SREL Reprint #2760




Bioavailability of Metals in the Soil Plant Environment and its Potential Role in Risk Assessment

R. Naidu1, S. Rogers1, V. V. S. R. Gupta1, R. S. Kookana1, N. S. Bolan2, and D. C. Adriano3

1CSIRO Land and Water, Private Mail Bag. No. 2, Glen Osmond, Adelaide, South Australia
2Department of Soil Science, Massey University, Palmerston North, New Zealand
3Savannah River Ecology Laboratory, Drawer E, Aiken, South carolina 29802, USA

Introduction: Metal contamination of soil environments and the assessment of its potential risk to terrestrial and aquatic biota and public health is one of the most challenging tasks confronting scientists today. This is partly due to the plethora of soil biochemical and physical processes controlling the fate of metals and partly because of the difficulty associated with the assessment of their availability. A credible method for the assessment of "bioavailability" of metals and other contaminants is lacking.
The definition of "bioavailability" and the concept on which it is based are unclear, the methods adopted vary throughout the world, and therefore there is no single standard technique for the assessment of either plant availability of metals or their ecotoxicological impacts on soil biota. Some of the difficulties probably arise because of confusion with the understanding of the bioavailability concept (see Chapter 1) and relating this to the measurement of metal availabilities. For example, a number of investigators relate bioavailability to that fraction of extractable metals that correlates with the total metal uptake by plants. Although this has been quite successful with certain plan and soil types, its applicability has often been found to be fraught with limitations. Firstly, as bioavailability is often assessed by chemical extractions, it is likely that extractants may release those pools of metals which the plant roots and microorganisms do not exploit in the soil solution. This is supported by the definition proposed in Chapter 1 which suggests that the concept of bioavailability is fundamental to toxicology and it is not the same as bioavailable fraction, which is largely a measure of solubility. Secondly and more importantly, chemical extraction methods do not consider physiological and biochemical factors associated with plants and microbes, e.g. transport of metals across the cell membranes. The parameters that control the membrane transport of metals are species-specific and possibly dictate the rate of uptake by different plant and microbes from the same bioavailable pool of metals in soils.

SREL Reprint #2760

Naidu, R., S. Rogers, V. V. S. R. Gupta, R. S. Kookana, N. S. Bolan, and D. C. Adriano. 2003. Bioavailability of metals in the soil plant environment and its potential role in risk assessment. p. 21-57 In: R. Naidu, V. Gupta, S. Rogers, R. Kookana, N. Bolan and D. Adriano (Eds.). Bioavailability, Toxicity and Risk Relationships in Ecosystems. Science Publishers, Inc.

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