Review: A bioavailability-based rationale for controlling metal and metalloid contamination of agricultural land in Australia and New Zealand

Metal pollution of agricultural land in Australia and New Zealand is less severe than that documented in many European countries, due to the lower density of urban developments and a lower level of industrialisation. However, Australia and New Zealand are highly dependent on plant production systems based on plant-microbial symbioses (e.g. Rhizobium, mycorrhizae) and other natural biogeochemical processes for maintaining nutrient status in soils that are generally low in nutrients and, in Australia, also low in organic matter. Data linking metal concentrations in soil to agricultural and ecological effects are sparse for Australia and New Zealand, and regulatory frameworks and guidelines to control metal contamination of soils rely heavily on data generated in countries of the northern hemisphere. Adoption of benchmark concentrations for metal contaminants from these countries has led to inappropriate levels being chosen for several elements. These problems could be avoided and metal contamination of soils could be more effectively controlled if instead of relying on total concentrations of metals in soil and soil amendments, regulations and guidelines considered the biologically active fractions. This review considers the advantages and disadvantages of a bioavailability-based approach to the control of metal contamination of soils and suggests improvements needed to avoid both over- and under-protective measures.