Glyphosate in Queensland Waterways: An Ecological Risk Assessment

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Water Quality Monitoring

Background:

• Glyphosate is a common herbicide in the Great Barrier Reef catchment, used as an alternative to other herbicides.
• Glyphosate and its metabolite AMPA are not included in routine water quality monitoring programs for the Great Barrier Reef.
• This exclusion means they are absent from key reporting and risk assessment tools.

Purpose of the Study:

• To evaluate if the exclusion of glyphosate and AMPA from routine monitoring is justified.
• To compare detected surface water concentrations with aquatic ecosystem protection guidelines.

Main Methods:

• Surface water samples were collected from 18 sites between 2006 and 2024.
• Detected concentrations of glyphosate and AMPA were compared against established water quality guidelines.
• Analysis considered glyphosate's environmental fate, including soil adsorption and aquatic toxicity.

Main Results:

• Glyphosate was detected above the limit of reporting in 48 of 272 samples across five sites, with a maximum concentration of 11 µg/L.
• AMPA was detected above the limit of reporting in 60 of 262 samples across four sites, with a maximum concentration of 5 µg/L.
• Maximum detected concentrations were significantly lower (16 times lower for glyphosate) than the default guideline value for 99% species protection.

Conclusions:

• Detected concentrations of glyphosate and AMPA pose a minimal ecological risk based on current Australian and New Zealand guidelines.
• The low aquatic toxicity and strong soil adsorption of glyphosate support its continued exclusion from routine monitoring frameworks.
• Periodic monitoring is still recommended to identify any emerging concerns regarding glyphosate and AMPA levels.