Pyrethroid sources to indoor air include applications by exterminators and residents within buildings, penetration of pyrethroids from outdoors associated with
drift from agricultural settings and treatment of surrounding outdoor settings or
neighboring apartments/buildings, and resuspension of dust that absorbed pyrethroids or volatilization from dust and indoor surfaces. Indoor pesticide application
equipment that directly increases air concentrations include ready-to-use products
with a trigger pump spray, pressurized aerosol cans, compressed air sprayers,
broadcast applications, coils, and vaporizers.
Li et al. [10] evaluated the indoor air levels during and post-application for a
series of controlled mosquito control applications using four different application
methods (mosquito coil, liquid vaporizer, vaporizing mat, and aerosol spray). They
measured sub-μg/m
3 levels of several pyrethroids during the application with air
concentrations decreasing 1–2 orders of magnitude within 12 h following the
application (Table 2). They also observed lower air levels when windows were
opened as opposed to closed, which is consistent with higher ventilation rates
reducing air concentrations. The percentage of pyrethroids in the particulate phase
varied from 40 to >95% for dimefluthrin, allethrin, cypermethrin, and tetramethrin,
with compounds having lower vapor pressure being more associated with the
particulate phase [10]. An older study quoted by Li et al. reported ppm air concentrations of various pyrethroids in residue over very short-time intervals of minutes
[40]. Li et al. suggested that the apparent higher levels measured previously reflected
the timing between the application and the sample collection and the sampling
duration [41]. Multiple sample collection indicates, not surprisingly, that the peak
air concentrations are during the pyrethroid application. To avoid unnecessary
pesticide exposure, typical labels caution against vulnerable individuals, such as
children, being in the room when spraying is done, and the sprayed area should be
adequately ventilated before it is reoccupied. Nazimek et al. measured 1.3–5.2 μg/m
3
of transfluthrin in the indoor air after application of gel and liquid formulas in an
electro-vaporizer application, though the levels were below detection 18–24 h after
the application [41]. An evaluation of multiple pyrethroids in residences in South
Korea found that the air concentration of the sum of pyrethroids present (Table 3)
was inversely related to the time since it was last sprayed but not to frequency of use,
room sprayed, or if products were stored indoors [44]. Vesin et al. [46] used a high
sensitivity proton-transfer-reaction mass spectrometer (HS-PTRMS) to measure
time-resolved gas-phase air concentrations of transfluthrin emitted during an electric
vaporizer application and reported a constant increase until the unit was unplugged,
then reaching 4.9 μg/m
3 after 8 h at a room air exchange rate (AER) of 0.35 h
À1 and
8.5 μg/m
3 at an AER of 0.14 h
À1 . Once the vaporizer was unplugged, the air
concentration decreased exponentially at a rate based on the AER. They also
reported that the air concentrations continued to rise reaching a steady-state concentration of 16 μg/m
3 after 33 h for the lowest AER (0.14 h
À1 ) examined.
Pyrethroid exposure of children and pregnant women is of particular concern
since pyrethroids can affect the neurological system and potentially other organs
[47–49]. Ingestion of food contaminated with pyrethroids and inadvertent ingestion
of household dust in treated residences are generally larger exposure routes than
234
C. P. Weisel
drift from agricultural settings and treatment of surrounding outdoor settings or
neighboring apartments/buildings, and resuspension of dust that absorbed pyrethroids or volatilization from dust and indoor surfaces. Indoor pesticide application
equipment that directly increases air concentrations include ready-to-use products
with a trigger pump spray, pressurized aerosol cans, compressed air sprayers,
broadcast applications, coils, and vaporizers.
Li et al. [10] evaluated the indoor air levels during and post-application for a
series of controlled mosquito control applications using four different application
methods (mosquito coil, liquid vaporizer, vaporizing mat, and aerosol spray). They
measured sub-μg/m
3 levels of several pyrethroids during the application with air
concentrations decreasing 1–2 orders of magnitude within 12 h following the
application (Table 2). They also observed lower air levels when windows were
opened as opposed to closed, which is consistent with higher ventilation rates
reducing air concentrations. The percentage of pyrethroids in the particulate phase
varied from 40 to >95% for dimefluthrin, allethrin, cypermethrin, and tetramethrin,
with compounds having lower vapor pressure being more associated with the
particulate phase [10]. An older study quoted by Li et al. reported ppm air concentrations of various pyrethroids in residue over very short-time intervals of minutes
[40]. Li et al. suggested that the apparent higher levels measured previously reflected
the timing between the application and the sample collection and the sampling
duration [41]. Multiple sample collection indicates, not surprisingly, that the peak
air concentrations are during the pyrethroid application. To avoid unnecessary
pesticide exposure, typical labels caution against vulnerable individuals, such as
children, being in the room when spraying is done, and the sprayed area should be
adequately ventilated before it is reoccupied. Nazimek et al. measured 1.3–5.2 μg/m
3
of transfluthrin in the indoor air after application of gel and liquid formulas in an
electro-vaporizer application, though the levels were below detection 18–24 h after
the application [41]. An evaluation of multiple pyrethroids in residences in South
Korea found that the air concentration of the sum of pyrethroids present (Table 3)
was inversely related to the time since it was last sprayed but not to frequency of use,
room sprayed, or if products were stored indoors [44]. Vesin et al. [46] used a high
sensitivity proton-transfer-reaction mass spectrometer (HS-PTRMS) to measure
time-resolved gas-phase air concentrations of transfluthrin emitted during an electric
vaporizer application and reported a constant increase until the unit was unplugged,
then reaching 4.9 μg/m
3 after 8 h at a room air exchange rate (AER) of 0.35 h
À1 and
8.5 μg/m
3 at an AER of 0.14 h
À1 . Once the vaporizer was unplugged, the air
concentration decreased exponentially at a rate based on the AER. They also
reported that the air concentrations continued to rise reaching a steady-state concentration of 16 μg/m
3 after 33 h for the lowest AER (0.14 h
À1 ) examined.
Pyrethroid exposure of children and pregnant women is of particular concern
since pyrethroids can affect the neurological system and potentially other organs
[47–49]. Ingestion of food contaminated with pyrethroids and inadvertent ingestion
of household dust in treated residences are generally larger exposure routes than
234
C. P. Weisel