Pesticide concentration in rivers and discharge to oceans. Image: Associate Professor Federico Maggi, University of Sydney, Dr Francesco Tabiella, United Nations and Dr Fiona Tang, Monash University.
About three million tonnes of agricultural pesticides are used across the globe each year, yet little is known about where or in which environments these chemicals end up after their initial application.
A global study published today in Nature, which analysed the geographic distribution of 92 of the most commonly used agricultural pesticides, found that approximately 70,000 tonnes of potentially harmful chemicals leach into aquifers each year, impacting ecosystems and freshwater resources.
Associate Professor Federico Maggi, the study’s lead author from the University of Sydney’s School of Civil Engineering, said: “Our study has revealed that pesticides wander far from their original source. In many cases these chemicals end up a long way downstream and often, though in much smaller amounts, all the way to the ocean.”
The study showed that about 80 percent of applied pesticides degrade into daughter molecules – or byproducts – into soil surrounding crops.
“This degradation of pesticides often occurs as a ‘cascade’ of molecules into the surrounding environment, which can persist in the environment for a long time and can be just as harmful as the parent molecule or applied pesticide. One such example is glyphosate. Although it is highly degradable, it breaks down into a molecule known as AMPA that is both highly persistent and toxic,” said Associate Professor Maggi.
While the study found that only a fraction of pesticides enter river systems after field application, once in the water most of the active ingredients end up in the ocean, with potential negative impacts on marine wildlife and coral reefs. This puts at risk the very basis of marine and freshwater food chains.
“On paper, 0.1 percent leaching into fresh waterways might not sound like much,” said Associate Professor Maggi. “But it only takes a tiny amount of pesticides to have a negative impact on the environment.”
The study showed that 730 tonnes of pesticides enter rivers each year, with about 13,000 kilometres of rivers reaching chemical concentrations above safety limits for a number of aquatic plants and invertebrates, with poorly understood consequences on rivers’ ecosystems.
