An agricultural-based alternative to the problems of remediating surface contaminated soil uses amendments and green plants to decontaminate or stabilise soils polluted with heavy metals. We are studying both decontamination and stabilisation procedures as related to the remediation of Pb contaminated soils. Soil amendments may make Pb more available for plant uptake or change Pb to less soluble forms. As measured by Toxicity Characteristic Leaching Procedure, Pb concentrations were reduced to less than 1 mg Pb L-1 in some treatments. Changes in soil Pb to less soluble forms were reflected in the results of sequential chemical extraction and X-ray fine structure analysis.
Soil amendments can also aid in the establishment and growth of plants to reduce erosion.
Their application to soil, coupled with harvesting and processing of green plants capable of absorbing and translocating Pb from roots to shoots, may be a feasible alternative to current engineering-based remediation techniques. However, this approach does not account for various soil properties, such as pH, organic matter content, and cation exchange capacity, that are known to influence root uptake of metals. For risk assessment purposes, a simple, predictive method of estimating root uptake of metals that is based on site-specific soil and crop data is needed so that the importance of the produce ingestion pathway and subsequent influence on human exposure can be quantitatively assessed. Ideally, it should be possible to develop a statistically-reliable relationship between plant and soil metals levels that includes appropriate weighing factors for various soil properties. This paper presents preliminary predictive equations for estimating root uptake of As, Cd, Cu, and Zn in fruiting and root vegetables to draw attention to this issue, so that the importance of this pathway and subsequent influence on human exposure can be more accurately assessed.