The need to monitor fungicide risk
Australia currently has no organised, long-term way of monitoring levels of commercial fungicides in soil and waterways, leading environmental scientists have cautioned.
This is despite the fact that in Australasia over 7,500 tonnes of copper fungicides are applied to grapes, fruit and vegetable crops every year, representing 13 per cent of the global total, and that copper can remain in the soil for 1,000 years or longer.
In a new review of the current science related to the widespread use of fungicides by vegetable, fruit and grape growers, University of Queensland PhD researcher Adam Wightwick says the risk to the environment posed by the use of fungicides in horticultural production systems has received relatively little attention compared to other types of agrochemicals, such as insecticides and herbicides.
The claims appear in a new book, Fungicides (Intech, December 2010), prepared via the CRC for Contamination Assessment and Remediation of the Environment (CRC CARE) and Department of Primary Industries, Victoria (DPI).
In the book the authors point out that farmers rely heavily on protective fungicide sprays, particularly in wet growing seasons. At the same time, however, it expresses concern that not enough is known about the long-term environmental risks posed by the use of fungicides. The amount of formal monitoring was also too low to allow an accurate assessment to be made over time.
"There is relatively little ecotoxicological data detailing concentrations causing adverse effects to soil and aquatic organisms for even the most widely used fungicides for which to adequately assess the risks," Wightwick says.
Forty-seven different fungicides are currently registered for use on grapes alone in Australia, mainly to control mildew diseases.
The potential environmental risks posed by these fungicides are assessed as part of their product registration and farmers apply these chemicals according to label and industry recommendations, Wightwick says. However, to date both in Australia and globally, there has been little post registration monitoring of these compounds in the environment and this represents a significant knowledge gap.
"Fungicides tend to be applied repeatedly as protective sprays over a specific period of the year, and so may arguably pose a greater environmental risk than other types of agrochemicals, such as insecticides, which tend to be applied more sporadically to eradicate pest outbreaks," Wightwick explains.
"Because of the lack of environmental monitoring and ecotoxicological data, we currently do not know if there is cause for concern about fungicides or not," Wightwick says.
In the case of copper fungicides, which have been in use for more than a century in some places, levels in soil have been found to reach 10 or 20 times the natural copper present in soils, pointing to the potential for a steady build-up in copper over time.
As far as vineyards are concerned, research in a range of soils tested from temperate regions of Australia is indicating that the copper accumulated so far does not appear to be causing long-term harm to microbial function. However, research at the University of Adelaide has shown that soil microbial activity is significantly less in avocado orchards where high levels of soil copper have built up from regular fungicide use.
That study also suggested that copper is more likely to have detrimental effects upon soil organisms responsible for nutrient cycling and continued soil health than on the plants themselves.
"Another important consideration is that there has been a continual evolution of new fungicidal compounds in a race to overcome fungicide resistance and improve their effectiveness. As more farmers adopt newer fungicides there is a need to consider the costs and benefits of this adoption, as newer chemicals may not necessarily pose a lower environmental risk than those they replace," the researchers state.
The community is becoming more aware that use of agrochemicals including fungicides may harm living organisms in water and soil, and this can potentially change the natural structure and function of ecosystems, the researchers point out. "As a result, the need to protect the natural environment has become part of the mainstream public policy debate."
In the future, they warn, the debate is likely to be complicated by the large projected increase in the human population, from 6.5 billion people in 2005 to 9 billion people in 2050. This will place huge demands on food production leading to significant increases in the use of agricultural chemicals, including fungicides, to meet world demand.
"To ensure the sustainability of agricultural production systems, a balance needs to be found between controlling fungal disease risks to crops and protecting terrestrial and aquatic ecosystems.
"Research into the potential environmental risks posed by fungicide use is needed so that evidence-based policy decisions can be made on the future management of fungicide use in horticultural crops."
The study Environmental Risks of Fungicides Used in Horticultural Production Systems, by Adam Wightwick, Robert Walters, Graeme Allinson, Suzanne Reichman and Neal Menzies, appears in the new book Fungicides, Intech, 2010 (available via: http://www.intechopen.com/articles/show/title/environmental-risks-of-fungicides-used-in-horticultural-production-systems).