New research reveals that agricultural pesticides have a widespread and concerning impact on global waterways.

This study, conducted in collaboration with Australian scientists and the Food and Agriculture Organization of the UN, examined 92 commonly used agricultural pesticides and uncovered that they surpass safe levels in approximately 13,000 kilometres of rivers worldwide.

Approximately 710 tonnes of pesticide active ingredients are estimated to leach into the Earth’s oceans annually. The analysis focused on 144 major water catchment areas, which collectively account for about 940,000 tonnes of pesticide use annually, out of the global yearly usage of roughly 3 million tonnes.

Highlighted in the study were notable pesticide “hotspots” around the world. Rivers in regions such as the central and western United States (such as the Mississippi and Sacramento), Argentina (Parana), India (Ganges), East China (Yangtze, Pearl, and Yellow (Huang He) River), and South East Asia (Irrawaddy and lower Mekong) experience the highest exposure to land pesticides.

“Rivers in Europe received an intermediate pesticide yield from land with hotspots along the Po and Danube.”

Surprisingly, even though just a fraction (less than 0.1%) of the agricultural pesticides used in the examined catchment areas ultimately made their way to the oceans, their impact remains substantial.

“Although this amount is less than 0.1% of net inputs, it is a cause of decreased species richness of stream invertebrates with little known consequences on near-coast ecosystems,” the researchers noted.

Lead author of the study, Associate Professor Federico Maggi from the University of Sydney, emphasised that even small quantities of these pesticides lead to concentrations exceeding safety thresholds.

The research indicated that 82% of pesticides break down into other compounds over time, while 10% remain as residues within the soil. About 7.2% (around 68,000 tonnes) leach into aquifers—porous rocks or sediment that store groundwater.

“In many observed cases pesticide active substances may degrade into a cascade of daughter substances which can be as toxic as the parent and occasionally even more persistent [in the environment],” the scientists noted.

It’s estimated that 730 tonnes of pesticides end up in river systems annually, with 710 tonnes ultimately reaching the oceans.

In excess of 13,000 kilometres of rivers, pesticide levels surpass the safety limit of 1 microgram per litre, leading to inadequately understood consequences for aquatic ecosystems. This research underscores the imperative need for better management and mitigation of agricultural pesticide usage to safeguard the integrity of global water systems and the ecosystems they support.

“It is not the pesticide use only that is important,” Maggi said. “What is important is the load – that is, the applied mass and toxicity of individual active ingredients.”

Dr Francesco Tubiello, a study co-author and senior environmental statistician at the Food and Agriculture Organization of the UN, said in a statement: “We must 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.”