Higher Tier Exposure Assessments in Rice Paddy Areas: An American Perspective

Publisher Summary This chapter presents examples that demonstrate a tiered process for modeling rice in the US. The tiers presented are a stepwise increase in representing processes in a more realistic manner and each tier is designed to be protective. However, model results must be approached with an understanding of potential deficiencies and therefore certain caveats pertain to the analyses. The model calculates an estimated environmental concentration (EEC) in the water column that could be released from the rice paddy. There is also a more refined screening level model for ecological risk assessment developed by EFED that includes degradation and holding times in the rice paddy. Tier 1 is the most conservative and is designed as a screening process. For most crops, Tier 1 consists of using the GENEEC2 and FIRST models to evaluate ecological risk and drinking water risk, respectively. If the pesticide does not pass the Tier 1 risk assessment, then Tier 2 is conducted. Tier 2 involves running the Pesticide Root Zone Model (PRZM) with the Exposure Analysis Modeling System (EXAMS) with Environmental Fate and Effects Department (EFED) standard crop and standard water body scenarios. Tier 4 uses actual pesticide use and aquatic monitoring data.