9/13/2010 

To: Docket – ID No. EPA-HQ-OAR-2010-0600 

From: Elaine Manning, Sector Based Assessment Group 

Subject: Post Proposal Revisions for Styrene Butadiene Rubber Facilities Risk and 

Technology Assessment 

The attached minor revisions were made to the Styrene Butadiene Rubber source 

category risk assessment which was included in the proposal for the Group I Polymers 

and Resins; Marine Vessel Loading Operation; Mineral Wool Production; 

Pharmaceuticals Production; and Printing and Publishing Industry rulemaking issued on 

October 10, 2008. The updated Table 3.7-1 Summary of Emissions from the Styrene 

Butadiene and Latex Production Source Category and Table 3.7-2 Summary of Source 

Category Level Risk for Polymers & Resins I - Styrene Butadiene Rubber and Latex 

Production reflecting the minor changes are attached. The most significant change from 

the October 10, 2008 proposal is the change in the maximum individual risk (MIR) and 

hazard index (HI). Since the October 10, 2008 proposal several styrene butadiene rubber 

production facilities have stopped production and we received updated emissions 

information. Based on the facilities left in this source category and using the updated 

emissions information, the MIR for cancer has gone up to 10 in a million from the 

previously proposed MIR of 7 in a million. The HI is now 0.2, up from the value of 0.1 

at proposal. The acute results remain the same. The attached Appendices 1, 6, and 7 

provide the supporting information for the changes. 

The MACT-allowable emissions of the compound (1,3-butadiene) driving the risk 

from this source category is estimated to be approximately the same as the modeled 

actual emissions; therefore, the risks results are equal. 

In addition to the risk presented by source category alone as presented in the 

attached Source Category Level Risk table, additional analysis was performed to access 

the “facility-wide” risk. The results of the residual risk associated with all categories at 

the one facility (facility-wide) are presented in the attached Appendix 6. We used the 

National Air Toxics Assessment (NATA) database for estimating facility-wide risks due 

to our lack of more recent facility-specific emissions data for some of the source 

categories included in the facility-wide analyses. Additionally, because we have not yet 

begun our thorough residual risk review for most source categories, we are unable at this 

time to estimate allowable facility-wide emissions. Thus, our facility-wide analysis is 

based solely on actual emissions. 

The facility-wide MIR and HI available in Appendix 6 are based on emissions, as 

identified in the NATA database, from all emissions sources at the identified facilities. 

The facility with the maximum facility-wide risks is estimated to have a cancer MIR of 

70 in a million and an HI of 1. The source category contribution to the facility-wide risk 
at this facility is about 5% for the MIR and 10% for the HI. The facility with the next 

highest MIR is 40 in a million with an HI of 1. The source category contribution to the 

facility wide MIR is 5% and 10% for the HI. 

 
Table 3.7-1 Summary of Emissions from the Styrene – Butadiene and Latex 

Production Source Category 

Prioritized Inhalation Dose-Response Value 

Identified by OAQPS 

HAP Emissions (tpy) 

Number of 

Facilities 

Reporting HAP 

(6 facilities in 

data set) 

Unit Risk 

Estimate for 

Cancer? 

Reference 

Concentration 

for Noncancer? 

Health 

Benchmark 

Values for Acute 

Noncancer? 

PBHAP? 

Styrene 275 6 Υ Υ

1,3-Butadiene 14 6 Υ Υ Υ

Ethyl Benzene 4 4 Υ 

Xylenes (Mixture of o, 

m, and p Isomers) 4 2 Υ Υ

Carbon Disulfide 3 1 Υ Υ

Acrylic Acid 0.8 3 Υ Υ

Toluene 0.7 2 Υ Υ

Benzene6 0.7 1 Υ Υ Υ

Methanol 0.6 1 Υ Υ

Acrylonitrile 0.1 1 Υ Υ Υ

Vinylidene Chloride 0.05 1 Υ 

Hydrochloric Acid 0.04 1 Υ Υ

Ethyl Acrylate 0.04 1 Υ

Methyl Methacrylate 0 1 Υ Υ
Table 3.7-2 Summary of Source Category Level Risks for Polymers & Resins I - Styrene 

Butadiene Rubber and Latex Facilities 

Result HAP “Drivers” 

Facilities in Source Category 

Number of Major Source Facilities Estimated to 

be in Source Category 6 n/a 

Number of Facilities Identified in NEI and 

Modeled in Risk Assessment 6 n/a 

Cancer Risks 

Maximum Individual Lifetime Cancer Risk (in 1 

million) 10 1,3-butadiene 

Number of Facilities with Maximum Individual Lifetime Cancer Risk: 

 Greater than or equal to 100 in 1 million 0 n/a 

 Greater than or equal to 10 in 1 million 1 1,3-butadiene 

 Greater than or equal to 1 in 1 million 4 1,3-butadiene, acrylonitrile 

Chronic Noncancer Risks 

Maximum Reproductive Hazard Index 0.2 1,3-butadiene 

Number of Facilities with Maximum Reproductive Hazard Index: 

 Greater than 1 0 n/a 

Acute Noncancer Screening Results

Maximum Acute Hazard Quotient 

2 

0.6 

0.09 

styrene (REL) 

styrene (AEGL-1) 

styrene (AEGL-2) 

Number of Facilities With Potential for Acute 

Effects 1 styrene 

Acute Noncancer Refined Results

Maximum Acute Hazard Quotient 0.4 styrene (REL) 

Number of Facilities With Potential for Acute 

Effects 0 

Population Exposure 

Number of People Living Within 50 Kilometers 

of Facilities Modeled 6,700,000 n/a 

Number of People Exposed to Cancer Risk: 

 Greater than or equal to 100 in 1 million 0 n/a 

 Greater than or equal to 10 in 1 million 3 n/a 

 Greater than or equal to 1 in 1 million 25,000 n/a 

Number of People Exposed to Reproductive Hazard Index: 

 Greater than 1 0 n/a 

Estimated Cancer Incidence (excess cancer cases 

per year) 0.004 n/a 

Contribution of HAP to Cancer Incidence 

 1,3-butadiene 98% n/a 

 ethyl benzene 1% n/a 
Attachments: Appendix 1 Revised Emissions Inventory Support Memorandum 

 Appendix 6 Detailed Risk Modeling Results 

 Appendix 7 Acute Impacts Refined Analysis Figures