Although nearly three million tons of agricultural pesticides are used across the globe each year, little is known about where these chemicals end up after their initial application.
Now, a team of scientists led by the University of Sydney has analyzed the geographical distribution of 92 of the most widely used agricultural pesticides, and discovered that about 70,000 tons of these potentially harmful chemicals leach into aquifers, rivers, oceans, and soils each year, impacting a variety of ecosystems and freshwater resources.
“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,” said lead author Federico Maggi, an associate professor of Environmental Engineering at Sydney.
Maggi and his colleagues found that nearly 80 percent of applied pesticides degrade into by-products known as “daughter molecules” that leach into the 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,” Maggi explained.
While only a small fraction of pesticides was found to enter river systems after field application, once in the water, most of their active ingredients end up in the ocean. This negatively impacts marine wildlife and coral reefs, and often puts the very basis of marine and freshwater food chains at risk.
As Maggi explained, “on paper, 0.1 percent leaching into fresh waterways might not sound like much. But it only takes a tiny amount of pesticides to have a negative impact on the environment.”
According to the researchers, 730 tons of pesticides enter rivers each year, causing about 13,000 kilometers of rivers to reach chemical concentrations above safety limits for a variety of aquatic plants and invertebrates.
Although the scientists used a large collection of publicly accessible geospatial data, the results are a conservative estimate, since some pesticides – such as legacy pesticides and those used in aquaculture, public spaces, and private dwellings – were not included in the analysis.
To mitigate the negative impact of pesticides leaching into the environment, officials “should urgently adopt sustainable management strategies to promote reductions in field applications of harmful pesticides and set in place systems to effectively monitor their use under the 2030 Sustainable Development Agenda,” concluded co-author Francesco Tubiello, a senior environmental statistician at the United Nations’ Food and Agriculture Organization.
The study is published in the journal Nature.
Pesticides are substances used to prevent, destroy, repel, or mitigate any pest ranging from insects, animals, and weeds to microorganisms such as fungi, molds, bacteria, and viruses.
While they play a significant role in controlling pests that damage or hinder agricultural productivity, they can have negative impacts on the environment when not used appropriately or managed effectively.
Pesticides can reach water bodies such as rivers, lakes, and even oceans through run-off from agricultural fields or through leaching into groundwater. This contamination can disrupt aquatic ecosystems, harming or killing off certain species and leading to an imbalance.
Pesticides are not always specific to the target pests. They can also impact non-target organisms, including beneficial insects, birds, and mammals. For instance, pesticides like neonicotinoids have been linked to the decline in bee populations, a serious issue given the critical role bees play in pollination.
Through the above-mentioned mechanisms, pesticides can lead to a loss of biodiversity. By eliminating certain species or disrupting ecosystems, they can negatively impact the overall health of the environment.
Some pesticides do not break down quickly and can accumulate in the environment or within organisms. They can also biomagnify, meaning they become more concentrated as they move up the food chain. This can lead to high levels of the chemicals in top predators, posing serious health risks.
Pests can develop resistance to pesticides, requiring increasing amounts of the chemicals to achieve the same level of control. This can result in a vicious cycle of ever-increasing pesticide use, known as the ‘pesticide treadmill’.
Pesticides can alter the balance of fungi and bacteria in the soil, reducing its fertility and leading to a reduction in crop yields over time.
Given these environmental concerns, many are advocating for more sustainable pest management strategies, such as integrated pest management (IPM) which relies on a combination of biological control, habitat manipulation, modification of cultural practices. Further research into alternative, less harmful pest control methods and stricter regulation of pesticide use is also part of the solution.