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Ferroalloys Production NESHAP:

URE for Nickel Compounds

Points for Discussion

March 9, 2012
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Overview

• NiPERA is the human and environmental health scientific research 

arm of the Nickel Institute, an association of worldwide nickel 

producing companies representing ~90 percent of global nickel 

production. 

• Our concern is that the URE value EPA used for nickel compounds 

in this rulemaking is not well-founded. It should be corrected, so 

that a more accurate and scientifically sound value is used.

• Cancer risk from nickel emissions was not the basis for finding the 

residual risk in Ferroalloys Production (FP) to be unacceptable; the 

HI for manganese was the driver. So correcting the URE for nickel 

would not change the finding of unacceptable residual risk. But it 

would provide a more appropriate basis for estimating nickel-related 

cancer risks here and in future proceedings.
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Assumptions for Deriving URE

• For purposes of deriving a URE to apply to the mix of nickel 

compounds present in FP emissions, we are prepared to make the 

following assumptions, even though we question several of these 

points:

– All nickel compounds are potentially carcinogenic to some extent, and a 

single URE can be applied to all of them as a group (total nickel) for 

purposes of estimating cancer risk.

– URE values derived from occupational studies of nickel refineries 

processing sulfidic ores (where nickel subsulfide is a major component 

of emissions) can be used to assess cancer risks associated with 

environmental exposures from sources (like Ferroalloys Production) 

where nickel subsulfide is a minor component of nickel emissions (if it 

present at all). But the focus should be on refinery studies where Ni3S2

was relatively less prominent.

– A linearized, non-threshold exposure-response model can be used to 

assess cancer risk from low-level environmental exposures to nickel.
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EPA’s Approach

• In its residual risk assessment, EPA used 

the IRIS URE value for nickel subsulfide

(i.e., 4.8 x 10-4 per μg/m3) and applied it to 

the maximum estimated exposure 

concentration of total nickel (i.e, all nickel 

species combined) from emissions at 

Ferroalloys Production facilities.

• There are logical problems with this 

approach.
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Logic Problems

• While it was a major component of total nickel in the 4 nickel refinery 

studies on which the IRIS URE value for nickel subsulfide is based, 

Ni3S2is at most a minor component of total nickel in emissions from 

Ferroalloys Production.

• Even in the 4 nickel refinery studies from which the IRIS URE value 

was derived, EPA did not find an increased cancer risk of 4.8 x 

10-4 per μg/m3. Nor has any other regulatory body. 

• What EPA found was an upper bound estimate URE of 2.4 x 10-4

per μg/m3for workers exposed to the mix of nickel compounds 

present in the 4 nickel refineries. It then arbitrarily doubled that 

value to derive a presumptive URE for Ni3S2 of 4.8 x 10-4 per μg/m3

based on the assumption that Ni3S2 constituted 50% of the nickel 

species to which the refinery workers were exposed but was 

responsible for 100% of the cancer risk – with the other nickel 

compounds having no carcinogenic effect. 
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Logic Problems (continued)

• If EPA now chooses to assume that all nickel compounds are carcinogenic 

– so that they all presumably contributed to the increased cancer risk seen 

in the refinery studies – it would not be logical to apply to total nickel 

emissions from FP facilities the artificially doubled URE that EPA 

constructed for Ni3S2 at a time when it assumed that Ni3S2 alone was 

responsible for the cancers seen in the refinery cohorts. 

• Surely, the mix of nickel compounds present in emissions from Ferroalloys 

Production (where Ni3S2is a minor component at best) does not have a 

higher carcinogenic potency than the mix of nickel compounds present at 

refineries processing sulfide nickel matte (where Ni3S2 was a major 

component of total nickel). 

– Yet, in its residual risk assessment, EPA assumes that total nickel in FP 

emissions has twice the carcinogenic potency as total nickel in the refinery 

studies (4.8 x 10-2 versus 2.4 x 10-2). That cannot be the case. 

– Rather, the opposite clearly is the case – i.e., the mix of nickel compounds 

present at sulfide nickel matte refineries is more carcinogenic than the mix of 

nickel compounds in FP emissions. So a URE greater than 2.4 x 10-2 cannot 

logically be justified even if EPA is determined to stick with outdated IRIS values. 
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EPA Should Use the TCEQ’s URE 

for Nickel Compounds

• The IRIS value for exposure to a mix of nickel compounds – 2.4 x 

10-4 – is more than a quarter century old. A more updated URE is 

now available and should be used instead. 

• Just recently, the Texas CEQ calculated a URE value for nickel 

compounds in a manner consistent with EPA guidelines and utilizing 

a five-person peer review process (overseen by TERA) that is even 

more elaborate than the one used by EPA. A second peer review 

took place just recently when the authors of the TCEQ Nickel 

Documentation published a journal article based on their work in 

developing the URE.

• The URE values developed by the TCEQ are 1.6 x 10-4 per μg/m3

based on a comparison to overall U.S. mortality and survival rates 

and 1.7 x 10-4 per μg/m3 based on a comparison to Texas-specific 

mortality and survival rates. 
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TCEQ URE (continued)

• The TCEQ’s URE value has a sounder scientific 

grounding than EPA’s IRIS value for a number of 

reasons:

– In developing URE values, the TCEQ corrected certain 

methodology/calculation errors that EPA had made.

– The TCEQ performed more refined and sophisticated modeling 

than EPA did in 1985.

– The TCEQ used additional and updated data from the last 25 

years that were not available to EPA in 1985.

– The TCEQ emphasized refinery studies where the mix of nickel 

compounds more closely matches the mix of nickel compounds 

in FP emissions and in ambient air generally.

– The TCEQ’s work has undergone two rounds of peer review 

that, in combination, must certainly have been as searching and 

careful as the peer review to which EPA’s risk assessment was 

subjected in 1985.
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TCEQ URE (continued)

• In recognition of the foregoing points, peer reviewers 

selected by EPA recently endorsed use of the TCEQ 

URE values to assess cancer risks associated with 

emissions of nickel compounds to the ambient air.

• As EPA pointed out, “two reviewers suggested using the 

URE derived by the TCEQ for all Ni compounds as a 

group, rather than the one derived by the Integrated Risk 

Information System (IRIS, 1991) specifically for Ni 

subsulfide. The third reviewer did not comment on an 

alternative approach.” 77 Fed. Reg. at 9318 (Feb. 16, 

2012).
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The TCEQ URE Value Is 

Conservative

• The TCEQ’s URE value was derived using a linear, non-threshold 

multiplicative relative risk model as a conservative default 

assumption.

– But both mechanistic data and results of epidemiological and animal 

studies indicate that nickel-related carcinogenicity has an actual or 

practical threshold, a point recently accepted by the EU’s Scientific 

Committee on Occupational Exposure Limits.

• The TCEQ’s URE value assumes all nickel compounds are 

carcinogenic and that a single URE (derived from studies of workers 

whose nickel exposures contained a significant Ni3S2 component) 

can be applied to total nickel compounds as a group.

– But it is widely accepted that different nickel compounds have different 

carcinogenic potential and potencies – with nickel subsulfide being the 

most potent. 

– A recent paper by B. Conard & S. Seilkop calculates that the 

carcinogenic potency of nickel subsulfide is at least 5.6 times as great 

as that of nickel oxide.
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TCEQ Conservatism (continued)

• The TCEQ’s URE value is based on studies of sulfide nickel matte 

refinery workers for whom nickel subsulfide constituted a high 

percentage of total nickel exposure (50% by EPA’s somewhat 

arbitrary estimate; 82% by a more careful analysis cited in a recent 

paper by B. Conard & S. Seilkop).

– By contrast, nickel subsulfide is no more than a minor component of 

total nickel emissions from FP facilities, if it is present at all. For 

example, a 2009 paper by D. Sivulka & S. Seilkop calculated that 

occupational nickel exposures at a high nickel alloy manufacturing 

facility in the U.S. were 85% oxidic nickel and 7% metallic nickel, with 

essentially no sulfidic nickel being present.

– And the TCEQ itself cautioned that there is a significant difference in 

nickel subsulfide exposure between the cohort workers used to derive 

the URE and environmental exposures of the general population, thus 

driving its URE to overestimate risks.
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Conclusion

• The URE value derived by the TCEQ based on overall 

U.S. mortality and survival rates (1.6 x 10-4 per μg/m3) 

should be used in the residual risk assessment for the 

Ferroalloys Production NESHAP and in other instances 

where EPA assesses respiratory cancer risk associated 

with exposure to nickel compounds in the ambient air.

• This change would not alter EPA’s tentative finding that 

residual risk under the Ferroalloys Production MACT 

scenario is unacceptable. But it would correct the 

problem in EPA’s current approach and would ensure 

that EPA’s nickel risk assessment is based on the latest 

available sound science.