Banned Fungicide Benomyl Detected 141 Times in Victorian Raw Water Supplies

Legacy Benomyl Contamination in Victoria’s Water Catchments

A Freedom of Information review published on 28 July 2026 has revealed that Benomyl, a fungicide banned in Australia by the Australian Pesticides and Veterinary Medicines Authority (APVMA) in 2006, was detected 141 times across 43 raw water supplies in northern Victoria between 2017 and 2026. The detections were recorded in untreated raw water monitored by Grampians Wimmera Mallee Water (GWMWater), Central Highlands Water, Lower Murray Water, and North East Water. Regional water authorities have moved quickly to reassure the public, confirming that treated drinking water remains safe and compliant with current regulatory standards.

The significance of these findings extends well beyond drinking water compliance. Benomyl was withdrawn from Australian agricultural use two decades ago, yet it continues to appear in raw water catchments at a frequency that raises serious questions about legacy agricultural chemical persistence, catchment management, and the adequacy of current environmental assessment frameworks for agricultural land transitions. For environmental professionals working in Victoria’s agricultural regions, this case illustrates how legacy contaminants can remain active hazards long after regulatory bans take effect.

For developers, councils, lawyers, and land managers operating in or adjacent to Victoria’s northern agricultural catchments, this news is directly relevant to site assessment scoping, conceptual site model development, and environmental due diligence programmes. The detections point to a broader challenge: standard historical land use reviews and routine pesticide suites may not be capturing the full spectrum of legacy agrochemical risk present in catchment soils and groundwater systems.

Key details of the Benomyl detections and ADWG compliance thresholds

Raw water detections of Benomyl averaged 0.03 micrograms per litre (µg/L) across the monitoring period from 2017 to 2026. This concentration represents approximately 0.03 per cent of the health guideline value of 90 µg/L established under the Australian Drinking Water Guidelines (ADWG 2011, as updated). The highest individual raw water detection was recorded at 0.26 µg/L at Tullaroop Reservoir. A farm channel located outside domestic supply infrastructure recorded a peak concentration of 0.54 µg/L, which, while still a small fraction of the ADWG health guideline, is notable given that the location sits outside the treatment barriers applied to potable supplies.

Benomyl has a typical environmental half-life of approximately one year under most soil and aquatic conditions. Its continued detection at a cumulative count of 141 events across 43 separate raw water sources over a nine-year monitoring window is therefore difficult to explain through natural persistence alone. Researchers and land use specialists have proposed three plausible explanations: the drawdown of historical farm stockpiles that were held after the 2006 ban, the ongoing availability of unregistered legacy products through online channels, and the possibility that some laboratory results reflect the misidentification of structurally related benzimidazole fungicides. This last point is technically significant because Benomyl degrades rapidly in the environment to its primary metabolite, Carbendazim, a compound with its own toxicological profile and regulatory status.

Carbendazim is a benzimidazole fungicide that shares structural and toxicological characteristics with Benomyl. It is classified as a reproductive toxicant and is highly toxic to earthworms, soil microorganisms, and aquatic organisms. Where Benomyl is detected in environmental samples, Carbendazim should be considered a co-contaminant or the primary residue form present. Other related compounds warranting inclusion in targeted analytical suites include Thiabendazole and Thiophanate Methyl, both of which are registered or historically used in Australian horticulture and share metabolic pathways with Benomyl.

A critical regulatory gap compounds the complexity of these detections. Benomyl does not have assigned default guideline values (DGVs) under the ANZG 2018 Water Quality Guidelines for aquatic ecosystems. This absence means that while human health compliance against the ADWG 90 µg/L threshold is straightforward to assess, quantifying the ecological risk to receiving waterways, wetlands, and aquatic habitats within affected catchments requires case-by-case derivation of site-specific guideline values. This is a resource-intensive process that is frequently overlooked in routine environmental assessments.

Australian regulatory context: ADWG, ANZG 2018, and the Environment Protection Act 2017 (Vic)

Australia’s primary framework for assessing human health risk from chemicals in drinking water is the ADWG, published by the National Health and Medical Research Council (NHMRC) and the Australian Government Department of Health. The ADWG 2011 (as updated) sets the health guideline value for Benomyl at 90 µg/L, a concentration based on tolerable daily intake calculations and assumed lifetime exposure through potable water consumption. The detections reported in Victoria’s raw water supplies are orders of magnitude below this threshold, which explains why treated water authorities are confident in their public health statements. However, the ADWG is a health-based framework for treated potable water: it does not govern raw water quality, catchment management obligations, or ecological protection in receiving environments.

In Victoria, water storage managers and catchment authorities operate under obligations established by the Safe Drinking Water Act 2003 (Vic) and the Safe Drinking Water Regulations 2015 (Vic), which require proactive risk management through Water Quality Management Plans. These instruments sit alongside the broader General Environmental Duty (GED) imposed by the Environment Protection Act 2017 (Vic), which requires persons conducting activities that may pose risks to human health or the environment to understand and minimise those risks.

References and related sources

• Primary source: gwmwater.org.au
• melbourne-insider.au
• melbournefoe.org.au
• theweeklyadvertiser.com.au
• themodernregulator.com
• ANZG Water Quality Guidelines
• Australian Drinking Water Guidelines

How iEnvi can help

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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: 29 Jul 2026

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