Time Integrated Indoor Air Sampling using a Membrane Based Passive Sampler James E. Whetzel Hilary G. Trethewey Jay W. Hodny, Ph.D., Inc. NEMC August 2011
Goal: Evaluate Human Risk Evaluate presence of VOC/SVOCs throughout the home Challenges include: 1. Heterogeneous system 2. Intermittent contaminant signal 3. Active home The longer the sampling the time the more representative of potential exposure Unobtrusive long term sampler
Time Integrated Sampler Problem short term sampler Snap shot rather than realistic exposure picture Active sampling complex and intrusive Courtesy of Severn Trent Laboratories S olution Membrane based passive sampler Long term s ampling realis tic expos ure S imple to use and unobtrusive
Tool: GORE Module Passive Sampler GORE Membrane (eptfe ) Waterproof, vapor permeable C hemically-inert P rotects s ample integrity E ngineered sorbents (ins ide the membrane) Hydrophobic Collect VOCs, SVOCs GORE-TEX Membrane Vapors pass through Water & soil particles remain outside Adsorbents
Passive Sampling Traditional: Site screening Semi-quantitative VI Line of evidence New application: Risk evaluation using concentration values
Calculating Concentrations dm dt = D 1 C X = S A L S=sampling rate vol/t 0 ( C ) dm dt X C 0 C 0 =0 at t=0 Diffusion m = mass t = time D = diffusion coefficient (A/L) = geometric parameter describing shape of sampler Cx = concentration of analyte in the module at time, t = x Co = concentration at time, t = 0
Determining Sampling Rate, S S = 1 C dm dt
Toluene Sampling Rate 0.100 5 ppb Toluene y = 0.00067x + 0.00646 R 2 = 0.98687 0.090 SR = 2.56 Lt/hr 0.080 0.070 Mass (ug) 0.060 0.050 0.040 0.030 0.020 0.010 0.000 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 Exposure Time (min)
Determining Sampling Rate, S Uptake rates are independent of: -Temperature -Relative humidity -Air flow rate
24 Hour Air Sampling Trial y = 1.003*x 0.43 R 2 = 0.955 N = 27 Site A Site B Linear
Testing in Homes Four samplers hung in several areas Basements Bedrooms Family rooms One module removed after 1, 3, 5, and 7+ days TO17 comparative sampling four homes 24 to 36 Hours
Sampling 24 to 180 hours Bedrooms Closets TO-17Comparative Sampling (24 36 Hrs) Basement s
Results Mass Uptake m,p-xylene, 1,2,4-TMB, Naphthalene HOUSE 1 HOUSE 2 0.600 3.000 MASS, UG 0.500 0.400 0.300 0.200 m,p-xylene, 1.25ug/m^3 R 2 =0.992 1,2,4-TMB, 1.74ug/m^3 R 2 =0.996 Naphthalene, 0.32ug/m^3 R 2 =0.999 MASS, UG 2.500 2.000 1.500 1.000 m,p-xylene, 31.1ug/m^3 R 2 =0.915 1,2,4-TMB, 6.36ug/m^3 R 2 =0.996 Naphthalene, 0.75ug/m^3 R 2 =0.951 0.100 0.500 0.000 24 78 123 TIME, HR 0.000 35 70 131 180 TIME, HR HOUSE 3 HOUSE 4 0.350 0.9 MASS, UG 0.300 0.250 0.200 0.150 0.100 m,p-xylene, 0.78ug/m^3 R 2 =0.754 1,2,4-TMB, 0.50ug/m^3 R 2 =0.971 Naphthalene, 0.63ug/m^3 R 2 =0.971 MASS, UG 0.8 0.7 0.6 0.5 0.4 0.3 0.2 m,p-xylene, 10.8ug/m^3 R 2 =0.807 1,2,4-TMB, 0.70ug/m^3 R 2 =0.884 (3 pts) Naphthalene, 0.58ug/m^3 R 2 =0.997 0.050 0.1 0.000 24 98 120 169 TIME, HR 0 24 72.00 121 TIME, HR 168
Results Mass Uptake Benzene, Toluene & PCE HOUSE 1 HOUSE 2 0.250 1.200 0.200 1.000 Toluene R 2 < 0.1 Conc. 50.2 ug/m^3 MASS, UG 0.150 0.100 0.050 Toluene R 2 = 0.782 Conc. 3.31ug/m^3 Benzene R 2 0.75 Conc. 0.74ug/m^3 MASS, UG 0.800 0.600 0.400 0.200 Benzene R 2 < 0.1 Conc. 2.22 ug/m^3 PCE Conc. R 2 0.1 Conc. 0.34 ug/m^3 0.000 24 78 123 0.000 35 70 131 180 TIME, HR TIME, HR HOUSE 3 HOUSE 4 0.350 0.450 0.300 0.250 Toluene (3pts) R 2 = 0.804 Conc. 3.35ug/m^3 0.400 0.350 Toluene R 2 <0.1 Conc. 14.17 ug/m^3 0.300 MASS, UG 0.200 0.150 PCE R 2 < 0.1 Conc. 0.33ug/m^3 MASS, UG 0.250 0.200 0.100 0.150 Benzene R 2 <0.1 Conc. 0.90 ug/m^3 0.050 Benzene R 2 < 0.1 Conc. 0.73ug/m^3 0.100 0.050 0.000 24 98 120 169 TIME, HR 0.000 24 72 121 169 TIME, HR
Compound, Correlation, Concentration 4 Homes Compound R^2 Conc.,ug/m^3 <0.1 0.73 Low MW High MW Benzene Toluene m,p-xylene 1,2,4-TMB Naph 0.75 0.74 <0.1 0.9 <0.1 2.22 0.782 3.31 0.804 3.35 <0.1 14.17 <0.1 50.2 0.754 0.78 0.992 1.25 0.807 10.8 0.915 31.1 0.971 0.5 0.884 0.7 0.996 1.74 0.996 6.36 0.999 0.32 0.997 0.58 0.971 0.63 0.951 0.75
Concentration Comparisons by Compound Groups 100.00 Benzene to Xylene 24 to 180 Hours 10.00 1,2,4-TMB to 2-Methyl Naphthalene 24 to 180 Hours 10.00 Passive, ug/m^3 1.00 Passive, ug/m^3 1.00 0.10 0.01 0.01 0.10 1.00 10.00 100.00 0.10 0.10 1.00 10.00 Active, ug/m^3 Active, ug/m^3 100.00 Benzene to Xylene 24 Hours 10.00 1,2,4-TMB to 2-Methyl Naphthalene 24 Hours 10.00 Passive, ug/m^3 1.00 Passive, ug/m^3 1.00 0.10 0.01 0.01 0.10 1.00 10.00 100.00 Active, ug/m^3 24 Hour LOQ ~ 0.15ug/m^3 (0.03ppbV) 0.10 0.10 1.00 10.00 Active, ug/m^3
Observation s 24 Hour Home Sampling Good correlation for broad range of compounds One to Seven Day Sampling Correlation improved with shorter sampling period Best when active and passive sampling times similar Overall correlation better with higher MW compounds
Questions to Answer Did air concentrations for lighter MW compounds decrease over sampling period? or Does sampler have higher capacity for heavier compounds?
Test Plan Passive samplers set out for 4 Days 24 hour samples taken for each of 4 day period Compare mass of 4 day samples with sum of 1 day samples Calculate concentrations for each sampling event If mass of 4 day sample = sum of 1 day samples uptake is constant and unaffected by higher MW compounds If mass of 4 day sample doesn t equal sum rate changed over time If each 1 day sample conc. similar constant air conc.
Target Compounds Detected Low MW Toluene Ethylbenzene Xylenes Octane (C8) Tetrachloroethen e High MW Undecane (C11) 1,2,4-Trimethyl benzene Naphthalene 1,4-Dichlorobenzene Compounds found in each sampling event above reporting limit of 0.05ug
Results Mass Comparisons,ug 0.14 Toluene, Ethylbenzene, Xylenes, PCE (Low MW) Toluene 0.10 1 Day Samplers Ethylbenzene mpxylene PCE 4 Day Sampler 0.06 0.02 Day 1 Day 2 Day 3 Day 4 Undecane, 1,2,4-TMB, Naphthalene, 1,4-DCB (High MW) 0.14 Undecane 4 Day Sampler 0.10 0.06 1 Day Samplers 1,2,4-TMB Naphthalene 1,4-DCB 0.02 Day 1 Day 2 Day 4 Day 3
Results - Concentration Comparisons 4.0 3.5 Day 1 Day 2 Day 3 Day 4 3.0 Conc., ug/m^3 2.5 2.0 1.5 4Day Sampler Low MW High MW 1.0 0.5 0.0 Minimal variability over 4 days Significant low bias on lower MW compounds Less bias on higher MW compounds
Changing Air Concentrations? Answers Did air concentrations change over time or did uptake change rate change? Concentrations remained fairly constant Does sampler have higher capacity for heavier compounds? Uptake changed for lower MW compounds indicating approaching equilibrium
Conclusions Good method for unobtrusive indoor air sampling Provide concentration results for risk analysis Sampling best for up to 24 hours for low concentration of low MW compounds Future Investigations Use adsorbents with greater capacity for low MW compounds
Acknowledgements Ian McMullen and Harry Anderson, W.L. Gore &