A study from Environmental Pollution compared pesticide residues in soil from organic and conventional farms across the European Union and found that organic farms had up to 90% fewer residues. However, researchers suggest that the existence of any residues in organic soil is a result of either highly persistent chemicals that last beyond organic transition or contamination via pesticide drift. This study took a combined approach to examine pesticide use on farms by interviewing farmers to qualitatively assess pesticide application and testing soil samples from those farms to measure actual pesticide residues. Conventional farmers reported a wide range of chemical application while organic farmers did not report application of any of the tested synthetic chemicals. One conventional farmer alone reported the use of 69 different chemicals, while two sites reported 19, and three sites reported nine. The highest reported input was the insecticide chlorantraniliprol, while the highest residue concentration detected in soil samples was the herbicide glyphosate. Residue testing of soil across all sites revealed that conventional farms had much higher concentrations of pesticides than organic farms (70-90% higher), with a maximum detection of 16 different residues per sample versus a significantly lower maximum of only 5 residues/sample for organic farms. Because organic certification bans the use of the detected chemicals, the researchers suggest that these residues are likely from historical applications predating the transition to organic. These results indicate that many pesticides can persist in soil over long periods of time. The researchers also suggest that detection of some chemicals in organic farms may be a result of pesticide drift from nearby conventional farms. The occurrence of drift from conventional spraying events creates a baseline level of contamination in the environment that can be unavoidable, despite efforts made by organic farmers to prevent contamination.

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