93
Sampling and Analysis
and rugged resin sampling tube which with modifcation is the backbone
of modern air samplers for measuring ambient levels of pesticides in air. It
can be adapted to smaller scale versions for assessing human exposures in
a variety of conditions. When preceded by a glass fber flter, one sampling
tube could yield results for particulates and vapors. This device was used to
assess exposures to pesticides in several use scenarios in fulflling requirements of California’s unique Toxic Air Contaminant Act (Baker et al., 1996). It
was used to gather data on pesticide exposures needed for IR-4 registrations
for minor use pesticides on specialty crops, as well as several other applications (Hengel and Lee, 2014).
But one size did not ft all pesticides and related contaminants of potential
interest. Some highly volatile fumigants, such as methyl bromide and sulfuryl fuoride, were not trapped by XAD/Chromosorb resins requiring use
of an alternative adsorbent—activated charcoal. Filters are typically made
of glass or quartz fber, and adsorbents are typically XAD, Chromosorb 100
series, Carbopack, Tenax, or silica gel, among others (Kosikowska and Biziuk,
2010). With these substitutions practically all pesticides could be analyzed by
accumulative sampling in air.
6.2.2 Physical Properties of the Analyte
Methods for sampling of semivolatile organic compounds (SVOCs) including pesticides and their solvent carriers depend on the vapor pressure of the
analyte (Woodrow et al., 2003) (Table 6.1). At vapor pressures (P) greater than
0.1 Pa, the pesticide is primarily in the vapor phase. Fumigants including
methyl bromide (P = 216,645 Pa) and 1,3-D (P = 3,866 Pa) and the herbicide
S-ethyl dipropylthiocarbamate (EPTC) (P = 4.5 Pa) are collected as vapors
on adsorbents, adsorbent coatings, and impingers, or can be sampled from
whole air in canisters. If the vapor pressure is less than 10 −5 Pa, such as occurs
for paraquat and the salts of many herbicides, they will be found primarily in
the particulate or aerosol form. Aerosols are captured on flters and inertial
TABLE 6.1
Sampler Design Based on Vapor Pressure
Saturation Vapor
Example
Pressure (Pa)
Sampler Design
Vapors
Methyl bromide, S-ethyl
>10 −1
Adsorbents,
dipropylthiocarbamate
canisters, impingers
(EPTC)
Vapors + aerosols
Chlorinated hydrocarbons
10 −5 to 10 −1
Filters, adsorbents
and organophosphates
Aerosols
Phenoxy herbicide salts and
<10 −5
Filters, impactors,
paraquat
cyclone separators
Source: Adapted from Woodrow et al. (2003).
Sampling and Analysis
and rugged resin sampling tube which with modifcation is the backbone
of modern air samplers for measuring ambient levels of pesticides in air. It
can be adapted to smaller scale versions for assessing human exposures in
a variety of conditions. When preceded by a glass fber flter, one sampling
tube could yield results for particulates and vapors. This device was used to
assess exposures to pesticides in several use scenarios in fulflling requirements of California’s unique Toxic Air Contaminant Act (Baker et al., 1996). It
was used to gather data on pesticide exposures needed for IR-4 registrations
for minor use pesticides on specialty crops, as well as several other applications (Hengel and Lee, 2014).
But one size did not ft all pesticides and related contaminants of potential
interest. Some highly volatile fumigants, such as methyl bromide and sulfuryl fuoride, were not trapped by XAD/Chromosorb resins requiring use
of an alternative adsorbent—activated charcoal. Filters are typically made
of glass or quartz fber, and adsorbents are typically XAD, Chromosorb 100
series, Carbopack, Tenax, or silica gel, among others (Kosikowska and Biziuk,
2010). With these substitutions practically all pesticides could be analyzed by
accumulative sampling in air.
6.2.2 Physical Properties of the Analyte
Methods for sampling of semivolatile organic compounds (SVOCs) including pesticides and their solvent carriers depend on the vapor pressure of the
analyte (Woodrow et al., 2003) (Table 6.1). At vapor pressures (P) greater than
0.1 Pa, the pesticide is primarily in the vapor phase. Fumigants including
methyl bromide (P = 216,645 Pa) and 1,3-D (P = 3,866 Pa) and the herbicide
S-ethyl dipropylthiocarbamate (EPTC) (P = 4.5 Pa) are collected as vapors
on adsorbents, adsorbent coatings, and impingers, or can be sampled from
whole air in canisters. If the vapor pressure is less than 10 −5 Pa, such as occurs
for paraquat and the salts of many herbicides, they will be found primarily in
the particulate or aerosol form. Aerosols are captured on flters and inertial
TABLE 6.1
Sampler Design Based on Vapor Pressure
Saturation Vapor
Example
Pressure (Pa)
Sampler Design
Vapors
Methyl bromide, S-ethyl
>10 −1
Adsorbents,
dipropylthiocarbamate
canisters, impingers
(EPTC)
Vapors + aerosols
Chlorinated hydrocarbons
10 −5 to 10 −1
Filters, adsorbents
and organophosphates
Aerosols
Phenoxy herbicide salts and
<10 −5
Filters, impactors,
paraquat
cyclone separators
Source: Adapted from Woodrow et al. (2003).