Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p20
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 20/21)
Character Range: 1397520–1400387

soil originated and are highly variable. Some authors (Reimann & Garrett 2005) argue that natural background concentrations no longer exist anywhere in the world due to man-made activities and global transport of contaminants. Therefore, the term ambient background concentration (ABC) as suggested by Zhao et al. (2007) is used rather than background concentration.

Metal concentrations in soils are easily and quickly measured; therefore, the preference is to directly measure the ABC in known unpolluted reference soils. However, finding a similar unpolluted reference soil to the contaminated soil is not always possible for a wide variety of reasons. The complexity and problems associated with measuring the ABC are discussed in a series of papers in Human and Ecological Risk Assessment, vol. 9 (2003) and by Reimann and Garrett (2005). Reliable ABC values for a soil with similar physicochemical and structural properties to the soil being investigated cannot always be obtained or the measured values are compromised in one or more ways. If reliable background concentrations cannot be obtained, then a modelling method should be used.

3.3.2         Background concentration models
A model able to predict the background concentrations of metals in Australian soils was developed by Hamon et al. (2004). In this study, a large number of remote sites in Australia and South-East Asia were surveyed for metal concentrations in soil. Principal component analysis revealed strong associations of many metals (for example, As, Co, Cr, Cu, Ni, Pb) with structural elements of soil minerals (Fe and Mn). Linear regressions were developed that permit the prediction of background soil metal concentrations using only Fe or Mn concentrations (Figure 6).
Figure 6. Example relationships between the logarithm of iron concentration of soil and background Cu and Ni concentrations (modified from Hamon et al. 2004). The red and black lines are the 95th and 50th percentile of the relationships respectively.

The equations developed by Hamon et al. (2004 [Table 15, Section 2.4.9.1]) can be used to estimate the background concentration. Hamon et al. (2004) calculated the 'background concentrations' using the equation that encompassed the upper 95th percentile of the data. However, Zhao et al (2007) argued that this approach is not conservative as the poorer the relationships, the larger the 95th percentile will be and hence the larger the estimates of ABC will be. They argue that this may lead to under-protection of soils (by deriving larger ABCs which are added to limit values base on added metal concentrations). Given the above and the purpose of EILs, the 50th percentile of the data (that is, the regression equation) should be used to estimate ABC values.

The relationships developed by Hamon et al. (2004) take the form
    ABC  = a* log Fe or Mn + b