Page

1 Introduction

1.1 Objectives

1.2 Terminology

2 Overview of the method for deriving soil quality guidelines

2.1 Precision of estimates and rounding of added contaminant limits

3 Zinc

3.1 Zinc compounds considered

3.2 Exposure pathway assessment

3.3 Toxicity data

3.4 Normalisation relationships

3.5 Sensitivity of organisms to zinc

3.6 Calculation of soil quality guidelines for fresh zinc contamination

3.6.1 Calculation of soil quality guidelines for fresh zinc contamination based on no observed effect concentration and 10% effect concentration toxicity data

3.6.1.1 Calculation of soil-specific added contaminant limits

3.6.1.2 Calculation of ambient background concentration values

3.6.1.3 Examples of soil quality guidelines for fresh zinc contamination based on no observed effect concentration and 10% effect concentration data

3.6.2 Calculation of soil quality guidelines based on protecting aquatic ecosystems from leaching of fresh zinc contamination

3.6.3 Calculation of soil quality guidelines for fresh zinc contamination based on lowest observed effect concentration and 30% effect concentration toxicity data, and based on 50% effect concentration toxicity data

3.6.3.1 Calculation of soil-specific added contaminant limits

3.6.3.2 Calculation of ambient background concentration values

3.6.3.3 Examples of soil quality guidelines for fresh zinc contamination based on lowest observed effect concentration and 30% effect concentration data, and based on 50% effect data

3.7 Calculation of soil quality guidelines for aged zinc contamination

3.7.1 Calculation of an ageing and leaching factor for zinc

3.7.2 Calculation of soil quality guidelines for aged zinc contamination based on no observed effect concentration and 10% effect concentration toxicity data

3.7.2.1 Calculation of added contaminant limits for aged zinc contamination based on no observed effect concentration and 10% effect concentration toxicity data

3.7.2.2 Calculation of ambient background concentration values

3.7.2.3 Examples of soil quality guidelines for Australian soils with aged zinc contamination based on no observed effect concentration and 10% effect concentration data

3.7.3 Calculation of soil quality guidelines for aged zinc contamination based on lowest observed effect concentration and 30% effect concentration toxicity data and based on 50% effect concentration toxicity data

3.7.3.1 Calculation of added contaminant limits for aged zinc contamination based on lowest observed effect concentration and 30% effect concentration and based on 50% effect concentration toxicity data

3.7.3.2 Calculation of ambient background concentrations

3.7.3.3 Examples of soil quality guidelines for Australian soils with aged zinc contamination based on lowest observed effect concentration and 30% effect concentration data, and based on 50% effect concentration toxicity data

3.8 Reliability of the zinc soil quality guidelines

3.9 Comparison with other guidelines

4 Arsenic

4.1 Arsenic compounds considered

4.2 Exposure pathway assessment

4.3 Toxicity data

4.4 Normalisation relationships

4.5 Sensitivity of organisms to arsenic

4.6 Calculation of soil quality guidelines for fresh arsenic contamination

4.6.1 Calculation of soil quality guidelines for fresh arsenic contamination based on no observed effect concentration and 10% effect concentration toxicity data

4.6.1.1 Calculation of ambient background concentration values

4.6.2 Calculation of soil quality guidelines for fresh arsenic contamination based on protecting aquatic ecosystems from leaching

4.6.3 Calculation of soil quality guidelines for fresh arsenic contamination based on lowest observed effect concentration and 30% effect concentration toxicity data, and based on 50% effect concentration toxicity data

4.7 Calculation of soil quality guidelines for aged arsenic contamination

4.7.1 Calculation of an ageing and leaching factor for arsenic

4.7.2 Calculation of soil quality guidelines for aged arsenic contamination

4.7.3 Calculation of ambient background concentration values

4.8 Reliability of the soil quality guidelines

4.9 Comparison with other guidelines

5 Naphthalene

5.1 Compounds considered

5.2 Exposure pathway assessment

5.3 Toxicity data

5.4 Normalisation relationships

5.5 Sensitivity of organisms to naphthalene

5.6 Calculation of soil quality guidelines for fresh naphthalene contamination

5.6.1 Calculation of soil quality guidelines for fresh naphthalene contamination based on no observed effect concentration and 10% effect concentration toxicity data

5.6.1.1 Calculation of ambient background concentration values

5.6.2 Calculation of soil quality guidelines for fresh naphthalene contamination based on lowest observed effect concentration and 30% effect concentration data, and based on 50% effect concentration toxicity data

5.7 Calculation of soil quality guidelines for aged naphthalene contamination

5.8 Metabolites of naphthalene

5.9 Reliability of the soil quality guidelines

5.10 Comparison with other guidelines

6 DDT

6.1 Compounds considered

6.2 Pathway risk assessment

6.3 Toxicity data

6.4 Normalisation relationships

6.5 Sensitivity of organisms to DDT

6.6 Calculation of soil quality guidelines for fresh DDT contamination

6.6.1 Calculation of generic soil quality guidelines for fresh DDT contamination based on no observed effect concentration and 10% effect concentration toxicity data

6.6.2 Calculation of soil quality guidelines for fresh DDT contamination based on lowest observed effect concentration data and 30% effect concentration data, and based on 50% effect concentration toxicity data

6.7 Calculation of soil quality guidelines for aged contamination

6.8 Reliability of soil quality guidelines

6.9 Important metabolites of DDT

6.10 Comparison with other guidelines

7 Copper

7.1 Copper compounds considered

7.2 Exposure pathway assessment

7.3 Toxicity data

7.4 Normalisation relationships

7.5 Sensitivity of organisms to copper

7.6 Calculation of soil quality guidelines for fresh copper contamination

7.6.1 Calculation of soil quality guidelines for fresh copper contamination based on no observed effect concentration and 10% effect concentration toxicity data

7.6.1.1 Calculation of soil-specific added contaminant limits

7.6.1.2 Calculation of ambient background concentration values

7.6.1.3 Examples of soil quality guidelines for fresh copper contamination based on no observed effect concentration and 10% effect concentration data

7.6.2 Calculation of soil quality guidelines for fresh copper contamination based on lowest observed effect concentration and 30% effect concentration toxicity data, and on 50% effect concentration data

7.6.2.1 Calculation of soil-specific added contaminant limits

7.6.2.2 Calculation of ambient background concentration values

7.6.2.3 Examples of soil quality guidelines for fresh copper contamination in Australian soils based on lowest observed effect concentration and 30% effect concentration toxicity data, and on 50% effect concentration data.

7.7 Calculation of soil quality guidelines for aged copper contamination

7.7.1 Calculation of an ageing and leaching factor for copper

7.7.2 Calculation of soil quality guidelines for aged copper contamination based on no observed effect concentration and 10% effect concentration toxicity data

7.7.2.1 Calculation of soil-specific added contaminant limits

7.7.2.2 Calculation of ambient background concentration values

7.7.2.3 Examples of soil quality guidelines for aged copper contamination in Australian soils based on no observed effect concentration and 10% effect concentration data.

7.7.3 Calculation of soil quality guidelines for aged copper contamination based on LOEC and 30% effect concentration toxicity data, and on 50% effect concentration data.

7.7.3.1 Calculation of soil-specific added contaminant limits

7.7.3.2 Calculation of ambient background concentration values

7.7.3.3 Examples of soil quality guidelines for aged copper contamination in Australian soils based on lowest observed effect concentration and 30% effect concentration data

7.8 Reliability of the soil quality guidelines

7.9 Comparison with other guidelines

8 Lead

8.1 Lead compounds considered

8.2 Exposure pathway assessment

8.3 Toxicity data

8.4 Normalisation relationships

8.5 Sensitivity of organisms to lead

8.6 Calculation of soil quality guidelines for fresh lead contamination

8.6.1 Calculation of soil quality guidelines for fresh lead contamination based on NOEC and 10% effect concentration toxicity data

8.6.1.1 Calculation of soil-specific added contaminant limits

8.6.1.2 Calculation of ambient background concentration values

8.6.1.3 Examples of soil quality guidelines for fresh lead contamination in Australian soils based on no observed effect concentration and 10% effect concentration data

8.6.2 Calculation of soil quality guidelines for fresh lead contamination based on LOEC and 30% effect concentration toxicity data and on 50% effect concentration data

8.6.2.1 Calculation of soil-specific added contaminant limits

8.6.2.2 Calculation of ambient background concentration values

8.6.2.3 Examples of soil quality guidelines for fresh lead contamination in Australian soils based on lowest observed effect concentration and 30% effect concentration data and on 50% effect concentration data

8.7 Calculation of soil quality guidelines for aged lead contamination

8.7.1 Calculation of an ageing and leaching factor

8.7.2 Calculation of soil quality guidelines for aged lead contamination based on NOEC and 10% effect concentration toxicity data

8.7.2.1 Calculation of soil-specific added contaminant limits

8.7.2.2 Calculation of ambient background concentration values

8.7.2.3 Examples of soil quality guidelines for aged lead contamination in Australian soils based on no observed effect concentration and 10% effect concentration data.

8.7.3 Calculation of soil quality guidelines for aged lead contamination based on LOEC and 30% effect concentration toxicity data and on 50% effect concentration data

8.7.3.1 Calculation of added contaminant limits

8.7.3.2 Calculation of ambient background concentration values

8.7.3.3 Examples of soil quality guidelines for aged lead contamination in Australian soils based on lowest observed effect concentration and 10% effect concentration data and on 50% effect concentration data.

8.8 Reliability of the soil quality guidelines

8.9 Comparison with other guidelines

9 Nickel

9.1 Nickel compounds considered

9.2 Exposure pathway assessment

9.3 Toxicity data

9.4 Normalisation relationships

9.5 Sensitivity of organisms to nickel

9.6 Calculation of soil quality guidelines for fresh nickel contamination

9.6.1 Calculation of soil quality guidelines for fresh nickel contamination based on no observed effect concentration and 10% effect concentration toxicity data

9.6.1.1 Calculation of soil-specific added contaminant limits

9.6.1.2 Calculation of ambient background concentration values

9.6.1.3 Examples of soil quality guidelines for fresh nickel contamination in Australian soils based on no observed effect concentration and 10% effect concentration data

9.6.2 Calculation of soil quality guidelines for fresh nickel contamination based on LOEC and 30% effect concentration toxicity data, and on 50% effect concentration data

9.6.2.1 Calculation of soil-specific added contaminant limits

9.6.2.2 Calculation of ambient background concentration values

9.6.2.3 Examples of soil quality guidelines for fresh nickel contamination in Australian soils based on lowest observed effect concentration and 30% effect concentration data, and based on 50% data

9.7 Calculation of soil quality guidelines for aged nickel contamination

9.7.1 Calculation of ageing and leaching factors for nickel

9.7.2 Use of ageing and leaching factors in the methodology

9.7.3 Calculation of soil quality guidelines for aged nickel contamination based NOEC and 10% effect concentration toxicity data

9.7.3.1 Calculation of soil-specific added contaminant limits

9.7.3.2 Calculation of ambient background concentration values

9.7.3.3 Examples of soil quality guidelines for aged nickel contamination in Australian soils based on no observed effect concentration and 10% effect concentration data

9.7.4 Calculation of soil quality guidelines for aged nickel contamination based on LOEC and 30% effect concentration toxicity data, and on 50% effect concentration data

9.7.4.1 Calculation of soil-specific added contaminant limits

9.7.4.2 Calculation of ambient background concentration values

9.7.4.3 Examples of soil quality guidelines for fresh nickel contamination in Australian soils based on lowest observed effect concentration and 30% effect concentration data, and based on 50% effect concentration data

9.8 Reliability of the soil quality guidelines

9.9 Comparison with other guidelines

10 Trivalent chromium

10.1 Chromium (III) compounds considered

10.2 Exposure pathway assessment

10.3 Toxicity data

10.4 Normalisation relationships

10.5 Sensitivity of organisms to trivalent chromium

10.6 Calculation of soil quality guidelines for fresh trivalent chromium contamination

10.6.1 Calculation of added contaminant limits for fresh trivalent chromium contamination

10.6.2 Calculation of ambient background concentration values for fresh trivalent chromium contamination

10.6.3 Examples of soil quality guidelines for fresh trivalent chromium contamination in Australian soils

10.7 Calculation of soil quality guidelines for aged trivalent chromium contamination

10.7.1 Calculation of an ageing and leaching factor for trivalent chromium

10.7.2 Calculation of added contaminant limits for aged trivalent chromium contamination

10.7.3 Calculation of ambient background concentration values

10.7.4 Examples of soil quality guidelines for aged trivalent chromium contamination in Australian soils

10.8 Reliability of the soil quality guidelines

10.9 Comparison with other guidelines

11 Summary

12 Bibliography

13 Appendices

13.1 Appendix A: Raw toxicity data for zinc

13.2 Appendix B. Raw toxicity data for arsenic

13.3 Appendix C: Raw toxicity data for naphthalene

13.4 Appendix D: Raw toxicity data for DDT

13.5 Appendix E: Raw toxicity data for copper

13.6 Appendix F: Explanation of the selection of the soil properties that control the added contaminant limits for copper

13.7 Appendix G. Raw toxicity data for lead

13.8 Appendix H: Raw toxicity data for nickel

13.9 Appendix I: Raw toxicity data for trivalent chromium

14 Glossary

15 Shortened forms

1                   Introduction

1.1              Objectives

The objective of this guideline is to derive EILs for arsenic (As), copper (Cu), chromium III (Cr (III)), dichlorodiphenyltrichloroethane (DDT), naphthalene, nickel (Ni), lead (Pb) and zinc (Zn) using the methodology detailed in Schedule B5b to:

• illustrate the flexibility of the methodology—being able to derive soil contaminant limits that provide different levels of protection, and use different toxicity data
• illustrate the magnitude and appropriateness of the  soil contaminant limits
• compare the EILs with those of overseas jurisdictions.

1.2              Terminology

The term ‘soil quality guideline’ (SQG) is used in this guideline to describe any concentration-based limit for contaminants in soils.

A combination of lowest observed effect concentration (LOEC) and 30% effect concentration data (EC30) has been adopted in the NEPM for the derivation of EILs. Equivalent data for EC10 and EC50 is included for information purposes only.

2                   Overview of the method for deriving soil quality guidelines

Soil quality guidelines can have various purposes. The National Environment Protection (Assessment of Site Contamination) Measure (NEPM) contains a specific type of SQG, the ecological investigation level (EIL), to guide the assessment of contaminated sites in Australia. The EILs were derived in such a manner that when they are exceeded it indicates that terrestrial ecosystems may experience harmful effects due to the presence of contaminants. The EILs are thus used to indicate when further investigation is necessary.

However, SQGs with other purposes can and have been developed. For example, the Dutch have three sets of SQGs, each with a different purpose. These are target levels (their purpose is to indicate the long-term goals for the concentration of contaminants), maximum permissible levels (their purpose is to define the maximum level of contamination that is considered acceptable), and intervention levels (their purpose is to define the maximum permitted concentration before some immediate action is required).

As a result of consultation conducted in developing the Australian methodology in November 2008, three different sets of ecotoxicity data were used to derive SQGs. The three sets of SQGs are termed SQG(NOEC & EC10), SQG(LOEC & EC30) and SQG(EC50) reflecting the type of ecotoxicity data that was used in their generation. A summary of the three types of SQGs, the data used and likely ecotoxicological effects that would be expected to occur if these are met is presented in Table 1. A combination of lowest observed effect concentration (LOEC) and 30% effect concentration data (EC30) has been adopted in the NEPM for the derivation of EILs.

Table 1. The relationship between the three types of soil quality guidelines (SQGs), the data that is used to derive the SQGs and the type of toxic effects that would be experienced if the SQGs are met.

An overview of the SQG derivation methodology (detailed in Schedule B5b) is presented in Figure 1. One of the key aims in developing the methodology was to account for the availability and toxicity of the contaminant in the soil being studied. To do this, key soil and site-specific factors that are known to modify the toxicity of contaminants had to be accounted for. One factor that was incorporated into the methodology was the background concentration. In order to do this, the data used to derive the SQGs was expressed in terms of the amount of contaminant that had to be added to the soil to cause toxicity. When this toxicity data was used in accordance with the methodology, the resulting value was termed the added contaminant level (ACL). An ambient background concentration (ABC) specific to the soil being investigated was then added to the ACL to calculate the SQG.

ACL values are generated as part of the methodology of deriving SQGs. Thus, it is necessary to differentiate the ACLs generated in deriving SQG(NOEC & EC10) from those generated in deriving SQG(LOEC & EC30) and SQG (EC50) values. The ACL generated in deriving an SQG(NOEC & EC10) is termed the NOEC and EC10-based ACL (ACL(NOEC & EC10)). Similarly, ACLs generated in deriving SQG(LOEC & EC30) and SQG (EC50) values are referred to as the LOEC and EC30-based ACL (ACL(LOEC & EC30)) and the EC50-based ACL (ACL(EC50)).

Figure 1. Overview of the  methodology for deriving soil quality guidelines based on NOEC and EC10 data (SQG(NOEC & EC10)) indicated by the green (far left) arrows, based on LOEC and EC30 data (SQG(LOEC & EC30)) indicated by the orange (middle) arrows and based on EC50 data (SQG(EC50)) indicated by the red (far right) arrows. As part of this process, ACLs and ABCs are calculated. The differences between the three SQGs are presented in Table 1.

The key steps in the methodology are:

1. determining the purpose of the SQG and the appropriate level of protection
2. determining the most important exposure pathways
3. collating and screening the toxicity data
4. determining whether the contamination is fresh or aged and whether there are ageing/leaching factors available to account for this
5. normalising the toxicity data
6. calculating the ACL
7. accounting for biomagnification
8. measuring or calculating the ABC
9. calculating SQG(NOEC & EC10),  SQG(LOEC & EC30) and SQG(EC50) values for fresh contamination in soils with different land uses
10. calculating SQG(NOEC & EC10),  SQG(LOEC & EC30) and SQG(EC50) values for aged contamination in soils with different land uses.

These key steps and the decision pathway involved in deriving ACL(NOEC & EC10) and SQG(NOEC & EC10) values are provided in Figure 2 below. Exactly the same procedure would be used to derive SQG(LOEC & EC30) and SQG(EC50) values, except that different toxicity data would be used (Table 1). Details of the methodology for calculating SQGs are provided in Schedule B5b.

Land has a variety of potential uses, and the level of protection that is appropriate for each land use varies. For example, it is appropriate for a higher level of protection to be applied to areas of ecological significance compared to industrial land. The recommended levels of protection for various land uses are provided in Schedule B5b and are used in this guideline.  For contaminants that do not biomagnify, the recommended level of protection of species for areas of ecological significance, urban residential/public open space and commercial/industrial land are 99%, 80% and 60% respectively. For contaminants that biomagnify, the recommended levels of protection of species for areas of ecological significance, urban residential/public open space and commercial/industrial land are 99%, 85% and 65% respectively. SQGs were generated for areas of ecological significance, urban residential land/public open space, and commercial/industrial land uses.

The contamination at many contaminated sites is not fresh, rather it has been there for some years. The biological availability (bioavailability) and toxicity of many contaminants decreases over time (that is, it ages) due to binding to soil particles, chemical and biological degradation and a range of other processes. Furthermore, in many laboratory-based ecotoxicity experiments that spike soils with soluble metal salts, ecotoxicity is overestimated due to a lack of leaching of soluble salts which affect metal sorption. These factors have been addressed in recent risk assessments for metals in soils using ’ageing/leaching‘ factors, and can be accounted for by multiplying the toxicity data by an ageing/leaching factor and thus deriving SQGs for aged contamination. Site-specific assessments of a contaminant’s bioavailability can also be made, but these are usually conducted as part of a more detailed site-specific (Tier 2) ecological risk assessment. When ageing/leaching factors were available for the test chemicals examined in this study, SQGs were derived for aged contamination.

When contaminants are introduced to soil, some will bind strongly to the soil while others are mobile and will move off-site. Leaching to groundwater is a key off-site migration pathway and can result in aquatic ecosystems being exposed to contaminants. Therefore, the potential of contaminants to leach is an important characteristic that affects the environmental fate and effect they cause. The leaching potential is not controlled solely by the physicochemical properties of contaminants, but also by the properties of the soil containing the contaminant and climatic conditions. It is not possible or appropriate to account for the potential to leach in deriving practical SQGs at a generic level, rather this should be done as part of a more detailed site-specific ecological risk assessment.

Given the available data, the most complete set of SQGs was derived for each of the eight contaminants. A summary of what SQGs could be derived is presented below.

• For chromium (III), copper, nickel and zinc, it was possible to derive a set of soil-specific SQGs using each of the three types of toxicity data for each of the three land uses for both fresh and aged contamination.
• For arsenic and lead, it was possible to derive generic (not soil-specific) SQGs using each of the three types of toxicity data for each of the three land uses and for both fresh and aged contamination.
• For DDT and naphthalene, it was possible to derive generic (not soil-specific) SQGs using each of the three types of toxicity data for each of the three land uses but only for fresh contamination.

In addition, SQGs that account for the potential of contaminants to leach (and therefore should protect aquatic ecosystems) were derived for arsenic and zinc. This was only done for these contaminants to illustrate how this is done and what effect it has on the resulting SQGs compared to the SQGs that do not account for leaching.

2.1              Precision of estimates and rounding of added contaminant limits

In order to increase the readability and ease of use of this report the ACL, ABC and SQG values presented in the various tables have all been rounded off using the following scheme:

• all values <1 were rounded off to the nearest 0.1
• all values between 1 and 10 were rounded off to the nearest whole number
• all values between 10 and 100 were rounded off to the nearest multiple of 5
• all values between 100 and 1000 were rounded off to the nearest multiple of 10
• all values greater than 1000 were rounded off to the nearest 100 units.

Figure 2. Schematic of the methodology for deriving soil quality guidelines (SQGs) (modified from Heemsbergen et al. 2008). Green arrows show the path when the preceding question was answered with a ‘yes’ while the red arrows indicate the path when the answer was ‘no’. Blue arrows indicate the path when there is no choice.

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 matter (%) + clay content (%)]  (equation 1)

The background concentration was then subtracted from the total concentration data to derive the added concentration toxicity value.

The toxicity database used to calculate the SQG(NOEC & EC10) values for Zn included EC10 and NOEC toxicity data for nine soil processes (Table 2), 14 invertebrate species and 1 invertebrate community measurement (Table 3) and 22 plant species (Table 4). The raw data used to generate Tables 2–4 is provided in Appendix A. There was sufficient data (that is, toxicity data) for at least five species or soil processes that belong to at least three taxonomic or nutrient groups (Schedule B5b) available to derive SQG(NOEC & EC10) values using a species sensitivity distribution (SSD) methodology. Given that Zn does not biomagnify, the level of protection recommended for non-biomagnifying contaminants was used to generate the SQG for each land use.

Table 2. The geometric mean values of the zinc toxicity data (expressed in terms of added Zn) for individual soil processes.

Table 3. The geometric mean values of zinc (Zn) toxicity data (as added Zn) for soil invertebrate species and an invertebrate community.

Table 4. The geometric mean values of the zinc (Zn) toxicity data (expressed in terms of added Zn) for individual plant species.

3.4              Normalisation relationships

A normalisation relationship is an empirical model that predicts the toxicity of a single contaminant to a single species using soil physicochemical properties (for example, soil pH and organic carbon content). Seven normalisation relationships were reported in the literature for Zn toxicity (Table 5). Three were developed for Australian soils (Broos et al. 2007; Warne et al. 2008a; Warne et al. 2008b) and four have been derived for European soils (Lock & Janssen 2001; Smolders et al. 2003). Three of the relationships were for plants, two for microbial functions and two for soil invertebrates. Of these, relationships 14, 6 and  7 were used to derive Zn SQGs. Relationship number 5 for wheat was not used, as an equivalent field-based relationship for Australian soils was available and field-based normalisation relationships provide better estimates of toxicity in the field (Warne et al. 2008a) and thus are preferred to laboratory-based relationships (Schedule B5b).

Normalisation relationships are used to account for the effect of soil characteristics on toxicity data, so the resulting toxicity data more closely reflect the inherent sensitivity of the test species. All the Zn toxicity data in Tables 2–4 was normalised to their equivalent toxicity in the recommended Australian reference soil (Schedule B5b) (Table 6). Depending on the conditions under which the toxicity tests were conducted, the normalised toxicity data could be higher or lower in the reference soil compared to the original toxicity data in the test soil.

Table 5. Normalisation relationships for the toxicity of zinc to soil invertebrates, soil processes and plants.

CEC = cation exchange capacity (cmolc/kg); OC = organic carbon content (%); PNR = potential nitrification rate; SIN = substrate induced respiration.

Table 6. Values of soil characteristics for the recommended Australian reference soil to be used to normalise toxicity data

3.5              Sensitivity of organisms to zinc

The toxicity data (geometric means) used by the SSD method to calculate the ACL is shown in Table 2 for soil processes, Table 3 for soil invertebrates and Table 4 for plants. Figure 3 shows the SSD (that is, a cumulative distribution of the geometric means of the species) for all species for which there was Zn toxicity data. Toxicity data for plants, soil processes and soil invertebrates was evenly spread in the SSD, which indicates that these groups of organisms all have a similar sensitivity to Zn. Therefore, all the toxicity data was used to derive the ACLs, thus increasing the quantity of data used in the SSD method and increasing the reliability of the ACL values.

Figure 3. The species sensitivity distribution (plotted as a cumulative frequency against added zinc (Zn) concentration) for soil processes, soil invertebrates and plant species to Zn.

3.6              Calculation of soil quality guidelines for fresh zinc contamination

Soil quality guidelines were derived for fresh zinc contamination using three different sets of toxicity data: NOEC and EC10; LOEC and EC30; and EC50. The methods by which they were calculated and the resulting ACL and SQG values are presented in the following sections.

3.6.1         Calculation of soil quality guidelines for fresh zinc contamination based on no observed effect concentration and 10% effect concentration toxicity data

3.6.1.1         Calculation of soil-specific added contaminant limits

The NOEC and EC10 toxicity data were normalised using the equations presented in Table 5 to the Australian reference soil (Table 6) and then the lowest geometric mean for each species/soil microbial process was entered into the BurrliOZ species sensitivity distribution (Campbell et al. 2000) method. The SSD generated a single numerical value (that is, the ACL(NOEC & EC10) for each desired level of protection. These ACL(NOEC & EC10) values only apply to the Australian reference soil.

The ACL(NOEC & EC10) value for the Australian reference soil with an urban residential land/public open space use was approximately 100 mg/kg. These ACL(NOEC & EC10) values for the reference soil were then used to calculate ACL(NOEC & EC10) values for a range of soils (that is, soil-specific ACL(NOEC & EC10)) for each group of organisms using the same normalisation relationships as before but in the reverse manner. The following explains how the soil-specific ACL(NOEC & EC10) values for soils with an urban residential /public open space land use were calculated as an example of how this was done for each of the land uses.

Soil-specific ACL(NOEC & EC10) values for soil processes varied with soil pH and ranged from 20 to 330 mg/kg added Zn for soils with pHs between 4 and 7.5 (Table 7). The soil-specific ACL(NOEC & EC10) values for invertebrates (Table 8) varied with cation exchange capacity (CEC), with values ranging from 60 to 420 mg/kg for soils with CEC values ranging from 5 to 60 cmolc/kg. Soil-specific ACL(NOEC & EC10) values for plants (Table 9) were pH- and CEC- specific and ranged from 20 to 910 mg/kg for soils with pHs between 4 and 7.5 and CEC values between 5 and 60 cmolc/kg.

Table 7. Soil-specific ACL values for zinc (Zn) based on no observed effect concentration and 10% effect concentration toxicity data that should theoretically protect 80% of soil processes in soils with pH values ranging from 4.0 to 7.5.

Table 8. Soil-specific ACL values for zinc (Zn) based on no observed effect concentration and 10% effect concentration toxicity data that should theoretically protect 80% of invertebrate species in soils with CEC ranging from 5 to 60 cmolc/kg.

Table 9. Soil-specific ACL values for zinc (Zn) based on no observed effect concentration and 10% effect concentration toxicity data that should theoretically protect 80% of plant species in soils with pH values ranging from 4.0 to 7.5 and CEC values ranging from 5 to 60 cmolc/kg.

These soil-specific ACL(NOEC & EC10) values for each organism group (presented in Tables 7 to 9) were then merged into a single set of soil-specific ACL(NOEC & EC10) values—so that the lowest ACL(NOEC & EC10) value for each combination of soil pH and CEC was adopted (Table 10). The ACL(NOEC & EC10) values presented in Table 10 should protect at least 80% of soil processes, soil invertebrate and plant species and these ranged from 20 to 330 mg/kg in soils with pH values between 4 and 7.5 and CEC values between 5 and 60 cmolc/kg. The ACL(NOEC & EC10) values presented in Tables 79 are the ACLs for individual groups of organisms and should not be used as ACL(NOEC & EC10) values.

Table 10. Soil-specific added contaminant limits based on no observed effect concentration and 10% effect concentration toxicity data (ACL(NOEC & EC10), mg/kg) for zinc (Zn) that theoretically protect at least 80% of soil processes, soil invertebrate species and plant species in soils with a pH ranging from 4.0 to 7.5 and CEC values ranging from 5 to 60 cmolc/kg. These values may be used as ACLs(NOEC & EC10)  for Zn in freshly contaminated soils with an urban residential /public open space land use.

The same methods as described above were used to generate the ACL (NOEC & EC10) values for areas of ecological significance and commercial/industrial land uses. The ACL (NOEC & EC10) values for these land uses are presented in Tables 11 and 12.

Table 11. Soil-specific added contaminant limits based on no observed effect concentration and 10% effect concentration toxicity data (ACL(NOEC & EC10), mg/kg) for zinc (Zn) that theoretically protect at least 99% of soil processes, soil invertebrate species and plant species in soils with a pH ranging from 4.0 to 7.5 and CEC values ranging from 5 to 60 cmolc/kg. These values may be used as ACLs(NOEC & EC10) for Zn in freshly contaminated soils for areas of ecological significance.

Table 12. Soil-specific added contaminant limits based on no observed effect concentration and 10% effect concentration toxicity data (ACL(NOEC & EC10), mg/kg) for zinc (Zn) that theoretically protect at least 60% of soil processes, soil invertebrate species and plant species in soils with a pH ranging from 4.0 to 7.5 and cation exchange capacity (CEC) values ranging from 5 to 60 cmolc/kg. These values may be used as ACLs(NOEC & EC10) for Zn in freshly contaminated soils with a commercial/industrial land use.

3.6.1.2         Calculation of ambient background concentration values

To convert ACLs to SQGs, the ambient background concentration (ABC) needs to be added to the ACL. Three methods of determining the ABC were recommended in the methodology for deriving SQGs (Schedule B5b). The preferred method is to measure the ABC at an appropriate reference site. However, where this is not possible the methods of Olszowy et al. (1995) and Hamon et al. (2004) were recommended, depending on the situation.

For sites with no history of contamination the method of Hamon et al. (2004) was recommended to estimate the ABC. In this method, the ABC for Zn varies with the soil iron concentration (Table 13). Predicted ABC values for Zn range from 3 to 60 mg/kg in soils with iron concentrations between 0.1 and 20%.

Table 13. Zinc (Zn) ABC calculated using the Hamon et al. (2004) method.

For aged contaminated sites (i.e. the contamination has been in place for at least two years, see Schedule B5b) the methodology recommends using the 25th percentiles of the ABC data for the ‘old suburbs’ of Olszowy et al. (1995) (see Table 14). The ABC values for Zn in ‘new suburbs’ were similar to the values predicted by the Hamon et al. (2004) method. Therefore it is recommended that the Hamon et al. (2004) method be used to generate ABC values for new suburbs (that is, <2 years old) as soil-specific values will be generated, while for old suburbs with aged contamination (that is, >2 years) it was recommended that the 25th percentile of the ABC data from old suburbs (Olszowy et al. 1995) be used.

Table 14. Zinc (Zn) ABC based on the 25th percentiles of Zn concentrations in ‘old suburbs’ (i.e. >2 years old) from various states of Australia (Olszowy et al. 1995).

3.6.1.3         Examples of soil quality guidelines for fresh zinc contamination based on no observed effect concentration and 10% effect concentration data

To calculate an SQG(NOEC & EC10), the ABC value is added to the ACL(NOEC & EC10). ABC values vary with soil type. Therefore, it is not possible to present a single set of SQG(NOEC & EC10) values. Thus, two examples of SQG(NOEC & EC10) values for urban contaminated soils are provided below. These examples would be at the low and high end of the range of SQGs values (but not the extreme values) generated for Australian soils.

3.6.2         Calculation of soil quality guidelines based on protecting aquatic ecosystems from leaching of fresh zinc contamination

As indicated in the exposure pathway assessment, the log Kd values for Zn measured in a range of Australian soils were below 3 and therefore there is the potential in some soils for Zn to leach to groundwater and effect aquatic ecosystems. Although the calculation of SQGs based on protecting aquatic ecosystems from the effects of leached contaminants is not included in the EIL derivation methodology (Schedule B5b), the calculations are presented here to illustrate the recommended approach and what effect this has on the resulting SQGs. The following SQGs were based on the ACL(NOEC & EC10) values for urban residential/public open space land use.

The soil-specific SQGs for Zn that accounted for leaching potential were calculated using the US EPA method (US EPA 1996).

SQG = Cw . (Kd + (θw + θa . H) / ρb) . DAF    (equation 2)

where SQG is the appropriate soil quality guideline in soil (mg/kg), Cw is the target soil leachate concentration (mg/L) (that is, the Australian and New Zealand freshwater quality guideline for Zn, (ANZECC and ARMCANZ 2000)), Kd is the soilwater partition coefficient (L/kg), θw is the water-filled soil porosity Lwater/Lsoil), θa is the air-filled soil porosity (Lair/Lsoil), ρb is the dry soil bulk density (kg/L), H is the Henry’s law constant (unitless), and DAF is the dilution and attenuation factor[2]. The values of DAF used in the calculations were 1 and 20. There is a linear relationship between the DAF and the SQGs, thus the SQGs calculated using a DAF of 20 are 20 times larger than those calculated using a DAF of 1.

The value for θw was set to 0.1 Lwater/Lsoil, θa was set to 0.1 Lair/Lsoil and ρb was set to 1.3 kg/L. The calculated SQG values when DAF was 1 and 20 are presented in Tables 15 and 16 respectively.

Table 15. Soil-specific zinc (Zn) soil quality guidelines (SQG(NOEC & EC10), mg total Zn/kg) based on protecting groundwater ecosystems from groundwater leaching when the dilution and attenuation factor (DAF) was 1.

Table 16. Soil-specific zinc (Zn) soil quality guidelines (SQG(NOEC & EC10), mg total Zn/kg) based on protecting groundwater ecosystems from groundwater leaching when the dilution and attenuation factor (DAF) was 20.

3.6.3         Calculation of soil quality guidelines for fresh zinc contamination based on lowest observed effect concentration and 30% effect concentration toxicity data, and based on 50% effect concentration toxicity data

In addition to calculating SQG(NOEC & EC10) values, two other sets of SQGs corresponding to two other levels of protection were generated. T hese were the SQG(LOEC & EC30), which indicate concentrations above which moderate toxic effects would occur and the SQG(EC50), which indicate concentrations above which marked toxic effects would occur.

3.6.3.1         Calculation of soil-specific added contaminant limits

The Zn SQG(LOEC and EC30) and SQG(EC50) and associated ACL values were calculated using the methodology, except the input data for the SSD was changed to the appropriate type (Table 1). This data is presented in Tables 24 and the raw data can be found in Appendix A. These measures of toxicity were not available in all instances, so, to maximise the data available to calculate SQG(LOEC and EC30) and SQG(EC50) values, the available toxicity data was converted to these measures using conversion factors. The NBRP (cited in Heemsbergen et al. 2008) derived a set of conversion factors for Cu and Zn (Table 17). These experimentally-based conversion factors were used rather than the generic conversion factors presented in Heemsbergen et al. (2008), which is consistent with the approach recommended in the  methodology for deriving SQGs. Table 18 shows the ACL(LOEC & EC30) and ACL(EC50) values for the Australian reference soil (that is, a pH of 6 and a CEC of 10 cmolc/kg) with areas of ecological significance, urban residential/public open space and commercial/industrial land uses. The set of soil-specific Zn ACL(LOEC & EC30) and ACL(EC50) values for each land use are presented in Tables 19 and 20.

Table 17. Conversion factors used to convert various measures of toxicity for cations such as copper and zinc. The conversion factors were obtained from unpublished data from the Australian National Biosolids Research Program and were cited by Heemsbergen et al. (2008).

Table 18. Zinc (Zn) added contaminant levels based on lowest observed effect concentration and 30% effect concentration data (ACL(LOEC & EC30)), and based on 50% effect concentration data (ACL(EC50)) for the Australian reference soil with various land uses.

Table 19. Soil-specific added contaminant limits based on lowest observed effect concentration and 30% effect concentration toxicity data (ACL(LOEC & EC30), mg/kg) for fresh zinc (Zn) that should theoretically provide the appropriate level of protection (that is, 99, 80 or 60% of species) to soil processes, soil invertebrate species and plant species in soils with a pH ranging from 4.0 to 7.5 and CEC values ranging from 5 to 60 cmolc/kg. These are the recommended ACL(LOEC & EC30) values in freshly contaminated soils with each land use.

Table 20. Soil-specific added contaminant limits based on 50% effect concentration toxicity data (ACL(EC50), mg/kg) for fresh zinc (Zn) that should theoretically provide the appropriate level of protection (that is, 99, 80 or 60% of species) to soil processes, soil invertebrate species and plant species in soils with a pH ranging from 4.0 to 7.5 and cation exchange capacity (CEC) values ranging from 5 to 60 cmolc/kg. These are the recommended ACL(EC50) for Zn in freshly contaminated soils with each land use.

3.6.3.2         Calculation of ambient background concentration values

The ABC values for freshly contaminated soils were calculated using the method set out in this Schedule and presented in Table 13.

3.6.3.3         Examples of soil quality guidelines for fresh zinc contamination based on lowest observed effect concentration and 30% effect concentration data, and based on 50% effect data

In order to calculate the SQG(LOEC & EC30) and SQG(EC50) values the soil-specific ABC has to be added to the ACL(LOEC & EC30) and ACL(EC50) values, respectively. Therefore, the SQG(LOEC & EC30) and SQG(EC50) values will always be at least as large as those presented in Tables 19 and 20. Examples of the SQG(LOEC & EC30) and SQG(EC50) values are provided below.

3.7              Calculation of soil quality guidelines for aged zinc contamination

3.7.1         Calculation of an ageing and leaching factor for zinc

In addition to calculating SQGs in recently contaminated soils (that is, contamination is <2 years old), an equivalent set of levels was derived for soils where the contamination is aged (that is, it has been present for ≥2 years). The Zn SQG(NOEC & EC10), SQG(LOEC & EC30) and SQG(EC50) for aged sites were calculated using the methods set out in Schedule B5b and this Schedule, the only difference being that laboratory toxicity data based on freshly spiked soils or soils that had not been leached were multiplied by an ageing/leaching factor. A factor (3 for Zn) was developed by Smolders et al. (2009) that accounted for ageing and leaching of various metals. This ageing and leaching factor (ALF) has been incorporated into the methodology to derive the Flemish soil quality guidelines (VLAREBO 2008). Therefore, the raw toxicity data (Appendix A) for Zn that was generated using freshly spiked and non-leached soils was multiplied by this conversion factor and the geometric means for each species and soil process recalculated (Tables 21–23). It should be noted that the values in Tables 21–23 are not simply the data from Tables 2–4 multiplied by 3, as the correction factor was not applied to all the data (for example, data from the field-based NBRP was not adjusted).

3.7.2         Calculation of soil quality guidelines for aged zinc contamination based on no observed effect concentration and 10% effect concentration toxicity data

3.7.2.1         Calculation of added contaminant limits for aged zinc contamination based on no observed effect concentration and 10% effect concentration toxicity data

The lowest geometric mean of the age-corrected toxicity data for each species/soil microbial process that was used to derive the aged ACL(NOEC & EC10) values is presented in Table 21 for soil processes, Table 22 for soil invertebrate species and Table 23 for plant species. The conversion of the fresh toxicity data to account for ageing/leaching and the resulting toxicity values are presented in Appendix A.

Table 21. The geometric mean values of the aged and age-corrected zinc (Zn) toxicity data (expressed in terms of added Zn) for soil processes.

Table 22. The geometric mean values of the aged and age-corrected zinc (Zn) toxicity data (expressed in terms of added Zn) for soil invertebrate species.

Table 23. The geometric mean values of the aged and age-corrected zinc (Zn) toxicity data (expressed in terms of added Zn) for plant species.

For each urban residential/public open space land use, soil-specific ACL(NOEC & EC10) values were derived separately for soil processes, soil invertebrate species and plant species (data not shown). Within each land use type, the soil-specific ACL(NOEC & EC10) values for each organism group were then merged so that the lowest ACL(NOEC & EC10) value for each combination of soil pH and CEC was adopted (Table 24). These should theoretically protect 99%, 80% and 60% of all soil processes, soil invertebrate species and plant species that are exposed to aged Zn contamination in soils that  are in an area of ecological significance, or have an urban residential/public open space, commercial/industrial land use, respectively.

Table 24. Soil-specific added contaminant limits based on no observed effect concentration and 10% effect concentration toxicity data (ACL(NOEC & EC10), mg/kg) for aged zinc (Zn) contamination that should theoretically provide the appropriate level of protection (i.e. 99, 80 or 60% of species) to soil processes, soil invertebrate species and plant species in soils with a pH ranging from 4.0 to 7.5 and CEC values ranging from 5 to 60 cmolc/kg. These are the recommended ACL(NOEC & EC10) values for Zn in aged contaminated soils with each land use.