Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p4
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 4/21)
Character Range: 1355345–1358304

to one species and the physicochemical properties of the soils where the tests were conducted. These empirical relationships are usually obtained using data from laboratory studies in which a single species is exposed to a single contaminant in different soils. Normalisation relationships have generally been developed using linear regression analysis techniques including forward and backward step-wise regression (Smolders et al. 2004; Rooney et al. 2006; Broos et al. 2007; Warne et al. 2008a) or partial least squares (PLS) regression (Lock & Janssen 2001). It is important that only soil physicochemical properties that are not significantly correlated to each other are used to develop normalisation equations. Although there are no generally accepted rules, researchers have generally only reported or recommended the use of normalisation equations that have coefficients of determination (r2) or adjusted coefficients of determination (adj r2) greater than 0.5 (that is, they explain more than 50% of the variation in toxicity values). This is quite reasonable as, if a relationship does not explain at least 50% of the variation, then using it to normalise other toxicity data could introduce considerable error.

A number of studies have successfully developed normalisation relationships for plants, microbial processes and soil invertebrates. The main soil characteristics affecting the toxicity of inorganic contaminants appear to be pH, clay content, cation exchange capacity and organic matter content (Lock & Janssen 2001; Smolders et al. 2003; Smolders et al. 2004; Rooney et al. 2006; Song et al. 2006; Broos et al. 2007; Warne et al. 2008a, 2008b).
Figure 3. An example of the effect that soil pH can have on toxicity values (shaded diamonds). Toxicity data shown are SIN EC 10 from the NBRP program.
Normalisation equations can, in principle, be developed for any combination of contaminant, species, and toxicity end point. However, they should only be developed using ecologically relevant species, measures and toxicity end points for the ecosystem that is being protected. In addition, it is preferable from an implementation point of view, that relatively easy and relatively cheap-to-measure, accurate, repeatable soil characteristics are used to derive normalisation relationships. Otherwise, the costs and difficulty of determining unusual soil characteristics will inhibit application of the relationships.

In Australia, empirical relationships have been obtained between soil characteristics and toxicity data for a limited set of contaminants and end points to date. Examples of relationships between toxicity and soil characteristics from the NBRP program are:
Microbial (substrate induced nitrification  SIN) see also Figure 3
SIN log EC10  Zn = 0.55*pH – 0.55   R2 = 0.74 (equation 9)
Plant (toxicity)
log EC10  Zn  = 0.271 * pH + 0.702 * log CEC adj.  R2 = 0.66  (equation 10)

where pH is the soil pH (0.01 M CaCl2), CEC