Department of Pesticide Regulation Environmental Monitoring and Pest Management

1020 N Street, Room 161

Sacramento, CA 95814

Environmental Hazards Assessment Program Study #151

October 10, 1996


Methyl bromide is a widely used pesticide for fumigation of stored product pests. In 1994, the Department of Pesticide Regulation (DPR) placed restricted material permit conditions on commodity fumigations. 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 safety 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 an institution. 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.

Different sizes of buffer zones are required for treatment, aeration, and method of aeration. The DPR will monitor the air concentrations of methyl bromide associated with a chamber fumigation to assess the effectiveness of the buffer zones.


To monitor methyl bromide concentrations associated with a chamber fumigation to determine effectiveness of buffer zone distances.


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 - Randy Segawa

Field Coordinator - Nan Singhasemanon

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

The fumigation chambers are located at two adjacent nut production companies in Winters, Calif. Each company has a chamber consisting of two smaller chambers for fumigation of product prior to storage or export. The site is located near residential areas, approximately 90 ft from the nearest residence. Samplers will be placed around the fumigation chambers at the buffer zone distances of 40 ft and 50 ft for each respective chamber and in the yard or fenceline of nearest residences during the fumigation and aeration. 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. During the treatment holding period the flow rate will be set to 15 ml/min for a total collection volume of approximately 11 liters. During the aeration period, flow rates will be set to achieve a total collection volume of 11 liters. Once samples are collected, each tube opening will be tightly capped and samples will be placed on dry ice and remain frozen until analysis.

Monitoring will include the period during treatment, and the aeration period following.

The total number of samples to be collected are:

9 stations x 2 sample intervals + 1 matrix blank = 19 samples.


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. A matrix blank will be submitted to the laboratory as a quality assurance measure. Concentrations for primary and secondary tubes will each be reported to detail any occurance of breakthrough in the primary tube.


Results will be reviewed to verify that concentrations did not exceed the 24-hour time-weighted average target level of 0.21 ppm 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 in October to early November. A final report will be completed after all chemical analysis are received from the laboratory.