Volatilization Losses of Methyl Bromide and Chloropicrin from Drip Fumigated Beds Covered with Totally Impermeable Tarp

Transcription

1 Volatilization Losses of Methyl Bromide and Chloropicrin from Drip Fumigated Beds Covered with Totally Impermeable Tarp H. Ajwa 1, D. Sullivan 2, M. Stanghellini 3, W. Ntow 1, M. Holdsworth 2, and J. Hunzie 1 1 University of California-Davis, 2 Sullivan Environmental Consulting, 3 TriCal INTRODUCTION Fumigants are regulated primarily based on air emissions. Predicted emissions (soil surface flux) and product toxicology are used by CAL-EPA and more recently by the USEPA, to establish application rates, buffer zones, and use limits (e.g., township caps and VOC regulations) for fumigants. Fumigant emissions reduction strategies include the use of virtually impermeable film (VIF) and totally impermeable film (), water seals, and fumigant degraders such as thiosulfate. Methyl bromide and chloropicrin are currently under re-registration and preliminary indications are that uses may be limited by large buffer zones. In California, some counties are currently limiting Pic rates and setting buffer zones in anticipation of revised federal and state regulations. A registration package for a drip-applied emulsifiable concentrate formulation of Methyl bromide/pic is being prepared for future submission to the USEPA. The lower application rate needed for drip fumigation should result in smaller buffer zones and lower total emissions compared to shank broadcast applications. Emissions data are needed to support the registration of this drip formulation and would provide crucial information on mitigation measures for the MB drip application method. Although registrants are responsible for supplying emission data to regulators for proposed labeled use conditions, we feel there are opportunities, in support of the strawberry industry, to explore additional emissions reduction methods to develop management practices that will allow us to use the limited amount of methyl bromide for a longer time than would be afforded if only the current standard application methods (shank injection) are used. The main goal of this study was to develop management practices that can significantly reduce fumigation emissions while achieving good soil pest control. This research focuses on testing methods using to reduce emissions in drip application to strawberry fields. The specific objective was to evaluate sealing practices vs. standard low density polyethylene (LDPE) tarp for reduction of fumigant off-gassing. METHODS Fumigant Application: The experiments were conducted in Salinas on two fields. Each field was approximately one acre and consisted of 48 beds (52 inches center-to-center) that were 28 feet long (28 x 28 ft). The two fields were separated from each other by more than 15 ft to avoid cross contamination. The fields contained the same soil type, soil moisture, same drip tape characteristics, and were prepared by cooperating growers following standard strawberry production practices. 51-1

2 An emulsifiable concentrate formulation of MB plus Pic (MB/Pic, 46/54 plus 1.6% emulsifier) at 354 lbs/ac was drip-applied in 1.5 inches of water to raised beds through two drip tapes (.67 gpm/1ft) on September 3, 28. Field 1 was covered with 1.38 mil LDPE tarp and Field 2 was covered with 1.25 mil (VaporSafe TM by Raven Industries). Field Sampling: Methyl bromide and chloropicrin emission rates were determined for each field using the off-site indirect method. This method uses the Industrial Source Complex Short Term (ISCST3) model and an atmospheric dispersion model used by EPA for regulatory purposes. In this method, the fumigant concentrations in the atmosphere around the field are measured and used with the ISCST3 dispersion model to back-calculate the field emission rate. Volatilization flux measurements were obtained by using air samplers (pumps) positioned at a minimum of 8 locations around each field as shown below. Location of air monitoring stations around the field: 447 m 2 (1 acre) Off-field air monitoring station Weather Station The air was sampled at a height of 1.5 m above the soil surface. Air concentration measurements were obtained by collecting fumigant on charcoal or XAD sampling tubes. A flow rate of 5 ml/min was used to draw air through the tubes and to ensure that sufficient air volume will be sampled. 51-2

3 Air sampling and fumigant concentration measurement: Each field had 8 sampling pumps for charcoal and 8 sampling pumps for XAD-4. Sampling was conducted on a six-hour basis for the first the first 48 hours, then every 12 hours (sunrise and sunset) for the rest of the sampling periods (Days 3 to 14). Sampling of each site was within 1% of the sampling period (the six hour period should be sample within 4 min. for each field). Air concentration measurements were obtained by collecting MB on petroleum charcoal sorbent tubes and chloropicrin on XAD-4 resin tubes. A flow rate of 5 ml/min was used to draw air through the tubes and to ensure that sufficient air volume was sampled. The samples were stored on dry ice (upon exchange of tubes), and then transferred to the laboratory for analysis. In the laboratory, the charcoal and XAD-4 resin were immediately extracted with ethyl acetate and hexane, respectively, and fumigant concentration was determined by using a gas chromatography equipped with an Electron Capture Detector (µecd). RESULTS AND DISCUSSION Methyl bromide flux rates and cumulative emissions relative to the amount applied as calculated by the ISCST3 model are shown in Figures 1 and 2, respectively. Peak emissions were approximately 4% lower in the field compared to the LDPE field. MB mass loss relative to the amount applied was 64% for the LDPE tarp and 45% for the. The use of reduced total methyl bromide emissions relative to LDPE tarp by approximately 3%. Chloropicrin flux rates and cumulative emissions relative to the amount applied as calculated by the ISCST3 model are shown in Figures 3 and 4, respectively. Peak emissions were approximately 33% lower in the field compared to the LDPE field. Pic total mass loss relative to the amount applied was 31% for the LDPE tarp and 23% for the. The use of reduced total chloropicrin emissions relative to LDPE tarp by approximately 26%. While the demonstrated significant emissions reduction for both methyl bromide and chloropicrin compared to LDPE, the peak and total emissions for both compounds under both film types were uncharacteristically high. High early MB and Pic emission rates and mass losses from the field were believed to be due to significant leaks in the drip irrigation systems during the application. A significant volume of irrigation water was discovered at one corner of the fields immediately after application. This leak in the irrigation line is likely the leading contributor to the high early volatilization losses found in this study. Lack of emulsifier in the formulation (1.6% instead of 5%) may have also contributed to the volatilization losses of fumigants from the dry, uncovered furrows in both fields. In addition, the field preparation in Field 1 was substandard in that large clods were present at the soil surface. Cloddy surface conditions are conducive to allowing the escape of fumigant emissions. In some areas of the field, these clods also created many small punctures in the film, thereby compromising the film s integrity. 51-3

4 This study emphasizes the fact that leaks in the drip irrigation systems, lack of emulsifier in the formulation, and poor soil preparation can lead to significant volatilization losses of fumigants. We speculate that without adequate emulsifier content, co-distillation of Pic and MB may have enhanced Pic volatilization from the dry furrows, as the peak and total chloropicrin emissions found in this study are far greater than found in several other studies on chloropicrin drip emissions. This study was repeated in early September 29. Data analysis is in progress. AKNOWLEDGEMENTS This research was funded by the California Strawberry Commission. The authors also wish to thank the Air Monitoring Group at the Department of Pesticide Regulations (California EPA) for helping in collecting field samples and TriCal, Eval/Mitsui, and Kuraray America for providing materials and support. 51-4

5 Figure 1. Methyl bromide flux rates as estimated by the ISCST3 model, Salinas, Methyl bromide emission rates (ug/m2/sec) /3/9 1/1/9 1/2/9 1/3/9 1/4/9 1/5/9 1/6/9 1/7/9 1/8/9 1/9/9 1/1/9 1/11/9 1/12/9 1/13/9 1/14/9 Figure 2. Methyl bromide volatilization losses relative to amount applied (164 lbs/ac), Salinas, MB mass loss relative to applied (%) /3/9 1/1/9 1/2/9 1/3/9 1/4/9 1/5/9 1/6/9 1/7/9 1/8/9 1/9/9 1/1/9 1/11/9 1/12/9 1/13/9 1/14/9 51-5

6 Figure 3. Chloropicrin flux rates as estimated by the ISCST3 model, Salinas, Chloropicrin emission rates (ug/m2/sec) /3/9 9/3/9 18: 1/1/9 1/1/9 18: 1/2/9 1/2/9 18: 1/3/9 1/3/9 18: 1/4/9 Figure 4. Chloropicrin volatilization losses relative to amount applied (19 lbs/ac), Salinas, Chloropicrin mass loss relative to applied (%) /3/9 9/3/9 18: 1/1/9 1/1/9 18: 1/2/9 1/2/9 18: 1/3/9 1/3/9 18: 1/4/9 51-6