Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 1/5)
Character Range: 1576526–1579375

4                   Arsenic

4.1              Arsenic compounds considered
The metalloid As occurs in a number of oxidation states: -3 (-III), 0, +3 (III) and +5 (V). Arsenic (III) is the dominant form under reducing conditions and As (V) is the dominant form in oxidised soils. The SQG derivation methodology (Schedule B5b) is only suitable for the aerobic portion of soils. SQGs for As were therefore calculated using only well oxidised soil studies. Therefore, arsenic will predominantly be present as As (V) but, as all the toxicity studies expressed toxicity in terms of total arsenic, the SQGs generated in this study are for total arsenic. For waterlogged soils, a separate As SQG should be derived, due to the difference between As (III) and As (V) in both toxicity and bioavailability in these soils. The chemical abstract service number (a unique identification number for each chemical) for As is 7440-38-2.

4.2              Exposure pathway assessment
The two key considerations in determining the most important exposure pathways for inorganic contaminants such as As are whether they biomagnify and whether they have the potential to leach to groundwater. A surrogate measure of the potential for a contaminant to leach is its watersoil partition coefficient (Kd). If the logarithm of the Kd (log Kd) of an inorganic contaminant is less than 3 then it is considered to have the potential to leach to groundwater (Schedule B5b). The log Kd reported by Crommentuijn et al. (2000) was 2.28 L/kg, so As has the potential in some soils to leach to groundwater. This is consistent with information regarding human health problems experienced in Bangladesh from the presence of As in groundwater. The methodology for EIL derivation (Schedule B5b) does not advocate the routine derivation of EILs that account for leaching potential. Rather, it advocates that this is done on a site-specific basis as appropriate. However, the calculations are presented here to illustrate the recommended approach and the effect that this would have on the resulting SQGs.

Arsenic is not known to biomagnify in oxidised soils (Heemsbergen et al. 2009) and therefore only direct toxicity routes of exposure were considered in deriving the SQGs.

4.3              Toxicity data
The raw toxicity data for As is presented in Appendix B. The toxicity data (geometric means for each species) used to calculate the SQGs is presented in Table 29. There was toxicity data for three soil invertebrate species, five terrestrial animal species and 13 species of plants. These meet the minimum data requirements recommended by Heemsbergen et al. (2008) to use the BurrliOZ SSD method (Campbell et al. 2000).
Table 29. Geometric mean values of arsenic (As) toxicity data (expressed in terms of total As) for soil invertebrate species, terrestrial bird and mammal species