Mercury speciation in soils of the industrialised Thur River catchment (Alsace, France)

Methylmercury (MeHg) and total Hg (THg) concentrations in soil profiles were monitored in the Thur River basin (Alsace, France), where a chlor-alkali plant has been located in the city of Vieux-Thann since the 1930s. Three soil types were studied according to their characteristics and location in the catchment: industrial soil, grassland soil and alluvial soil. Contamination of MeHg and THg in soil was important in the vicinity of the plant, especially in industrial and alluvial soil. Concentrations of MeHg reached 27 ng g1 and 29,000 ng g1 for THg, exceeding the predictable no effect concentration. Significant ecotoxicological risk exists in this area and remedial actions on several soil types are suggested. In each type of soil, MeHg concentrations were highest in topsoil, which decreased with depth. Concentrations of MeHg were negatively correlated with soil organic matter and total S, particularly when MeHg concentrations exceeded 8 ng g1. Under these conditions, MeHg concentrations in soil seemed to be influenced by THg, soil organic matter and total S concentrations. It was found that high MeHg/THg ratios (near 2%) in soil were mainly related to the combined soil environmental conditions such as low THg concentrations, low organic C/N ratios (<11) and relatively low pH (5–5.5). Nevertheless, even when the MeHg/THg ratio was low (0.04%), MeHg and THg concentrations were elevated, up to 13 ng g1 and to 29,000 ng g1, respectively. Thus, both THg and MeHg concentrations should be taken into account to assess potential environmental risks of Hg

Total mercury concentrations in an industrialized catchment, the Thur River basin (north-eastern France): geochemical background level and contamination factors

River bottom sediments and soils were collected from the industrialized Thur River basin (north-eastern France) to assess mercury contamination. The regional geochemical background level of total mercury was evaluated to calculate mercury contamination factors (Fc) in soils and river bottom sediments. Our estimate of the mean background mercury levels in river sediments and soils, not affected by human activities, was 232 ng g1 (range: 27–406 ng g1). Sediments contaminated by the effluent from a chlor-alkali plant yielded the highest contamination factors (Fc¼1784). Contamination factors of surficial soils within 1 km of the industrial site range from 6.3 to 43.6. This contamination is attributed to diffuse atmospheric deposition from this local plant. However, even upstream from this industrial area elevated contamination factors were recorded for river bottom sediments (Fc¼3.2 to 26.4) and for one alluvial soil profile (Fc¼10). This is possibly due to past pollution resulting from waste water discharges. Mercury contamination in the different horizons of alluvial soils is not correlated with soil organic carbon content, but may be the result of occasional accidental pollution arising from the introduction of contaminated suspended particulate matter by the Thur River during periods of flooding

Modeling of liming in acid agricultural soils of Libreville (Gabon)

Soil acidification is an ongoing natural process which can be enhanced by human activities or can be controlled by appropriate soil management practices. Two highly acidified urban garden soils, CHA and NTO, were subjected to single-extraction procedure by water to determine the extractable concentrations of Ca, Mg, K, Na, Al, Cu, Fe, Mn, Pb, Zn and . A modeling of effects of liming on soil solution was carried out from initial pH to pH 8.0 using the PHREEQC-2 code coupled with the PHREEQC.dat thermodynamic database. In NTO soil solution, liming increased the concentration of all cations, exception of Al when in CHA soil solution concentration of Ca, Cu, Fe and Pb increased. The chemical speciation of cations was evaluated in the soil solution. Basic cations Ca, Mg, K and Na were found as free forms (Ca2+, Mg2+, K+, Na+) and sometimes complexed by sulfate (,). The concentration of the toxic free ion Al3+ decreased quickly and was replaced by less toxic hydroxide complexes. For the other metals, relative to the total soluble metal concentrations the amounts of free Cu2+ (1%-99%) and Zn2+ (74%-97%) were not different in soil solutions when the amounts of free Pb2+ (10%-93%) and Fe2+ (65%-98%) in NTO soil solution were generally higher than those of CHA soil solution (8%-34% and 43%-84%, respectively). Statistical correlation analysis used to predict the change occurred in the concentration of the free ion in the soil studied showed significant influence of pH,  and  on Al3+, Fe2+, Pb2+ and Zn2+. Key-words: tropical acid soils, urban garden, liming, modeling, PHREEQC-

Evaluation of a potential candidate for heavy metal phytostabilization in polluted sites of the Mediterranean littoral (SE Marseille): endomycorrhizal status, fitness biomarkers and metal content of Atriplex halimus spontaneous populations

This study showed that Atriplex halimus forms endomycorrhizae on heavy metal polluted-soils. But no variation of chlorophylls content in leaves was observed. Only low concentrations of heavy metals were found in leaves compared with the high levels of pollutants in the soil. A. halimus appears as a good candidate for phytostabilization of heavy metals in brackish soils

Effets potentiels des contaminants sur l’environnement continental : différentes échelles et leviers de la recherche scientifique pour les réduire

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Vulnérabilité des sols maraîchers du Gabon (région de Libreville) (acidification et mobilité des éléments métalliques)

L urbanisation est en forte croissance dans le monde, surtout en Afrique. Nourrir cette population urbaine nécessite de doubler la production agricole d ici 2030. Une des solutions semble être l agriculture urbaine. Le Gabon, comme d autres pays d Afrique, connait un essor de l agriculture urbaine, en particulier à Libreville. Mais aucune étude concrète de l impact dans le pays de l agriculture en milieu urbain sur les propriétés bio-physico-chimiques, et le comportement des métaux dans les sols n a encore été réalisée. Dans ce contexte, l objectif de ce travail était d étudier l impact des cultures maraîchères urbaines sur les propriétés des sols, ainsi que la présence de certains métaux dans les sols et les plantes cultivées. Le maraîchage urbain est pratiqué sous abri ou en plein air et souffre encore de maux qui freinent son développement (niveau d études des maraîchers, précarité du foncier, accès limité aux fertilisants, à l eau d irrigation ). Les sols de Libreville sont sablo-limoneux ou argilo-sablo-limoneux. La teneur des métaux est en général faible et les risques de contamination dans la chaîne alimentaire limités. Les sols cultivés depuis moins de 10 ans et les sols sous abri ne subissent pas un impact significatif vis-à-vis des sols non cultivés. En outre, les sols cultivés en plein air depuis au moins 10 ans sont acidifiés et leurs paramètres de fertilité et la teneur des métaux diminuent significativement. Le pH est bien corrélé à la spéciation chimique des métaux et il y a une bonne mobilité de Mn, Pb et Zn dans les sols. La teneur en métaux dans les légumes cultivés à Libreville était inférieure aux limites autorisées par la FAO. L amarante et l oseille accumulent bien les métaux, en particulier dans les feuilles qui sont consommées. La simulation du chaulage des sols cultivés en plein air depuis au moins 10 ans à l aide du logiciel PHREEQC, montre qu une stabilisation du pH à 6-7 améliorerait la fertilité des sols. Des expériences in situ et au laboratoire sont nécessaires pour confirmer ces résultats et tester d autres apports minéraux et/ou organiques.Urbanization is growing rapidly worldwide, especially in Africa. Feed this urban population requires to double agricultural production before 2030. One of solution seems to be urban agriculture. Gabon, like other African countries, is experiencing a boom of urban agriculture, particularly in Libreville. But no concrete study of the impact of urban agriculture on the bio-physico-chemical properties and behavior of metals in soils has yet been carried out in the country. In this context, the objective of this work was to study the impact of urban gardening on soil properties, and the presence of metals in soils and crops.The urban gardening is practiced under cover or in open air and some factors hinder its development (instruction level of gardeners, land insecurity, fertilizers, limited access to water ...). Soils in Libreville are sandy-loam or clay-sandy-loam. The content of metals is generally low and the risk of contamination in the food is limited. Soils cultivated for less than 10 years and soils cultivated under cover do not undergo a significant impact of agricultural practices. In contrast, soils cultivated in open air for at least 10 years are acidified, their fertility parameters and metal content decreasing significantly. The pH is correlated with the chemical speciation of metals and there is a good mobility of Mn, Pb and Zn in soils. Metal content in vegetables grown in Libreville was below the limits allowed by the FAO. Amaranth and sorrel accumulated many metals, especially in the leaves that are consumed parts. The simulation of the liming of agricultural soils cultivated in open air for at least 10 years with the PHREEQC software shows that stabilization to pH 6-7 would improve soils fertility. Some experiments in situ and in laboratory are needed to confirm these results and other mineral and/or organics inputs tests.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Évaluation du risque sanitaire de sols pollués méditerranéens : choix de variables et spatialisation

The concept of health risk needs to be compared with the notions of hazard, vulnerability, capacity and danger so as to consider it in an integrative way and choose appropriate variables for its spatialization. In this multidisciplinary reflection, we particularly questioned "how to integrate the physical sensitivity of the population when considering soil pollution in order to locate the most vulnerable areas in a context of health risk ? ". The Marseilleveyre massif located south of Marseille (Bouches-du-Rhône) is adequate object of study for both semantic and spatial enforcements. Highly contrasted in its issues, this territory is at the same time included in the core area of the Calanques National Park (PNCal) and remains affected by a diffuse soil pollution resulting from past industrial activities located on the coast. This core area of the PNCal is however inhabited in its periphery and welcomes many users. A model of generalization of the methodology developed in this case study is then proposed in order to perform this production and this mode of visualization of the information which could constitute a precious base of aid to the consultation

Évaluation du risque sanitaire de sols pollués méditerranéens : choix de variables et spatialisation

International audienc

Évaluation du risque sanitaire de sols pollués méditerranéens : choix de variables et spatialisation

International audienc

Does phosphate enhance the natural attenuation of crude oil in groundwater under defined redox conditions?

8th International-Association-of-Hydrological-Sciences Groundwater Quality Conference (GQ), Univ Florida, Gainesville, FL, APR, 2013International audienceAfter a crude oil spill caused by a broken pipeline in 2009 to a gravel aquifer in southern France, degradation processes under various redox conditions progressively established, but at rates that predict a long life-time of the source under natural attenuation after partial source removal. In this study, we aimed at identifying the rate-limiting factors for each redox condition, with special emphasis on phosphate as limiting nutrient. The study was conducted in laboratory microcosms assembled with material collected on site: sediments, water from monitoring wells, oil and microbial sludge. Redox conditions were promoted by adding electron acceptors (either oxygen, nitrate, limonite (FeO(OH)), cryptomelane (K(Mn4+, Mn2+)(8)O-16), or sulfate). For each condition, the role of phosphate was studied by repeated additions for up to 290 days. The results showed a very strong stimulation of aerobic and denitrifying rates of oil degradation by phosphate, provided that oxygen and nitrate were repeatedly supplied. Phosphate caused also a marked stimulation of methanogenic degradation, and a relatively small stimulation of metal reduction. These anaerobic processes started only after marked lag phases, and phosphate shortened the lag phase for methanogenic degradation. Degradation of aromatic and aliphatic hydrocarbons with less than 8 carbons, including benzene, was confirmed even under unstimulated conditions. It is concluded that degradation rates at the site are limited by both, availability of electron acceptors and availability of phosphate needed for promoting microbial growth. (C) 2014 Elsevier B.V. All rights reserved