Water Quality Australia publishes final ANZG 2018 Default Guideline Values for Ammonia, Chromium (III), and Simazine.

Finalisation of ANZG 2018 Default Guideline Values for Ammonia, Chromium (III), and Simazine

Water Quality Australia published the final Default Guideline Values (DGVs) for three major toxicants under the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZG 2018) on 1 April 2026. The finalised DGVs apply to ammonia in freshwater, chromium (III) in freshwater, and simazine in marine water. This update closes the transitional period for these specific analytes, meaning any ongoing or future site assessment, wastewater discharge authorisation, or aquatic ecosystem risk assessment that references interim or draft values for these three parameters is now operating outside the current regulatory framework.

The update is formally recorded on the Water Quality Australia website content change log and represents a regulatory update requirement under the National Water Quality Management Strategy (NWQMS). For environmental consultants, hydrogeologists, site auditors, and their clients, including property developers, industrial operators, local councils, and wastewater managers, the publication of these final DGVs is not a procedural footnote. It necessitates a review and update of screening criteria tables, conceptual site models, and quantitative risk assessment inputs for any project where these analytes are relevant.

The broader significance lies in how pervasive these contaminants are across Australian land use types. Ammonia and chromium (III) appear routinely in landfill leachate, industrial wastewater, and agricultural runoff. Simazine, a herbicide used extensively across agricultural and urban settings, has measurable pathways to coastal and estuarine marine environments. Practitioners who continue to apply superseded ANZECC 2000 trigger values or any previous ANZG 2018 draft figures for these three analytes are now formally non-compliant with the current national water quality guidelines framework.

Key details of the finalised ANZG 2018 Default Guideline Values

The ANZG 2018 framework replaced the Australian and New Zealand Environment and Conservation Council (ANZECC) and Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) 2000 guidelines as the primary national reference document for water quality protection. The framework introduced a tiered risk-based approach, with Default Guideline Values representing the concentrations below which adverse biological effects are not anticipated in 80%, 90%, 95%, or 99% of species, depending on the selected level of ecosystem protection. The finalisation of DGVs for the three analytes announced on 1 April 2026 means practitioners must now apply these values in place of both the old ANZECC 2000 trigger values and any interim or draft numbers that may have been in circulation during the guideline development process.

Ammonia toxicity in freshwater is well established, with un-ionised ammonia (NH3) being the acutely toxic fraction to aquatic organisms. The ANZG 2018 framework applies species sensitivity distribution methodology to derive DGVs that are pH and temperature dependent, which means practitioners cannot apply a single flat threshold across all receiving environments. The final DGV for ammonia in freshwater requires that assessments account for site-specific water chemistry conditions, particularly pH, because the proportion of un-ionised ammonia relative to total ammonia nitrogen shifts significantly as pH rises. A discharge that is compliant at pH 7.0 may exceed the protection threshold at pH 8.5 under the same total ammonia nitrogen concentration.

Chromium (III) in freshwater presents a different assessment challenge. Chromium exists in two primary oxidation states at contaminated sites, trivalent chromium (III) and hexavalent chromium (VI), with very different toxicological profiles and regulatory treatment. The finalisation of the chromium (III) DGV is significant because it provides a definitive benchmark for the reduced form, which is the predominant species under anaerobic or reducing conditions typical of landfill leachate plumes and some industrial groundwater impacted zones. Practitioners assessing chromium at contaminated sites must now apply the correct DGV for the relevant speciated form and cannot treat total chromium as a conservative proxy without appropriate justification in the risk assessment methodology.

Simazine is a triazine herbicide that has been used in broad-acre agriculture, horticulture, and urban weed management across Australia for decades. Its marine water DGV under ANZG 2018 is relevant to discharge pathways reaching estuaries, coastal waterways, and near-shore marine environments. Simazine is moderately persistent in the environment, and its presence in stormwater and agricultural drainage reaching coastal marine receptors makes the finalised marine DGV directly applicable to stormwater quality assessments, drainage licence conditions, and coastal development projects. The ANZECC 2000 trigger value for simazine in marine water is now formally superseded for assessment purposes.

Australian context: ANZG 2018 DGVs, NEPM 2013, and state regulatory frameworks

The ANZG 2018 guidelines sit within the National Water Quality Management Strategy and are adopted by Commonwealth, state, and territory governments as the primary technical reference for surface water and marine water quality protection. In Australian practice, DGVs are used as screening criteria in contaminated land assessments under the National Environment Protection (Assessment of Site Contamination) Measure 1999 as amended in 2013 (NEPM 2013), particularly where groundwater discharges to or interacts with surface water receptors. The NEPM 2013 Health Investigation Levels and Ecological Investigation Levels for soil are one part of the assessment framework, but for aquatic ecosystem protection the ANZG 2018 DGVs are the operative thresholds. Now that the DGVs for ammonia, chromium (III), and simazine have been finalised, practitioners and regulators alike are required to apply these current values across all relevant assessments, with superseded ANZECC 2000 figures and any previously circulated interim or draft values no longer acceptable as the basis for regulatory decisions or site risk assessments.

References and related sources

• Primary source: www.waterquality.gov.au
• ANZG Water Quality Guidelines

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This is an iEnvi Machete news summary. Prepared by iEnvi to summarise the source article for contaminated land, groundwater, remediation, approvals and site risk professionals.

Published: 07 Apr 2026

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