Time Integrated Indoor Air Sampling using a Membrane Based Passive Sampler

Transcription

1 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

2 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

3 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

4 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

5 Passive Sampling Traditional: Site screening Semi-quantitative VI Line of evidence New application: Risk evaluation using concentration values

6 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

7 Determining Sampling Rate, S S = 1 C dm dt

8 Toluene Sampling Rate ppb Toluene y = x R 2 = SR = 2.56 Lt/hr Mass (ug) Exposure Time (min)

9 Determining Sampling Rate, S Uptake rates are independent of: -Temperature -Relative humidity -Air flow rate

10 24 Hour Air Sampling Trial y = 1.003*x 0.43 R 2 = N = 27 Site A Site B Linear

11 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

12 Sampling 24 to 180 hours Bedrooms Closets TO-17Comparative Sampling (24 36 Hrs) Basement s

13 Results Mass Uptake m,p-xylene, 1,2,4-TMB, Naphthalene HOUSE 1 HOUSE MASS, UG m,p-xylene, 1.25ug/m^3 R 2 = ,2,4-TMB, 1.74ug/m^3 R 2 =0.996 Naphthalene, 0.32ug/m^3 R 2 =0.999 MASS, UG m,p-xylene, 31.1ug/m^3 R 2 = ,2,4-TMB, 6.36ug/m^3 R 2 =0.996 Naphthalene, 0.75ug/m^3 R 2 = TIME, HR TIME, HR HOUSE 3 HOUSE MASS, UG m,p-xylene, 0.78ug/m^3 R 2 = ,2,4-TMB, 0.50ug/m^3 R 2 =0.971 Naphthalene, 0.63ug/m^3 R 2 =0.971 MASS, UG m,p-xylene, 10.8ug/m^3 R 2 = ,2,4-TMB, 0.70ug/m^3 R 2 =0.884 (3 pts) Naphthalene, 0.58ug/m^3 R 2 = TIME, HR TIME, HR 168

14 Results Mass Uptake Benzene, Toluene & PCE HOUSE 1 HOUSE Toluene R 2 < 0.1 Conc ug/m^3 MASS, UG Toluene R 2 = Conc. 3.31ug/m^3 Benzene R Conc. 0.74ug/m^3 MASS, UG Benzene R 2 < 0.1 Conc ug/m^3 PCE Conc. R Conc ug/m^ TIME, HR TIME, HR HOUSE 3 HOUSE Toluene (3pts) R 2 = Conc. 3.35ug/m^ Toluene R 2 <0.1 Conc ug/m^ MASS, UG PCE R 2 < 0.1 Conc. 0.33ug/m^3 MASS, UG Benzene R 2 <0.1 Conc ug/m^ Benzene R 2 < 0.1 Conc. 0.73ug/m^ TIME, HR TIME, HR

15 Compound, Correlation, Concentration 4 Homes Compound R^2 Conc.,ug/m^3 < Low MW High MW Benzene Toluene m,p-xylene 1,2,4-TMB Naph < < < <

16 Concentration Comparisons by Compound Groups Benzene to Xylene 24 to 180 Hours ,2,4-TMB to 2-Methyl Naphthalene 24 to 180 Hours Passive, ug/m^ Passive, ug/m^ Active, ug/m^3 Active, ug/m^ Benzene to Xylene 24 Hours ,2,4-TMB to 2-Methyl Naphthalene 24 Hours Passive, ug/m^ Passive, ug/m^ Active, ug/m^3 24 Hour LOQ ~ 0.15ug/m^3 (0.03ppbV) Active, ug/m^3

17 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

18 Questions to Answer Did air concentrations for lighter MW compounds decrease over sampling period? or Does sampler have higher capacity for heavier compounds?

19 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.

20 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

21 Results Mass Comparisons,ug 0.14 Toluene, Ethylbenzene, Xylenes, PCE (Low MW) Toluene Day Samplers Ethylbenzene mpxylene PCE 4 Day Sampler 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 Day Samplers 1,2,4-TMB Naphthalene 1,4-DCB 0.02 Day 1 Day 2 Day 4 Day 3

22 Results - Concentration Comparisons Day 1 Day 2 Day 3 Day Conc., ug/m^ Day Sampler Low MW High MW Minimal variability over 4 days Significant low bias on lower MW compounds Less bias on higher MW compounds

23 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

24 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

25 Acknowledgements Ian McMullen and Harry Anderson, W.L. Gore &