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 Leader||Pam Wofford|
|Senior Staff Scientist||Bruce Johnson|
|Field Coordinators||Kevin Bennett and Dave Kim|
|Laboratory Liaison||Carissa Ganapathy|
|Analyzing Laboratory||California Department of Food and Ariculture, Center for Analytical Chemistry|
|Agency and Public Contact||Madeline Brattesani|
All questions concerning this project should be directed to Madeline Brattesani at
IV. STUDY DESIGN
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
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.
V. SAMPLING METHODS
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.
VI. CHEMICAL ANALYSIS
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
VII. DATA ANALYSIS
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
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.