Toxicant default guideline values for water quality in aquatic ecosystems

Throughout the Water Quality Guidelines, we provide context and detailed guidance on how to use default guideline values (DGVs) correctly.

You can search for toxicant DGVs for the protection of aquatic ecosystems in freshwater and marine water.

Where possible, DGVs for toxicants have been derived using the species sensitivity distribution (SSD) approach, using methods described in the ANZECC & ARMCANZ (2000) guidelines for DGVs published in 2000 and Warne et al. (2018) for all DGVs published since 2000. Where the SSD approach could not be used, the less preferred ‘assessment-factor approach’ was used, following the method described in the ANZECC & ARMCANZ (2000) guidelines. Refer to Deriving guideline values for details.

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Retrieval of default guideline values for fresh and marine water

Search results provide the DGVs and information to support them.

Medium — whether the DGV applies to freshwater or marine water. For ground water and brackish and hypersaline surface water, see the guidance provided below in Guideline values for other water types.

Reliability classification — DGVs are classified as very high, high, moderate, low, very low or unknown. Classification is mainly based on the number and type (chronic, acute or a mix of both) of data used to derive the guideline value, as well as the fit of the statistical (SSD) model to the data (refer to details).

We have updated the reliability classification of all DGVs from the ANZECC & ARMCANZ (2000) guidelines to reflect the current classification (refer to Warne et al. 2018).

Publication date — year of publication of the DGV.

DGVs for different levels of species protection — where DGVs have been derived using the SSD method, guideline values are provided for 99, 95, 90 and 80% species protection. The DGV that is applicable to your situation depends on the current or desired condition of the ecosystem and the associated level of protection that is assigned. In most cases:

high ecological/conservation value system — apply 99% species protection DGV
slightly to moderately disturbed system — apply 95% species protection DGV
highly disturbed system — apply 90 or 80% species protection DGV.

Guideline values derived using the less preferred assessment-factor method cannot be related to a percentage of species protected; they are assigned an ‘unknown’ level of species protection. Refer to Level of protection for additional guidance on determining an ecosystem condition and associated level of protection.

Specific comments and general comments — for some toxicants, important context or guidance helps you to better understand the DGV and, in some cases, its implementation.

Downloadable files — we provide links to:

toxicant DGV technical briefs for details of the DGV, including background on the toxicant and its toxicity, available and final toxicity data, final DGVs and any associated caveats to their use, supporting information and references
toxicant data table, showing raw data that were considered acceptable for inclusion in the guideline value derivation dataset, and the associated toxicity test details
toxicant quality assessment worksheet, which provides the details of the quality assessment scores for each of the toxicity data values assessed for inclusion in the DGV derivation.

Guideline values for other water types

Default guideline values have been derived for fresh and marine waters but not for groundwater or brackish or hypersaline surface waters.

Groundwater

Groundwater is often considered as a source of chemical stressors to surface waters and has historically been managed as such, with guideline values for the relevant community values being applied at the point the groundwater expresses at the surface. However, while groundwater plays a significant role in sustaining surface waters and their various community values, groundwater ecosystems themselves may be important and require protection. These ecosystems function differently to surface water ecosystems and, hence, DGVs derived to protect surface water ecosystems may not be applicable to groundwater ecosystems. We provide some additional information and guidance on how the Water Quality Guidelines should be applied to groundwater, but this is an area that needs further development.

Brackish and hypersaline water (including estuaries)

There are generally too few ecotoxicological data for brackish (i.e. of a salinity between fresh and marine) and hypersaline (i.e. of a salinity greater than seawater) systems to be able to derive DGVs for these types of waters.

Estuaries are typically brackish and sometimes even hypersaline. In addition to the lack of relevant ecotoxicological data, estuarine systems are highly variable and dynamic, especially in relation to their physico-chemistry (e.g. salinity, turbidity) and, therefore, it is not possible to derive DGVs that would be appropriately applicable to all estuarine waters all the time.

In most cases, it will be necessary to make a professional judgment about an appropriate guideline value for brackish or hypersaline waters. The appropriateness of the freshwater and marine water DGVs should be carefully assessed and compared relative to the local conditions (e.g. water physico-chemistry, local species). This would include examination of the supporting data used to derive the DGVs. Note that it is possible that neither the freshwater nor the marine water DGVs will be appropriate to use. Nevertheless, some guidance is provided below.

For metals that are affected by hardness or other key toxicity modifying factors (e.g. pH, dissolved organic carbon, alkalinity), it is possible to use the freshwater DGVs for brackish waters with salinities up to 2 ppt, by applying the hardness corrections in Warne et al. (2018) or other such corrections as may be published in the future for certain metals. The water hardness at this salinity is approximately 350–400 mg/L (as CaCO3), which roughly corresponds to the upper limit of the range of water hardness values for which the hardness corrections were developed (ANZECC/ARMCANZ 2000). The values of the relevant toxicity modifying factors in the water should always be verified before the DGV is corrected. For higher salinities, the marine DGVs for metals are recommended. Where salinity of an estuarine water body changes frequently (i.e. with the tidal cycle), the lowest of the marine and freshwater DGVs for metals is recommended. The above recommendations apply unless available evidence indicates a different approach is needed. For example, decisions would need to take into account the relative reliability of marine and freshwater DGVs, and whether there is or appears to be a difference in toxicity between freshwater and marine water.

For other toxicants, and if there is little relevant information to support a decision, we recommend that you adopt the lower of the two DGVs (freshwater or marine) as an interim measure. The assessment of ecosystem receptor lines of evidence is always recommended as part of a weight of evidence process to improve understanding of the impacts of toxicants (including metals) in estuarine/brackish waters. As a part of this, it might be necessary to derive a locally relevant guideline value.

Reliability classification for default guideline values

The primary purpose of the reliability classification scheme for toxicant guideline values is to provide a quick and transparent way of indicating the general level of confidence in a guideline value. The classification scheme can be applied to both DGVs and site-specific guideline values.

Guideline values are assigned a level of reliability based on 4 factors:

method used to derive the guideline value (SSD or assessment factor)
number of species for which appropriate quality toxicity data are available (5 to 7, 8 to 14 or ≥ 15)
type of toxicity data (chronic, a mixture of chronic and converted acute, a mixture of chronic fresh and chronic marine data, or only converted acute values)
a visual assessment of the fit of the SSD to the toxicity data (good or poor).

There are 6 classes of reliability: very high, high, moderate, low, very low and unknown reliability (Table 1).

Table 1 Details of the reliability classification for toxicant guideline values (adapted from Warne et al. 2018)
Derivation method	Type of toxicity data	Number of data	Model fit	Reliability
Species sensitivity distribution	Chronic	≥ 15	Good	Very high
		≥ 15	Poor	Moderate
		8–14	Good	High
		8–14	Poor	Moderate
		5–7	Good	Moderate
		5–7	Poor	Low
	Combined chronic and converted acute or Combined chronic fresh and chronic marine	≥ 15	Good	Moderate
		≥ 15	Poor	Low
		8–14	Good	Moderate
		8–14	Poor	Low
		5–7	Good	Moderate
		5–7	Poor	Low
	Converted acute	≥ 15	Good	Moderate
		≥ 15	Poor	Low
		8–14	Good	Moderate
		8–14	Poor	Low
		5–7	Good	Low
		5–7	Poor	Very low
Assessment factor	Chronic or converted acute	< 5	Not applicable	Unknown

The reliability of a guideline value helps indicate whether it would benefit from the acquisition and incorporation of more toxicity data into the derivation. Higher reliability guideline values can be derived using the method described in Warne et al. (2018).

Ecotoxicity data needed for the derivation can be obtained from:

more recent data in the literature, including more recent water quality guideline value documents or their equivalent from other jurisdictions
generating new data.

Refer to Warne et al. (2018) for more details on the reliability classification.

Improved guideline values can be submitted, via the third-party guideline value derivation process, for national consideration and endorsement as DGVs.

Application of default guideline values

Although the Water Quality Guidelines’ DGVs are not mandatory, unless specified as so by the relevant state, territory or local jurisdiction, we provide guidance here on how the DGVs should be applied.

Our DGVs are mostly derived according to risk assessment principles using data from laboratory tests in clean water. They represent the current best estimates of the concentrations of toxicants that should have no significant adverse effects on the aquatic ecosystem. However, and in keeping with the over-riding principle of continual improvement, where the concentration of a contaminant is below the appropriate guideline value, then the over-riding objective should be to continue to improve, or at least maintain, water quality (i.e. not to allow increases in concentration up to the guideline value).

DGVs are based on direct toxic effects of individual toxicants. Where possible, a hierarchy of chemical measurements (that is, total, dissolved, then bioavailable fractions) should be used for comparison with the DGVs. Preferably, you would do this assessment together with the measurement of other lines of evidence, using a weight-of-evidence process.

The reliability of a guideline value helps indicate how you should use that guideline value. Guidance for how to use the DGVs based on their reliability classification is provided in Table 2. This would also apply to site-specific guidelines values.

Table 2 Guidance on the use of default guideline values (DGVs) according to their reliability
DGV reliability	Adequate for assessing water quality?	Use guidance
Very high	Yes	Use these DGVs in the context of the accompanying supporting information. Use with other lines of evidence if possible or needed.
High	Yes	Use these DGVs in the context of the accompanying supporting information. Use with other lines of evidence if possible or needed.
Moderate	Yes	Use these DGVs in the context of the accompanying supporting information. Use with other lines of evidence to account for the lower reliability of the DGVs and improve overall confidence in the assessment. Supplement the DGV derivation with additional chronic toxicity data if possible to improve the DGVs’ reliability.
Low	No	Use only as interim values, with a plan to improve DGV reliability or derive site-specific guideline values by acquiring relevant additional chronic toxicity data to enable derivation of a moderate reliability guideline value at the least. If used, use with other lines of evidence to sufficiently account for the lower reliability of the DGVs and improve the overall confidence in the assessment. Document the justification for using these DGVs.
Very low	No	Use only as interim values, with a plan to improve DGV reliability or derive site-specific guideline values by acquiring relevant additional chronic toxicity data to enable derivation of a moderate reliability guideline value at the least. If used, use with other lines of evidence to sufficiently account for the lower reliability of the DGVs and improve the overall confidence in the assessment. Document the justification for using these DGVs.
Unknown	No	Use only as interim values, with a plan to improve DGV reliability or derive site-specific guideline values by acquiring relevant additional chronic toxicity data to enable derivation of a moderate reliability guideline value at the least. If used, use with other lines of evidence to sufficiently account for the lower reliability of the DGVs and improve the overall confidence in the assessment. Document the justification for using these DGVs.

DGVs in the Water Quality Guidelines classified as very high, high or moderate represent an adequate screening point for assessing water quality in conjunction with other relevant lines of evidence (weight of evidence).

Sometimes, an assessment of water quality using a high or very high reliability DGV in the absence of other lines of evidence may be appropriate. For example, where the DGV is significantly above the measured environmental concentrations.

DGVs classified as either low, very low or unknown reliability should only be used as interim values with a commitment to improving their reliability or deriving site-specific guideline values.

If low, very low or unknown reliability DGVs are used, then the justification for their use must be provided. Due to the lower confidence in the low, very low or unknown reliability DGVs, additional lines of evidence need to be used in conjunction with these DGVs when assessing water quality.

DGVs should always be used in the context of all accompanying supporting information, for example:

In most cases, DGVs classified as either moderate, low, very low or unknown will have certain data limitations that could be addressed by acquiring more chronic toxicity data
Very high and high reliability DGVs can have specific limitations, which should have been documented, and that may need to be taken into account. Examples of this are provided in Warne et al. (2018).

Determining if a toxicant DGV has been exceeded

The guidance provided here is general and jurisdictions should always be consulted for any additional specific requirements for determining exceedances of toxicant guideline values for aquatic ecosystem protection.

Determining exceedances of DGVs should be done as part of a weight of evidence approach for water/sediment quality assessment, where relevant pressure, stressor and/or ecosystem receptor indicators are measured to make an overall assessment of whether water/sediment quality is acceptable.

The Monitoring section of the ANZG website provides guidance on comparing monitoring data to guideline values. This guidance recommends that the 95th percentile of the monitoring data for a toxicant be compared with the DGV. Thus, a DGV shall be regarded as being exceeded if the 95th percentile of the monitoring data, having been rounded according to the Australian Standards SAA 2706-2003 to the same number of significant figures in the DGV, exceeds the DGV, taking into account the accuracy of the chemical analysis for the toxicant.

This approach is more stringent than for guideline values derived using the reference site approach (e.g. the physical and chemical stressor DGVs), because the toxicant DGVs are based on actual biological effects data and, so, by implication, exceedance of a DGV indicates a potential for ecological harm. Because the proportion of values required to be less than the DGV is very high (95%), a single observation greater than the DGV would be legitimate grounds for determining that an exceedance has occurred in most cases, even early in a sampling program. However, the need or otherwise for subsequent management action would depend on an overall assessment of risk/impact based on all the lines of evidence.

As noted above, the accuracy of the chemical analysis for a toxicant in a water sample should also be taken into account when determining an exceedance of a DGV. It is essential that analytical measurements are as accurate as possible given available analytical techniques. Commercial analytical laboratories will report the uncertainty of an analysis, such as a 95% confidence interval around the measurement, upon request. Consideration may need to be given as to whether the lower 95% confidence interval of the measurement does or does not exceed the DGV. The implications of this may differ depending on the purpose of the assessment (e.g. regulatory compliance versus general ecosystem health/condition assessment) and also between jurisdictions.

Finally, and in keeping with the over-riding principle of continual improvement, where the concentration of a toxicant is below the appropriate guideline value, then the over-riding objective should be to continue to improve, or at least maintain, water quality (i.e. not to allow increases in concentration up to the guideline value).

When there is no default guideline value for a toxicant

It might be deemed appropriate to derive a site-specific guideline value where there is no DGV for a toxicant. The Water Quality Guidelines provide guidance on deriving site-specific guideline values, while complementary and additional guidance can also be found in van Dam et al. (2019) and Huynh & Hobbs (2019). State and territory governments may also have their own guidance for deriving and applying site-specific guideline values, and you should always consult with them at the outset on appropriate methods.

You could derive a site-specific guideline value using either reference-site data (for instance 80th percentile of background or reference-site data) or biological-effects data.

In some cases, it might be more beneficial and cost-effective to derive a DGV that can be applied to your site, and then propose it for inclusion in the Water Quality Guidelines.

References

ANZECC & ARMCANZ 2000, Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

Batley, GE, van Dam, RA, Warne, MStJ, Chapman, JC, Fox, DR, Hickey, CW & Stauber, JL 2018, Technical Rationale for Changes to the Method for Deriving Australian and New Zealand Water Quality Guideline Values for Toxicants, Australian Government Department of Agriculture and Water Resources, Canberra.

Huynh T & Hobbs D. 2019. Deriving site‐specific guideline values for physico‐chemical parameters and toxicants. Report prepared for the Independent Expert Scientific Committee on Coal Seam Gas and Large Coal Mining Development through the Department of the Environment and Energy. Canberra (AU).

OECD 1992, Report of the OECD Workshop on Extrapolation of Laboratory Aquatic Toxicity Data to the Real Environment, OECD Environment Monographs No. 59, Organisation for Economic Co-operation and Development, Paris.

OECD 1995, Guidance Document for Aquatic Effects Assessment, OECD Environment Monographs No. 92 (Series on Testing and Assessment: Ecotoxicity Testing No. 3), Organisation for Economic Co-operation and Development, Paris.

Warne, MStJ, Batley, GE, van Dam, RA, Chapman, JC, Fox, DR, Hickey, CW & Stauber, JL 2018, Revised Method for Deriving Australian and New Zealand Water Quality Guideline Values for Toxicants, Australian Government Department of Agriculture and Water Resources, Canberra.

van Dam RA, Hogan AC, Humphrey CL & Harford AJ 2019, How specific is site-specific? A review and guidance for selecting and evaluating approaches for deriving local water quality benchmarks, Integrated Environmental Assessment and Management 15: 683–702.