Environ. Sci. Technol. 1998, 32, 1386-1390
Air and Surface Chlorpyrifos Residues following Residential Broadcast and Aerosol Pesticide Applications CHENSHENG LU AND RICHARD A. FENSKE* Department of Environmental Health, School of Public Health and Community Medicine, University of Washington, Seattle, Washington 98195-7234
Ambient air at three different heights and surface chlorpyrifos residues were measured for 7 days following broadcast (Dursban) and total release aerosol (K-RID) chlorpyrifos applications for flea control in four dormitory rooms. All rooms were ventilated with forced air for 30 min immediately following applications. One room of each type was then maintained with no ventilation, while the other rooms were ventilated by forced air for an additional 4 h and by ambient air on subsequent study days. Peak air concentrations of 118 µg/m3 (broadcast) and 82 µg/m3 (aerosol) were measured at 4-12 h postapplication. Concentrations decreased rapidly over the first 4 days postapplication and remained low (1 µg/m3) and relatively constant on days 5-7. Forced air ventilation reduced air concentrations only transiently in the broadcast room, and subsequent ambient air ventilation had little effect. In the aerosol room, however, ventilation decreased air concentrations substantially. Broadcast applications resulted in 7.5 times more total deposited chlorpyrifos on carpets than aerosol applications; however, dislodgeable residues on carpets were only 2-fold greater. Chlorpyrifos residues deposited on nontarget surfaces (e.g., furniture) by aerosol applications were 140-500 times greater than by broadcast applications. The estimated total absorbed chlorpyrifos doses for broadcast and aerosol applications (12-33 µg/ kg) were near the no observable effect level (NOEL, 30 µg/kg) on day 1 but not on the remaining days. Future studies should measure airborne particulates and assess residue dislodgeability from nontarget surfaces, as these pathways are likely contributors to human exposure. Accurate estimates of exposure in these environments will also require detailed analysis of human activities.
Introduction Commercial and consumer application of pesticides is a common pest control practice in residential and institutional environments. The U.S. Environmental Protection Agency has conducted a systematic investigation of pesticides in indoor air (1) and has developed methods for measuring environmental concentrations in homes (2). Several investigators have focused on exposures immediately following residential pesticide applications in an effort to develop exposure assessment guidelines for product registration and to estimate acute toxicity risks for children (2-9). * Corresponding author phone: (206)543-0916; fax: (206)616-2687; e-mail:
[email protected]. 1386
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Pesticide applications in the home can normally be classified into one of four categories: (1) broadcast (pressurized fan spray with dilute formulated material), (2) total release aerosol (fogger or other devices from which an aerosol is emitted from a fixed source), (3) crack-and-crevice (pin stream spray treatment of baseboards or insect entry points), and (4) structural control (foundation perimeter or crawl space treatment). Broadcast and aerosol applications are employed to treat large interior surfaces (e.g., floors, carpets, furniture) and consequently may result in significant dermal exposure for occupants as well as respiratory exposures. This study was designed to evaluate potential exposure to air and surface residues of chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate], following broadcast and total aerosol release applications over a 7-day period and to determine the effect of ventilation on residue dissipation.
Methods Field and Application Conditions. The study was conducted in four unoccupied college dormitory rooms with identical dimensions (4.8 × 3.4 × 2.7 m). Floor surface area and volume in each room were 15.94 m2 and 42.8 m3, respectively. All rooms were carpeted wall-to-wall with 0.64 cm thick nylon pile. Each room contained two study desks and one cabinet. No heating or air conditioning systems were in operation during the study. Two broadcast and two total release aerosol applications were conducted according to label instructions for flea control. Broadcast applications were conducted by a licensed pest control applicator. The formulated product, Dursban L.O. (EPA Registration No. 464-571), contains 41.5% chlorpyrifos. The formulation was applied from approximately 40 cm above the carpet as a 0.5% aqueous spray (40 mL/3.8 L of water) with a hand-held fan broadcast nozzle attached to a CO2-pressurized tank. The entire floor was sprayed in about 1 min per room. The furniture surfaces were not sprayed. Total release aerosol applications were conducted with aerosol cannisters (K-RID foggers) purchased in a local K-mart store in New Jersey in 1990. The fogger contained 0.5% chlorpyrifos by weight. The cannisters were weighed before and after application to obtain total mass released and placed on a 40 cm high stool that was located in the center of the room. Windows and doors were closed prior to and for 2 h during cannister activation. Each of the four study rooms was ventilated for 30 min immediately following application by opening the two windows and door and placing a 51 × 51 cm box fan on a 76-cm high table in the doorway to draw air out of the room, thereby creating cross ventilation. At the end of this initial ventilation period, the windows and door in one room of each application type were closed, and the fan was turned off. In the other room, the door and windows were left open, and the fan operated for an additional 4 h. On subsequent days, the windows and doors of the ventilated rooms were opened for 8 h/day to allow ambient air movement. Sampling. Air samples were collected with ORBO-44 tubes [Supelpak 20E (20/40), Supelco, Inc.] attached to personal air sampling pumps (HFS 513, Gilian). Pumps were calibrated with the sampling train in line to 1 L/min before and after each sampling period. Samplers were attached at three heights (25, 100, 175 cm) to a pole placed in the center of the room. Samples were collected prior to application and at the following time intervals (h) for 2 days postapplication: 0-4, 4-8, 8-12, 12-24, 24-36. Twentyfour hour samples were collected on days 3-7. Sampling S0013-936X(97)00671-8 CCC: $15.00
1998 American Chemical Society Published on Web 04/10/1998
tubes were capped, stored in an ice chest for transport to the laboratory, and stored at -20 °C until analysis. The floor of each study room was sectioned into 113 (929 cm2) squares, and sections were assigned randomly for either deposition or wipe sampling. Deposition samples were double-layer 12-ply, all-cotton, individually wrapped, 7.6 × 7.6 cm surgical gauze pads backed by aluminum foil. These samplers were placed on the target surface (carpet) and horizontal surfaces (desks and cabinets) prior to application and were collected 15 min postapplication. In the aerosol application rooms, each wall and the ceiling were divided into quadrants, and a sampler was placed in the center of each quadrant, resulting in 20 additional deposition samples. Wipe samples were collected with a surgical gauze pad sprayed lightly (2 mists) with distilled water. Areas to be wiped were marked by disposable cardboard frames. A 100 cm2 surface area was wiped with three strokes; wiping of the same surface was then repeated with a second pad, changing the wipe orientation 90°. A new disposable plastic glove was worn for each wipe sample to avoid cross-contamination of samples. Wipe samples were collected in triplicate in the broadcast rooms, and one additional sample was collected in the aerosol rooms at the following times (h) postapplication: 1, 5, 9, 21, 33. Wipe samples were then collected in duplicate at 12-h intervals on days 3-7 (4 samples per day). All pads were placed in glass sample jars in an ice chest for transport to the laboratory and were stored at -20 °C until analysis. Analysis. Granular contents of the ORBO-44 tubes were transferred into serum vials filled with 10 mL of GC-grade toluene. A subset of the samples was analyzed for breakthrough into the secondary section of the tubes. Capped vials were shaken at high speed (100 cpm) for 5 min on a mechanical shaking table and allowed to sit for 30 min, and the extracts were transferred to GC autosampler vials for analysis. Gauze pads were extracted in 30 mL of toluene on the same shaking table for 30 min. Samples were analyzed on a Varian 3700 gas chromatography equipped with an electron capture detector. Heptachlor epoxide was added to all samples as an internal standard. Replicate injections were conducted for each sample. The limit of detection for 1-µL injections was 3 pg/ µL. The detection limit for air samples was 30 ng/sample or 500 ng/m3. The detection for wipe samples was 90 ng/sample or 90 ng/100 cm2. Spike/recovery studies were conducted for each sampling medium. Mean recoveries (( standard deviation) were as follows: ORBO-44 tube, 98.03% ( 2.8; gauze pads, 100.9% ( 2.5. Data have not been adjusted since recoveries were essentially 100%. Solvent blanks run with each set of samples had no detectable chlorpyrifos. Air, deposition, and wipe samples collected in triplicate in each room prior to application had no detectable chlorpyrifos. Field spikes demonstrated no losses during transport and storage.
Results Deposition Sampling. Mean chlorpyrifos deposition on the carpet in the two broadcast rooms was 21 µg/cm2 (C V ) 59%), with no significant difference in levels between rooms (Table 1). According to label instructions for broadcast application, spraying 1 gal (3.8 L) of a 0.5% aqueous spray per 1600 ft2 (148.6 m2) (maximum label rate) should result in a carpet deposition of 12.9 µg/cm2. Thus, the deposition levels in this study exceeded theoretical deposition by 63%. Deposition on horizontal furniture surfaces (nontarget) averaged 0.004 µg/cm2 (Table 1) or 0.017% of the average carpet deposition. Ventilation for 30 min post-application did not affect target or nontarget surfaces deposition values. Aerosol applications resulted in a mean chlorpyrifos deposition on the carpet in the two rooms of 2.8 µg/cm2,
TABLE 1. Chlorpyrifos Deposition Levels on Target (Carpets) and Nontarget Surfaces application type
ventilation status
broadcast
on off overalle on off overalle on off overalle on off overalle on off on off
broadcast aerosol aerosol aerosol aerosol
surface carpets (target) furniture (nontarget) carpets (nontarget) furniture (nontarget) walls (nontarget) ceiling (nontarget)
N
mean concn (µg/cm2)
CV (%)
9 9 18 3 3 6 10 10 20 3 3 6 16 16 4 4
19.7a 22.3a 21.0 0.004b 0.003b 0.004 2.9c 2.7c 2.8 1.79d 1.83d 1.81 0.09 0.06 0.02 0.02
75 46 59 16 15 18 29 35 31 35 28 28 70 33 32 63
a Not significantly different (ANOVA, p > 0.05). b Not significantly different (ANOVA, p > 0.05). c Not significantly different (ANOVA, p > 0.05). d Not significantly different (ANOVA, p > 0.05). e Averaging data of both vent-on and vent-off rooms.
with no significant difference in levels between rooms (Table 1). Deposition samples collected from walls and ceilings (Table 1) had substantially lower chlorpyrifos levels than those on the floor or furniture surfaces: wall and ceiling samples averaged 2.6% and 0.68% of floor deposits, respectively. Extrapolation of deposition values to total surface areas resulted in a total measured deposition of 480 mg per room. The weight of formulated material released from the two cannisters was identical (173 g each). If the formulation was 0.5% active ingredient by weight, as stated on the label, 867 mg of chlorpyrifos should have been released per room. Thus, the estimated total mass deposited was only 55% of the theoretical deposition. Deposition on horizontal furniture surfaces averaged 1.8 µg/cm2 (Table 1) or 65% of the average carpet deposition. As in the broadcast application, postapplication ventilation did not affect target or nontarget surface deposition values. Average chlorpyrifos levels deposited on the carpet by the aerosol application were 7.5 times lower than the average broadcast deposition. Aerosol deposition values were also less variable than those found in the broadcast rooms. However, aerosol deposition was 500 times greater on nontarget furniture surfaces than was broadcast deposition immediately following application and 140 times greater at 5 h post-application. Air Concentrations. All rooms were ventilated with a fan and open windows and doors for 30 min following applications. The term “vent-on” employed here refers to additional forced air ventilation provided on day 1 (fan + open windows and door) and ambient air movement on subsequent study days (open windows and doors only), while the term “ventoff” represents no additional ventilation. Air concentrations varied inversely with sampling height in all rooms in the first 12 h post-application, and these differences continued for an additional 24 h in some rooms (Table 2). This pattern was most pronounced in the broadcast vent-off room, as illustrated in Figure 1. Peak concentrations occurred most often in the period 4-8 h post-application. Concentrations at all sampling heights were substantially higher on the day of application (0-12 h) than on the following day (12-36 h) for all rooms. In broadcast rooms, time-weighted averages (TWA) for day 1 ranged from 23 to 64 µg/m3 for the three heights, while TWAs for day 2 were approximately one-half those of day 1 (14-28 µg/m3). Additional ventilation did not affect air concentrations substantially in these rooms. Differences in VOL. 32, NO. 10, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Air Concentrations (µg/m3) Measured at Three Different Heights (25, 100, and 175 cm) for 7 Days following Chlorpyrifos Broadcast and Aerosol Application air concentrationa vent-on 100 25
days postapplication
sampling duration (h)
1 1 1 1 2 2 3 4 5 6 7
4 4 4 12-h TWAb 12 12 24-h TWAb 24 24 24 24 24
1 1 1 1 2 2 2 3 4 5 6 7
Aerosol 4 18.2 25.1 4 9.6 13.4 4 18.2 20.5 12-h TWAb 15.3 19.6 12 3.5 8.9 12 0.6 7.5 b 2.1 8.2 24-h TWA 24 0.4 6.1 24 2.3 1.6 24 0.3 0.2 24 2.6 2.6 24 0.3 0.5
175
175
vent-off 100 25
Broadcast 28.3 13.7 20.3 29.9 46.9 60.4 21.7 56.4 117.9 28.8 43.7 67.0 18.8 51.4 54.7 36.8 36.4 51.8 22.9 40.5 64.3 31.8 42.3 59.7 15.7 15.4 28.4 13.4 19.2 23.3 12.7 15.5 27.8 15.7 16.8 27.8 14.2 15.4 28.1 14.6 18.0 25.6 1.8 3.2 2.4 5.3 4.6 4.9 6.6 7.9 9.5 7.6 8.2 8.6 3.7 4.0 3.2 0.4 1.1 1.1 0.2 2.4 2.5 1.1 1.0 0.3 0.6 1.1 1.8 1.5 2.3 1.3 30.5 23.1 19.4 24.3 13.8 9.1 11.5 6.8 5.9 3.5 1.4 0.4
16.3 82.2 30.2 42.9 14.1 10.5 12.3 6.1 7.5 0.6 0.2 2.5
33.8 70.3 32.9 45.7 7.0 13.5 10.2 8.4 6.3 0.6 0.4 2.3
47.7 71.4 25.6 48.2 9.3 11.1 10.2 11.4 6.2 0.3 0.5 2.6
FIGURE 2. Chlorpyrifos residues (µg/cm2) removed from carpets by wipe sampling on day of application and day following application.
TABLE 3. Wipe Sample Recoveries of Chlorpyrifos from Treated Surface (Floor) for 7 Days Following Broadcast and Aerosol Application application ventilation days (h) type status post-application broadcast
on
broadcast
off
aerosol
on
aerosol
off
a Unit of air concentration data, µg/m3. b TWA, time-weighted average ) sum of the products of concentration and time for each sampling period, divided by total sampling time.
FIGURE 1. Air concentrations (µg/m3) of chlorpyrifos at three sampling heights for 7 days following indoor broadcast application and a 30-min ventilation period. concentration due to sampling height were no longer evident on day 3 or on subsequent study days (see Figure 1). In the aerosol vent-off room, TWAs for day 1 at the three sampling heights were virtually identical (43-48 µg/m3) and much greater than on day 2 (10-12 µg/m3). A similar relationship between day 1 and day 2 concentrations was evident in the aerosol vent-on room, but the values in this room were consistently lower than those in the nonventilated room. Differences across aerosol rooms did not disappear until day 5. The TWAs (all heights averaged) for days 3-7 ranged from 0.9 to 8.1 µg/m3 in broadcast rooms and from 0.4 to 8.6 µg/ m3 in aerosol rooms. The overall 7-day TWA in broadcast rooms was two times that of aerosol rooms for all three 1388
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a
1 (1 h) 1 (5 h) 1 (9 h) 2 (21 and 33 h) 3 4 5 6 7 1 (1 h) 1 (5 h) 1 (9 h) 2 (21 and 33 h) 3 4 5 6 7 1 (1 h) 1 (5 h) 1 (9 h) 2 (21 and 33 h) 3 4 5 6 7 1 (1 h) 1 (5 h) (9 h) 2 (21 and 33 h) 3 4 5 6 7
N 3 3 3 6 4 3a 4 4 4 3 3 3 6 4 4 4 4 4 4 4 4 8 4 4 4 4 4 4 4 4 8 4 4 4 4 4
mean concn (ng/cm2) CV (%) 143 199 22 24 8 5 4 1 6 186 105 23 19 20 3 4 3 6 131 30 22 15 2 3 3 2 1 98 28 25 10 2 1 3 2 2
87 25 96 63 64 12 118 58 37 85 77 103 56 104 124 56 21 95 101 99 68 105 27 99 132 78 67 109 88 79 69 90 25 118 111 117
One sample missing.
sampling heights (7.1 vs 3.3, 10.6 vs 5.5, and 16.0 vs 7.7 µg/m3 for 175, 100, and 25 cm, respectively). Surface Residues. Following broadcast applications, wipe sampling of carpets conducted within 1 h post-application removed an average of 165 ng/cm2 in the two rooms or only 0.78% of the initial deposit (Figure 2 and Table 3). Wipe values at 5 h postapplication were of similar magnitude. However, samples collected 9 h postapplication were substantially lower in both rooms (22-23 ng/cm2) and remained so for day 2. Ventilation did not appear to affect wipe sample values. In the vent-on room, wipe values decreased to
