The Results of Monitoring the Department of Conservation and Land Management Program of Applying Granulated Herbicides by Helicopter. A Report to the Environment Protection Authority. EPA Bulletin 435 June 1990.

In 1989 an investigation of the environmental impacts of two herbicides proposed for helicopter application by the Department of Conservation and Land Management (CALM), was carried out by the Environment Protection Authority (EPA)...

The environmental impacts of these chemicals on the aquatic environment was also monitored at five sites. The chemicals were leached into adjacent streams and intermittently detected at relatively low concentrations generally, but ranging from 0.8 to 38.0ug/L atrazine and 1.5 to 18ug/L hexazinone.

There was no observed effect on aquatic growth in the Blackwood River, however in the streams at two application sites there did appear to be some impact on aquatic invertebrate drift...

At Grimwade there was no control sampling site because the entire catchment of the small tributary was to have herbicide applied. The observed herbicide concentrations were relatively low during and after application and therefore an adverse impact on stream fauna was not expected.
Detection of atrazine at low concentrations was unexpected since it was not applied as part of the programme. Its presence indicates that there may be a residual component to this herbicide remaining in the soil from previous applications in the catchment two years ago or it may be a result of spraying firebreaks on 5 July 1989. The herbicides used on the firebreaks were 2kg/ha atrazine and 1.5kg/ha hexazinone...

Grimwade Site: Hexazinone 4.4ug/L highest level 28/7/89, Atrazine 0.8ug/L highest level 28/7/89.

https://epa.wa.gov.au/EPADocLib/398_B435.pdf