The combined toxicity of 22 of the most common pesticides found in waterwaysflowing into the Great Barrier Reef is in many cases not meeting pollutionreduction targets.

University of Queensland researchers, along with the Queensland Department ofEnvironment and Science, reached the conclusion after devising a new method toestimate the percentage of species protected in waterways that discharge tothe Great Barrier Reef.

School of Earth and Environmental Sciences’ Associate Professor Michael Warnesaid research looking at cumulative impacts and multiple stressors wascritical for the reef’s health.

“We’ve known for a while that rivers and creeks that discharge to the reefusually contain multiple pesticides,” Dr Warne said.

“Different pesticides affect different organisms, for example, herbicides willaffect organisms that photosynthesise – such as seagrass, corals, mangrovesand algae – while insecticides affect insect larvae in freshwater andcrustaceans – including crabs, prawns and lobsters.

“Previously, assessments of the risk posed by pesticides have only examinedpesticides individually, or estimated the toxicity of a couple of pesticidesduring a single day.

“As part of this project we have developed a method that allows us to estimatethe combined toxicity of up to 22 of the most common pesticides found inwaterways that discharge to the Great Barrier Reef, and to do this for theentire wet season.”

The team applied this method to all pesticide monitoring data for rivers andcreeks discharging into the reef.

“We then obtained data on land-use, spatial and hydrological variables foreach catchment where we had pesticide monitoring data,” Dr Warne said.

“From there, we estimated pesticide mixture toxicity and the percent ofspecies protected for the entire Great Barrier Reef catchment area (GBRCA),the six natural resource management (NRM) regions that make up the GBRCA andindividual waterways.”

The research revealed that the pesticide reduction target in the Reef 2050Water Quality Improvement Plan is not being met, with 97 per cent of speciesbeing protected across the entire GBRCA, compared to the plan’s 99 per centtarget.

There were marked differences in the risk that pesticides posed between thesix NRM regions.

Dr Warne said it was estimated that only the Cape York region met the target.

“The estimated per cent of protected species for individual waterways washighly variable, going from greater than 99 per cent to as low as 71 per cent,again emphasising the need for ongoing work to reduce the risk posed bypesticides.”

By having estimates of the risk posed by pesticides for NRM regions andindividual waterways, governments, farmers and conservationists can recognisewhich areas pose the greatest risk and where to maximise efforts.

“More work is needed across the entire GBRCA to reduce the risk thatpesticides pose,” Dr Warne said.

“All stakeholders need to come together to reduce pesticide concentrations inwaterways through better management practices or by using less toxicpesticides.”

The research has been published in two reports available on the Reef WaterQuality Improvement Plan website, and are available here and here.

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