International audience | Stabilization of soil contaminated with trace elements is a remediation practice that does not reduce the total content of contaminants, but lowers the amounts of mobile and bioavailable fractions. This study evaluated the efficiency of Fe0 to reduce the mobility and bioavailability of Cr, Cu, As and Zn in a chromated copper arsenate (CCA)-contaminated soil using chemical, biochemical and biotoxicity tests. Contaminated soil was stabilized with 1% iron grit. This treatment decreased As and Cr concentrations in leachates (by 98% and 45%, respectively), in soil pore water (by 99% and 94%, respectively) and in plant shoots (by 84% and 95%, respectively). The stabilization technique also restored most of analyzed soil enzyme activities and reduced microbial toxicity, as evaluated by the BioTox™ test. After stabilization, exchangeable and bioaccessible fractions of Cu remained high, causing some residual toxicity in the treated soil

International audience | Urban atmospheres contain complex mixtures of air pollutants including mutagenic and carcinogenic substances such as benzene, diesel soot, heavy metals and polycyclic aromatic hydrocarbons. In the frame of a European network for the assessment of air quality by the use of bioindicator plants, the Tradescantia micronucleus (Trad-MCN) test was applied to examine the genotoxicity of urban air pollution. Cuttings of Tradescantia clone #4430 were exposed to ambient air at 65 monitoring sites in 10 conurbations employing a standardised methodology. The tests revealed an elevated genotoxic potential mainly at those urban sites which were exposed to severe car traffic emissions. This bioassay proved to be a suitable tool to detect local ‘hot spots’ of mutagenic air pollution in urban areas. For its use in routine monitoring programmes, however, further standardisation of cultivation and exposure techniques is recommended in order to reduce the variability of results due to varying environmental conditions.

8 pages | International audience | Microbial transformations of nitrification and denitrification are the main sources of nitrous oxide (N2O) from soils. Relative contributions of both processes to N2O emissions were estimated on an agricultural soil using 15N isotope tracers (15NH4+ or 15NO3-), for a 10-day batch experiment. Under unsaturated and saturated conditions, both processes were significantly involved in N2O production. Under unsaturated conditions, 60% of N-N2O came from nitrification, while denitrification contributed around 85-90% under saturated conditions. Estimated nitrification rates were not significantly different whatever the soil moisture content, whereas the proportion of nitrified N emitted as N2O changed from 0.13 to 2.32%. In coherence with previous studies, we interpreted this high value as resulting from the decrease in O2 availability through the increase in soil moisture content. It thus appears that, under limiting aeration conditions, some values for N2O emissions through nitrification could be underestimated.

International audience | In order to determine the mechanisms of the retention of 60Co, 85Sr and 134Cs in natural silica sand columns, desorption experiments were performed by changes of pH and ionic strength and by injection of natural organic matter (NOM). Injection of KCl (0.1 M) resulted in a high release of 60Co (60-100%) and 85Sr (72-100%) but a smaller release of 134Cs (31-66%). Only limited release of 60Co (66%) and 85Sr (71%) and no release of 134Cs were observed by injection of NOM. The different percentages of desorption were related to the chemical characteristics of the organic colloids previously retained in columns before the desorption step. The results evidenced different sorption processes on energetically heterogeneous surface sites. According to the initial conditions, the binding of the radionuclides to the solid phase resulted from weak and easily reversible sorption processes to strong association probably by inner sphere complexes. The rather weak release of 134Cs by KCl was attributed to the strong retention of 134Cs by clay coatings on the natural silica sand surfaces. © 2005 Elsevier Ltd. All rights reserved.

Physicochemical and biological characterisation of different dredged sediment deposit sites in France

International audience | In the context of biosolids utilisation in forestry, effects of sludge application on mushroom metal concentration were studied in six sites of maritime pine forests in the South-West of France. Municipal sludge were applied at a rate of 6 T dry matter per hectare. Edible mushrooms were collected two years after sludge application. As, Cd, Cu, Hg, Pb, Se and Zn concentrations were determined. Results showed a high variability for trace element concentrations in mushrooms collected from control areas. No significant correlation was found between soil parameters (pH and trace elements concentrations) and mushroom trace element concentrations. Even if the concentration of trace metals increased in the soils, sludge application did not affect As, Cu, Se and Zn concentrations in carpophores but slightly increased Cd, Pb and Hg concentrations on some sites. This effect is dependent on sludge type and sites

International audience | A lysimeter approach (under natural climatologic conditions) was used to evaluate the effect of four metal immobilizing soil treatments [compost (C), compost + cyclonic ashes (C + CA), compost + cyclonic ashes + steel shots (C + CA + SS)) and cyclonic ashes + steel shots (CA + SS)] on metal leaching through an industrially contaminated soil. All treatments decreased Zn and Cd leaching. Strongest reductions occurred after CA + SS and C + CA + SS treatments (Zn: -99.0% and -99.2% respectively; Cd: -97.2% and -98.3% respectively). Copper and Pb leaching increased after C (17 and > 30 times for Cu and Pb respectively) and C + CA treatment (4.4 and > 3.7 times for Cu and Pb respectively). C + CA + SS or CA + SS addition did not increase Cu leaching; the effect on Pb leaching was not completely clear. Our results demonstrate that attention should be paid to Cu and Pb leaching when organic matter additions are considered for phytostabilization of metal contaminated soils

International audience | Some drinking water reservoirs under the vineyards of Burgundy are contaminated with herbicides. Thus the effectiveness of alternative soil management practices, such as grass cover, for reducing the leaching of glyphosate and its metabolite, AMPA, through soils was studied. The leaching of both molecules was studied in structured soil columns under outdoor conditions for 1 year. The soil was managed under two vineyard soil practices: a chemically treated bare calcosol, and a vegetated calcosol. After 680 mm of rainfall, the vegetated calcosol leachates contained lower amounts of glyphosate and AMPA (0.02% and 0.03%, respectively) than the bare calcosol leachates (0.06% and 0.15%, respectively). No glyphosate and only low amounts of AMPA (<0.01%) were extracted from the soil. Glyphosate, and to a greater extent, AMPA, leach through the soils; thus, both molecules may be potential contaminants of groundwater. However, the alternative soil management practice of grass cover could reduce groundwater contamination by the pesticide.Glyphosate and AMPA leached in greater amounts through a chemically treated bare calcosol than through a vegetated calcosol.Glyphosate and AMPA leached in greater amounts through a chemically treated bare calcosol than through a vegetated calcosol.

International audience | The herbicide diuron is frequently applied to vineyard soils in Burgundy, along with repeated treatments with Bordeaux mixture (a blend of copper sulfate and calcium hydroxide) that result in elevated copper concentrations. Cu could in principle affect the fate and transport of diuron or its metabolites in the soil either directly by complexation or indirectly by altering the populations or activity of microbes involved in their degradation. To assess the effect of high Cu concentrations on diuron transport, an experiment was designed with ten undisturbed columns of calcareous and acidic soils contaminated with 17–509 mg kg−1 total Cu (field-applied). Grass was planted on three columns. Diuron was applied to the soils in early May and in-ground lysimeters were exposed to outdoor conditions until November. Less than 1.2% of the diuron applied was found in the leachates as diuron or its metabolites. Higher concentrations were found in the effluents from the grass-covered columns (0.1–0.45%) than from the bare-soil columns (0.02–0.14%), and they were correlated with increases in dissolved organic carbon. The highest amounts of herbicide were measured in acidic-soil column leachates (0.98–1.14%) due to the low clay and organic matter contents of these soils. Cu also leached more readily through the acidic soils (32.8–1042 μg) than in the calcareous soils (9.5–63.4 μg). Unlike in the leachates, the amount of diuron remaining in the soils at the end of the experiment was weakly related to the Cu concentrations in the soils. Cu accumulation, from Bordeaux mixture, in vineyard soils may be affecting microbial activity and thus slightly increasing the persistence of diuron in the soils. Cu accumulation, from Bordeaux mixture, in vineyard soils may be affecting microbial activity and thus slightly increasing the persistence of diuron in the soils.

36 ref. doi: 10.1016/j.envpol.2004.07.031 | International audience | In order to better understand the fate of metals during the biodegradation of organic matter in soils, an in vitro incubation experiment was conducted with metal-rich and metal-free leaves of Arabidopsis halleri introduced in a non-contaminated soil. During incubation of these microcosms, we followed the partitioning of Zn and Cd between the solution and their solid components, by determining the metal contents of six soil fractions and dissolved metals after granulo-densimetric separations at selected times. Microbial biomass and exchangeable metals in K2SO4 solutions were also determined at the same times, and two main stages were identified. The first one takes place after a fast abiotic transfer of Zn and Cd from readily soluble plant tissues onto fine soil constituents, keeping metals away from the liquid phase: during about 14 days, microbial biomass increased as well as metal contents of some soil fractions, particularly those rich in particulate organic matter. During the second stage, between 14 and 60 days and for the metal-rich microcosms, Zn and Cd contents in solution increased, while microbial biomass decreased instead of staying constant as in control. A change of Zn and Cd speciation is assumed, from non-toxic adsorbed forms to more toxic species in solution. Remaining metal-rich plant residues seem to create a stable organic C compartment in the soil.