Studies with Diesel Exhaust Particulate: Implications for ...Wall-flow Diesel Particulate Filter 26...
Transcript of Studies with Diesel Exhaust Particulate: Implications for ...Wall-flow Diesel Particulate Filter 26...
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Webinar
Nanotoxicology Specialty Section
Society of Toxicology
December 14, 2011
Thomas W. Hesterberg, PhD, MBA
Director, Product Stewardship, Sustainability,
and Environmental Health
Navistar, Inc.
Chicago, USA
Studies with Diesel Exhaust Particulate:
Implications for the Potential Human Health
Hazards of Nanoparticles
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Introduction
2
• At early stages of assessing human health risks of
nanoparticles
• Animal and in vitro studies of nanoparticles
• Substantial uncertainties
• May not be relevant to humans
• Nanoparticles are a major constituent of diesel exhaust
• Many animal inhalation and human epidemiology studies
of DE over last 30 years
• More recent human volunteer exposure studies
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Diesel Exhaust Particles
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Traditional Diesel Exhaust (TDE)
Exhaust from engines utilizing old technologies:
– Pre-1988 diesel engines sold and in use prior to the
US EPA diesel particulate standards
– “Transitional“ 1988-2006 diesel engines
• Progressive improvements in engine design, but
• Prior to the full-scale implementation of multi-component
after-treatment systems
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Diesel Particle Size Distribution
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Occupational Exposures to Diesel PM
Exposure Group DPM (ug/m3)
Ambient < 4
Truckers 10
Railroad works 70
Surface miners 88
Underground miners 830
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Lung Cancer in Railroad Workers
• Small elevation in lung cancer risk, but cause
is uncertain
• Cancer risk does not increase with exposure
or duration of employment
• Lack of exposure measurements
• Possible confounding from cigarette smoking
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Lung Cancer in Truck Drivers
No change in
lung cancer risk
after truck
dieselization
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Lung Cancer in Underground Miners
Despite
underground
miners having
the highest
occupational
exposures to
diesel exhaust,
no change in
lung cancer risk
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Chronic Animal Studies of Diesel
Exhaust and Carcinogenicity
• No tumors observed in mice or hamsters
• Tumors in rats only at very high exposures(1,000 ug/m3)
• Thought to be non-specific response to “lung overload”
• Seen with inert dusts, e.g., talc, TiO2, carbon black, that are not in
the nanoparticle size range
• Lung overload-related tumors not observed in humans,
even in coal miners exposed to overload levels of coal dust
• Inflammation and other lung effects observed were similar
to what is seen with larger particles, e.g. amorphous silica
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Lung Tumor Excess in Rats Seen Only
Above Lung Overload Exposures
Threshold for Lung Overload
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Mutagenicity Studies
• Diesel particulate matter contains mutagenic
compounds, but
• Mutagenic compounds are not bioavailable
• Explains why tumors not seen in animal studies,
except above overload levels in rats
• Whole diesel exhaust not likely to be mutagenic
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Summary
Diesel Exhaust Lung Cancer Studies
• Human workplace studies show small increase in lung
cancer, but no exposure-response demonstrated
• Miners, who have highest DE exposures show no
increase in lung cancer
• Lung cancer not found in mice or hamsters and only at
very high “lung overload” exposures in rats
• No unusual toxicity noted in the lungs of animals
exposed chronically to diesel exhaust nanoparticles
(Hesterberg et al. Critical Reviews in Toxicology 36:727-726, 2006)
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Human Volunteer Exposures to TDE
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• Reviewed 30 human volunteer studies
• Studies used exposure chambers
• Allows control and precise measurement of exposure
conditions
• Exposed 2-3 hours to diesel exhaust
• Studies performed in UK, Sweden, and USA
• Traditional Diesel Exhaust (TDE) engines
• Many used 20 year old diesel engine
• No exhaust after treatment which has been required since
2007
(Hesterberg et al. Inhalation Toxicology 22(8):679-694, 2010)
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Some Caveats
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• Diesel exhaust (DE) exposure also contains:
• Larger-sized particles in the fine range
• Gases: carbon monoxide, nitrogen dioxide, nitric acid,
carbon dioxide
• Volatile organic compounds
• Other nanoparticles (NPs) may have properties
different diesel exhaust NPs
• DE particles may be less toxic than other
nanoparticles
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Controlled and Ambient Exposure to
Diesel Particulate Matter
Controlled
diesel
exposures 5 to
10 times
higher than
ambient
exposures
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Controlled and Ambient Exposure
to Diesel Particles
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Workplace Nanoparticles vs. DE Studies
CNT
Handling
Metal Oxide
Handling
CNT
Machining
Metal Oxide
Reactor Cleanout
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Lung Function
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Lung Inflammation
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Lung Inflammation
and Blood Clotting
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Cardiovascular System
ET-1)
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Diesel Exhaust Studies and NP Toxicity
• High diesel exhaust nanoparticle exposures may elicit
transient, subclinical effects in human volunteers
• Effects generally less or not seen at lower exposure levels
• Responses similar to those observed with larger particles
• These studies do not provide evidence of a unique toxicity
of nanoparticles compared to larger particles
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Hesterberg et al. Inhalation Toxicology 22(8):679-694, 2010
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Evolution of US Heavy Duty Diesel
On-Road Emission Standards
0.01 0.10
0.2
1.2
2.5
4.0
5.0
0.0
NO
x [
g/
BH
P-h
r]
PM [g/BHP-hr]
1994
0.0
1998
2002
2007 (NTDE)
2010 (NTDE)
ULSD 15 PPM (10/06)
500 PPM (10/93)
FUEL SULFUR
Fuel Sulfur
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New Technology Diesel Exhaust
(NTDE)
Exhaust from engines utilizing new technologies:
– Meets EPA & CARB 2007 emissions standards
– Fully integrated electronic control systems
– Ultra low sulfur diesel fuel (< 15 ppm)
– Oxidation catalysts
– Wall-flow diesel particulate filters (DPFs)
– Applies to both new and retrofitted engines
25
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Key to Emissions Reductions in NTDE Wall-flow Diesel Particulate Filter
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Trapped PM Cell Plugs
Exhaust (PM, CO, HC) Enter
Porous Ceramic Wall
Exhaust (CO2, H2O) Out
Adapted from MECA , 2000
Reductions: 95+% PM 80 to 100% HC, CO 80 to 99+% toxins
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100.
2.09 1.94 1.19 0.90 0.15 0.45 0
10
20
30
40
50
60
70
80
90
100
Veh1-baseline Veh1-DPF1 Veh1-DPF1+SCR1 Veh1-DPF1+SCR2 Veh2-DPF2 Veh3-DPF3 Veh4-DPF4
NTDE: Lower Particulate Emissions
CARB Study: Herner et al., EST 43:5928-5933, 2009, data from Table 2. Transit Buses: UDDS Test Cycle
TDE
NTDE Pe
rce
nt
of
TD
E
27
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Most Toxic Air Contaminants (TACs)
in TDE are Not Found in NTDE — Others Reduced to Near-Zero Levels —
• Aniline
• Antimony compounds
• Arsenic
• Beryllium compounds
• Cadmium
• Chlorine (chloride)
• Chlorobenzene and derivatives
• Chromium compounds
• Cobalt compounds
• Ethylbenzene
• Inorganic lead
• Manganese
• Mercury
• 4-Nitrobiphenyl
• Nickel
• Selenium
• Styrene
• Xylene isomers and mixtures
• o-Xylenes
• p-Xylenes
• m-Xylenes
28
Ullman et al, SAE 2003-01-1381, 2003
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NTDE Reduces Emissions Across a
Broad Spectrum of Compounds Category Reduction Relative to TDE
Single Ring Aromatics 82%
PAH 79%
Alkanes 85%
Hopanes/Steranes 99%
Alcohols & Organic Acids 81%
Nitro-PAHs 81%
Carbonyls 98%
Inorganic Ions 71%
Metals & Elements 98%
Organic Carbon 96%
Elemental Carbon 99%
Dioxins/Furans 99% 29
Khalek et al., JAWMA 2011.
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PM Composition and Mass Comparisons
30
100.0
2.3 2.5
0
10
20
30
40
50
60
70
80
90
100
TDE NTDE CNG
Pe
rce
nt
TDE
PM Mass
Lev-On et al., SAE 2002-01-0432,
2002. Transit Bus.
TDE
OC
EC
Sulfate
Nitrate
NTDE
CNG
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PM Composition and Mass Comparisons
31
100
2.3
8.9
0
10
20
30
40
50
60
70
80
90
100
TDE NTDE Gasoline
Pe
rce
nt
of
TDE
PM Mass TDE
OC
EC
WSOC
Nitrate
Cheung et al., Env. Sc. Tech. 43:6334-6340, 2009. Passenger
Gasoline
NTDE
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0
100
200
300
400
500
600
700
CO PM NOx HC NMHC CO2
Pe
rce
nt
of
TDE
NTDE
CNG
Gasoline
NTDE: Lower Regulated Emissions Also Similar or Better than CNG or Gasoline
32 Hesterberg et al., ES&T 42:6437-45, 2008.
TDE
(2010 Std)
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Recent NTDE Nanoparticle Study In Vitro Test Results
33 33
• Catalytic after-treatment results in higher number of nanoparticles
• More nanoparticles associated with lower ―toxicity‖ in DTT and macrophage assays
Herner et al. ES&T 45:2413-19, 2011
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34
McDonald et al., Env Health Perspectives 112:1307-12, 2004, developed from Figures 2-4.
3
1.8
1.5
1.8
1
0
1 1 1
0
1 1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Viral Burden Histopathology Inflammation (TNFa) Oxidative Stress
Re
lati
ve R
esp
on
se
TDE
NTDE
Filtered Air
Animal Inhalation Study Traditional Diesel Exhaust (TDE) vs
New Technology Diesel Exhaust (NTDE)
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35
Recent Human Volunteer Studies Traditional Diesel Exhaust (TDE) vs
New Technology Diesel Exhaust (NTDE)
50
60
70
80
90
100
110
120
130
Ex Vivo Thrombus Formation
Acetylcholine Vasodilation
Pe
rce
nt
Filte
red
Air
TDE
NTDE
Filtered Air
NTDE gave same response as
Filtered Air
Lucking et al. Circulation 123:1721-1728, 2011.
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Research In Progress
Advanced Collaborative Emissions Study (ACES)
• Managed by the Health Effects Institute
• Funded by government agencies and industry
• Lifespan inhalation study in rodents
• Lung disease and cancer are main endpoints
• Two more years to complete
36
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Summary on NTDE vs TDE
• PM levels in NTDE are 100-fold lower than in TDE
• NTDE PM is chemically very different from TDE
• Similar to CNG and gasoline PM
• NTDE emissions generally lower than CNG or gasoline
• Biological effects of TDE were not observed with NTDE
• NTDE should be evaluated separately from TDE
37
Hesterberg et al, JAWMA, 61:894–913, 2011.
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NTDE and NP Toxicity
• High diesel exhaust nanoparticle exposures may elicit transient, subclinical effects in human volunteers
• Effects generally less or not seen at lower exposure levels
• Responses similar to those observed with larger particles
• Effects not observed with New Technology Diesel Exhaust
• These studies do not provide evidence of a unique toxicity of nanoparticles compared to larger particles
38
Hesterberg et al., Inhalation Toxicology 22(8):679-694, 2010.
Hesterberg et al., JAWMA, 61:894–913, 2011.