IT'S common knowledge within the cotton industry that the volume of pesticides used in growing crops has fallen dramatically since the 1990s, thanks to the adoption of genetically-modified varieties and modern management practices.
But new research has also confirmed a significant reduction in the relative risk farm chemicals, such as herbicides, insecticides and fungicides, pose to the environment.
Lead researcher Dr Mick Rose, who is a NSW Department of Primary Industries research scientist, said the three-year study was prompted by conversations within both the Australian and global cotton industries about developing sustainability targets.
"The driver was to see where they're at, and how far they'd come since the late 1990s and early 2000s, and start to really benchmark that so that they could develop sustainability targets going into the future around pesticide use and trying to reduce those offsite impacts," he said.
Dr Rose said the assessment was the first industry-wide study in almost 20 years to quantify changes in the relative risk of pesticides resulting from the switch to GM cotton varieties and implementation of farm stewardship programs such as Cotton Australia's myBMP.
Based on pesticide use data collected by Crop Consultants Australia since 1988, Dr Rose said the study found the total environmental toxic load - the hazard posed by cotton chemical to different parts of the environment - had decreased more than 70 per cent since 2000.
Researchers identified and ranked 15 chemicals used in cotton, and some herbicides used in other crops, with the highest toxicity to bees, water fleas, algae and fish.
They then monitored residues at 21 sites across the Barwon, Namoi and Murrumbidgee catchments in 2018 and 2019.
Nine chemicals were found at least once in monthly samples, and the herbicides atrazine, simazine and diuron were detected in more than 30pc of samples.
"Nevertheless, the levels of these and other pesticides are generally lower than those found in previous studies 10-20 years ago, and are below common ecotoxicology thresholds," Dr Rose said.
"The volume has come down and the toxicity of the newer chemistry being used is also lower, so the actual wider hazard to the environment has come down even more, particularly for insects and aquatic organisms exposed to herbicides."
By contrast, the hazard to terrestrial plants from herbicides had fluctuated up and down during the past 12 years.
Dr Rose said this was caused by the recent emergence of glyphosate resistant weeds and farmers resorting to "some of those older, more persistent and potentially more toxic chemicals" to control them.
In other news
The research identified which insecticides were posing the highest hazard for non-target pollinators and invertebrates.
The top three were fipronil, phorate and neonicotinoids, which are used as both sprays and seed dressings.
The Australian Pesticides and Veterinary Medicines Authority has been reviewing the use of fipronil and its risks to human health and the environment since 2003.
The review's scope has been expanded several times, as recently as last year.
A Cotton Research and Development Corporation-funded two-year follow up project is now undertaking a more in-depth assessment of the "true risk" of neonicotinoids, such as thiamethoxam, which are banned in Europe.
Dr Rose said much of the previous research had focused on the toxicity of neonicotinoids when used as sprays, not in seed dressings.
"Because the seed is basically purchased with the dressing already applied, the actual exposure to non-target organisms is likely to be very different when used as an over-the-top spray," he said.
"That's one part of the research in this project. The second part is following up on our sustainability indicators and targets and trying to take them a step further as well ... in the context of planetary boundaries, things like water use, biodiversity loss, greenhouse gas emissions."
Dr Rose said the cotton industry has historically had a poor image for its environmental record but was actively working to both reduce its ecological impacts and debunk common myths in order to appease new consumer demands.
"Consumers now want and do have access to markets where they know how things are produced," he said.
"That has become a lot more important in the marketing of products as well, being able to demonstrate that it's been done ethically and sustainably.
:The cotton industry has really come a long way in the last five to 10 years to be able to take advantage of those markets, and social licence, within Australia to demonstrate to people in the cities and people in the country as well, that the cotton industry is doing the best they possibly can."
