Department of Pesticide Regulation
Environmental Monitoring and Pest Management Branch
1020 N Street, Room 161
Sacramento, CA 95814-5624

Environmental Hazards Assessment Program Study #163


June 20, 1997


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 parts per million (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 include buffer zones. These are areas that must be maintained between the application site and places where people conduct certain activities or practices. 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 24-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.

People adjacent to some agricultural areas have expressed concerns about methyl bromide fumigations and the effectiveness of the permit conditions near "sensitive" sites such as residential neighborhoods, schools, day care centers, and hospitals.


To monitor air concentrations near sensitive sites at methyl bromide applications identified by the county agricultural commissioner.


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

Key personnel include:

Project LeaderPam Wofford
Senior Staff ScientistBruce Johnson
Field CoordinatorsKevin Bennett and Dave Kim
Statistician/ModelerTerrell Barry
Laboratory LiaisonCarissa Ganapathy
Analyzing LaboratoryCalifornia Department of Food and Ariculture, Center for Analytical Chemistry
Agency and Public ContactMadeline Brattesani

All questions concerning this project should be directed to Madeline Brattesani at (916) 324-4100.


The application sites will be chosen by the county agricultural commissioner. Ideally, there will be houses, schools, or other sensitive sites that are just outside the buffer zone.

For each application monitored, 12 - 16 monitoring stations will be established. Four stations will be established 30 feet from the edge of the treated area--one station at the center of each side. Eight stations will be established at the resident buffer zone distance specified by the permit conditions--one station at the center of each side and one station at each corner. Up to four additional stations will be established at the resident buffer zone distance and placed directly between the treated area and sensitive sites. Monitoring will be carried out for for 48 hours--two 6-hour periods and three 12-hour periods beginning with the start of application.

For each application:

The minimum total number of samples to be collected are:

12 stations x 5 sample intervals = 60 samples

The maximum to be collected are:

16 stations X 5 sample intervals = 80 samples.


Air monitoring will be conducted using SKC personal air sampling pumps. Each air sampler will be positioned approximately four feet above ground level and will be fitted with activated charcoal vapor collection tubes, stacked two in a series, consisting of a 400 milligram primary tube and a 200 milligram secondary tube. Flow rates will be set at 15 milliliters per minute. Once samples are collected, each tube opening will be tightly capped and samples will be placed on dry ice and remain frozen until analysis.

A weather station will be set up next to the treatment area to measure wind speed, wind direction, ambient air temperature, and relative humidity.


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 separately to document any breakthrough in the primary tube.


Results will be reviewed to determine if the buffer zones were adequate to assure that concentrations do not exceed the 24-hour target level for residential areas. In addition, the weather data and measured concentrations will be entered into the Industrial Source Complex-Short Term (version 3) computer model to confirm that the measurements taken represent the entire buffer zone surrounding the application.


Monitoring will occur as soon as suitable fields are located for study. A final report will be completed after all chemical analysis are received from the laboratory.