Mechanistic Model for Simulating Pesticide Uptake into Maize Pollen.

Seed coatings protect agricultural crops from pests, but they can expose pollinators to residues. We extended a dynamic model for pesticide uptake from soil into maize plants with a flower compartment, including nectar and pollen. Field experiments with seed/soil and spray applications were simulated successfully. Calibrated loss rates usually exceeded dissipation rates empirically fitted to declining concentrations due to continuous delivery of chemicals seen by the model (soil to plant components). Simulated dissipation consists of growth dilution and degradation (nonvolatile compounds) with half-lives fitted for imidacloprid in pollen of 0.2 to 0.9 days, close to observations following spray application. Our model predicts that mobile, persistent, and nonvolatile chemicals are potentially translocated to pollen if present in soil. This is relevant also for persistent, mobile, and toxic (PMT) chemicals released from reclaimed wastewater or via sewage sludge application. Our model can be incorporated into existing frameworks to estimate the exposure of pollinating insects.