Vapor Intrusion:Regulatory Priorities and Toxicological
Complexities
Robert P. DeMott, Ph.D., DABT
ENVIRON International [email protected]
Florida Section – AIHA Conference 24 March 2006
Presentation Outline
Introduction
Rise of Regulatory / Risk Assessment approaches
Toxicological Complexities
Case Study – Inhalation Toxicity
Inhalation Exposures – New Tricks for an Old Dog
Early “environmental” controls focused on vapor inhalation- Industrial hygienists, ACGIH, OSHA
- In workplace – direct, obvious pathway
Ambient air also early focus – Clean Air Act, Ambient Air Quality Standards
For “contaminated sites” – inhalation exposures more complex, indirect
In a Distant Time….
Facing workplace needs, scientists with names like Patty, Zenz, and Hayes invented tools, approaches, and ultimately set safe limits for workers…
Highly Empirical
Tightly Linked to Human Reactions / Responses
Golden Age
Industrial hygiene viewdominates inhalationcontrol / risk evaluations
Progress to the “Part-Per-Million Era”
Workplace safety leaps forward
Toxicologists Serve As Trusted Advisors
Dark Ages --
Love Canal and the rise of “Sites”
Soil and groundwaterbecome focus
Direct contact pathwaysfirst addressed
Inhalation involves transport – more complex, later emerging
New Age
New type of scientists/technocrats bring new approach
“Risk Assessment”
Re-derivation of toxicity values / level of safety
New Age
Modeling andextrapolationused to protectagainst uncertainties
Toxicologists relegated to new role…
“The Future is Now…”
Risk assessors/regulators stopped downplaying inhalation exposures
Limitation was always getting vapor concentration to assign- Soil – “volatilization factor”
- Groundwater – Andelman shower model
Tools and approaches emerged to consider “Vapor Intrusion” and resultant pathways
Soil Vapor Intrusion Pathway
Migration from subsurface into overlying buildings
Increased attention as a potentially significant indoor air exposure
EPA and many states provide target screening levels derived via “Risk Assessment” approach
Conceptual Model
Pressure-driven flow- Building
underpressurization- Stack Effect- Wind loading- Ventilation systems- Barometric pressure
- Diffusion through cracks
Factors Affecting Soil Vapor Intrusion
Source Characteristics- Soil or groundwater
- Concentration and location
- Biodegradability
Soil Characteristics- Air permeability, moisture content, surface cover
Building Construction- Foundation type (basement, slab-on-grade, etc.)
- Foundation openings (crack size)
- HVAC system, air exchange rate
- Depressurization
Florida Factors
Conditions can enhance groundwater vapor transport- Highly transmissive soils (sands)
- Shallow water table
- High temperatures
Several FDEP GCTLs exceed EPA groundwater targets protective of indoor air
Florida-specific targets would be lower than current groundwater targets for numerous chemicals
Technological Tipping Point
Johnson & Ettinger Model (1991):
Steady-state upward diffusion
Intrusion through a perimeter crack
Source can be soil, soil gas, groundwater, or NAPL
Generically conservative but beware of misapplication
Can be customized to site conditions
Science Regulation Recognition
OSWER GuidanceRCRA, CERCLAAnd BrownfieldsJ&E Model
Publication
1991
ASTM RBCAGuidance
1995
2001
Draft RCRA EISupplemental Guidance
2002
MA State Guidance
199320
02
EPA OSWERGuidance
MI StateGuidance
1998
1994
Redfield RifleRegulatory Invest.
EPA OSWERGuidance
Denver Post/Redfield Rifle
2000
Moffett FieldRegulatory Invest.
2004
Mt. View,Tallevast.
15 Years from Concept to Cause
EPA Creates Guidance
Consolidated, Multi-program Guidance (Superfund, Brownfields RCRA)
States conforming
Tiered Approach
- Common in modern risk-based guidance
- Intended to promote efficiency
- Simplified tiers rely on intentional protective bias
2002 OSWER Guidance
- Primary Screening
- Volatile and toxic compounds present?
- Buildings present?
- Immediate response required? (health effects,noxious odor, explosive levels)
2002 OSWER Guidance
- Secondary Screening- generic risk-based screening tables (groundwater, soil gas)
- Site-specific screening values (modify eqn inputs)
- Site-Specific Assessment- Field investigations- Soil gas, indoor air monitoring
State Initiatives
Groundbreakers:Massachusetts – 1992
Groundwater standards based on vapor intrusion
Connecticut – 1996 Michigan – 1998Default numerical criteria
Following Suit:NY, PA, CA, IL, LA, TX, VA, others
Florida - Wait and See
Regulatory Pressures
Regulatory prioritiesoften controlled by inertia
Perceived regulatory gap is a motivator
- Indoor air “discoveries”
- Media attention
New guidance breaks the logjam
Redfield Rifle Site
TCA plume beneath Denver neighborhood
“Site” work and recognition of potentially affected neighbors -- mid-90s
Actually incorporated residential mitigation into site remedy
2002 – Denver Post runs acclaimed series of stories
Media HelpsFocuses Attention
Moffett Field – Silicon Valley
TCE Plume
Dates back to DoD days
Semiconductor manufacturing
Local hydrogeology creates far reaching plume
Public awareness fueled by media buzz
Recalibrating Risk
Risk assessment based approach applies protective bias for uncertainties
Substantially lower than occupational limits
Do NOT account for ambient background !
“Screening” means “Standard”
“Won’t Hurt You” vs. “Safe”
Chemical C / NCEPA Generic
Screening Values (ppb)
OSHA PEL TWA(ppb)
ACGIH TLV TWA
(ppb)
Tetrachloroethene C 12 100,000 25,000
Trichloroethene C 0.41 100,000 50,000
Vinyl Chloride C 11 100,000 5,000
Benzene C 9.8 10,000 500
Carbon Tetrachloride C 2.6 10,000 5,000
Chloroform C 2.2 -- 10,000
1,1,1-Trichloroethane NC 400 350,000 350,000
1,2-Dichloroethene (cis) NC 8.8 200,000 200,000
1,2-Dichloroethene (trans)
NC 18 200,000 200,000
Naphthalene NC 0.57 10,000 10,000
Toxicological Complexities
TCE- Just what exactly is the toxicity of this stuff??
Napthalene- Non-carcinogen yesterday, carcinogen today
1,4-Dichlorobenzene- It’s OK here, but not there?
Trichloroethylene
Cancer potency estimate withdrawn in 1989 – still used
New EPA value -- 2002- ~ 65-times more potent- Much comment/debate ensued
Doesn’t use latest EPA approach for dealing with cancer mechanisms
Last NAS review -- 2005… no resolution expected for years
Science Continues to Emerge
Crit. Rev. Toxicol. 34: 386-445, 2004.
Cancer vs. Non-Cancer
Napthalene
PAH (MGP) plumes
Reference dose- Threshold for response- Apply uncertainty factors (margin of safety)
Cancer slope factor – linear, no-threshold assumption
New screening level 3-300 fold lower (depending on state/region)
Paradox Wrapped Inside a Conundrum…
1,4-dichlorobenzene- Common ambient levels (sanitizer)
- EPA carcinogen …. Or Not…
PPM levels OK in the “lounge”
10-fold (or more) lower CLEANUP Target for environment
“Imagine a plant…”
Risk-Based Wrap Up
Train has left the station
Can’t argue against protection
Complexities left for scientists to work out
•Role for industrial hygienists…
Just remember your trusted advisors … toxicologists
CSI: Tampa….
Vapor Exposure Case Study
Workplace vs. Environmental Vapors
Liver Damage in Haz Waste Workers
Investigation after multiplecomplaints of illness
Survey of self-reportedindications (symptoms)
Clinical testing (ALT, AST) indicated numerous abnormal results
Chronic, ongoing problem or discrete event?
Haz. Waste Facility Events
Liquid wastes being incinerated
Soil being chemically treated and incinerated
Flash fire occurs while processing drums, fire extinguisher system discharges
Employees cleanup fire suppressant foam
Several employees acutely, observably ill over next two weeks
Many employees with complaints
Good Hypothesis – Partial Fit
Tennessee Dept. of Health concluded- Workplace exposure caused effects
- Detection was confounded by background incidence of hepatitis and other challenges to liver function
- Liquid wastes being processed at time of fire not liver toxicants
- “Unknown compound” formed mixing solvents and fire suppressant (baking soda)
Median ALT By Date Drawn
0
200
400
600
800
1000
1200
1400
1600
1800
Pre-empl 10/31 11/30 1/18 1/22 1/30 2/1 2/6 3/7-Pre
Date
Medi
an A
LT
Spike In Liver Enzymes Defines Critical Time Point
Clinical Chemistry Supports Discrete Event (S!)
Patients with ALT > 1000, By Date
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Pre-empl 10/31 11/30 1/18 1/22 1/30 2/1 2/6 3/7-Pre
Range of Dates
Lev
el o
f A
LT
Patient A
Patient B
Patient C
Patient D
Patient E
Patient F
Patient G
Patient H
Soil Chemistry
Tentatively Identified Compounds
Obscure sulfur mustard-related compounds
Breakdown products from chemical warfare agents
Remediation at nearby arsenal for this type of compound ongoing
Refined Timeline Refines Possibilities
Key uncertainty – employee with obvious signs a week too late – lead to reconsideration
Overlap between:Soil processing (18 Jan, 19 Jan)Tower fire (16 Jan)
But –- Also processed soil (25 Jan, 26 Jan)- Arrival and staging of soil rolloffs (15 Jan)
Second Source Unfolds
Rolloffs were from munitions depot cleanup
Chemical-warfare agent containing soil supposedly segregated, sent elsewhere
Sampling of containers documents low levels of known components/breakdown products
Case Study Lessons
Look for “gators in the weeds”
Force-fitting hypothesisshuts out search for answer
Data that “don’t fit”- Noise or Hint?
Conclusions
New Approaches, New Regulatory Priorities
Challenge to Occupational Exposure Paradigm
Industrial Hygienists – role in bridging workplace and contaminated site regulation
Need for “old skills” never ends…