Mark Harris, PhD Principal Health Scientist ChemRisk Inc. Houston Air Toxics Workshop II

ChemRisk

Houston Air Quality: Modeling, Monitoring and Risk Associated

with Hazardous Air Pollutants (HAPs)

Mark Harris, PhD

Principal Health ScientistChemRisk Inc.

Houston Air Toxics Workshop II June 12, 2007

ChemRisk

Houston Air Quality: Outline

• Recent Events

• Mayor’s Task Force Report

– data utilized

– risk characterization

• Conclusions

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Current Situation

• Houston complies with Clean Air Act (CAA) criteria pollutant standards except for ozone

• Coming into compliance with the CAA ozone standard is important:– Human health (asthma)– Federal funding– Remain competitive with other metropolitan areas

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Current Situation

Table from “The State of Health” Report for Houston and Harris County (2007)

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Houston Air Quality: HAPs Recent Events

• 2005 – “In Harm’s Way” series by Dina Cappiello• Four neighborhoods near industrial facilities• Compared results to ESLs and to more stringent values

used by the federal government and other states• Compared results to NATA background• Assessed TCEQ monitoring data/some in home sampling

as well

• Summer 2006: Mayor’s Task Force report• Survey of 179 air pollutants, 10 county area• Used modeled annual average air concentrations

from EPA’s 1999 National Air Toxics Assessment (NATA) and some monitoring data

• Ranked pollutants based on theoreticalcancer risk

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• September 2006: The Control of Air Toxics Report

• Rice University, UH Law Center, Baylor College of Medicine, Texas Southern University, and UTMB

• 4 HAPs: benzene, 1,3-butadiene, formaldehyde, diesel particulates

• Follow up to Mayor’s Task Force Report

• Based on TCEQ monitoring data and compared concentrations to other cities


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• 2007: UT School of Public Health Preliminary Report

• Retrieved Texas Cancer Registry Data• TCEQ & NATA data for benzene and

1,3-butadiene• Estimated rate ratios based on distance

from HSC and air concentrations

• 2007: Mayor’s benzene reduction plan• Focused on ship channel facilities• Suggested modifications for facilities• Houston City Council authorized litigation • Novel in that most facilities targeted are

not in Houston


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• Reports have limitations – Selection of modeling data– Modeled values reflect upper bound of monitoring data– Use of worst-case toxicity values– Risks not placed into perspective– Transparency – Statistical procedures unclear– Lack of cost benefit analyses– Errors in reported information– Failure to consider met data in some cases– Reports comprise parts of a risk assessment but we are

missing key pieces


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Risk Assessment - HAPs

RiskRiskCharacterizationCharacterization

Dose-ResponseDose-ResponseAssessmentAssessment

RiskRiskManagementManagement

HazardHazardIdentificationIdentification

ExposureExposureAssessmentAssessment

Cost/BenefitCost/BenefitAnalysesAnalyses

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Focus on Mayor’s Task Force Report

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Mayor’s Task Force Report

• Utilized ASPEN data as opposed HAPEM• Some use of monitoring data• Higher of CAL EPA or EPA toxicity criteria

for a chemical• Calculated cancer risk on a census tract

basis using ASPEN data • Ranked chemicals using risk estimates• Forms basis for other reports and recent

actions by Mayor’s office

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Houston Air Quality: Mayor’s Report

• 12 chemicals flagged as “definite” risks:

• “Those substances for which there was compelling and convincing evidence of significant risk to the general population or vulnerable subgroups at current ambient concentrations..”

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Definite Health Risks per the Mayor’s Task Force Report

• Ozone• Fine Particulate

Matter• 1,3-Butadiene• Chromium VI• Benzene• Ethylene dibromide

• Acrylonitrile• Formaldehyde• Acrolein• Chlorine• Hexamethylene

Diisocyanate• Diesel Particulate

Matter

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Our Evaluation

• Comparison of NATA modeled air concentrations for certain HAPs to monitoring results

• Risk Characterization– Sprinkles, a thunderstorm or hurricane?

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NATA Air Modeling

• As part of NATA, air concentrations were modeled by EPA using ASPEN and HAPEM for 895 census tracts in our 10 county area

• Air concentrations used by EPA to predict risk• 1999 vintage information• We pulled the modeled air concentrations into

ArcGIS, and plotted with TCEQ air monitoring locations

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Houston Air Quality: Air Modeling

Benzene 1,3 Butadiene

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Houston Air Quality: Monitoring Data

• Obtained air monitoring data from TCEQ for several HAPs

• 24 hour canisters taken every 6th day • 15 sites available, east Harris County• 13 sites 2003-2006, 2 sites 2005-2006

• Hourly auto GC data • 8 sites available, east Harris County • 6 sites 2003-2006, 1 site 2005-2006, 1 site

2004-2006

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Houston Air Quality: 24 hour canister data

Channelview C15/AH115

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Benzene Concentration (ug/m3)

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ASPEN: 4.97 ug/m3, 94th percentileHAPEM: 4.37 ug/m3, 93rd percentile

• Period of Record: 1/2003 to 1/2006

• 160 measurements, 24 hour canisters collected every 6 days


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1,3 Butadiene Concentration (ug/m3)

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HAPEM: 0.91 ug/m3, 72nd percentileASPEN: 1.14 ug/m3, 80th percentile

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Houston Air Quality: Auto GC data


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Benzene Concentration (ug/m3)

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ASPEN: 4.97 ug/m3, 94th percentileHAPEM: 4.37 ug/m3, 91st percentile


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1,3 Butadiene Concentration (ug/m3)

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HAPEM: 0.91 ug/m3, 74th percentileASPEN: 1.14 ug/m3, 82nd percentile

• Period of Record: 1/2003 to 8/2006

• N Benzene = 1131 N 1,3 Butadiene = 902

• Auto GC data used to determine daily averages

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• Results for Channelview monitor typical• Results for Auto GC daily averages matches well

with 24 hour cans taken every 6 days• Modeled benzene concentration typically at or

greater than the 90th percentile of monitoring data• Modeled 1,3-butadiene concentration typically at

or greater than 70th percentile, often over 80th percentile

Houston Air Quality: Modeled vs. Monitored Air Concentration

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Mayor’s Task Force Report

• Our attempt to place the risks into perspective

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Risk Characterization

• Total excess cancers for census tract over a lifetime = CR x pop– where,

• CR = cancer risk in a census tract for an airborne pollutant• pop = population of census tract

• Example– population of a census tract = 4,000 people– theoretical excess cancer risk for a chemical = 1 x 10-5

– Total excess cancers for census tract = 4,000 x 1 x 10-5

– Total excess cancers for census tract = 0.04

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Total Excess Cancers for the 895 Census Tracts in the 10 County Area

ChemicalUSEPA Toxicity Criteria

Number of Excess CancersCalEPA Toxicity Criteria Number

of Excess Cancers

Acrylonitrile 5 20

Cr VI 23 282

EDB 26 8

Formaldehyde 0 60

Benzene 68 253

Butadiene 23 131

Total 144 754

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Risk Characterization• In the population of the study area (4,715,407), approximately

1 in 3 (or 1,556,085) will develop cancer in their lifetime• 33% background rate• Using EPA Toxicity Criteria - these HAPs add an additional 0.003% to

the background rate over a lifetime• Using CAL EPA Toxicity Criteria - these HAPS add an additional

0.016% to the background rate over a lifetime

• Excess cancers associated with these chemicals would be very difficult if not impossible to detect

• Risk characterization does not support the conclusion that there is “compelling and convincing evidence of significant risk” associated with these HAPs

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Conclusions

• Mayor’s Report missing perspective

• Modeling data is conservative relative to measured air concentrations in the Houston area

• Risk Characterization indicates a level of increased risk that would be very difficult to detect

• More important to focus meeting ozone criteria

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Co-Authors

• Dr. Laurie Haws

• Mr. Andrew Tachovsky

• Dr. Spencer Williams

• Ms. Ly Nguyen

• Ms. Laura Scott

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Thank you!

• Are there any questions?

• For further information:Mark Harris, Ph.D.

Principal Health Scientist

ChemRisk, Inc.

10375 Richmond Ave, Suite 350

Houston, TX 77042

phone: 713-974-6200 ext. 1001

fax: 713-974-6111

email: [email protected]

Documents

Mark Harris, PhD Principal Health Scientist ChemRisk Inc. Houston Air Toxics Workshop II