Toxicity of cadmium to soil microbial activity: effect of sewage sludge addition to soil on the ecological dose

10 pages, 4 figures, 4 tables.Cadmium has a toxic effect on soil microbial activity which plays an important role in nutrient cycling and, therefore, in maintaining soil fertility. In addition, the mobility of this heavy metal in soil is affected by the addition of urban wastes such as sewage sludge. This study was conducted to determine the effect of sewage sludge amendment of a semiarid soil, previously polluted with Cd, on the toxic effect of this heavy metal on soil microbial biomass and its activity. Dehydrogenase activity, ATP content, microbial soil respiration and microbial biomass carbon were used as bioindicators of the toxic effect of Cd. The inhibition of microbial activity and biomass by different Cd concentrations ranging from 0 to 8000 mg Cd kg−1 soil was described by three mathematical models in order to calculate three ecological doses of Cd: ED50, ED10, and ED5. In general, higher ED values were calculated for the sewage sludge amended soil than for unamended soil. Thus the Cd toxicity to microbial activity of the sewage sludge amended soil can be considered lower than that of the unamended soil. Moreover, increased ED values with time after soil Cd contamination were observed.Peer reviewe

Le magmatisme basique hercynien et post-hercynien du Système central espagnol: essai de caractérisation des sources mantelliques

Les manifestations du magmatisme basique dans le Système central espagnol s’étalent de façon sporadique sur une période de 140 Ma. Les données géochimiques suggèrent des sources mantelliques variables pour les cinq suites magmatiques reconnues. Une contribution crustale significative est mise en évidence dans les magmas Gb1 à Gb3, mis en place en liaison avec l’orogénèse hercynienne. Elle témoigne de processus d’hybridation intracrustal et/ou du recyclage de matériaux d’origine continentale dans le manteau. En revanche, le magmatisme post-collisionnel ultérieur montre une empreinte crustale négligeable dans la suite lamprophyrique alcaline Gb4, extraite d’un réservoir source de type OIB. La suite tholéiitique Gb5 pourrait témoigner d’un manteau source métasomatisé par un composant d’origine crustale [ABSTRACT] Hercynian and post-Hercynian basic rocks from the Spanish Central System: estimates of Central Spain subcontinental mantle. Basic magmatism in central Spain occurred sporadically during a long period of ca. 140 Ma. The geochemical data on representative samples from the five igneous episodes show that different mantle reservoirs were tapped. Crustal involvement (via recycling in mantle sources or by hybridization at emplacement levels) was important in the basic magmas related to the Hercynian orogeny (Gb1 to Gb3 suites). Samples occurring as later dykes have signatures ranging from OIB-like values (Gb4 alkaline lamprophyres) to those of a formerly enriched subcontinental lithospheric mantle (tholeiites Gb5