Environ. Sci. Technol. 2008, 42, 934–939
Comparing Surface Residue Transfer Efficiencies to Hands using Polar and Nonpolar Fluorescent Tracers E L A I N E A . C O H E N H U B A L , * ,† MARCIA G. NISHIOKA,‡ WILLIAM A. IVANCIC,‡ MICHELE MORARA,‡ AND PETER P. EGEGHY§ National Center for Computational Toxicology, U.S. EPA, Research Triangle Park, North Carolina 27711, Battelle Memorial Institute, Columbus, Ohio 43201, and National Exposure Research Laboratory, U.S. EPA, Research Triangle Park, North Carolina 27711
Received July 6, 2007. Revised manuscript received October 31, 2007. Accepted November 5, 2007.
Transfer of chemicals from contaminated surfaces such as foliage, floors, and furniture is a potentially significant source of both occupational exposure and children’s residential exposure. Increased understanding of relevant factors influencing transfers from contaminated surfaces to skin and resulting dermalloading will reduce uncertainty in exposure assessment. In a previously reported study, a fluorescence imaging system was developed, tested, and used to measure transfer of riboflavin residues from surfaces to hands. Parameters evaluated included surface type, surface loading, contact motion, pressure, duration, and skin condition. Results of the initial study indicated that contact duration and pressure were not significant for the range of values tested, but that there are potentially significant differences in transfer efficiencies of different compounds. In the study reported here, experimental methods were refined and additional transfer data were collected. A second fluorescent tracer, Uvitex OB, with very different physicochemical properties than riboflavin, was also evaluated to better characterize the range of transfers that may be expected for a variety of compounds. Fluorescent tracers were applied individually to surfaces and transfers to skin were measured after repeated hand contacts with the surface. Additional trials were conducted to compare transfer of tracers and coapplied pesticide residues. Results of this study indicate that dermal loadings of both tracers increase through the seventh brief contact. Dermal loading of Uvitex tends to increase at a higher rate than dermal loadings of riboflavin. Measurement of co-applied tracer and pesticide suggest results for these two tracers may provide reasonable bounding estimates of pesticide transfer.
Introduction Although monitoring for surface contamination in work with radioactive materials and dermal monitoring of pesticide exposure to agricultural workers have been standard practice * Corresponding author phone: (919) 541-4077; e-mail:
[email protected]. † National Center for Computational Toxicology, U.S. EPA. ‡ Battelle Memorial Institute. § National Exposure Research Laboratory, U.S. EPA. 934
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for 50 years, regular surface sampling and dermal monitoring methods have been applied to industrial and residential contamination only since the 1980s. In recent years, there have been significant advances in tools available to measure and assess dermal exposures resulting from contacts with contaminated surfaces (1). However, due to the complexity of this system, there are still important gaps in our understanding of determinants of dermal transfer and how best to measure and assess resulting exposure. To identify major uncertainties associated with quantifying dermal exposures resulting from contact with contaminated surfaces it is useful to consider pathways and mechanisms for these exposures. Transfer of contaminants from a contaminated surface to skin is a function of (1) contaminant form (residue, particle, formulation, age, physicochemical properties); (2) surface characteristics (hard, plush, porous, surface loading, previous transfer); (3) nature of interaction between contaminant and surface; (4) skin characteristics (moisture, age, loading); (5) contact mechanics (pressure, duration, smudge, repetition); and (6) environmental conditions (temperature, relative humidity). Currently, it is not clear which of these many factors will drive transfer and under what conditions. Increased understanding of the most significant factors for influencing transfers from contaminated surfaces to skin and resulting dermal loading is required to reduce uncertainty in exposure assessment (2). Transfer of pesticide residues has been studied previously by hand press to pesticide spiked surfaces (3–6). Currently, there are no direct methods for measuring pesticide residues on hands. As such, in each of these studies the hand was wiped or rinsed with 2-propanol to collect transferred pesticide for quantification. In addition to uncertainty introduced by use of a rinse or wipe, conducting studies with directed pesticide contact to children is clearly unethical. Video fluorescent imaging is one approach that has been used successfully in both occupational and residential settings to explore dermal exposure mechanisms and mitigation strategies (7–9). Application of nontoxic fluorescent tracers provides an opportunity to design studies that address limitations of pesticide transfer studies and lend insight on occupational and residential pesticide exposures to both children and adults. In a previously reported study, a fluorescence imaging system was developed, evaluated (10), and used to measure transfer of riboflavin (Vitamin B2) residues from surfaces to hands for multiple contacts (11). Results of this initial study indicated that surface loading and skin condition were important parameters affecting residue transfer of riboflavin. Contact duration and pressure were not significant for the range of values tested, and surface type was not significant after the first contact. Preliminary results also suggested potentially significant differences in transfer efficiencies of different compounds. Limitations of this study included surface loadings that were relatively high compared with contaminant loadings expected in residential environments using current crack and crevice application methods. In addition, only one fluorescent surrogate was evaluated limiting our ability to evaluate the effect of compound properties on transfer efficiency and to extrapolate results to a range of current use pesticides. In the study presented here, experimental methods developed previously were refined and dermal transfer data were collected using both Uvitex OB (lipophilic) and riboflavin (hydrophilic). Residue transfers to three types of dislodgeable residue sampling tools were also collected using these two fluorescent tracers and five different organophosphate (OP) 10.1021/es071668h CCC: $40.75
2008 American Chemical Society
Published on Web 12/19/2007
TABLE 1. Hand Contact Trialsa Trial Number parameter surface type surface loading contact type skin condition tracer
1 a b c d e
2 A B c d e
3 A b C D E
4 a B C D E
5 A b C d e
6 a B C d e
7 a b c D E
8 A B c D E
9 A b c d E
10 a B c d E
11 a b C D e
12 A B C D e
13 A b c D e
14 a B c D e
15 a b C d E
16 A B C d E
a Key: Surface, skin, and contact parameters. A ) carpet; a ) laminate. B ) low surface loading (0.2 g/cm2); b ) high surface loading (2 g/cm2). C ) uniform press; c ) smudge. D ) dry hand; d ) moist hand. E ) Riboflavin; e ) Uvitex.
and pyrethroid pesticides. There were two main objectives of this study: evaluate impact of parameters related to compound, surface, and skin on transfer efficiency; and relate transfer of tracers to transfer of representative pesticides with similar physicochemical properties.
Methods and Materials Study Design. This study was performed using both riboflavin and Uvitex OB as surrogates for pesticide residues, and videoimaging technology to quantify dermal loadings of fluorescent tracers following contact with tracer-treated surfaces. The approach was as follows: (1) Apply fluorescent tracer to test surfaces. (2) Conduct controlled hand-transfer experiments varying selected parameters. (3) Measure mass of tracer transferred and estimate surface and dermal contact areas. (4) Assess relative transfers of tracers and pesticides using transferable residue sampling techniques. A number of fluorescent tracers were considered, especially those used in previous studies. Safety was the overriding concern in choosing tracers. Two tracers were selected having physicochemical properties that bound properties of several pesticides of interest: Uvitex OB (Ciba Specialty Chemicals) and riboflavin. Pesticides selected are of current interest due to widespread use in the United States for residential and agricultural applications. Chlorpyrifos and diazinon were OPs used most extensively in the indoor residential market and are still being measured in U.S. homes. Pyrethroids are now the dominant residential-use insecticides. Cis- and transpermethrin as well as esfenvalerate are commonly found in homes at measurable levels. Parameters evaluated in this study included tracer, surface type, surface loading, contact motion, and skin condition. Eight experiments or trials involving contact with riboflavintreated surfaces, and 8 experiments involving Uvitex-treated surfaces (Table 1) were conducted; each experiment was repeated in triplicate. Because riboflavin can be washed from hands, 3 subjects were recruited for riboflavin experiments; each person completed all 8 experiments. In contrast, because Uvitex cannot be washed from hands, 24 subjects were recruited to gather triplicate data for each of the 8 Uvitex experiments. As described previously (2), the Youden ruggedness test (12) was used to select parameter combinations for each trial. By using this design, more than one parameter could be varied at a time minimizing the number of trials required to test for main effects of all parameters. The experimental plan used here is a 1/2 fractional replication of a 3 × 25 factorial (Table 1). Tested parameter values for this study and the previous study are summarized in Table 2. Available data for octanol/water partition coefficient, vapor pressure, and water solubility for tested pesticides and tracers are listed in Table 3. Study design, protocols, and consent forms were approved by the Battelle Memorial Institute IRB for use of human subjects, and subsequently reviewed by the EPA administrator for human subjects experiments. Application of Tracers to Test Surfaces. General protocols for spray applications to surfaces have been discussed
TABLE 2. Study Parameter Values parameter
initial experiments
refined experimentsa
tracer skin condition surface type surface loading contact motion contact duration contact pressure contact number
riboflavina dry, moist, or sticky carpet or laminate 2 or 10 µg/cm2 press or smudge 2 or 20 s 0.1 or 1 psi multiple
riboflavinb or Uvitexc dry or moist carpet or laminate 0.2 or 2 µg/cm2 press or smudge 2 sd 0.1 psid multiple
a Refined experiments added Uvitex, reduced loading levels, and reduced number of parameters tested. b Relatively water soluble. c Relatively water insoluble. d Parameter was not varied in study.
previously (2). Detail of differences specific to this study are presented in the Supporting Information (Section S1). In general, an improved spray system was used to deliver smaller, finer droplets to test surfaces than in the previous study. Measured variability in loading across a platform was 25% with riboflavin solution and 14% with Uvitex OB solution. Each application surface (platform), 60 cm × 180 cm, was platted into 3 rows of 11 blocks. One block per row was allocated to a deposition coupon, 10 blocks were used for dermal contact. Each block was used only once. Contact Trials and Transfer Off Protocols. For each experiment, the subject was instructed on contact motion and skin condition for surface contact. Contact duration was held at 2 s and contact pressure was held at approximately 0.1 psi for all experiments. For dry condition, hands were washed, dried, and then held up in room air for 30 s. For moist condition, hands were washed, dried and then held 8–10 cm away from outlet of CoolMist vaporizer for 20 s. To familiarize subjects with the feel of 0.1 psi contact, subjects practiced 10 presses on a scale prior to initiating an experiment. The subject contacted surface in an unused area (block), had the hand imaged, and then repeated contact motion in a new area. A series of seven sequential contacts with surface using the same motion constituted one experiment. Measurement of Dermal Loading. The fluorescent imaging system described in Ivancic et al. (1) was used to monitor and measure fluorescence on hands following contact with tracer-treated surface. Details of the fluorescent lamp configurations and wavelength settings for each of the tracers are presented in the Supporting Information (Section S2). For tests with riboflavin, a full calibration curve of riboflavin (different points) was obtained with each subject. Different amounts of a 100 µg/mL aqueous riboflavin solution were deposited on the hand to simulate different riboflavin loadings. In contrast, for Uvitex, each subject completed one experiment with his right hand, and a series of 3–6 different calibration curve points was imaged on his left hand. Uvitex OB calibration curve solution was prepared as an aqueous solution of Uvitex in 0.1% Pluronic (emulsifier to suspend VOL. 42, NO. 3, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 3. Properties of Tested Pesticides and Tracers
a
analyte
octanol/water partition
vapor pressure (mPa)
water solubility (mg/L)
diazinon chlorpyrifos tech. permethrinc cis-permethrin trans-permethrin esfenvalerate riboflavin uvitex OB
6,400a 50,000b 3,160,000d naf na 1,660,000b 0.035g not available
0.097 @ 20 °Cb 2.5 @ 25 °Cb 0.0013 @ 20 °Ce 0.0025 @ 20 °C 0.0015 @ 20 °C 0.067 @ 25 °Cb negligible 0.000003 @ 20 °Ci
40 @ 20 °Cb 2 @ 25 °Cb 0.2 @ 20 °Cb na na 0.1
loading (µg/cm2)
p < 0.01
surface type
surface loading
contact motion
first contact (ANOVA) p < 0.05 p < 0.01 p < 0.1 p < 0.05 p ) 0.001 p < 0.001 repeated contact (Mixed-Effects Model) p > 0.1 p < 0.001 p < 0.001
Bold text indicates parameter is statistically significant at p < 0.05. evaluation. a
0.059 versus 0.017 µg/cm2/contact, respectively, at the lower surface loading. Rates of change are significantly different (p < 0.0001) in each condition. At the 0.2 µg/ cm2 surface loading (low loading), Uvitex transfers more efficiently than riboflavin. Results of statistical analysis to identify significant parameters for characterizing residue transfers are presented in Table 4. These results show that effects of surface loading on transfer from surfaces to hands under study conditions
b
skin condition
contact number
p > 0.1 p > 0.1
b
p < 0.05
p < 0.001
Contact number only relevant to repeated contact
is significant at alpha ) 0.05. Surface type is significant only with initial contact and skin condition is significant only with repeated contacts. Comparison of “first contact” to “repeated contact” results suggests that effect of surface type appears to diminish with repeated contact while effect of skin condition appears to increase with repeated contact. Although effect estimates are similar for surface type: 0.126 (initial) versus 0.127 (repeated) there is loss of significance VOL. 42, NO. 3, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 5. Evidence of Importance of Factors Tested across Surface-to-Skin Transfer Experimentsa parameter
initial experiments
tracer skin condition surface type surface loading contact motion contact duration contact pressure contact number
refined experiments bO bO bO bb bO --bb
bO OO bO bO OO OO bb
a Symbols: -- not tested; OOnot found to be significant; bO mixed results or marginally significant at p < 0.10; bb significant at p < 0.05 in all tests.
TABLE 6. Estimated Transfers of Pesticides to Hand for First Contact based on PUF Roller Transfer Efficiencies transfer for first contact, %
compound
FIGURE 2. Comparison of transfers of fluorescent tracers and pesticides to various sampling media. with repeated contact due to increased variability (i.e., standard error increases). For skin condition, the effect estimate increases greatly with repeated contacts, from 0.045+/- 0.047 to 0.178 +/- 0.082, indicating effect of skin condition does indeed appear to increase with repeated contacts. Although increased variability with repeated contact has implications for interpretation of significance, the trends identified in this analysis are of interest. Pesticide Transfer Trials. Transfer efficiencies (percent transfers) of tracers and coapplied pesticides are presented in Figure 2. In a general sense, transfers vary by a factor of 10 for the three media used: 18 ( 17% (all analytes, all surfaces) for aqueous wipe, 2.6 ( 1.6% for PUF Roller, and 0.29 ( 0.48% for C18 disks. Ratio of riboflavin to Uvitex transfer was 2.75 for C18 disks; 0.6 for PUF Roller, and 1.9 for aqueous wipe. Transfer rates for Uvitex with all media were similar to those for the three pyrethroids; transfer of riboflavin to PUF Roller and C18 disk were less consistent, but appeared to bound transfers of the two OPs. Measurements of pesticide transfer from these trials suggest that results of hand-contact trials for the two tracers may provide reasonable bounding estimates of pesticide transfer. Comparison of Hand Contact Trial Results with Pesticide Transfer Trial Results. Estimated percent transfer of pesticides to hands that might occur for an initial contact is listed in Table 6 for both riboflavin and Uvitex. Details of this analysis are presented in the Supporting Information (Section S4) This analysis suggests a potentially significant difference between organophosphate insecticides, previously used in indoor residential formulations, and currently used pyrethroid insecticides. Transfer of pyrethroid insecticides to hands and other dermal surfaces may be 3–7 times greater than transfer of organophosphate insecticides.
Discussion Results from this study and Cohen Hubal et al. (2) are summarized and compared in Table 5. Overall conclusions from the combined data indicated that tracer type, surface type, contact motion, and skin condition were all significant 938
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diazinon chlorpyrifos cis-permethrin trans-permethrin esfenvalerate
based on PUF based on PUF Roller and Roller and average based riboflavin Uvitex OB on PUF Roller 3.2 9.3 33 33 26
6.1 16 29 35 25
4.6 13 31 34 26
factors under test conditions of these studies. Transfer was greater for laminate (over carpet), smudge (over press), and moist skin (over dry). Number of contacts was a significant factor in both studies. In this study, number of contacts had an impact on significance of tracer, surface type, and skin condition. This result is relevant for application of this data in exposure assessment. Real-world exposures are seldom the result of an individual contact. Use of a fluorescent imaging system in this series of studies allowed us to investigate the potential impact of multiple contacts. In the previous study (higher surface loadings), dermal loadings appear to reach a maximum by the fourth or fifth contact (2). In the experiments described here with lower surface loadings (Figure 1), dermal loadings appear to increase through the seventh contact, suggesting that at lower surface loadings, more contacts may be required to reach an effective equilibrium between loading of residue on hand and surface (or saturation of dermal loading). Due to the many factors that may affect surface-to-skin transfer, data collected in this study should be applied carefully to assess exposure. Laboratory surface loadings (0.2 and 2.0 µg/cm2) may still be higher than what might be expected on average across residential surfaces following a crack and crevice treatment (19). However, current crack and crevice application techniques result in nonuniform distributions with a wide range in loading depending on location (20). Evaluation of results obtained in this study suggest that depending on physicochemical properties of the residue, transfer efficiency may increase as surface loading decreases. Thus, although this study does not provide estimates of transfer at the lowest loadings, our results indicate a physically plausible trend that should be considered when extrapolating to real-world conditions. In addition, properties of the surface residue impact availability of compound for transfer. The two tracers studied represent extremes of water solubility, with one highly soluble and the other essentially insoluble. However, both tracers have very low vapor pressures unlike organophospate pesticides. Finally, this study was designed to assess transfers of
pesticides shortly after application. Compounds in other forms (e.g., particle bound) may transfer differently. On the whole, data developed in these studies will reduce uncertainty in screening-level exposure assessments that are based on limited default assumptions. In particular, these results are currently being used with the SHEDS model to improve estimates of exposures resulting from hand-tomouth behavior (21, 22). However, the importance of multiple contacts for characterizing residue transfers to skin and the need to link dermal loading with absorption to characterize dose suggest that measurement and modeling approaches incorporating important temporal aspects of the system need to be adapted for use in assessing exposures resulting from dermal contact with contaminated surfaces.
Acknowledgments The authors acknowledge laboratory assistance of K. Andrews, J. Sowry, M. McCauley, A. Gregg, and C. Lukuch of Battelle. We also acknowledge Tom McCurdy of U.S. EPA for helpful review of this manuscript. The United States Environmental Protection Agency through its Office of Research and Development funded the research described here under contract 68-D-99-011 to Battelle. It has been subjected to Agency review and approved for publication.
Supporting Information Available Detailed methods and summary results for the transfer experiments (both tracer and pesticide). This information is available free of charge via the Internet at http://pubs.acs.org.
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