Study #150

Department of Pesticide Regulation Environmental Monitoring and Pest Management

1020 N Street, Room 161

Sacramento, CA 95814

October 1, 1996


Methyl bromide is a widely used pesticide registered for use as a preplant soil fumigant, a structural fumigant, and a fumigant for control of stored products pests. The Department of Pesticide Regulation (DPR) has reviewed the health related studies on methyl bromide and determined that a 24-hour time-weighted average concentration of 0.21 ppm provides a 100 fold margin of exposure to protect the public health. This 0.21 ppm target level has been used to develop permit conditions for field, commodity, and other types of fumigation.

The permit conditions involve buffer zones. These are areas that must be maintained between the application site and those places where people are active. The buffer zone is not an exclusion zone; people can walk or drive through a buffer zone and still not be at risk because they are spending only a short time near the application site. The size of the buffer zone varies based on the amount of time a person would normally spend doing a certain activity. The 0.21 ppm target level for methyl bromide is based on a twenty four-hour continuous exposure. For example, a person could be exposed to 0.42 ppm for 12 hours or 0.63 ppm for eight hours without exceeding the 0.21 ppm, 24-hour time-weighted average. Accordingly, buffer zones must be larger if the activity can be conducted for 24 hours, such as spending time at home or in a hospital. The buffer zone can be reduced when the activity is conducted for less than 12 hours, such as a normal work shift or a round of golf.

Another factor which could potentially affect the size of buffer zones is temperature. To test whether the lower methyl bromide emissions in colder winter months offset the need for larger buffer zones, the DPR will be monitoring field applications of methyl bromide during the winter of 1996-1997. Several types of methyl bromide applications will be monitored to determine if buffer zones presently in place provide an adequate margin of safety during winter conditions.


To monitor field-applications of methyl bromide to determine effectiveness of buffer zone distances under winter climatic conditions.


This study will be conducted by personnel from the Environmental Hazards Assessment Program under the overall supervision of Roger Sava, Senior Environmental Research Scientist.

Key personnel include:

Project Leader - Pam Wofford

Senior Staff Scientist - Heinz Biermann

Field Coordinator - Nan Singhasemanon

Consulting Senior Supervisor- Randy Segawa

Consulting Statistician/Modeler - Terrell Barry

Analyzing Laboratory - California Department of Food and Agriculture.

Center for Analytical Chemistry

Agency and Public Contact - Peter Stoddard

All questions concerning this project should be directed to Peter Stoddard at (916) 324-4078.


Site Selection

Based on the 1993 and 1994 Pesticide use reports, Fresno, Merced, Monterey, Tulare, Ventura and Kern County had the highest number of winter applications and are recommended as the best potential locations for monitoring. The treatment site must be a soil application: shallow or deep injected, tarped or untarped, and broadcast or bed application. The application of methyl bromide must be completed in a single day to attain a full sampling period not compounded with application emmissions. A metereological weather station will be set up next to the treatment area to measure wind speed, wind direction, ambient temperature, and relative humidity.

Air Sampling

Air monitoring will be conducted using SKC personal air sampling pumps. Each air sampler will be positioned approximately 1.2 m (4 ft) above ground level and will be fitted with activated charcoal vapor collection tubes stacked, two in a series, consisting of a 400-mg primary tube and a 200-mg secondary tube. Flow rates will be set at 15 ml/min for a total collection volume of approximately 11 liters over the 12-hour sampling period. Once samples are collected, each tube opening will be tightly capped and samples will be placed on dry ice and remain frozen until analysis.

To monitor methyl bromide concentrations adjacent to a treated field, air sampling stations will be located around the treatment site. Four stations will be located at the center of each side of the field, approximately 10 meters out from the edge. Another four to eight sampling stations will be placed at the buffer-zone limit, depending on the size of the treatment. Additional sampling stations will be added if needed to address larger treatment areas.

Air samplers will be placed at the residential buffer zone limits to measure air concentrations, during and after application. On large application sites, additional samplers will be placed closer to the treatment and used in conjunction with the onsite weather data and the ISCST model to calculate potential concentrations surrounding the application site. If obstructions prohibit the placement of samplers at the buffer-zone limit, the samplers will be placed around the application at the maximum possible distance, and results will be modeled out to the limit. Monitoring will be carried out over two 12-hour periods, beginning with the start of application. An additional 12-hour samling period may be added for deep shank applications to assure monitoring of the maximum flux period.

For each application:

The minimum total number of samples to be collected are:

8 stations x 2 sample intervals = 16 samples.

The maximum to be collected are:

16 stations x 2 sample intervals = 32 samples (+ 16 if an additional period is needed).

Up to 5 different application types will be monitored.


Chemical analysis will be performed by the California Department of Food and Agriculture Center for Analytical Chemistry. Methyl bromide will be extracted with ethyl acetate and then analyzed by gas chromatography with an electron capture detector. Matrix blanks, spikes, and blind spikes will be submitted to the laboratory as a quality assurance measure. Concentrations for primary and secondary tubes will be reported seperately to document any breakthrough in the primary tube.


Results will be reviewed to determine if the buffer zones were adequate to assure the concentrations do not exceed the 24-hour health limit for residential areas. In addition, the weather data and measured concentrations will be entered into the ISCST model to confirm the measurements taken are representative for the entire buffer-zone surrounding the application.


Monitoring will occur sometime between November, 1996, and February, 1997 as soon as suitable fields are located for study. A final report will be completed after all chemical analysis are received from the laboratory.