular compartments: cytosolic, granular and debris fractions. Three distinct proxies of soil metal availability were investigated: CaCl2-extractable content dissolved content predicted by a semi-mechanistic model and free ion concentration predicted by a geochemical speciation model. Subcellular partitionings of Cd and Pb were modified along the gradient of metal exposure, while stable Zn partitioning reflected regulation processes. Cd subcellular distribution responded more strongly to increasing soil Cd concentration than the total internal content, when Pb subcellular distribution and total internal content were similarly affected. Free ion concentrations were better descriptors of Cd and Pb subcellular distribution than CaCl2 extractable and dissolved metal concentrations. However, free ion concentrations and soil total metal contents were equivalent descriptors of the subcellular partitioning of Cd and Pb because they were highly correlated. Considering lowly contaminated soils, our results raise the question of the added value of three proxies of metal availability compared to soil total metal content in the assessment of metal bioavailability to earthworm.

Favouring the bioavailability of Zn and Cu to enhance the production of lignin-modifying enzymes in Trametes versicolor cultures.

Metal effect on the enzyme secretion in fungi is usually related to total concentrations but not to bioavailable metal species. In this work, we aimed at enhancing the secretion of lignin-modifying oxidoreductases in Trametes versicolor by favouring the bioavailability of essential metals. For this purpose, the fungus was exposed to Cu or Zn in liquid culture media exhibiting different complexation levels. Metal speciation was determined experimentally or theoretically to quantify free metal species, supposed to be the most bioavailable, and species complexed to ligands. Although Zn(2+) contents were high in media, Zn had no effect on the oxidoreductase production. Conversely, Cu highly induced the manganese peroxidase and laccase productions until 40 and 310 times when compared to unexposed controls. This inductive potential was highly correlated to Cu(2+) contents in media. Furthermore, in poorly complexing media, the response threshold of oxidoreductases to Cu greatly decreased and an unexpected production of lignin peroxidase occurred.

Nature des sols et nature des colloı̈des circulant dans les eaux gravitaires : une étude in situ

Abstract Natural colloids circulating in gravitational waters collected in situ from various types of soil were studied. Their morphology and their nature were determined by analytical electron microscopy. Mobile colloids were found to be different according to the soil type (podzol, luvisol) and land use (forest soil, agricultural soil and soil under metallophyte grassland). In the podzol, the results showed a dominant organic colloidal phase, in association with Fe and Al and for the luvisols, a majority of colloidal associations of phyllosilicates–Fe. Results are discussed regarding to soil functioning.