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AMBIENT AIR CONCENTRATION OF HEXAVALENT CHROMIUM IN DISTRICT OF COLUMBIA: ANY
HEALTH CONCERN?
ByAbdullahi A. Asimalowo, Robert D. Day and Khin Sann Thaung
MONITORING & ASSESSMENT BRANCHAIR QUALITY DIVISION
DISTRICT DEPARTMENT OF THE ENVIRONMENT51 N STREET NE
WASHINGTON, DC 20002
2
Disclaimer
This presentation and the analysis therein, do not necessarily represent or express the opinion of the Department of the Environment or the District of
Columbia Government.
3
Acknowledgments
• DDOE: AQD Team, Cecily Beall, Rama Tangirala and Kofi Asante‐Duah
• ERG: Julie Swift, Ray Merraill & Jaime Hauser
• EPA: Michael Jones and Joanne Rice
4
Overview
• Cr(VI) Monitoring Program
• Ambient Cr(VI) Data Analysis
• Risk analysis• Discussion and Remarks
5
Chromium Types (video)
• Chromium
element in rocks, animals, plants, soil and volcanic dust and gases
• Common forms:– elemental chromium Cr– trivalent or Cr(III)– hexavalent or Cr(VI)
• Cr(III) is an essential nutrient • Cr and Cr(VI) are product of human activities
6
Chromium Sources
• Primary sources• Minor sources• Other sources: chromium based automotive catalytic
converters and tobacco smoke (ATSDR, 2008)
• In the District of Columbia, automobiles may be the primary sources.
7
District Cr(VI) Monitoring
• Start Date: March 2005
• Sampling is 1‐in‐6 schedule
• Co‐Lo every 8 to 10 weeks
8
Monitoring Method
• Cr(VI) ambient air TSP (STP)– sodium bicarbonate impregnated cellulose filter
• Sampling flow rate: 15 liters per minute• Sample duration is 24 hours per sampling period• Exposed filters analyzed by ERG at RTP lab • EPA Compendium Method IO‐3.5 inductively coupled
plasma/mass spectrometry (ICP/MS) for metals (Jones, 2009; EPA, 2007; Rice, 2003)
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Project Data Quality Objectives Ambient Cr(VI) in DC
• Cr(VI) data for 2006‐2008 period considered • Cr(VI) AQS Code 12115 (TSP‐STP) • Method Detection Limit (MDL) availability a major
factor in use of this method
• Minimum of 85% data completeness
• Data checks and comparisons with other Cr(VI) monitoring sites
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2006 Sampled Concentration vs MDL
0
0.01
0.02
0.03
0.04
0.05
0.06
2006010520060123200602102006022820060318200604
0520060423200605112006052920060616200
60704
20060722
2006080920060827200609142006100220
061020
20061107
200611252006121320061231
Time
Con
cent
ratio
n (n
g/m
3)
Cr. Conc. (ng/m3) MDL
12
2007 Sampled Concentration vs MDL
0
0.01
0.02
0.03
0.04
0.05
0.06
2007
0106
2007
0124
2007
0211
2007
0301
2007
0319
2007
0406
2007
0424
2007
0512
2007
0530
2007
0617
2007
0705
2007
0723
2007
0810
2007
0828
2007
0915
2007
1003
2007
1021
2007
1102
2007
1116
2007
1202
2007
1220
Time
Con
cent
ratio
n (n
g/m
3)
.Cr IV Conc MDL
13
2008 Sampled Concentration vs MDL
0
0.01
0.02
0.03
0.04
0.05
0.06
20080
10120
080119
20080
206
20080
224
2008031
32008
0331
200804
18200
80506
200805
24200
80611
200806
2920
080717
20080
80420
08082
220
08090
92008
0927
2008101
5200
81102
200811
20200
81208
200812
26
Time
Con
cent
ratio
n (n
g/m
3)
Sample Concentration (ng/m3) MDL
14
RawData Averages by Season
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
2006 2007 2008
Time
Con
cent
ratio
n ng
/m3
Spring Summer Fall Winter
July 4th 0.64 value excluded Mean = 0.026370 ng/m3
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CrVI 12115 All Sites
0
0.5
1
1.5
2
2.5
3
3.51/
10/2
005
3/10
/200
5
5/10
/200
5
7/10
/200
5
9/10
/200
5
11/1
0/20
05
1/10
/200
6
3/10
/200
6
5/10
/200
6
7/10
/200
6
9/10
/200
6
11/1
0/20
06
1/10
/200
7
3/10
/200
7
5/10
/200
7
7/10
/200
7
9/10
/200
7
11/1
0/20
07
1/10
/200
8
3/10
/200
8
5/10
/200
8
7/10
/200
8
9/10
/200
8
11/1
0/20
08
Con
cent
ratio
n (N
g/m
3)
11-1-43-12115-1 11-1-43-12115-2 12-103-26-12115-6 12-103-26-12115-7 12-57-3002-12115-6 12-57-3002-12115-713-89-2-12115-6 13-89-2-12115-7 17-31-4201-12115-6 17-31-4201-12115-7 18-97-57-12115-6 18-97-57-12115-721-193-3-12115-6 21-193-3-12115-7 21-43-500-12115-6 21-43-500-12115-7 22-51-1001-12115-6 22-51-1001-12115-725-25-42-12115-6 25-25-42-12115-7 26-163-33-12115-1 26-163-33-12115-2 28-45-8201-12115-6 28-45-8201-12115-728-47-8-12115-6 28-47-8-12115-7 29-510-85-12115-6 29-510-85-12115-7 36-5-110-12115-6 36-5-110-12115-736-55-1007-12115-6 36-55-1007-12115-7 44-7-22-12115-6 44-7-22-12115-7 45-25-1-12115-6 45-25-1-12115-748-201-1039-12115-1 48-201-1039-12115-2 48-203-2-12115-1 48-453-7000-12115-1 48-453-7000-12115-2 50-7-14-12115-650-7-14-12115-7 50-7-7-12115-6 50-7-7-12115-7 51-87-14-12115-6 51-87-14-12115-7
July 4th 11-DC=0.64526-MI=0.49629-MO=0.422 22-LA=0.36744-RI=0.192
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Health Concerns• Typical routes of exposure ingestion, inhalation and
absorption.• As mentioned earlier, chromium has different forms,
depending on the oxidation state, which ranges from ‐2 to +6 valence (ATSDR, 2008)
• Its health effect is a function of its valency. • Elemental, trivalent and Hexavalent states have been
noted to be most stable
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Health Concerns
• Mutagenic DNA lesions results from Cr(VI) reduction to Cr(III)
• Epidemiological results among Cr exposed workers show Cr to be carcinogenic via inhalation route of
exposure. • Animal data further supports human data and
implicates Cr(VI), against total Cr, as the carcinogen.Source: EPA, 1998a
20
Health Concerns cont.
Weight‐of‐Evidence Narrative
• Group A ‐
known human carcinogen via inhalation (EPA 1986, 1998a & b) .
• Carcinogenicity by the oral route of exposure cannot be determined and is classified as Group D (EPA
1998a & b).
Risk Analysis Assumptions
• Sample collection/analysis is devoid of significant errors
• Total ambient concentrations are captured and accounted for
in analysis
• District population is exposed to total ambient concentration
• Population respond equally to ambient concentration of the
pollutant
• No significant confounding factors in overall analysis
• Focus here is health risk from population exposure via
inhalation only
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Analysis Method
• 50% of yearly data below MDL, except 2006(48% below)
• 2 treatment types: – ND (non detect)=MDL/2– ND=MDL
• Other treatments of interest– Maximum Likelihood Estimate or Cohen’s Distribution
considered better (Helsel, 2005; Gilbert, 1987)Is 1‐in‐6‐sampling sufficient for calculating annual statistics using this
technique?
– Robust Regression Order Statistics (ROS)– Kaplan Meier (KM)
Ref Conc. & Unit Risk
• Reference Concentration (RfC)= 1X10‐4 mg/m3 Cr(VI) particulates
• Inhalation Unit Risk=1.2 X 10‐2 per mg/m3
Inhalation conc. @specified risk levels:
1 in 1,000,000 is 8X10‐5µ/m3
(IRIS‐USEPA, 1998)
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Risk Estimates
Cancer Risk
• 2 comparisons:
– Inhalation Unit Risk (IUR)*Annual Mean Conc.
– Annual mean compared with Regional Screening Levels (2.9E‐05) Region III
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Risk EstimatesNon‐cancer risk or Margin of Exposure (MOE)
MOE= Cr(VI) average concentration/RfC
Example: 2006
ND=MDL/2: 2.98E‐05µg/m3 / (1X10‐1 µg/m3) =0.000298
ND=MDL: 3.21034E‐05 µg/m3 / (1X10‐1 µg/m3)
= 0.000321034 MOE is less than 1
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Risk Estimates: Cancer
Cancer Risk
(Inhalation Unit Risk)*(annual Cr(VI) Mean)
Example 2006
ND=MDL/2: 1.2 x10‐2
per µg/m3*0.0000298µg/m3
=3.57E‐07
ND=MDL: 1.2 x10‐2
per µg/m3*0.0000321µg/m3
=3.85241E‐07
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Exposure Risk Estimate
YEAR Non‐Cancer Risk (MOE) CANCER RISK
ND=MDL ND=MDL/2 ND=MDL ND=MDL/2
2006 0.0003 0.0003 4E‐7 4E‐7
2007 0.0001 0.00009 1E‐7 1E‐7
2008 0.0001 0.00009 1E‐7 1E‐7
Risk Based Concentration Comparision 2006
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
2006010520060117200601292006021
0200
60222
2006030620060318200603302006041120060423200
60505
200605172006052920060610200606222006070420060716200607
2820
06080920060821200609022006091420060926200610
0820
06102020061101200611132006112520061207200612192006123
1
Date
Con
cent
ratio
n ng
/m3
MDL/2 ND=MDL Risk Based Concentration( RBC)
Risk Based Concentration Comparision 2007
0
0.03
0.06
0.09
0.12
0.15
0.18
200701062007011
82007013020
0702112007022320
07030720070319200703312007041
2200704242007050
62007051820
0705302007061120
07062320070705200707172007072
9200708102007082
22007090320
070915200709272007100920071021200710302007110
820071116200711
262007120820
071220
Date
Con
cent
ratio
n ng
/m3
M DL/2 ND=MDL Risk Based Concentration( RB C)
Risk Based Concentration Comparision 2008
0
0.029
0.058
0.087
0.116
0.145
0.174
2008
0101
2008
0113
2008
0125
2008
0206
20080
218
2008
0301
2008
0313
2008
0325
2008
0406
2008
0418
20080
430
2008
0512
2008
0524
2008
0605
2008
0617
2008
0629
2008
0711
2008
0723
2008
0804
2008
0816
2008
0828
2008
0909
2008
0921
2008
1003
2008
1015
2008
1027
2008
1108
2008
1120
2008
1202
2008
1214
2008
1226
Date
Con
cent
ratio
n ng
/m3
MDL/2 ND=MDL Risk Based Concentration( RBC)
31
Discussions
• Substituting non‐detect with MDL is very conservative; (EPA, 2009).
• The MDL/2 does not give a true estimate of ambient concentration
and the subsequent exposure measure either, as it tends to give a
measure that is considered higher than the true ambient
concentration (EPA, 2009; Helsel, 2005; Warren and Nussbaum, 2009).
• The true statistical reflection of ambient concentration is considered
to be maximum likelihood estimation (MLE), (ibid). Doubts however,
have been casted on this approach, with regards to 1‐in‐6 samples.
32
Discussions
• Acceptable cancer risk level is 1E‐06 or 1 in 1,000,000 (EPA 1998b).
• Current estimate using the conservative non‐ detect=MDL or MDL/2 still shows an estimate below the
acceptable level.
• Indoor concentration is worth noting too, as build up, resulting from proximity to road ways, and/or smoking may raise level to several fold higher than the ambient concentration.
33
Limitations
• Errors from using new sampling method
• MDL and MDL/2 are too conservative to give a true reflection of ambient air concentration and
subsequent exposure analysis
• Cohen method suggested need to be looked at even though sampling is 1‐in‐6.
34
Conclusions
• Cr(VI) concentration in the District’s ambient air is generally well below levels considered harmful.
• Occasional spikes of short duration observed • High percentage of non‐detect needs to be
accounted for
35
References• Agency for Toxic Substances and Disease Registry (ATSDR, 2008). Case Studies in Environmental Medicine (CSEM): Chromium Toxicity
http://www.atsdr.cdc.gov/csem/chromium/docs/chromium.pdf
• Agency for Toxic Substances and Disease Registry (ATSDR). (1993)
Agency for Toxic Substances and Disease Registry toxicological profile
for chromium. U.S. Department of Health and Human Services, Public Health Service Report # TP‐92/08.
• EPA (1998a). Toxicological Review of Hexavalent
Chromium. (CAS No. 18540‐29‐9) In Support of Summary Information on the Integrated
Risk Information System (IRIS). August 1998 . U.S. Environmental
Protection Agency Washington, DC .
• EPA (1998b). Integrated Risk Information System.http://www.epa.gov/ncea/iris/subst/0144.htm#inhalrfc
• EPA (2007). Measurement Methods for The NATTS Programhttp://www.epa.gov/ttn/amtic/files/ambient/airtox/NATTS_TAD_SECT_4.pdf
• EPA (2009). Air Toxics Data Analysis Workbook. http://www.epa.gov/ttnamti1/files/ambient/airtox/workbook/AirToxicsWorkbook6‐09.pdfHealth assessment document for chromium. Research Triangle Park, NC, United States Environmental Protection Agency, 1984 (Final report
No. EPA600/8‐83‐014F).
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References
• International Agency for Research on Cancer (1980). Some metals and metallic compounds. IARC Monographs on the
Evaluation of the Carcinogenic Risk of Chemicals to Humans, Vol.
23.
• Helsel D.R. (2005) Nondetects and data analysis: statistics for censored environmental data. John Wiley & Sons, Inc.,
Hoboken, NJ.
• Gilbert, R. O. (1987) Statistical methods for Environmental Pollution Monitoring, Van Nostrand Reinhold, NY.
• Jones, Mike (2009). Personal Communication with Authors. National Air Toxics Ambient Monitoring Program, Office of Air Quality Planning and Standards US Environmental Protection
Agency.
• Rice, Joann (2003): National Air Toxics Trends Stations (NATTS) Methods Overview
http://www.epa.gov/ttnamti1/files/ambient/pm25/workshop/atlanta/toxrice.pdf
• Warren, J. and Nussbaum, B. (2009) “Analyzing Datasets Containing Semi‐quantitative Values”. Course material. Office of
Environmental Information, EPA
• World Health Organization (1990). "Chromium (Environmental Health Criteria 61) International Programme on Chemical
Safety,." Geneva, Switzerland