Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 1/4)
Character Range: 1512418–1515332

3                   Zinc

3.1              Zinc compounds considered
The SQGs for Zn were derived using data for the following:
    * zinc metal (CAS No. 7440-66-6)
    * zinc oxide (CAS No. 1314-13-2)
    * zinc distearate (CAS Nos 557-05-1/91051-01-3)
    * zinc chloride (CAS No. 7646-85-7)
    * zinc sulphate (CAS No. 7733-02-0).

3.2              Exposure pathway assessment
The two key considerations in determining the most important exposure pathways for inorganic contaminants are whether they biomagnify (see Glossary) 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 Australian National Biosolids Research Program (NBRP) measured the log Kd of Zn in 17 agricultural soils throughout Australia. These measurements showed that in most soils the log Kd of Zn was below 3 L/kg (unpublished data). The log Kd value for Zn reported by Crommentuijn et al. (2000) was 2.2 L/kg. Therefore, there is the potential for Zn in some soils to leach to groundwater and affect aquatic ecosystems. However, 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 of Zn SQGs that account for leaching have been included here as an illustration of the process and the effect that this has on the resulting soil quality guidelines.

Zinc is an essential element and, as such, concentrations of Zn in tissue are highly regulated and it does not biomagnify (Louma & Rainbow 2008; Schedule B5b). Therefore, the biomagnification route of exposure does not need to be considered for Zn and the SQGs will only account for direct toxicity.

3.3              Toxicity data
Zinc is a well-studied inorganic contaminant and therefore a large dataset of toxicity values was available. Most studies presented their toxicity data in terms of added concentration (that is, the concentration of the contaminant added to the soil that causes a specified toxic effect) and so could be used without further modification. Some toxicity data was expressed in terms of total contaminant concentration but the background concentrations were reported. In such cases, the toxicity data was converted to an added concentration basis by subtracting the background from the total concentration. If toxicity data was expressed in terms of total contaminant concentration but the background concentration was not reported then the Dutch background correction equation (Lexmond et al. 1986) was used to estimate the background concentration.

background Zn = 1.5 * [2 * organic