Folkert van Oort

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.

Physical speciation of trace metals in Fe–Mn concretions from a rendzic lithosol developed on Sinemurian limestones (France)

Abstract Because of their high content in heavy metals, Fe–Mn concretions present in soils can be a source of release of trace metals in the environment. Metal-rich concretions were isolated from a top horizon of a Rendzic Lithosol developed on limestones in France. The distribution of metallic elements (Cr, Co, Ni, Cu, Zn, Pb) was studied at different scales: field sampling, isolated concretions, and individual particles. Methods of investigation combined bulk chemical analysis, optical microscopy, X-ray diffraction (XRD) and microanalysis using scanning and transmission electron microscopes. The concretions are constituted by concentric rings and contain quartz, feldspars, kaolinite, mica, goethite, and Ti oxide as crystalline phases. A strong heterogeneity in the chemical composition is evidenced at all different scales. The total composition of different populations of Fe–Mn concretions depends on field sampling. Metals are detected at the micrometer and nanometer scales with variable frequencies, occurrences reflecting the abundance of metal-bearing components and the size of metal clusters. Statistical treatments of microanalytical data show marked trends. A strong positive correlation of Mn (and to a lesser extent of Ca) with Ni, Zn, (and to a lesser extent with Co and Cu) indicates trace metals to be associated with poorly crystallized Mn–Ca-rich areas. The correlation of Pb with Fe and P suggests its incorporation in an Fe-rich phosphate component. No correlation of metals with well crystallized silicates, Fe-sesquioxides or sulfate minerals is established. Cr was diffusely distributed.

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.

Effects of heavy metal soil pollution on earthworm communities in the north of France

In the alluvial plain of Scarpe-Escault, in northern France, past emissions from a Zn smelter resulted in a notable Zn, Cd, and Pb-contamination of soils. The aim of this study was to assess the response of earthworm communities to a gradient of metal pollution. In 11 sites located within 4 kilometers of the smelter, according to the dominant wind direction, characteristic soil parameters and total metal contents were determined and 9 earthworm species were collected. The Kmeans clustering method, applied to the first two axes extracted by Principle coordinate analysis on species abundances, allowed to separate the 11 sites into 6 groups depending on their pollution status and the type of vegetation cover (cultivated soils, grasslands, poplar plantations). Significant differences were found between the 6 groups for the total density of earthworms, which varied from 392 ind.m - 2 in unpolluted grassland to 2 ind.m - 2 in the metallophyte grassland, where soil pollution was higher than in the other sites. Intermediate densities were found in unpolluted poplar plantations with 271 ind.m - 2 (but only 57 ind.m - 2 in polluted stands), and 52 ind.m - 2 in unpolluted cultivated soils. Metal pollution also reduced species richness (from 6 to 1 species). Aporrectodea caliginosa and Allolobophora chlorotica appeared to be the most sensitive to heavy metals. A. caliginosa was dominant in unpolluted grassland (about 45 ind.m - 2 ), absent in the most polluted site (35000, 8271 and 190 mg kg - 1 for Zn, Pb, and Cd, respectively), and present in polluted poplar plantation (1112, 616 and 12 mg kg - 1 for Zn, Pb, and Cd, respectively) although at a very low density (less than 1 ind.m - 2 ).

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.

Modeling field-scale vertical movement of zinc and copper in a pig slurry-amended soil in Brazil

Organic amendments often represent a source of trace metals (TMs) in soils, which may partly leach into the groundwater. The objectives of this study were (1) to validate Hydrus-2D for modeling the transport of Zn and Cu in an Alfisol amended with pig slurry (PS) by comparing numerical simulations and experimental field data, and (2) to model the next 50 years of TM movements under scenarios of suspended or continued PS amendments. First, between 2000 and 2008, we collected detailed Zn and Cu data from a soil profile in Santa Maria, Brazil. Two hypotheses about Zn and Cu reactivity with the solid phase were tested, considering physical, hydraulic, and chemical characteristics of six soil layers. Using a two-site sorption model with a sorption kinetic rate adjusted based on laboratory EDTA extractions, Hydrus simulations of the vertical TM transport were found to satisfactorily describe the soil Zn and Cu concentration profiles. Second, the long-term fate of Zn and Cu in the soil was assessed using the validated parameterized model. Numerical simulations showed that Zn and Cu did not present risks for groundwater pollution. However, future Cu accumulation in the surface soil layer would exceed the Brazilian threshold for agricultural soils.

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.

Prospective modeling with Hydrus-2D of 50 years Zn and Pb movements in low and moderately metal-contaminated agricultural soils.

Results of detailed modeling of in situ redistribution of heavy metals in pedological horizons of low and moderately metal contaminated soils, considering distinctly different long-term land use, are scarcely reported in literature. We used Hydrus-2D software parameterized with abundant available local soil data to simulate future Zn and Pb movements in soils contaminated by metallurgical fallout in the 20th century. In recent work on comparing different modeling hypotheses, we validated a two-site reactive model set with adjusted chemical kinetic constant values by fitting the 2005 Zn and Pb concentration profiles in soils, with estimated 1901-1963 airborne Zn and Pb loads (Mallmann et al., 2012a). In the present work, we used the same approach to simulate 2005-2055 changes in Zn and Pb depth-distribution and soil-solution concentrations, comparing two hypotheses of chemical equilibrium: i) the validated two-site model (one site at equilibrium and the other involved in kinetic reactions with pore water) set with adjusted kinetic EDTA extraction constants, and ii) a non-linear one-surface site adsorption equilibrium model. Simulated transfers were found generally lower and more realistic when using the two-site model. Simulations showed that consistent Zn redistribution and loss occurred in the moderately contaminated soil until 2055, i.e., more than one century after the main metal deposition, but negligible in low contaminated soils. Transfer of Pb was small in the three soils and under both hypotheses. In 2055, simulated Zn outflow concentrations remained under threshold values for drinking water.

Improving the relationship between soil characteristics and metal bioavailability by using reactive fractions of soil parameters in calcareous soils

The contribution of the nature instead of the total content of soil parameters relevant to metal bioavailability in lettuce was tested using a series of low-polluted Mediterranean agricultural calcareous soils offering natural gradients in the content and composition of carbonate, organic, and oxide fractions. Two datasets were compared by canonical ordination based on redundancy analysis: total concentrations (TC dataset) of main soil parameters (constituents, phases, or elements) involved in metal retention and bioavailability; and chemically defined reactive fractions of these parameters (RF dataset). The metal bioavailability patterns were satisfactorily explained only when the RF dataset was used, and the results showed that the proportion of crystalline Fe oxides, dissolved organic C, diethylene-triamine-pentaacetic acid (DTPA)-extractable Cu and Zn, and a labile organic pool accounted for 76% of the variance. In addition, 2 multipollution scenarios by metal spiking were tested that showed better relationships with the RF dataset than with the TC dataset (up to 17% more) and new reactive fractions involved. For Mediterranean calcareous soils, the use of reactive pools of soil parameters rather than their total contents improved the relationships between soil constituents and metal bioavailability. Such pool determinations should be systematically included in studies dealing with bioavailability or risk assessment.

Miscanthus bioenergy crop stimulates nutrient-cycler bacteria and fungi in wastewater-contaminated agricultural soil

Abstract Wastewater can be recycled in agricultural soil as fertilizer to increase crop yields. However, adding wastewater induces sometimes ecotoxicological issues such as pollution by toxic compounds, which may lead to the loss of arable land. Bioenergy crops such as Miscanthus × giganteus have been tested to rehabilitate polluted soils, but the impact of Miscanthus on soil microbes is unknown. Here, we evaluated the effects of Miscanthus cropping on bacterial and fungal taxonomic composition in a wastewater-contaminated soil using synchronic and diachronic evaluation strategies. A 3-year field experiment close to Paris was set up on an agricultural site irrigated by raw wastewater for more than one century, thus resulting in strong metal and organic contamination. Soil microbial taxonomic composition was characterized by direct analysis of soil DNA using metagenomic tools such as 454 pyrosequencing of ribosomal genes. Our results demonstrate that Miscanthus cropping stimulates specific populations of bacteria such as Rhizobiales, increased by 1.4 in relative abundance, Nistrospira (x1.5), Azospira (x2), and Gemmatimonas (x2), and fungi: Glomeromycota (x3) and Mortierella (x1.5) for fungi. Noteworthy, these microbial genera are known to be strongly involved in plant symbiosis, organic matter mineralization, and nutrient cycling. Overall our findings show that Miscanthus cropping enhances regeneration of soil microbiological functions and services in polluted soil by stimulating populations beneficial for soil fertility and crop production.