9/13/2010 

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

From: Elaine Manning, Sector Based Assessment Group 

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

Technology Assessment 

The attached minor revisions were made to the Nitrile Butadiene 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 3.8-1 Summary of Emissions from the Nitrile Butadiene Rubber 

Production Source Category and Table 3.8-2 Summary of Source Category Level Risk 

for Nitrile Butadiene 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 several nitrile butadiene rubber production facilities have stopped production. 

Based on the one facility left in this source category, the MIR for cancer has gone down 

to 2 in a million from the previously proposed MIR of 60 in a million. The HI is now 

0.009 down from the value of 0.9 at proposal. The attached Appendices 1 and 6 provide 

the supporting information for the changes. 

The MACT-allowable emissions from this source category are 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: “Detailed risk 

and 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 facility. 

The maximum facility-wide risks at the one facility with an operating nitrile butadiene 

process are estimated to be a cancer MIR of 5 in a million and an HI of 0.03. The source 

category contribution to the facility-wide risk at this facility is about 30% for both the 

MIR and HI. 
 

3.8-1 Summary of Emissions from the Nitrile Butadiene Rubber Production Source 

Category 

Prioritized Inhalation Dose-Response Value 

Identified by OAQPS 

HAP Emissions 

(tpy) 

Number of 

Facilities 

Reporting HAP 

(1 facilities in 

data set) 

Unit Risk 

Estimate for 

Cancer? 

Reference 

Concentration 

for 

Noncancer? 

Health 

Benchmark 

Values for Acute 

Noncancer? 

PBHAP? 

1,3-Butadiene 0.9 1 Υ Υ Υ

Acrylonitrile 0.9 1 Υ Υ Υ
Table 3.8-2. Summary of Source Category Level Risks for Nitrile Butadiene Rubber 

Production 

Result HAP “Drivers” 

Facilities in Source Category 

Number of Major Source Facilities Estimated to 

be in Source Category 1 n/a 

Number of Facilities Identified in NEI and 

Modeled in Risk Assessment 1 n/a 

Cancer Risks 

Maximum Individual Lifetime Cancer Risk (in 1 

million) 2 acrylonitrile, 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 0 n/a 

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

Chronic Noncancer Risks 

Maximum Reproductive Hazard Index 0.009 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 0.001 

0.00009 

acrylonitrile (AEGL-1) 

acrylonitrile (ERPG-2) 

Number of Facilities With Potential for Acute 

Effects 0 n/a 

Population Exposure 

Number of People Living Within 50 Kilometers 

of Facilities Modeled 1,000,000 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 0 n/a 

 Greater than or equal to 1 in 1 million 70 n/a 

Number of People Exposed to Reproductive Hazard Index: 

 Greater than 1 0 n/a 

Estimated Cancer Incidence (excess cancer cases 

per year) 0.0004 n/a 

Contribution of HAP to Cancer Incidence 

 acrylonitrile 72% n/a 

 1,3-butadiene 28% n/a 
Attachments: Appendix 1 Revised Emissions Inventory Support Memorandum 

 Appendix 6 Detailed Risk Modeling Results