Opname van cadmium door gewassen in moestuinen in de Kempen: risico-inventarisatie en maatregelen

Op basis van bestaande data is de opname van cadmium door enkele belangrijke moestuingewassen beschreven via een bodem-plant relatie. Gebruik makend van organische stof, pH, klei en het cadmiumgehalte van de bodem kan het gehalte in het gewas voorspeld worden. Met deze vergelijkingen is vervolgens het toelaatbare cadmiumgehalte in de bodem berekend waarbij de warenwetnorm (per gewas) wordt overschreden. Daarnaast is ook de totale blootstelling berekend (CSOIL) in geval van consumptie van gewassen die geteeld worden op met cadmium verontreinigde gronden. Uit de resultaten blijkt dat bij gangbare gehalten aan cadmium in de bodem in de Kempen de blootstelling via consumptie de MTR waarde overschrijdt, zeker in geval van (licht) zure gronden (pH lager dan 5,5). Verhoging van de bodem-pH en handhaving van het organische stofgehalte door toevoeging van compost of mest blijkt effectief om de blootstelling te reduceren. Dit is echter alleen van toepassing bij cadmiumgehalten in de bodem die liggen tussen 1 en 5 mg kg-1. Bij cadmiumgehalten in de bodem tussen 2 en 5 mg kg-1 zijn er beperkingen aan de keuze van de gewassen. Met name bladgroenten als sla, spinazie en andijvie kunnen dan beter niet geteeld worden. Bij cadmiumgehalten in de bodem van meer dan 5 mg kg-1 zou consumptie uit eigen tuin afgeraden moeten worden. De hier gepresenteerde advieswaarden zullen in 2004 verder getoetst worden middels experimenteel onderzoek in bestaande moestuinen

Soil chemical changes in ancient irrigated fields of Udhruḥ, southern Jordan

BioarchaeologyClassical & Mediterranean ArchaeologyArchaeology of the Near Eas

Adsorption, desorption and isotopic exchange of cadmium on illite: evidence for complete reversibility

Adsorption, desorption and isotopic exchange of Cd on illite clay have been studied at low Cd concentrations and low ionic strength. The results indicate that under the conditions of the experiments Cd sorption on illite is completely reversible. Long equilibration times (7–8 weeks) were shown to be essential because of slow desorption kinetics

Mineral CO2 sequestration by steel slag carbonation

Mineral CO2 sequestration, i.e., carbonation of alkaline silicate Ca/Mg minerals, analogous to natural weathering processes, is a possible technology for the reduction of carbon dioxide emissions to the atmosphere. In this paper, alkaline Ca-rich industrial residues are presented as a possible feedstock for mineral CO2 sequestration. These materials are cheap, available near large point sources of CO2, and tend to react relatively rapidly with CO2 due to their chemical instability. Ground steel slag was carbonated in aqueous suspensions to study its reaction mechanisms. Process variables, such as particle size, temperature, carbon dioxide pressure, and reaction time, were systematically varied, and their influence on the carbonation rate was investigated. The maximum carbonation degree reached was 74% of the Ca content in 30 min at 19 bar CO2 pressure, 100 °C, and a particle size o

The leaching of trace elements from municipal solid waste incinerator bottom ash at different stages of weathering

For a proper assessment of the environmental impact of the utilisation and disposal of Municipal Solid Waste Incinerator (MSWI) bottom ash it is necessary to understand weathering processes and their effects on (trace) element leaching. The authors have investigated the processes that control the leaching of Cd, Pb, Zn, Cu, and Mo from 3 categories of bottom ash: (A) unweathered bottom ash (grate siftings and unquenched samples), (B) quenched/non-carbonated bottom ash (freshly quenched and 6-week-old samples), and (C) weathered bottom ash (1.5- and 12-year-old samples). Leaching experiments were performed in a pH-stat at a large range of pH values. The speciation code MINTEQA2 was used for subsequent modelling of precipitation/dissolution processes. The speciation of trace elements in weathered bottom ash was also investigated by microanalytical techniques. In A- and B-type bottom ash the general controlling processes are thought to be precipitation/dissolution of relatively soluble minerals or, in the case of Cu in particular, extensive complexation with dissolved organic C. At the 'natural' pH of the samples, the leaching of Cd, Pb, Cu, Zn and Mo is generally significantly lower from C-type bottom ash than from less weathered types of bottom ash. This reduction in leaching is due to the neutralisation of bottom ash pH and the formation of less soluble species of these elements as weathering continues. In the more weathered (C-type) bottom ash trace element leaching does not seem to be solubility-controlled; although slow precipitation reactions cannot be totally excluded, it is hypothesised that the controlling mechanism in those samples is sorption to neoformed minerals

Sorption of trace metals on calcite: Applicability of the surface precipitation model

Published Sorption isotherm data of Cd2+, Mn2+, Zn2+, and Co2+ on calcite are adequately described by the surface precipitation model which was originally developed by FArley et al. (1985) for the sorption of cations on metal oxides. In addition to monolayer adsorption, the model accounts for the formation of a surface phase with a composition that is described by a solid solution having as end members the sorbent calcium carbonate mineral and a pure carbonate precipitate of the sorbing trace metal. The model thus specifies a continuum between adsorption and precipitation. This feature is supported in the literature by observations on the reaction kinetics and the amount of surface coverage during trace metal sorption on calcite. The apparent adsorption constants of these trace metals, as derived from the model, can be ranked according to the degree to which their ionic radii match the ionic radius of Ca2+

Measurement of humic and fulvic acid concentrations and dissolution properties by a rapid batch procedure.

Although humic substances (HS) strongly facilitate the transport of metals and hydrophobic organic contaminants in environmental systems, their measurement is hampered by the time-consuming nature of currently available methods for their isolation and purification. We present and apply a new rapid batch method to measure humic (HA) and fulvic (FA) acid concentrations and dissolution properties in both solid and aqueous samples. The method is compared with the conventional procedures and is shown to substantially facilitate HS concentration measurements, particularly for applications such as geochemical modeling where HS purification is not required. The new method can be performed within 1.5-4 h per sample and multiple samples can be processed simultaneously, while the conventional procedures typically require approximately 40 h for a single sample. In addition, specific dissolution properties of HS are identified and are consistent with recent views on the molecular structure of HS that emphasize molecular interactions of smaller entities over distinct macromolecular components. Because the principles of the new method are essentially the same as those of generally accepted conventional procedures, the identified HA and FA properties are of general importance for the interpretation of the environmental occurrence and behavior of HS

Carbonation of steel slag for CO2 sequestration: Leaching of products and reaction mechanisms

Carbonation of industrial alkaline residues can be used as a CO2 sequestration technology to reduce carbon dioxide emissions. In this study, steel slag samples were carbonated to a varying extent. Leaching experiments and geochemical modeling were used to identify solubility-controlling processes of major and trace elements, both with regard to carbonation mechanisms and the environmental properties of the (carbonated) steel slag. Carbonation was shown to reduce the leaching of alkaline earth metals (except Mg) by conversion of Ca-phases, such as portlandite, ettringite, and Ca-(Fe)-silicates into calcite, possibly containing traces of Ba and Sr. The leaching of vanadium increased substantially upon carbonation, probably due to the dissolution of a Ca-vanadate. The reactive surface area of Al- and Fe-(hydr)oxides increased with the carbonation degree, which tends to reduce the leaching of sorption-controlled trace elements. Sorption on Mn-(hydr)oxides was found to be required to adequately model the leaching of divalent cations, but was not influenced by carbonation. Consideration of these three distinct reactive surfaces and possible (surface) precipitation reactions resulted in adequate modeling predictions of oxyanion and trace metal leaching from (carbonated) steel slag. Hence, these surfaces exert a major influence on the environmental properties of both fresh and carbonated steel sla