Low-cost environmental traceability of pesticides is essential for safety.

We issue a call to action: in the context of safe design, all pesticides must be traceable via low-cost methods that are accessible for routine environmental monitoring by public institutions. Insights into the far-reaching impacts of pesticides depend on our ability to detect these chemicals in the environment. Once a pesticide is authorized for use, environmental monitoring serves as a critical warning system that complements risk assessments. Postregistration monitoring is recognized by different policy frameworks like e.g. the Water Framework Directive and the European Green Deal. However, we highlight an urgent concern: despite formal requirements for detectability in registration, novel pesticides are becoming progressively undetectable in practice. We demonstrate how mandated reductions in pesticide use measured as volume can drive chemical innovations that unintentionally undermine environmental accountability and safety. For example, volume can be decreased while maintaining effectiveness by increasing the specificity or toxicity of the pesticide. This phenomenon is analogous to 'analytical homeopathy,' where active ingredients remain effective even at extremely low dosages, rendering them undetectable by standard analytical chemistry. This issues a significant challenge: higher toxicity can imply lower environmental quality standards near detection limits. This leads to the troubling problem of "known unknowns": risks posed by active ingredients whose emissions remain unquantified under current field monitoring conditions. In response to this emerging threat, we propose a foundational principle: all synthetic pesticides should be detectable in the environment at the concentration of their active ingredients, enabling cost-effective and reliable monitoring. If neglected then the credibility and function of monitoring as a warning system for unintended biodiversity harm is increasingly undermined, regardless of formal analytical capabilities.