Cécile Quantin

Mn-oxide: a major source of easily mobilisable Co and Ni under reducing conditions in New Caledonia Ferralsols

Chemical and bacterial reduction and dissolution of Fe and Mn-oxide and the concomitant solubilisation of Co and Ni were studied in a surface horizon of a New-Caledonia Ferralsol. Chemical extractions showed that Mn and Co were in a large part associated in Mn-oxides. The main part of Ni was associated with goethite, but a very small fraction was also associated with Mn-oxides. Anaerobic reducing bacterial activity was responsible for Fe solubilisation at a smaller extent than for Mn solubilisation and consequently for associated metal release. Submicroscopic investigations revealed the presence of a Mn-oxide containing Co, Ni and Al, close to a lithiophorite–asbolane mixed-layers Mn-oxide, which can be considered as a main source of easily available metals in this soil. To cite this article: C. Quantin et al., C. R. Geoscience 334 (2002) 273–278.

Remanence of lead pollution in an urban river system: a multi-scale temporal and spatial study in the Seine River basin, France

Total lead (Pb) concentration and Pb isotopic ratio (206Pb/207Pb) were determined in 140 samples from the Seine River basin (France), covering a period of time from 1945 to 2011 and including bed sediments (bulk and size fractionated samples), suspended particulate matter (SPM), sediment cores, and combined sewer overflow (CSO) particulate matter to constrain the spatial and temporal variability of the lead sources at the scale of the contaminated Seine River basin. A focus on the Orge River subcatchment, which exhibits a contrasted land-use pattern, allows documenting the relation between hydrodynamics, urbanization, and contamination sources. The study reveals that the Pb contamination due to leaded gasoline that peaked in the 1980s has a very limited impact in the river nowadays. In the upstream Seine River, the isotopic ratio analysis suggests a pervasive contamination which origin (coal combustion and/or gasoline lead) should be clarified. The current SPM contamination trend follows the urbanization/industrialization spatial trend. Downstream of Paris, the lead from historical use originating from the Rio Tinto mine, Spain (206Pb/207Pbu2009=u20091.1634u2009±u20090.0001) is the major Pb source. The analysis of the bed sediments (bulk and grain size fractionated) highlights the diversity of the anthropogenic lead sources in relation with the diversity of the human activities that occurred in this basin over the years. The “urban” source, defined by waste waters including the CSO samples (206Pb/207Pbu2009=u20091.157u2009±u20090.003), results of a thorough mixing of leaded gasoline with “historical” lead over the years. Finally, a contamination mixing scheme related to hydrodynamics is proposed.

Can chromite weathering be a source of Cr in soils

Abstract At Niquelândia, Cr extracted from the soil (5,000-9,300 mg.kg−1) is likely the result of the Cr-bearing Fe-oxides compared to the Cr-spinels, showing that low Cr-containing minerals present in the dunite (enstatite, olivine and clay minerals) have been completely dissolved. The chromites, accumulated inside soil profiles, have undergone chemical weathering, leading to a Cr enrichment during soil genesis. Traces of dissolution inside the soil chromites suggest that they can be slowly weathered. In this case chromites could represent a diffuse source of available Cr(III) within the soil profiles.

Zinc Speciation in the Suspended Particulate Matter of an Urban River (Orge, France): Influence of Seasonality and Urbanization Gradient

Among trace metal pollutants, zinc is the major one in the rivers from the Paris urban area, such as the Orge River, where Zn concentration in the suspended particulate matter (SPM) can reach 2000 mg/kg in the most urbanized areas. In order to better understand Zn cycling in such urban rivers, we have determined Zn speciation in SPM as a function of both the seasonal water flow variations and the urbanization gradient along the Orge River. Using TEM/SEM-EDX and linear combination fitting (LCF) of EXAFS data at the Zn K-edge, we show that Zn mainly occurs as tetrahedrally coordinated Zn(2+) sorbed to ferrihydrite (37-46%), calcite (0-37%), amorphous SiO2 (0-21%), and organic-P (0-30%) and as octahedrally coordinated Zn(2+) in the octahedral layer of phyllosilicates (18-25%). Moreover, the Zn speciation pattern depends on the river flow rate. At low water flow, Zn speciation changes along the urbanization gradient: geogenic forms of Zn inherited from soil erosion decrease relative to Zn bound to organic-phosphates and amorphous SiO2. At high water flow, Zn speciation is dominated by soil-borne forms of Zn regardless the degree of urbanization, indicating that erosion of Zn-bearing minerals dominates the Zn contribution to SPM under such conditions.

Acidity control in Latosols under long-term pastures in the Cerrado region, Brazil

High acidity and aluminium saturation are among the main limiting factors for crop production in tropical soils. The aim of this work was to measure the acidity of Latosols under pastures in the Brazilian Cerrado and to assess the influence of clay mineralogy as a controlling parameter of soil acidity. Topsoils (n=73, 0-0.2m depth) of Latosols developed on different parent materials were sampled in two sub-regions of the Cerrado region. The main chemical characteristics weredetermined by standardprocedures,andkaolinite andgibbsite contentswere determinedby dissolution with sulfuric acid and thermogravimetric analyses. The exchangeable concentrations of calcium (Ca), magnesium (Mg), and potassium (K) varied considerably among soil samples, with ranges of 0-13.9cmolckg -1 (meanstandard deviation 1.77 � 1.91cmolckg -1 ) for Ca; 0.2-3.2cmolckg -1 (1.13 � 0.68cmolckg -1 ) for Mg; and 0-1.0cmolckg -1 (0.24 � 0.24cmolckg -1 ) for K. The mean concentration of exchangeable aluminium (Al) was 0.55 � 0.61cmolckg -1 (range 0-2.3cmolckg -1 ). The content of kaolinite (282 � 96gkg -1 ) was higher than of gibbsite (106 � 77gkg -1 ). The amount of exchangeable Al and Al saturation rate varied according to the mineralogy of the clay fraction of the soils. The contentofexchangeableAl 3+ remainedlowwhengibbsitewasthepredominantmineral,whereasitincreasedwithkaolinite content. The ratio kaolinite/(kaolinite+gibbsite) could be used as a useful indicator of the sensitivity of soils affected by acidity and Al toxicity. Additional keywords: Brazilian Cerrado soils, gibbsite, kaolinite, protonation, soil acidification.