A recipe for contamination: Mixtures of pesticides threatening the Great Barrier Reef

Before the investigation, we knew that

There had been pesticide contamination detected in some freshwater and marine habitats linked to the Great Barrier Reef, most likely transported from agricultural areas, through creeks and rivers, and then out to the marine areas.

Herbicides are most common; they affect seagrass and corals, which are important food and habitat areas for many animals including fish, dugongs and sea turtles.

Fixing the problem requires changes to farming practices to reduce the amount of pesticides running off paddocks, which the Queensland and Australian governments are assisting landowners to do.

However

The full extent of pesticide contamination needed to be understood in order to successfully manage the contamination. For example, we needed to know how widespread the pesticide contamination was, the types of pesticides organisms were exposed to, if they were at toxic levels, and importantly if the ecosystems were being exposed to mixtures of pesticides at the same time.

Therefore

In 2009 a large-scale, long-term pesticide monitoring program was funded by the two governments to evaluate the success of the management interventions over time. The results from the first year of that monitoring were examined to assess the extent of the pesticide contamination.

11 monitoring sites across 8 catchments with high agricultural land use

Water samples were analysed in a laboratory for a large range of herbicides and insecticides

Water samples were collected during the wet season of 2009-2010