Friday, 14 July 2006 - 8:35 AM

Heavy Metal Bioavailability Detection in Soils and Sediments by the BIOMET-Biosensor.

Ludo Diels and Karolien Vanbroekhoven. Flemish Institute for Technological Research, Boeretang 200, B-2400, Mol, Belgium

Historical mining activities (e.g. acid mine drainage), non-ferrous metals processing (e.g. landfill leakage or metal emissions), surface treatment and electronic industries (e.g. spills of heavy metal contaminated water) lead to the contamination of soils with heavy metals and metalloids. This contamination can cause severe risks to human health due to direct metal uptake into vegetables and due to spreading via wind (e.g. of dust) or via infiltration in the groundwater or via flooding. Metals and metalloids are always in a kind of equilibrium between the soil and soil pore water. Several factors influence this equilibrium and consequently influence the release of these metals from the soil (source) to the humans (receptor) via specific ways (plant uptake, breathing of air, drinking of groundwater etc.). Soil has an intrinsic capacity to bind metals via different processes as ion-exchange (on clay), adsorption to functional groups (on organic matter), precipitation (due to pH changes) and co-precipitation (on iron oxy-hydroxides), as well as integration in the mineral lattice. Besides these completely physico-chemical processes, micro-organisms play a role in the fate of metals resulting in different bio-geochemical processes as biosorption on biomass, bioprecipitation due to oxidation or reduction reactions, precipitation with sulfides, obtained through sulfate reduction etc. All these processes play a role in the retardation of the metal on its pathway from soil surface to other receptors as groundwater. This retardation can be seen as a natural attenuation process influencing the reduction in availability of the metal to plants, animals and human beings. Several methods were developed to measure the (bio)availability of these metals and metalloids. These methods are based on chemical (e.g. sequential extraction, AVS/SEM ratio etc.), physical (e.g. capacity sensors) or biological methods (e.g. bio-assays and biosensors). An advantage of the BIOMET®-sensor (based on light production by metal interacting bacteria) is the fact that they give a general interpretation of the availability of the metals (as a mixture) and of their risks compared to software models that try to calculate the speciation of the metals not taking into account unknown parameters or elements. The (bio)availability of metals can change in function of time due to changing conditions as pH, redox, presence of complexing agents etc. In conclusion, it's clear that there is a general need to come to an easy and cheap monitoring method of (bio)availability of metals and metalloids in soil in relation to their spreading to groundwater and surface water and the need to use these data in a general approach of evaluation of soil quality changes and influence on river basins. This talk will present some new ideas and approaches. The presentation will be illustrated with examples using the BIOMET®-sensor for instance on New Orleans sediment samples.

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Back to The 18th World Congress of Soil Science (July 9-15, 2006)