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

Abstract

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.

Enrichment and exposure assessment of As, Cr and Pb of the soils in the vicinity of Stawell, Victoria, Australia

“…The bioavailable fractions of toxic compounds in soil are linked to health risks. Typically, studies of hazardous elements in the environment have focussed on total values, and only more recently has research addressed exposure and biological assessments (Krachler et al 2001;McLaughlin et al 2000). Natural background concentrations in Australian soils are 0.2-30, 0.5-110 and \2-200 mg kg -1 for As, Cr and Pb, respectively (ANZECC/NHMRC 1992).…”

Cadmium and Zinc

“…So many factors can affect crop Cd and Zn accumulation in particular cases that only the key factors are discussed here. More information can be found in reviews of soil and plant factors that may affect accumulation of Cd in edible crop tissues [67][68][69][70]. Because soil Cd remains in the labile pool in Cd-enriched soils, the Cd remains phytoavailable; no method to transform soil Cd into low phytoavailable forms has been identified although soil management can reduce uptake such as by raising soil pH.…”

Fractionation and mobility of cadmium and zinc in urban vegetable gardens of Kano, Northern Nigeria

“…In Kano, Nigeria, untreated industrial, domestic, and abattoir wastewaters discharged into city streams and used for irrigation contain large amounts of toxic heavy metals (Binns et al 2003). Total soil concentration, though an important parameter, does not allow assessing the availability and subsequent environmental impact of heavy metals (McLaughlin et al 2000;Kabala and Singh 2001). Therefore, understanding the behavior, movement, retention, mobilization, and dynamic equilibria of heavy metals in a heterogeneous system such as a soil is imperative to characterizing their bioavailability, mobility (Gomes et al 2001), and possible contamination of the food chain (Yusuf et al 2003;Bakare et al 2004).…”