9/13/2010 

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

From: Elaine Manning, Sector Based Assessment Group 

Subject: Post Proposal Revisions for Polybutadiene Rubber Production Risk and 

Technology Assessment 

The attached minor revisions were made to the Polyutadiene Rubber Production 

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 3.6-1 Summary of Emissions from the 

Polybutadiene Rubber Production Source Category and Table 3.6-2 Summary of Source 

Category Level Risk for Polybutadiene Rubber 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 we received some updated emissions information for the polybutadiene 

rubber production facilities. Based on this new emissions information, the MIR for 

cancer has gone up to 30 in a million from the previously proposed MIR of 10 in a 

million. The HI is now 0.3, up from the value of 0.2 at proposal. The acute results also 

changed slightly. 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 Summary of 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 known facilities (facility-wide) are presented in the attached 

Appendix 6: “Detailed Risk Modeling Results”. 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 

30 in a million and an HI of 0.3 (both MIR and HI located at the same facility). The 
source category contribution to the facility-wide risk at this facility is over 90% for both 

the MIR and the HI. 

Table 3.6-1 Summary of Emissions from the Polybutadiene Rubber Production 

Source Category 

Prioritized Inhalation Dose-Response Value Identified 

by OAQPS 

HAPa Emissions 

(tpy) 

Number 

of 

Facilities 

Reporting 

HAP (5 

facilities 

in data 

set) 

Unit Risk 

Estimate for 

Cancer? 

Reference 

Concentration for 

Noncancer? 

Health Benchmark 

Values for Acute 

Noncancer? 

PBHAP? 

Hexane 1,584 4 Υ Υ 

Toluene 510 2 Υ Υ

1,3-Butadiene 74 5 Υ Υ Υ

Styrene 68 5 Υ Υ

Ethyl Benzene 23 1 Υ

Chlorobenzene 2 1 Υ Υ

Methanol 0.07 1 Υ Υ

Nickel 0.0007 1 Υ Υ Υ
Table 3.6-2 Summary of Source Category Level Risks for Polybutadiene Rubber Facilities 

Result HAP “Drivers” 

Facilities in Source Category 

Number of Major Source Facilities Estimated to 

be in Source Category 5 n/a 

Number of Facilities Identified in NEI and 

Modeled in Risk Assessment 5 n/a 

Cancer Risks 

Maximum Individual Lifetime Cancer Risk (in 1 

million) 301

 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 2 1,3-butadiene 

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

Chronic Noncancer Risks 

Maximum Reproductive Hazard Index 0.3 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 

12 

0.6 

0.2 

toluene (REL) 

toluene (AEGL-1) 

toluene (ERPG-2) 

Number of Facilities With Potential for Acute 

Effects 1 toluene (REL) 

Acute Noncancer Refined Results

Maximum Acute Hazard Quotient 1 toluene 

Number of Facilities With Potential for Acute 

Effects 0 

Population Exposure 

Number of People Living Within 50 Kilometers 

of Facilities Modeled 1,700,000 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 20 n/a 

 Greater than or equal to 1 in 1 million 24,000 n/a 

Number of People Exposed to Reproductive Hazard Index: 

 Greater than 1 0 n/a 

Estimated Cancer Incidence (excess cancer cases 

per year) 0.003 n/a 

Contribution of HAP to Cancer Incidence 

 1,3-butadiene 98% n/a 

 ethyl benzene 2% n/a 

 

1

 The individual source category risk is 20 in a million; however because of the close proximity of 2 

facilities in the source category the highest predicted MIR for the source category is 30 in a million. 
Attachments: Appendix 1 Revised Emissions Inventory Support Memorandum 

 Appendix 6 Detailed Risk Modeling Results 

 Appendix 7 Acute Impacts Refined Analysis Figures