Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 2/21)
Character Range: 1349874–1352833

al. 2000b). The extraction methods assume that they only extract that portion of the total amount of a chemical that is biologically available. This is a chemical approach to estimating the bioavailable fraction.

Available information suggests that only Germany (BBodSchV 1999) and Switzerland (Gupta et al. 1996) use a measure of chemical concentration other than the total contaminant concentration in soil. The German guidelines (BBodSchV 1999) have some soil TVs based on concentrations in NH4NO3 extracts for some inorganic contaminants (that is, TVs for cadmium) in the soil-to-plant pathway. This was only done if NH4NO3 extracts were better predictors (that is, showed better correlations) for internal plant concentrations from soil than the total soil concentration. The ammonium nitrate extract is considered by the German guidelines to be the bioavailable concentration of inorganics in soil.

The perfect chemical measure of bioavailability should give very similar toxicity values (for example, LC50) in a range of different soils for a given chemical tested on a given species. For soils, the perfect measure of bioavailability should overcome the effects that different soil characteristics have on toxicity and truly reflect the available fraction of the contaminant that causes the toxicity to the organism. Therefore, the ability of techniques to determine the bioavailable fraction can be assessed by comparing the variability of the toxicity values for one species across different soils—the measure with the smallest variability in toxicity values being the best measure of the bioavailable fraction (McLaughlin et al. 2000b). This approach was adopted by Broos et al. (2007) and Warne et al. (2008b) using microbial and plant toxicity data for Cu and Zn in 14 different Australian soils (field-based) using one source of contamination (soluble metal salts). In both cases, the variation in toxicity values based on total concentrations was smaller than or as small as those based on soil solution and CaCl2 extracts. Unpublished work from the Australian National Biosolids Research Program (NBRP) showed that the concentrations in ammonium nitrate and calcium chloride extracts were very highly related with coefficients of determination (r2) greater than 0.9. Therefore, although it is untested, it is highly likely that the data from the NBRP would reveal that variation in toxicity values across soils based on total concentrations would be lower than those based on ammonium nitrate.

A number of authors from Europe (Smolders et al. 2003; Smolders et al. 2004; Oorts et al. 2006; Zhao et al. 2006) have also found that extractable or soil solution measurements were not useful predictors of plant and microbial toxicity in soils and thus used total metal concentrations to develop normalisation relationships. In contrast, a number of other studies have reported various extractable measures to be better than total concentrations