Comparison of Environmental Risk Indices Related to Pesticide Spray Drift in Extensive Agriculture in Uruguay

Pesticide spray drift is an off-target pathway in extensive cropping systems that can lead to the exposure of non-target organisms and nearby human populations. This study compared drift-related risk indices for pesticides commonly used in Uruguay using two indicator-based methodologies: POCER (terrestrial organisms and human health) and HAIR (aquatic organisms). Risk indices were calculated using locally derived drift deposition percentages measured at 5, 15, 30, 50, 75, and 100 m downwind under a conservative operational scenario (boom height 120 cm; mean wind speed 20 km h⁻¹) over residue-covered soil. Risk patterns varied according to active ingredient, droplet size, and distance. For bees, chlorpyrifos exceeded the risk threshold (RI ≥ 1) at all distances, while lambda-cyhalothrin exceeded this threshold with fine and medium droplets but not with very coarse droplets. Earthworm risk indices remained below the threshold (RI < 1) at 5 m for all active ingredients. For aquatic organisms, pyraclostrobin and several insecticides exceeded RI ≥ 1 at 15 m, and the use of coarser droplets reduced but did not always eliminate risk. For human health, most substances showed RI < 1 for bystanders and children, whereas paraquat required larger buffer distances under fine and medium droplets. Overall, the results support the use of scenario-based risk indices as comparative tools and suggest that fixed buffer distances may be insufficient for some active ingredients. Product-specific buffer zones and complementary drift mitigation practices should be considered.