Pesticides seeping out of intensive horticulture into waterways have long-concerned NSW north coast communities. Now a new Southern Cross University study provides evidence that bioreactors can significantly limit this toxic run-off.
The study is first evidence that microbial communities in woodchip bioreactors can effectively reduce the type of pesticides being used in intensive horticulture in NSW. However, some highly water-soluble pesticides may still get through.
In new research published by the journal Environmental Pollution, Southern Cross University researchers tested a woodchip bioreactor originally constructed** to mitigate nutrient run-off from fertiliser into the Solitary Islands Marine Park off the Coffs Coast.
Lead researcher Professor Kirsten Benkendorff and her team from the University's National Marine Science Centre found this same woodchip bioreactor has been successful in reducing the number and amount of pesticides escaping into the environment.
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Play video Video transcript
I'm Samantha Hesse. I'm the Biodiversity Project Officer at the City of Coffs Harbour. We've been working with Southern Cross University and North Coast Local Land Services, as well as Coffs Harbour Regional Landcare, since 2016 to better investigate the impacts that we're finding are coming from intensive plant agriculture activities such as bananas, blueberries and hothouse horticulture.
Part of this collaboration has allowed us to develop solutions for some of the issues, particularly the waste water issue that we've got from intensive plant agriculture. Bioreactors are one part of that solution. These simple structures act to treat the waste water that's come from these horticultural properties.
Hi, I'm Professor Kirsten Benckendorf from the National Marine Science Centre at Southern Cross University. Managing runoff from intensive horticulture can be a significant challenge, especially when we have steep catchments such as we do here in the Coffs Harbour region on the mid north coast of New South Wales.
So only between about 3 and 5 percent of the pesticides that are applied to crops actually stick to the plants. The rest of the pesticides runoff into the soil where they can impact the crops. So, these are all different types of pesticides that can affect the health of the soil and they can also run off after rain events and get into our waterways where they can impact seafood and above the environmental limits, they can actually be at illegal levels.
So, using effective drainage we can actually channel the water away from the hothouse through into these bioreactors and the bioreactor will then trap a lot of these pesticides and the nutrients. So we sampled soil from a transect starting at the front of the hothouse and then going through into the bioreactor and out the other side.
And what we found was really high levels of pesticides, 11 different pesticides in front of the hothouse, pretty high concentrations. But when we sampled further down into the bioreactor and below, we found both a lower number of pesticides and lower concentrations of the pesticides, thus meaning that we are actually absorbing some of those and breaking them down in the bioreactor.
We actually want farmers to consider minimising the use of pesticides whenever they can. Reduce overspray and not use pesticides in rainy weather. Also considering not using water soluble pesticides near aquatic waterways. Farmers are heavily exposed to these pesticides. So even though some of the more modern pesticides might be more expensive, they can actually degrade quicker in the environment, which means less exposure, and some of them are less toxic to both the environment and safer for human health.
We do have some key messages for growers. Number one, please contact your local council. You may require development consent for your horticulture activities, so please do check with council first in your local government area. The second thing is, please capture and treat your wastewater, your runoff from your operations.
These can be done through bioreactors. There are also other methods, but again, if you can capture and treat your wastewater, that stops that wastewater potentially contaminating our waterways. The other thing too is to try and optimise your water usage and your fertiliser usage. A lot of farmers are finding that the use of power plant systems, which are computerised controllers, they've managed to increase their water efficiency.
We've had one farmer actually report to us that he's reduced his fertiliser use by 75%. Another part of our collaboration with Southern Cross University and North Coast Local Land Services has been involving Coffs Harbour Regional Land Care. They run a lot of workshops for growers, they've put out a lot of documentation too, so there are a lot of articles that are of use to growers actually on Coffs Harbour Regional Land Care's website.
Also look again at your local council websites or contact a local cooperative such as AusGroup that we have here on the mid north coast of New South Wales. Also DPI, contact New South Wales DPI. They have a lot of resources and some dedicated people there who can help you with your new venture.
Two insecticides and nine fungicides were present in soil samples below the greenhouses. Yet the concentration of at least six of these pesticides decreased along a gradient into, through and below the bioreactor.
"When these toxic chemicals enter our waterways, they can cause harm to non-target organisms, including seafood like prawns, crabs and oysters. Exposure to pesticide residues also has potential implications for human health," said Professor Benkendorff.
Microorganisms found in soil can help breakdown some types of pesticides.
"However, we found a reduction in the types of soil microorganisms immediately below the greenhouses, where pesticide concentrations were high. This suggests that pesticides could be impacting the soil productivity," Professor Benkendorff added.
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A bioreactor is a vessel for biological reactions to take place. It creates a suitable environment for the types of microbes that are capable of degrading pesticides.
"The bioreactor was dominated by microbes that are known to be resistant to pesticides and have been previously associated with contaminant degradation," said Professor Benkendorff.
"In a previous study on the Hearnes Lake catchment published in Marine Pollution Bulletin, we found nine pesticides, including significantly high concentrations of the insecticide imidacloprid. This water-soluble pesticide has been banned from use in Europe and Canada.
"For this latest study, we found imidacloprid in the soil immediately below the greenhouses but then it disappeared, suggesting it may just wash straight through the bioreactor.
"We also found two pesticides, azoxystrobin and carbendazim, in high concentrations in the soil below the bioreactor."
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Both of these compounds - azoxystrobin and carbendazim - are systemic fungicides known to be harmful to aquatic life. Carbendazim is also regarded as harmful to human health and consequently this fungicide has been restricted for use in Australia.
"The discovery raises concerns about the source of carbendazim in this study, because it is banned from use on the crops grown at the study site," said Professor Benkendorff.
"Nevertheless, the results of this study are promising and can be used to better inform which pesticides may be safter for use near waterways."
*The woodchip bioreactor was designed by the North Coast Local Land Services. The bioreactors were initially constructed by the City of Coffs Harbour and North Coast Local Land Services in an effort to improve water quality where run-off from expanding agricultural practices was entering streams without any treatment.
The City of Coffs Harbour and North Coast Local Land Services are testing new and improved bioreactor designs, funded through the NSW Government's Marine Estate Management Strategy. These designs may also hold promise for capturing and degrading a grater suite of pesticides.
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Acknowledgements
This project was funded by the Australian Government Department of Agriculture, Water and the Environment via the Regenerative Agricultural Alliance Soil Extension Program.
*The bioreactor was constructed as part of a separate collaboration between North Coast Local Land Services, Coffs Harbour City Council and Coffs Harbour Regional Landcare Incorporated.
Study details
'Soil microbial communities and degradation of pesticides in greenhouse effluent through a woodchip bioreactor' by E Ewere, S White, R Mauleon, K Benkendorff
Published in Environmental Pollution
