1989 July – 1989 August: Maidments site (Blackwood River) WA. Pesticides: Atrazine, Hexazinone.

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 the Maidments site both hexazinone and atrazine were detected downstream of the target area. Again concentrations were not very high, however, there is some evidence suggesting that the small intermittent runnels at the head of the catchment may have contained significantly higher levels of herbicides for short periods during heavy rainfall.
These runnels only contain runoff during rainfall events. An independent sample from one of these intermittent runnels on 26 July contained 22mg/L atrazine and 5.8mg/L hexazinone. Some dilution can be expected downstream, particularly since only part of the stream catchment was sprayed.
A sample taken downstream during the same event but the day before measured 1.3 and 2.3 mg/L atrazine and hexazinone respectively. Likewise a downstream sample two days after measured 1.4 and 3.5mg/L atrazine and hexazinone respectively.

Maidments Site: Hexazinone 4.2ug/L highest level 20/8/89, Atrazine 2.1ug/L highest level 7/7/89.