New implication of pesticide regulatory management in soils: Average vs ceiling legal limits

To help regulatory agencies better interpret pesticide soil standards (PSSs) and promote pesticide soil regulations, this study revealed new PSS implications by introducing the average (i.e., PSS_AC) and ceiling (i.e., PSS_CC) legal limits of pesticides. The PSS_AC indicates the average legal limit of a pesticide in the soil over a duration (e.g., annual or monthly average), ensuring that no adverse human health effects can occur. The PSS_CC indicates the ceiling legal limit that cannot be exceeded by pesticide concentrations in the soil, which was introduced to comply with pesticide application in real-world scenarios. We introduced the regulatory ceiling factor (RCF) to screen whether a pesticide in the surface soil could be regulated using the PSS_AC and PSS_CC values. The results indicated that except for some pesticides with high lipophilicity and low degradability (e.g., legacy pesticides), many pesticides were eligible to be regulated by both average and ceiling legal limits. In addition, we conducted a case study to evaluate chlorpyrifos soil standards via a four-step regulatory procedure; the results indicated that our new interpretation using the simulated PSS_AC and PSS_CC values of chlorpyrifos demonstrated that most current chlorpyrifos soil standards can protect population health, which is in contrast to the findings of current regulatory studies. Furthermore, based on the new implication of PSSs interpreted in this study, we recommend that regulatory agencies clarify PSSs to avoid confusion and promote cost-efficient remediations, and recommend improving the regulatory communication between environmental agencies and pesticide manufacturers to define a comprehensive policy integrating PSSs and application patterns.