U.S. Environmental Protection Agency 

Office of Water

Standards & Risk Management Division

Washington, DC 20460 

Date: July 2013

USEPA Correction of the "Comparison of 

hydrofluorosilicic acid and 

pharmaceutical sodium fluoride as 

fluoridating agents—A cost–benefit 

analysis" by Hirzy et al. (2013)
Correction Summary

The petitioner cited the results of the cost-benefit analysis in Hirzy et 

al. (2013) for many of the assertions in the TSCA section 21 petition 

to prohibit the use of hydrofluorosilicic acid (HFSA) as a water 

fluoridation agent. 

EPA used the assumptions from Hirzy et al. (2013) and did not 

conduct an independent analysis. Therefore, EPA did not analyze the 

accuracy of the assumptions/inputs used in the Hirzy et al. (2013) 

cost-benefit analysis. The only correction that EPA made to the 

calculation was to divide the lifetime cancer risk by 70 years. Hirzy et 

al. (2013) assumed that the cancer risk was annualized. As a result, 

the lifetime cancer cases instead of the cancer cases per year were 

used in the cost-benefit analysis. The corrected cost-benefit analysis 

favors the use of HFSA over NaF (-$81M/year to -$8M/year) rather 

than NaF over HFSA, as calculated by Hirzy et al. ($1,011M/year to 

$6,191M/year). 
Column C D E F G H

Cost-Benefit Analysis for HFSA versus NaF (Hirzy et al. (2013) Case 1)

Arsenic conc (μg/L) Unit risk (μg/L)-1

Population cancer 

risk Exposed population

*Cancer Cases per year 

(error: lifetime cancer 

cases)

Cancer 

Treatment Cost 

per case

Formula C*D E*F

HFSA 7.8E-02 3.5E-05 2.7E-06 118000000 322 3500000

NaF 8.4E-04 3.5E-05 2.9E-08 118000000 3.5 3500000

Total Annual Health 

Costs 

($ Millions /year)

Annual Fluoridation 

Costs ($ 

Millions/year)

Total Social Cost 

($ Millions/year)

Net Benefits for NaF 

compared to HFSA 

($Millions/year)

Formula G*H/1000000 C+D E15-E16

HFSA 1127 23 1150 1018

NaF 12 120 132

Correction on next page

*The number of cancer cases for HFSA (320 vs. 322) and NaF (3.4 vs. 3.5) from Hirzy et al. (2013) are different due to rounding.
Column C D E F G H

Arsenic conc (μg/L) Unit risk (μg/L)-1 Lifetime cancer risk

*Correction: Annual 

cancer risk Exposed population

Cancer Cases per 

year

Formula C*D E/70 years F*G

HFSA 7.8E-02 3.5E-05 2.7E-06 3.9E-08 118000000 4.6

NaF 8.4E-04 3.5E-05 2.9E-08 4.2E-10 118000000 0.05

Cancer Treatment 

Cost per case

Total Annual Health 

Costs 

($Millions/year)

Annual Fluoridation 

Costs 

($Millions/year)

Total Social Cost 

($ Millions/year)

Net Benefits for NaF 

compared to HFSA 

($Millions/year)

Formula H*C/1000000 D+E F42-F43

HFSA 3500000 16 23 39 -81

NaF 3500000 0.2 120 120

*Correction using Hirzy et al. (2013) assumptions: Divide the lifetime cancer risk (or lifetime cancer cases) by 70 years. 

OW's Correction to the Hirzy et al. (2013) Case 1 Cost-Benefit Analysis for HFSA 

versus NaF
Column C D E F G H

Arsenic conc (μg/L) Unit risk (μg/L)-1 Population cancer risk

Exposed 

population

Cancer Cases per 

year (error: 

lifetime cancer 

cases)

Cancer Treatment Cost 

per case

Formula C*D E*F

HFSA 4.3E-01 3.5E-05 1.5E-05 118000000 1776 3500000

NaF 8.4E-04 3.5E-05 2.9E-08 118000000 3.5 3500000

Total Annual Health 

Costs 

($ Millions /year)

Annual 

Fluoridation Costs 

($ Millions/year)

Total Social Cost 

($ Millions/year)

Net Benefits for 

NaF compared to 

HFSA 

($Millions/year)

Formula G*H/1000000 C+D E15-E16

HFSA 6216 23 6239 6107

NaF 12 120 132

Cost-Benefit Analysis for HFSA versus NaF (Hirzy et al. (2013) Case 4)

Correction on next page

*The number of cancer cases for HFSA (1800 vs. 1776) and NaF (3.4 vs. 3.5)from Hirzy et al. (2013) are different due to rounding.
Column C D E F G H

Arsenic conc (μg/L) Unit risk (μg/L)-1 Lifetime cancer risk

*Correction: 

Annual cancer risk 

Exposed 

population Cancer Cases per year

Formula C*D E/70 years F*G

HFSA 4.3E-01 3.5E-05 1.5E-05 2.2E-07 118000000 25

NaF 8.4E-04 3.5E-05 2.9E-08 4.2E-10 118000000 0.05

Cancer Treatment 

Cost per case

Total Annual 

Health Costs 

($Millions/year)

Annual Fluoridation 

Costs ($Millions/year)

Total Social Cost 

($ Millions/year)

Net Benefits for 

NaF compared to 

HFSA 

($Millions/year)

Formula H*C/1000000 D+E F42-F43

HFSA 3500000 89 23 112 -8

NaF 3500000 0.2 120 120

OW's Correction to the Hirzy et al. (2013) Case 4 Cost-Benefit Analysis for 

HFSA versus NaF

*Correction using Hirzy et al. (2013) assumptions: Divide the lifetime cancer risk (or lifetime cancer cases) by 70 years.