# USE - EXPOSURE RELATIONSHIP OF PESTICIDES FOR AQUATIC RISK ASSESSMENT Yuzhou Luo, Frank Spurlock, Xin Deng, Sheryl Gill, Kean Goh Surface Water Protection Program Department of Pesticide Regulation California Environmental Protection Agency 1

# Background
 

## Aquatic exposure to pesticide use is required in 

## pesticide evaluations for surface water protection  

## DPR surface water protection program is developing a more consistent and transparent method for evaluating registration packages  

## Existing modeling approaches  

### Advanced models: require a large set of input data  

### Simple models: ignore spatial variability in climate, soil, crop, and/or topography 2

# Objective
 

## To develop a simple model to estimate aquatic 

## exposure to pesticides in California field conditions  

## The model is designed as a screening tool of pesticide evaluation for surface water protection in the pesticide registration processes  

## Use-exposure relationship: a statistical relationship as an abstraction, highlighting selected inputs/outputs of an existing model 3

# Variables
 

## Use  

### What’s used: chemical properties  

### Where used: use pattern/site (scenario)  

### How used: label rates and intervals  

## Exposure  

### Peak concentration in a certain return period  

### Exposure Index (EI) from edge -of-field concentrations  Dissolved: 1 - in - 3 year return 4 - day moving averages  Sediment- bound: 1 - in - 3 year return 10 - day moving average 4

# Conceptual model
 

## Regular modeling approach

 

## Use - exposure relationship  

### Direct linkage between input data to exposure  

### Exposure= f

(label rate, chemical property)| b  

### where b is a set of scenario -specific coefficients 5

# Development
 

## Select base model and scenarios  

## Select chemical properties  

### Aerobic soil metabolism half - life (AERO), and organic carbon - normalized adsorption coefficient (KOC)  

### Log - normal distribution parameterized by ~200 

### common pesticides (Spurlock, 2008)  

## Run stochastic simulations of the “regular approach”  

## Save results as input- output (use - exposure)  

## Perform regression analysis on the modeling results for the coefficient vector b 6

# Base model
 

## Pesticide Root-Zone Model (PRZM) is selected  

### Preference of its use by USPEA for pesticide risk assessment  

### Developed modeling scenarios for California  

### Uses in recent projects of risk assessments for California (e.g., OP cumulative risk study, red - legged frog study)  

### Continuous updates and supports

Format Inputs Outputs PRZM FORTRAN program Field conditions, chemical properties, applications Daily concentrations Use - exposure relationships Regression

equations Modeling scenarios, registrantsubmitted data Exposure index 7

# Modeling scenarios
 

## USEPA Tier 2 modeling scenarios for California  

### USEPA (2006). Organophosphate pesticides: revised cumulative risk assessment  

### USEPA (2008). USEPA Tier 2 crop scenarios for PRZM/EXAMS Shell  

### USEPA (2010). Effects Determinations for the California Red - legged Frog and other California Listed Species 8

# Processes
 

## Initialize PRZM model with one scenario  

## Run stochastic simulations with random AERO and KOC  

## Derive regression relationships between inputs and outputs AERO KOC EI AERO1 KOC1 EI1 AERO2 KOC2 EI2

... ... ... 9KOC*: a breakpoint for KOC EI : exposure index (i.e., peak concentration) BASE : base application rate, used to normalized the predictions RATE : equivalent application rate based on label rates and intervals 

### Model : ln (EI_BASE)= b 1 

### + b2 

### ln(AERO)+ b 3 

### ln[max(KOC,KOC*)] EI=EI_BASE*(RATE/BASE) 10

# Coefficients

11

# Discussions and future studies
 

## Selection of the base model  

## Modeling scenarios  

## Receiving water bodies 12

# Thank you!

Reference: Luo et al., 2010. PLoS ONE, 6(4 ): e18234 Contact: Yuzhou Luo, Ph.D. Environmental Scientist Department of Pesticide Regulation Cal/EPA 1001 “I” street, Floor 3B Sacrament, CA 95812 Email: yluo@cdpr.ca.gov Phone: 916.445.2090 Fax: 916.445.4405 13