Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:5:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 5 (pt 2/3)
Character Range: 1572998–1575890

an alkaline clay soil (pH 7.5, CEC 40) with a 10% iron content.
The resulting ACL(EC50), ABC and SQG(EC50) values are:
ACL(EC50)  3400  mg/kg
ABC        55    mg/kg
SQG(EC50)  3455  mg/kg

This SQG(EC50) would then be rounded off using the rules in section 2.1 to a value of 3500 mg/kg.

3.8              Reliability of the zinc soil quality guidelines
Based on the criteria established in the methodology for SQG derivation (Schedule B5b), the Zn SQGs were considered to be of high reliability. This occurred as the toxicity data set easily met the minimum data requirements to use the SSD method and normalisation relationships were available to account for soil characteristics.

3.9              Comparison with other guidelines
A compilation of SQGs for Zn from a number of jurisdictions is presented in Table 28. These SQGs have a variety of purposes and levels of protection and therefore comparison of the SQGs between each other and with the Zn SQGs is problematic. The guidelines for Zn range from 20 mg/kg (added Zn) for the Netherlands to 200 mg/kg (total Zn) for Canada. The superseded interim urban EIL (NEPC 1999) was 200 mg/kg total Zn and therefore at the top of the range of the international Zn guidelines.

The Zn ACL(NOEC & EC10) values in freshly contaminated urban residential/public open space soils ranged from 20330 mg/kg (added Zn) (Table 10). The corresponding values for urban residential/public open space soils with aged Zn contamination ranged from 45810 mg/kg (Table 24). The lowest ACLs (for sandy acidic soils) were very similar to the lowest of the international SQGs, but considerably lower than the superseded interim urban EIL. However, the largest ACLs (for neutral to alkaline, high CEC soils) were considerably larger than any of the international SQGs apart from the Dutch intervention level, which has a different purpose from the ACLs. Thus, in soils where the Zn has a low bioavailability, higher concentrations of Zn are permitted under the methodology than under the superseded interim urban EIL.

The intervention value in the Netherlands is 720 mg/kg total Zn. The range of ACL(EC50) values (which most closely relate to the Dutch intervention value) in freshly contaminated urban residential/public open space soils was 50940 mg/kg (Table 20). While the range for aged Zn contamination was 1252,300 mg/kg (Table 27), the Dutch value corresponds to the 60th and 25th percentile of the range of ACL(EC50) values for fresh and aged Zn contamination respectively. Therefore, depending on soil physicochemical properties, the ACL(EC50) values would permit considerably less (in high bioavailability soils) to considerably more (in low bioavailability soils) Zn than in the Netherlands.

Table 28. Soil quality guidelines for zinc (Zn) from international jurisdictions.
Name of zinc limit                         Numerical value of the limit