Nutrient Availability in the Surface Horizons of Four Tropical Agricultural Soils in Mali

Studies of nutrient availability are important for the understanding and the estimation of soil fertility in areas like West Africa, where low nutrient availability is still one of the major constraints for food production. Physico-chemical soil analyses were used to assess the fertility status of the surface horizon samples of four Malian agricultural soils, (Bougouni, Kangaba, Baguinéda and Gao abbreviated as Bgni, Kgba, Bgda and Gao). Soil texture was sandy loam for Bgni and Kgba, sandy clay loam for Bgda and loamy sand for Gao. Soil pH values varied from moderately acid for Bgda to neutral for the other sites. Organic carbon ranged from very low (for Gao) or low (for Bgni and Bgda) to medium (for Kgba). Total N, P and CEC were low for the four soils. Available contents of Fe and Mn in all soils, except Gao, were higher than the critical levels while available Cu and Zn contents (except in Kgba) were below or close to it. Results indicated that Kgba soil had a better macronutrient status for plant growth than the other sites

Fate of heavy metals during fixed bed downdraft gasification of willow wood harvested from contaminated sites

The combination of energy production from biomass with phytoremediation opens perspectives for bringing land with moderate metal contamination into safe and beneficial use. Small scale fixed bed downdraft gasifier installations (150 kWe-1 MWe) can be employed for on-site conversion of biomass to electricity and heat. To assess the fate of heavy metals, batch gasification operations were run in a small scale fixed bed downdraft gasifier (100 kW thermal power). The gasification of I kg of wood resulted in the production of 40 g of ashes, 1.2 kWh of electricity and 9 MJ of heat. Per kg dry mass of willow wood, 31 g bottom ashes, 7 g cyclone ashes,. 2 g filter ashes, and 18 g DM of gasifier bed ashes were produced. Cd, Zn and Pb were enriched by a factor 7-100 in the fly ashes compared to the bottom ashes. Low mass recoveries (30-40%) were found for Cd, Cr, Ni and Pb. This was mainly attributed to measurement uncertainties. 60% and more of recovered Cd, Pb and Zn were present in the finer filter and cyclone ashes, while Cr, Cu and Ni were mainly found in the bottom ashes and to a lesser extent the bed ashes. The scrubber placed after the hot cyclone has all essential role in intercepting the more volatile heavy metals before combustion of the gas. The bottom ashes constituted the largest fraction and ideally should be recycled if limits for metal contents are met. Only Cd and Zn exceeded Flemish threshold values for use of this fraction as a fertilizer, albeit by a small margin. This leaves perspectives for future research to optimise process parameters towards the production of bottom ashes that can be recycled. (C) 2005 Elsevier Ltd. All rights reserved

Comparative analysis of Cd and Zn impacts on root distribution and morphology of Lolium perenne and Trifolium repens: implications for phytostabilization

Backgrounds and aims The phytostabilization potential of plants is a direct function of their root systems. An experimental design was developed to investigate the impact of Cd and Zn on the root distribution and morphology of Lolium perenne and Trifolium repens. Methods Seedlings were transplanted into columns filled with washed quartz and irrigated daily with Cdor Zn-containing nutrient solutions during 1 month. Root biomass, root length density (RLD) and diameter were subsequently quantified as a function of depth. Pot experiments were also performed to quantify metal, lignin and structural polysaccharides concentrations as well as cell viability. Results Lolium perenne accumulated Cd and Zn in the roots whereas T. repens was unable to restrict heavy metal translocation. Cadmium and Zn reduced rooting depth and RLDbut induced thick shoot-borne roots in L. perenne. Cd-induced root swelling was related to lignification occurring in the exodermis and parenchyma of central cylinder. Hemicelluloses and lignin did not play a key role in root metal retention. Cadmium slightly reduced mean root cell viability whereas Zn increased this parameter in comparison to Cd. Conclusions Even though plant species like Lolium perenne and Trifolium repens may appear suitable for a phytostabilization scheme based on their shoot metal tolerance, exposure to toxic heavy metals drastically impairs their root distribution. This could jeopardize the setting up of phytostabilization trials. The metal-induced alterations of root system properties are clearly metal- and speciesspecific. At sites polluted with multiple metals, it is therefore recommended to first test their impact on the root system of multiple plant species so as to select the most appropriate species for each site

Feasibility Study of the Electrokinetic Remediation of a Mercury-Polluted Soil

This chapter is focused on the study of electroremediation of heavy metals from a real soil. Specifically, the case of the study was a soil from Almaden mining district, with a very high mercury concentration. The risk assessment of heavy metals depends on the mobility and bioavailability and not only on the total concentration. Therefore, this study evaluates the distribution of mercury into different fractions before and after the electrokinetic treatment. The electrokinetic experiments were performed in two operating scales that differ in more than two orders of magnitude. The results for both scales are consistent with the predictions of simple models, so it can be assumed that they are useful for the evaluation of a full-scale implementation. Two enhancing agents were studied in the application of electrokinetic process according to the mercury distribution in BCR fractions (Community Bureau of Reference). First, iodide was applied as complexing agent, and it was found that after treatment the most mobile fraction of mercury increased. Thus, to remove this mobile mercury fraction, electroremediation experiments were done with nitric acid as enhancing agent