This document summarizes the key variables that impact the assessment of short-term indoor air inhalation exposure risks from trichloroethylene (TCE). It discusses TCE uses, properties, exposures, fate and transport in various media, and how sampling duration, season, receptors, and toxicity values influence risk characterization. Variables like temporal indoor air concentrations, ambient air impacts, pressure differentials, and exposure assumptions must be considered to develop accurate risk assessments for TCE vapor intrusion.

1. 30th
Annual International Conference on
Soils, Sediments, Water and Energy
University of Massachusetts, Amherst
Morning Platform Session No. 02 – Room 168
23rd
October 2014
Presented By:
Peter W. Woodman, Ph.D.
Risk Management Incorporated
Acton, MA 01720-5676, USA
(978) 266-2878
IMPACT OF VARIABLES ON THE ASSESSMENT OF SHORT-
TERM TCE INDOOR AIR INHALATION EXPOSURE RISKS

2. TRICHLOROETHYLENE (TCE)
 TCE (Triclene; Vitran): CAS 79-01-6
 Chemical Structure:
 Chemical Uses:
 From the Late 1920’s, TCE widely used as an Industrial Solvent for
Greases, Fats, Waxes & Tars. Now, primarily used for Vapor Degreasing
of Metal Parts by Automotive & Electronics Manufacturers (ATSDR 2013).
 TCE has also been used a chain transfer agent for PVC production, and
in the production of Pharmaceuticals, Polychlorinated Aliphatics, Flame
Retardants, Pesticides and Insecticides (ATSDR 2013).
 Over the years, TCE has been found in Household Products, including
Typewriter Correction Fluid, Paint Strippers, Varnishes, Adhesives,
Lubricants, Spot Removers, Rug-Cleaning Fluids, Food Products and
Packaging Materials, Pesticides and Insecticides, sheet vinyl flooring and
pepper sprays, the majority of which could off-gas TCE vapors and impact
Indoor Air Quality (ATSDR 2013)!

3. TRICHLOROETHYLENE (TCE)
EXPOSURES
 Occupational & General Population Exposures to TCE
 Primary Exposure Routes & Pathways:
 Occupational & General Inhalation of TCE Vapors from Ambient Air.
 Note: Rural areas generally exhibit lower atmospheric TCE levels than
urban areas. Average Ambient Air TCE concentrations for suburban and
urban areas across the US = 0.54 – 2.75 µg/m3
(ATSDR 2013). The
MassDEP Ambient Air 24-hr average TEL for TCE = 36.52 µg/m3
and the
Annual AAL = 0.61 µg/m3
(MassDEP 2012).
 Occupational Inhalation of TCE Vapors or Dermal Contact with the
solvent during manufacturing operations or dealing with spills,
primarily as the result of poor management practices, including lack
of adequate ventilation and/or use of some form of PPE.
 Note: OSHA 8-hour TWA PEL is 535 mg/m3
; STEL = 1,605 mg/m3

4. TRICHLOROETHYLENE (TCE)
EXPOSURES
 General Population & Occupational Exposures to TCE
(cont.)
 Primary Exposure Routes & Pathways (cont.):
Occupational Indoor Air Inhalation Exposures to TCE vapors during new
Building Construction using TCE-containing products and materials in
poorly ventilated work areas.
General Indoor Air Exposures - Ingestion, Dermal Contact & Inhalation
from TCE-impacted Drinking Water – Includes “Shower Scenario” and off-
gassing of TCE vapors from Drinking Water at the tap (ATSDR 2013).
General Indoor Air Exposures – Inhalation of infiltrated TCE vapors from
Ambient Air (ATSDR 2013) or vapors from TCE-impacted soils or soil gas
located within 6 ft. horizontally from the structure or within 10 ft. measured
vertically down to the basement floor or foundation, plus completion of the
VIP for TCE vapors beneath the structure (MCP 310 CMR 40.0313, 2014).

5. TRICHLOROETHYLENE (TCE)
EXPOSURES
 General Population & Occupational Exposures to TCE
(Final)
 Primary Exposure Routes & Pathways (Final):
 Indoors – Inhalation of TCE vapors from completion of the VIP as it relates to
Preferential Migration Pathways (e.g., utility services entering the structure; sump pumps)
and from TCE vapors partitioning from impacted soil or groundwater to soil gas
either adjacent to or beneath the structure, which then permeate Indoor Air,
entering through seams or cracks in the walls, basement or foundation slab of the
structure.
 Note: The Typical Residential Indoor Air Concentration (TIAC) for TCE in MA
= 0.8 µg/m3
(90th Percentile) and the MA TCE Residential Threshold Value (TVr)
= 0.4 µg/m3
(MassDEP 2008, 2013, respectively). Indoor Air TCE Concentrations
detected above these values may indicate completion of the VIP and require
further evaluation as part of the “Multiple Lines of Evidence Approach” to fully
evaluate the VIP health risks (MassDEP 2013).
 Note: For sub-slab soil gas, the TCE Residential Screening Value = 28 µg/m3
.
Soil gas concentrations detected below this value indicate that completion of
the VIP is probably incomplete under current conditions (MassDEP 2013).

6. IMPACT OF VARIABLES ON DEVELOPMENT OF
TCE INDOOR EXPOSURE POINT
CONCENTRATIONS FOR THE VAPOR INTRUSION
PATHWAY
 Fate & Transport Mechanistic Effects on TCE
concentrations detected in:
 Air, Soil, Surface Water/Sediments and Groundwater & Food

7. TCE RELEASES – FATE &
TRANSPORT
 AIR:
TCE releases to the atmosphere are short-lived.
T½ 6.8 days as the result of photocatalytic degradation by Hydroxyl
Radicals (·OH) to Phosgene, Dichloroacetyl Chloride and Formyl
Chloride. Assuming first-order kinetics, loss of the remaining 50%
may take longer (ATSDR 2013).
Degradation rate is temperature dependent and thus varies with
the season, decreasing in the fall/winter, resulting in higher and more
persistent ambient air concentrations of TCE.
Most TCE surface releases to surface waters (HLC 0.011 atm-m3
/mol)
or soils readily volatilize to the atmosphere. However, TCE has a
relatively high mobility in soil resulting in percolation to the
subsurface and potentially groundwater, before volatilization can
occur (ATSDR 2013).

8. TCE RELEASES – FATE &
TRANSPORT
 SOIL:
 On soil surfaces, TCE will volatilize to the atmosphere or leach
(Low to Moderate sorption to soil - Log Koc 2.03 to 2.66 – Gabarini & Lion 1986)
into the subsurface. Depending on the soil type, TCE is not
readily degraded in the Vadose Zone. However, microbial
dechlorination of TCE appears to occur more readily in vegetated
vs. unvegetated soils (Walton & Anderson 1990).
 Under anaerobic/methanogenic soil conditions, TCE has been
degraded 100% to Vinyl Chloride within 10 days (Vogel and
McCarty 1985). Addition of electron donors to the soil promoted
further degradation to Ethylene (Freedman & Gossett 1989).
 TCE is considered a Dense Non-Aqueous Phase Liquid (DNAPL)
and can percolate through the unsaturated zone, displacing soil
pore water in the saturated zone, ultimately impacting
groundwater.

9. TCE RELEASES – FATE &
TRANSPORT
 WATER:
 Often present from dehalogenation of Perchloroethylene (PCE) in
groundwater, untreated drinking water or surface waters, or released
directly as TCE from landfill leachates or surface spills. Depending on
prevailing “Redox” conditions in the water, a conservative biodegradation
rate, in the range of 0.2 yr-1
, may be assumed for site screening
purposes, if TCE biodegradation products are detected (e.g.,
Dichloroethylene, Vinyl Chloride, Ethylene) (ATSDR 2013).
 Under anaerobic/methanogenic conditions, both PCE and TCE have
been fully degraded to Vinyl Chloride in groundwater within 10 days
(Vogel and McCarty 1985).
 Most TCE in surface waters is expected to volatilize to the atmosphere.
However, being a DNAPL with only moderate water solubility (1.07 to 1.366
g/L), the remainder is expected to submerge and interact with Sediments
(ATSDR 2013).

10. TCE RELEASES – FATE &
TRANSPORT
 SEDIMENTS:
 Liquid TCE releases can also impact sediments in ambient freshwater
settings, including: streams, lakes, ponds, canals, plus municipal or
industrial pipe influents or effluents, plus marine and estuarine
environments, either directly or via groundwater to surface water
discharges (ATSDR 2013; Pearson & McConnell 1975).
 TCE usually impacts sediments at concentrations less than the aqueous
solubility of TCE (1.07 to 1.366 g/L – ATSDR 2013). Occurs through diffusion,
which contributes to the rapid dissolution of TCE in the fractures and
macropores of the sedimentary particles (Lenczewski et al., 2006).
 Methanotrophs isolated from sediments in liquid culture can rapidly
degrade 650 ng/mL of TCE to 200 ng/L in 4 days at 20ºC, producing CO2,
but no Dichloroethylene or Vinyl Chloride (Fogel et al., 1986).

11. TCE RELEASES – FATE &
TRANSPORT
 FOOD:
 TCE can be absorbed by food products (e.g., fruits and vegetables – 0 to
5 ppbv) from the atmosphere and concentrated overtime (e.g., Shops,
Restaurants), especially when Ambient Air Concentrations exceed
38.5 µg/m3
(Grob et. al., 1990).
 TCE also found in Processed Foods (e.g., Dairy Products at 0.3 – 10
ppbv; Meats at 12 – 16 ppbv; Fruit Jellies at 20 – 50 ppbv; Chocolate Sauces (50
ppbv); Margarines at 440 – 3,600 ppbv; Yellow Corn Meal at 2.7 ppbv and
Fudge Brownie Mix at 2.4 ppbv), often from use of TCE-impacted
plant tap water (ATSDR 2013). Potential direct or indirect indoor
off-gassing sources of TCE from storage, or following ingestion
and discharge from the body and inhalation of TCE vapors,
respectively!?

12. IMPACT OF VARIABLES ON DEVELOPMENT OF
TCE INDOOR EXPOSURE POINT
CONCENTRATIONS FOR THE VAPOR INTRUSION
PATHWAY
 VARIABLES (cont.):
 Duration of TCE sample collection periods and seasons for each
Medium, especially:
 Short (4 – 8 hours)
 Long (24 – 48 hours)
 Continuous (1 – 2 years) and
 Spring, Summer, Fall & Winter, respectively.
 Note: In an earlier temporal monitoring study (2.5 years) of TCE Vapor
Intrusion from a dilute (10 - 50 µg/L) TCE groundwater plume beneath a
residence, indoor air TCE concentrations varied by three orders of magnitude
(<0.054 to 54 µg/m3
) in the house over the monitoring period, revealing marked
seasonal & temporal influences on the TCE Indoor Air Concentrations detected
(H. Holtone et al., Environ. Sci. Technol., 2013, 47 (23), pp 13347–13354). How applicable
the findings are to other sites is curently unknown.
.

13. IMPACT OF VARIABLES ON DEVELOPMENT OF
TCE INDOOR EXPOSURE POINT
CONCENTRATIONS FOR THE VAPOR INTRUSION
PATHWAY
 VARIABLES:
 During collection of Indoor Air samples, may also need to collect
Ambient Air samples & measure P (the pressure differential between the soil
surface and the enclosed space, Pa or g/cm-s2
)which, in the absence of earthen
floors, would include the basement or foundation slab inside the
structure.
 High ambient (outdoor) atmospheric concentrations of TCE detected relative to those
detected indoors, might indicate the potential for VI through building windows, and
cracked wall seams in the structure, and may help differentiate the primary TCE
source for remedial purposes, where required.
 The default P value used in the J & E Vapor Intrusion Model = 4 Pa (40 g/cm-s2
).
Lower values may indicate the presence of other VIPs (see above) or lack thereof;
although use of Pa values, when the depth of the TCE groundwater plume bgs is
shallow and close to the slab can invalidate the J & E Model because of the impact
on the capillary zone. In contrast, high Pa values detected, usually indicate a strong
driving force for phase partitioning of TCE vapors from sub-slab soil gas or
groundwater across the structure’s slab and the probable presence of major floor
cracks or holes there.

14. IMPACT OF VARIABLES ON HUMAN HEALTH
RISK CHARACTERIZATION OF TCE EXPOSURES
 VARIABLES (cont.)
Development of Representative Exposure Point Concentrations
for:
 Acute Exposures (24 hours or less)
 Subchronic Exposures (1 – to less than 7 years)
 Chronic Exposures (7 + years) and
 Lifetime Exposures (70 years).
 Ideally, one should try and match sampling times to the type of exposure
(e.g., Short/Longer Term Sampling Periods to Acute/Subchronic Exposures,
especially here, to address Short-term Indoor Air Inhalation Exposures from 1 to
24 days to 8 weeks and the Critical Receptors involved - see below).
Identification of Critical Receptors:
 Residential Newborns, Infants, Adults and Women of Childbearing Age or
Pregnant
 Occupational Exposures for Men, Women & Nearby Residents or Passers
-by.

15. IMPACT OF VARIABLES ON HUMAN HEALTH
RISK CHARACTERIZATION OF TCE EXPOSURES
 VARIABLES (cont.)
Exposure Assumptions for each Receptor:
Appropriate Exposure Route: Ingestion, Dermal Contact and Inhalation
Frequency
Duration
Averaging Periods for Non-Cancer and Cancer Endpoints of Toxicity
Relative Absorption Factors for Ingestion and Dermal Contact Exposures
Permeability Constants for Dermal Contact.
Use of EPA IRIS/MassDEP Toxicity Factors: Especially for the
Inhalation Route for Non-Cancer Endpoints (Subchronic or Chronic Reference
Concentrations (RfC) mg/m3
), or an adjusted RfC for Short-Term Exposures.

16. IMPACT OF VARIABLES ON HUMAN HEALTH
RISK CHARACTERIZATION OF TCE
INHALATION EXPOSURES
 VARIABLES (cont.):
 Scientific Acceptance of the Studies used in EPA’s IRIS to derive
the Chronic RfC for TCE in 2011 and associated adverse human
health effects.
 Non-Cancer Inhalation Exposures to TCE Vapors – From a human health risk
perspective, critical effects focus on Birth Defects in the form of Cardiac
Developmental Toxicity during the first 8 weeks of pregnancy or for women of
child-bearing age attempting to become pregnant or are unknowingly pregnant
during this 8- week window; plus a lesser impact on the Immune System (IRIS
2011; MassDEP 2014).
 For the developmental effects, EPA focused on a short-term oral study in rats
exposed via drinking water for GDs 1-22, showing increased cardiac
malformations (Johnson et al., 2003) and for immunological effects, another oral
study for mice exposed to TCE in drinking water for 30 weeks showing
decreased thymus weight (Keil et al., 2009). Candidate “Chronic” RfCs from
these studies (1.9 and 2.1 µg/m3
, respectively), yielded the current IRIS Chronic
RfC of 2 µg/m3
).

17. IMPACT OF VARIABLES ON HUMAN HEALTH
RISK CHARACTERIZATION OF TCE
INHALATION EXPOSURES
 VARIABLES (cont.):
 Scientific Acceptance of the Studies used in EPA’s IRIS to derive
the Chronic RfC for TCE in 2011 and associated adverse human
health effects (cont.).
 TRC (Laura Trozzllo & Darby Litz, 2014) has challenged the validity of the Johnson
et al., 2003 study, since fetal heart malformation results have not been replicated
in other studies, including an Inhalation study by Carney et al., 2006 and another
oral study by Fisher et al., 2001 on which Johnson collaborated. See: (http://
www.trcsolutions.com/NewsRoom/WhitePapers/Pages/default.aspx).
 In a TCE Risk Assessment Case Study conducted by the Alliance for Risk
Assessment (/AlLLIANCEFORRISK.ORG - April 15, 2013), the Johnson et al.,
2003 study for derivation of a candidate RfC was also considered highly
controversial and associated with low confidence and high uncertainty, relative to
the Keil et al., (2009) and NTP (1988) study findings. Based on an Uncertainty
Analysis conducted by the Alliance for the fetal malformation endpoint of toxicity,
Residential TCE Screening Levels derived by the Alliance ranged from 2.1 to
61.5 µg/m3
and Industrial Screening Levels ranged from 8.7 to 258.1 µg/m3
.

18. IMPACT OF VARIABLES ON HUMAN HEALTH
RISK CHARACTERIZATION OF TCE
INHALATION EXPOSURES
 VARIABLES (cont.):
 Scientific Acceptance of the Studies used in EPA’s IRIS to derive
the Chronic RfC for TCE in 2011 and associated adverse human
health effects (Final).
 MassDEP has conducted an extensive review of the two studies and the
supporting study for nephrotoxicity resulting from a 104-week gavage study in rats
(5 days/week), which yielded a candidate Chronic RfC of 3 µg/m3
(NTP 1988), plus
information from the NAS and SAB and discussions with study authors.
 Conclusion: MassDEP found no reason to discount the studies or
background information used to derive the Chronic RfC. See (
http://www.mass.gov/eea/massdep/toxics/sources/chemical-research-and-standar
).

19. IMPACT OF VARIABLES ON HUMAN HEALTH
RISK CHARACTERIZATION OF TCE
INHALATION EXPOSURES
 VARIABLES (cont.):
 Uncertainty involved in using the current EPA/IRIS Chronic
RfC to assess short-term human inhalation exposures to TCE
for Developmental Toxicity in Risk Characterizations, in
particular “Imminent Hazard Evaluations” (310 CMR 40.0950)
for Residential and Occupational Indoor Air exposures.
 Currently, no Final National Guidance on this issue. Available
“solutions” to address this issue can vary by States or Agencies (e.g.,
EPA Regions, ATSDR) as it relates to short-term Exposure Periods
(e.g., EPA Region 9 – approximately a 3-week period in the first trimester of
pregnancy – 12 weeks vs. MassDEP approximately 1 to 24 days in the first 8 weeks
of pregnancy), and use of Adjustment Factors (e.g., 0 to 3 for the RfC and
Acceptable Hazard Index (HI) Limits of 1, 3 or 10).

20. IMPACT OF VARIABLES ON HUMAN HEALTH
RISK CHARACTERIZATION OF TCE
INHALATION EXPOSURES
 VARIABLES (Final):
 Uncertainty involved in using the current EPA/IRIS Chronic RfC to
assess short-term human inhalation exposures to TCE for
Developmental Toxicity in Risk Characterizations, in particular
“Imminent Hazard Evaluations” (310 CMR 40.0950) for
Residential and Occupational Indoor Air exposures.
 However, MassDEP has issued early guidance on this issue to use the
Chronic RfC of 2 µg/m3
adjusted by a factor of 3 to address the short-term
exposure issue (MassDEP Fact Sheet March 27, 2014). MassDEP also
presented the option of using two of the updated MassDEP Shortforms
(Vlookup v.0114) – for Residential Exposures (sf12raih) and Office Worker,
Student, or Teacher Exposures (sf12osaih).
 Note: Neither of these MassDEP short forms takes into account the RfC
Adjustment Factor of 3. Further, since Exposure Duration and Averaging
Periods are the same and cancel out in these risk algorithms, it is not clear from
the MassDEP Fact Sheet if one is looking at 1-24 days or up to 8 weeks?

21. CURRENT MASSDEP & EPA REGION IX
TCE DEVELOPMENTAL TOXICITY RISK
SCREENING CONCENTRATIONS
RECEPTORS MassDEP/ORS
Screening Values
(µg/m3
) (HQ =3)
EPA Region 9 (July 9, 2014)
Interim TCE Indoor Response
Action Values (µg/m3
)
REMEDIATION
TARGETS:
Residential 2 -
Workplace 8 -
IMMINENT
HAZARDS:
Residential 6 2 (HQ = 1)
Workplace 24 8* or 7* (HQ =1)
URGENT
CONCERN
LEVELS:
Residential 20 6 (HQ = 3)
*Workplace (10 or
8-hour Workday)
60 *21 or 24* (HQ = 3)

22. CONCLUSIONS – VARIABLES &
UNCERTAINTIES IMPACTING
ASSESSMENT OF SHORT-TERM TCE
INDOOR AIR INHALATION EXPOSURES
 Common TCE Spill & Release Sources:
 Manufacturing Degreasing, Production of Chemicals &
Pharmaceuticals, Use of certain Household Products, New
Construction, Tank Car Accidents
 TCE Primary Exposure Routes & Pathways (Occupational
& General):
 Inhalation of Ambient Air
 Indoor Air - Ingestion, Dermal Contact & Inhalation from TCE-
Contaminated Drinking Water. Also, off-gassing of TCE vapors from
impacted Drinking Water at the tap
 Indoor Air – Inhalation of infiltrated TCE vapors from Ambient Air,
impacted soil & soil gas adjacent to structure through wall seams
and cracks, and completion of the VIP for impacted groundwater,
soil, and soil gas beneath the structure via an earthen floor or via
cracks and holes in the basement or foundation slab

23. CONCLUSIONS – VARIABLES &
UNCERTAINTIES IMPACTING
ASSESSMENT OF SHORT-TERM TCE
INDOOR AIR INHALATION EXPOSURES
 Fate & Transport Considerations:
 Air, Soil, Groundwater, Surface Water & Sediments, Food
 Useful for determining nature, extent and persistence of TCE
 Duration of TCE Sample Collection Period &
Season:
 Short, Long, Continuous, Spring, Summer, Fall & Winter – affects
TCE concentrations detected
 Collection of Ambient Air Samples & Slab
Pressure Differentials:
 Helps identify primary VIP – Outside or Sub-Slab Vapor Infiltration

24. CONCLUSIONS – VARIABLES &
UNCERTAINTIES IMPACTING
ASSESSMENT OF SHORT-TERM TCE
INDOOR AIR INHALATION EXPOSURES
 MCP Risk Characterization:
 Identify – Critical Receptors, Exposure Assumptions, especially for Short or
Long Durations
 Develop Representative Exposure Point Concentrations for Indoor Air
 Use MassDEP adjusted TCE RfC for assessment of Short-Term Indoor Air
Exposures, especially for pregnant women or women of child-bearing age.
 Need to constantly check MassDEP guidelines & EPA Guidance for Current
RfC Values used for Short-Term Indoor Air Exposures & for Derivation of
Developmental Toxicity Risk Screening Concentrations
 MCP Risk Findings:
 Uncertainty – reduce through addressing the Variables discussed and use
the multiple level of findings to meet MassDEP’s “Multiple-Lines-of-
Evidence” approach to clearly identify completion of the Indoor Air VIP and
assessment of the TCE Short or Long Term Exposure Risks for the Critical
Receptors