Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:20:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 20 (pt 2/4)
Character Range: 1591560–1594594

residential/public open space  50                90
Commercial/industrial                80                140

4.7              Calculation of soil quality guidelines for aged arsenic contamination

4.7.1         Calculation of an ageing and leaching factor for arsenic
Song et al. (2006) conducted some experiments to determine the effect of ageing As over three months in four soils. They found that in all soils the toxicity and extractability decreased and the extent of the decrease ranged from 2- to 12-fold (Song et al. 2006). Yang et al. (2002) and Fendorf et al. (2004) also found that As aged in soils with the majority occurring within the first few months. Yang et al. (2002) also found that As ageing did not always occur—it occurred in only 47% (i.e. 17 out of 36) of the soils they examined. Song et al. (2006) found that the extent of ageing was significantly correlated with oxalate-extractable iron and Olsen-P concentrations in the four test soils. However, they also noted that data on more soils was needed in order for the relationships to be considered more robust. Song et al. (2006) concluded that ageing of As 'should be taken into account during risk assessment'. Therefore, in order to account for ageing in a conservative manner (that is, one that is protective of the environment), the lowest ALF factor (2) determined by Song et al. (2006) was used to derive the aged SQGs. This ALF was applied to all the toxicity data.

4.7.2         Calculation of soil quality guidelines for aged arsenic contamination
As the available toxicity data can only be expressed as total As concentrations, ACL values could not be derived, so SQGs were derived. The ALF of 2 was applied to all the toxicity data; therefore the aged SQG(NOEC & EC10), SQG(LOEC & EC30) and SQG(EC50) values are exactly twice the corresponding fresh SQGs for arsenic. The resulting aged SQG(NOEC & EC10), SQG(LOEC & EC30) and SQG(EC50) values are presented in Table 35.
Table 35. Generic soil quality guidelines based on no observed effect concentration and 10% effect concentration toxicity data (SQG(NOEC & EC10)), lowest observed effect concentration and 30% effect concentration toxicity data (SQG(LOEC & EC30)), and based on 50% effect concentration toxicity data (SQG(EC50)) for soil with different land uses.
Land use                               SQG(NOEC & EC10)  SQG(LOEC & EC30)  SQG(EC50)
                                       (mg/kg total As)  (mg/kg total As)   (mg/kg total As)
  Areas of ecological significance     15                40                60
  Urban residential/public open space  40                100               180
  Commercial/industrial                60                160               290

4.7.3         Calculation of ambient background concentration values
Background levels of As are not elevated by historic pollution in urban residential/public open space soils, as can be seen by data from Olszowy et al. (1995) (Table 36). Therefore, in the future, if toxicity data can be expressed in terms