Monsanto s Field Trials for Assessing Dicamba Off-Target Movement Due to Volatility.

Transcription

1 Monsanto s Field Trials for Assessing Dicamba Off-Target Movement Due to Volatility.

2 Evaluating Volatility is a Three Step Process. WE NEED TO EXAMINE EACH STEP FOR ITS POSSIBLE CONTRIBUTION TO OFF-TARGET MOVEMENT AND EFFECTS FLUX STEP 1 Volatilization and vapor moves up from the soil and canopy Flux (μ g/m 2 /sec) Field volatility measurements show that volatility losses are small and only last for a short period of time The rate of volatilization is highest just after application within 24 hours after application Time After Application (hr) Cumulative Mass Lost to Volatility (% of Applied) These levels of volatility are predicted to have little down wind impact Time After Application (hr) We Have to Measure This 7 in. 1 yds. Total losses due to volatility are very low, equivalent to 7 inches out of a football field.

3 Evaluating Volatility is a Three Step Process. WE NEED TO EXAMINE EACH STEP FOR ITS POSSIBLE CONTRIBUTION TO OFF-TARGET MOVEMENT AND EFFECTS STEP 2 The dilution, vertical mixing, and lateral movement of vapor by wind and turbulence Wind dilutes vapors from the field and further reduces the amount of dicamba transported downwind. PERFUM model predicts air concentrations below the symptomology threshold at 5 meters outside of the treated fields Dicamba Acid Air Concentration (ng/m 3 ) % Symptomology 5% Symptomology Industry standard EPA models and results from several field studies indicate that volatility-related air concentrations downwind of the application area are not sufficient to cause symptomology. We Model This for Larger Fields Clarity Xtendimax Xtendimax + Powermax

4 Evaluating Volatility is a Three Step Process. WE NEED TO EXAMINE EACH STEP FOR ITS POSSIBLE CONTRIBUTION TO OFF-TARGET MOVEMENT AND EFFECTS STEP 3 Off-target deposition of vapor Modeling also predicts that re-deposition of any volatilized dicamba is very low and below EPA s no effect rate threshold. Deposition (fraction of applied) Deposition Due to Volatility (modeled) Deposition (fraction of applied) Distance from Application Area (ft) 2 2 "NO EFFECT RATE" PRIMARY MOVEMENT SECONDARY MOVEMENT COMPARED TO SPRAY DRIFT Distance from Application Area (ft) We Model This Deposition (fraction of applied) Deposition Due to Volatility and Spray Drift Deposition (fraction of applied) Distance from Application Area (ft) Distance from Application Area (ft) Note: "No effect rate" based on no reduction in plant height most sensitive endpoint established.

5 Why not evaluate volatility just by measuring air concentrations? A: Because air concentration is only a piece of the volatility picture. CONSIDER THE SCENARIO BELOW Which truck has the worst oil leak? HOW TO MEASURE VOLATILITY RATE IN THE FIELD The studies are performed in accordance with US EPA guidelines and estimate off-target movement using best in class EPA models. The data requirements are very specific. Air concentration is important for studying symptomology, but a rigorous measure of volatility potential also requires high quality data on wind speeds and air temperatures at several heights above the application area in order to: 1. Form a robust estimate of evaporation rate 2. Determine the amount of vapor that could be transported downwind 3. Compare volatilities across regions, locations, field sizes, or formulations. We cannot know without knowing how fast each truck was moving. We face a similar issue when studying volatility in the field, i.e., we need to know both air concentration and wind speed before we can calculate the rate of volatilization.

6 Are these studies representative of large scale commercial applications? A: Yes. Our measurement of volatility is on a per unit area basis. This enables scaling of the atmospheric models to much larger fields, typically 8 acre. AERMOD/PERFUM models will typically identify the highest off-target exposure at, for example, 5 meters from the field edge. AERMOD/PERFUM estimate deposition/concentration at every point in a large array of receptors surrounding the modeled 8 acre field. Air Concentration Distance Air Concentration 4 1 ac study field FLUX (μg/m 2 /sec) 8 AC Model Field We can also examine the concentrations at longer distances by working out from the worst case point.

7 Have you tested in a range of realistic weather conditions and soil? A: Yes. Our field flux studies represent a wide range of soil types and environmental conditions. Note the extreme air and soil temperatures. Number of Studies Completed Range of Soil Types Georgia 3 Soil Textures % Sand % Silt % Clay Texas 9 Sand Indiana 2 Loamy Sand Nebraska 4 Clay Australia 1 Clay Loam Loam Range of Environmental Conditions Maximum Air Templerature ( F) Maximum Soil Templerature (1mm)( F) Soil ph Soil Moisture at 2 in. depth (m 3 /m 3 ) Relative Humidity (%) Completed Ongoing/Planned Average Post Application Wind Speed (mph) 1 1

8 Do extreme temperatures affect volatility? A: No, not necessarily. Many factors affect volatility. Overall, temperature does not stand out as dominant in our data..4 Maximum Measured Rate of Volatilization (μg/m 2 /sec) mmhg 4.E-3 3.5E-3 3.E-3 2.5E-3 2.E-3 1.5E-3 VP of Pure Dicamba (average of 3 methods) VP of Pure Dicamba Over Xtendimax (ph 5.2) mmhg 1.E-9 8.E-1 6.E-1 4.E-1 2.E-1.E Temperature ( F) Maximum Air Temperature During Trial ( F) 1.E-3 5.E-34.E Temperature ( F)

9 How do we know that the diluted downwind air concentrations are too low to affect plants? A: Plant effects determined under constant exposure conditions is protective of field exposure and effects scenarios. Symptomology has been established in humidome tests with controlled levels of dicamba air concentrations. Extensive field data and large scale modeling indicates dilution by wind reduces air concentrations to below symptomology levels. 6 5 y =.914x R 2 = % PERFUM model predicts air concentrations below the symptomology threshold at 5 meters outside of the treated fields 42% 12 1% Symptomology Syptomology (%) % 3% 7% 19% 11% 25% NOTE Continuous exposure Confined environment No dilution in humidome vs. field dilution due to wind Greenhouse plants are more sensitive than field plants Dicamba Acid Air Concentration (ng/m 3 ) % Symptomology Clarity Xtendimax Xtendimax + Powermax Dicamba Acid Air Concentration (ng/m 3 ) 1% Symptomology 5% Symptomology Cropped Bareground