Occupational Exposure to Hexavalent Chromium, 10100-10385 [06-1589]

Agencies

• DEPARTMENT OF LABOR
• Occupational Safety and Health Administration

[Federal Register Volume 71, Number 39 (Tuesday, February 28, 2006)]
[Rules and Regulations]
[Pages 10100-10385]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-1589]



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Part II





Department of Labor





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Occupational Safety and Health Administration



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29 CFR Parts 1910, 1915, et al.



Occupational Exposure to Hexavalent Chromium; Final Rule

Federal Register / Vol. 71, No. 39 / Tuesday, February 28, 2006 / 
Rules and Regulations

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DEPARTMENT OF LABOR

Occupational Safety and Health Administration

29 CFR Parts 1910, 1915, 1917, 1918, and 1926

[Docket No. H054A]
RIN 1218-AB45


Occupational Exposure to Hexavalent Chromium

AGENCY: Occupational Safety and Health Administration (OSHA), 
Department of Labor.

ACTION: Final rule.

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SUMMARY: The Occupational Safety and Health Administration (OSHA) is 
amending the existing standard which limits occupational exposure to 
hexavalent chromium (Cr(VI)). OSHA has determined based upon the best 
evidence currently available that at the current permissible exposure 
limit (PEL) for Cr(VI), workers face a significant risk to material 
impairment of their health. The evidence in the record for this 
rulemaking indicates that workers exposed to Cr(VI) are at an increased 
risk of developing lung cancer. The record also indicates that 
occupational exposure to Cr(VI) may result in asthma, and damage to the 
nasal epithelia and skin.
    The final rule establishes an 8-hour time-weighted average (TWA) 
exposure limit of 5 micrograms of Cr(VI) per cubic meter of air (5 
[mu]g/m\3\). This is a considerable reduction from the previous PEL of 
1 milligram per 10 cubic meters of air (1 mg/10 m\3\, or 100 [mu]g/
m\3\) reported as CrO3, which is equivalent to a limit of 52 
[mu]g/m\3\ as Cr(VI). The final rule also contains ancillary provisions 
for worker protection such as requirements for exposure determination, 
preferred exposure control methods, including a compliance alternative 
for a small sector for which the new PEL is infeasible, respiratory 
protection, protective clothing and equipment, hygiene areas and 
practices, medical surveillance, recordkeeping, and start-up dates that 
include four years for the implementation of engineering controls to 
meet the PEL.
    The final standard separately regulates general industry, 
construction, and shipyards in order to tailor requirements to the 
unique circumstances found in each of these sectors.
    The PEL established by this rule reduces the significant risk posed 
to workers by occupational exposure to Cr(VI) to the maximum extent 
that is technologically and economically feasible.

DATES: This final rule becomes effective on May 30, 2006. Start-up 
dates for specific provisions are set in Sec.  1910.1026(n) for general 
industry; Sec.  1915.1026(l) for shipyards; and Sec.  1926.1126(l) for 
construction. However, affected parties do not have to comply with the 
information collection requirements in the final rule until the 
Department of Labor publishes in the Federal Register the control 
numbers assigned by the Office of Management and Budget (OMB). 
Publication of the control numbers notifies the public that OMB has 
approved these information collection requirements under the Paperwork 
Reduction Act of 1995.

ADDRESSES: In compliance with 28 U.S.C. 2112(a), the Agency designates 
the Associate Solicitor for Occupational Safety and Health, Office of 
the Solicitor, Room S-4004, U.S. Department of Labor, 200 Constitution 
Avenue, NW., Washington, DC 20210, as the recipient of petitions for 
review of these standards.

FOR FURTHER INFORMATION CONTACT: Mr. Kevin Ropp, Director, OSHA Office 
of Communications, Room N-3647, U.S. Department of Labor, 200 
Constitution Avenue, NW., Washington, DC 20210; telephone (202) 693-
1999.

SUPPLEMENTARY INFORMATION: The following table of contents lays out the 
structure of the preamble to the final standards. This preamble 
contains a detailed description of OSHA's legal obligations, the 
analyses and rationale supporting the Agency's determination, including 
a summary of and response to comments and data submitted during the 
rulemaking.

I. General
II. Pertinent Legal Authority
III. Events Leading to the Final Standard
IV. Chemical Properties and Industrial Uses
V. Health Effects
    A. Absorption, Distribution, Metabolic Reduction and Elimination
    1. Deposition and Clearance of Inhaled Cr(VI) From the 
Respiratory Tract
    2. Absorption of Inhaled Cr(VI) Into the Bloodstream
    3. Dermal Absorption of Cr(VI)
    4. Absorption of Cr(VI) by the Oral Route
    5. Distribution of Cr(VI) in the Body
    6. Metabolic Reduction of Cr(VI)
    7. Elimination of Cr(VI) From the Body
    8. Physiologically-Based Pharmacokinetic Modeling
    9. Summary
    B. Carcinogenic Effects
    1. Evidence From Chromate Production Workers
    2. Evidence From Chromate Pigment Production Workers
    3. Evidence From Workers in Chromium Plating
    4. Evidence From Stainless Steel Welders
    5. Evidence From Ferrochromium Workers
    6. Evidence From Workers in Other Industry Sectors
    7. Evidence From Experimental Animal Studies
    8. Mechanistic Considerations
    C. Non-Cancer Respiratory Effects
    1. Nasal Irritation, Nasal Tissue Ulcerations and Nasal Septum 
Perforations
    2. Occupational Asthma
    3. Bronchitis
    4. Summary
    D. Dermal Effects
    E. Other Health Effects
VI. Quantitative Risk Assessment
    A. Introduction
    B. Study Selection
    1. Gibb Cohort
    2. Luippold Cohort
    3. Mancuso Cohort
    4. Hayes Cohort
    5. Gerin Cohort
    6. Alexander Cohort
    7. Studies Selected for the Quantitative Risk Assessment
    C. Quantitative Risk Assessments Based on the Gibb Cohort
    1. Environ Risk Assessments
    2. National Institute for Occupational Safety and Health (NIOSH) 
Risk Assessment
    3. Exponent Risk Assessment
    4. Summary of Risk Assessments Based on the Gibb Cohort
    D. Quantitative Risk Assessments Based on the Luippold Cohort
    E. Quantitative Risk Assessments Based on the Mancuso, Hayes, 
Gerin, and Alexander Cohorts
    1. Mancuso Cohort
    2. Hayes Cohort
    3. Gerin Cohort
    4. Alexander Cohort
    F. Summary of Risk Estimates Based on Gibb, Luippold, and 
Additional Cohorts
    G. Issues and Uncertainties
    1. Uncertainty With Regard to Worker Exposure to Cr(VI)
    2. Model Uncertainty, Exposure Threshold, and Dose Rate Effects
    3. Influence of Smoking, Race, and the Healthy Worker Survivor 
Effect
    4. Suitability of Risk Estimates for Cr(VI) Exposures in Other 
Industries
    H. Conclusions
VII. Significance of Risk
    A. Material Impairment of Health
    1. Lung Cancer
    2. Non-Cancer Impairments
    B. Risk Assessment
    1. Lung Cancer Risk Based on the Gibb Cohort
    2. Lung Cancer Risk Based on the Luippold Cohort
    3. Risk of Non-Cancer Impairments
    C. Significance of Risk and Risk Reduction
VIII. Summary of the Final Economic Analysis and Regulatory 
Flexibility Analysis
IX. OMB Review Under the Paperwork Reduction Act of 1995
X. Federalism
XI. State Plans

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XII. Unfunded Mandates
XIII. Protecting Children from Environmental Health and Safety Risks
XIV. Environmental Impacts
XV. Summary and Explanation of the Standards
    (a) Scope
    (b) Definitions
    (c) Permissible Exposure Limit (PEL)
    (d) Exposure Determination
    (e) Regulated Areas
    (f) Methods of Compliance
    (g) Respiratory Protection
    (h) Protective Work Clothing and Equipment
    (i) Hygiene Areas and Practices
    (j) Housekeeping
    (k) Medical Surveillance
    (l) Communication of Chromium (VI) Hazards to Employees
    (m) Recordkeeping
    (n) Dates
XVI. Authority and Signature
XVII. Final Standards

I. General

    This final rule establishes a permissible exposure limit (PEL) of 5 
micrograms of Cr(VI) per cubic meter of air (5 [mu]g/m\3\) as an 8-hour 
time-weighted average for all Cr(VI) compounds. After consideration of 
all comments and evidence submitted during this rulemaking, OSHA has 
made a final determination that a PEL of 5 [mu]g/m\3\ is necessary to 
reduce the significant health risks posed by occupational exposures to 
Cr(VI); it is the lowest level that is technologically and economically 
feasible for industries impacted by this rule. A full explanation of 
OSHA's rationale for establishing this PEL is presented in the 
following preamble sections: V (Health Effects), VI (Quantitative Risk 
Assessment), VII (Significance of Risk), VIII (Summary of the Final 
Economic Analysis and Regulatory Flexibility Analysis), and XV (Summary 
and Explanation of the Standard, paragraph (c), Permissible Exposure 
Limit).
    OSHA is establishing three separate standards covering occupational 
exposures to Cr(VI) for: general industry (29 CFR 1910.1026); shipyards 
(29 CFR 1915.1026), and construction (29 CFR 1926.1126). In addition to 
the PEL, these three standards include ancillary provisions for 
exposure determination, methods of compliance, respiratory protection, 
protective work clothing and equipment, hygiene areas and practices, 
medical surveillance, communication of Cr(VI) hazards to employees, 
recordkeeping, and compliance dates. The general industry standard has 
additional provisions for regulated areas and housekeeping. The Summary 
and Explanation section of this preamble (Section XV, paragraphs (d) 
through (n)) includes a full discussion of the basis for including 
these provisions in the final standards.
    Several major changes were made to the October 4, 2004 proposed 
rule as a result of OSHA's analysis of comments and data received 
during the comment periods and public hearings. The major changes are 
summarized below and are fully discussed in the Summary and Explanation 
section of this preamble (Section XV)
    Scope. As proposed, the standards apply to occupational exposures 
to Cr(VI) in all forms and compounds with limited exceptions. OSHA has 
made a final determination to exclude from coverage of these final 
standards exposures that occur in the application of pesticides 
containing Cr(VI) (e.g., the treatment of wood with preservatives). 
These exposures are already covered by the Environmental Protection 
Agency. OSHA is also excluding exposures to portland cement and 
exposures in work settings where the employer has objective data 
demonstrating that a material containing chromium or a specific 
process, operation, or activity involving chromium cannot release 
dusts, fumes, or mists of Cr(VI) in concentrations at or above 0.5 
[mu]g/m\3\ under any expected conditions of use. OSHA believes that the 
weight of evidence in this rulemaking demonstrates that the primary 
risk in these two exposure scenarios can be effectively addressed 
through existing OSHA standards for personal protective equipment, 
hygiene, hazard communication and the PELs for portland cement or 
particulates not otherwise regulated (PNOR).
    Permissible Exposure Limit. OSHA proposed a PEL of 1 [mu]g/m\3\ but 
has now determined that a PEL 5 [mu]g/m\3\ is the lowest level that is 
technologically and economically feasible.
    Exposure Determination. OSHA did not include a provision for 
exposure determination in the proposed shipyard and construction 
standards, reasoning that the obligation to meet the proposed PEL would 
implicitly necessitate performance-based monitoring by the employer to 
ensure compliance with the PEL. However, OSHA was convinced by 
arguments presented during the rulemaking that an explicit requirement 
for exposure determination is necessary to ensure that employee 
exposures are adequately characterized. Therefore OSHA has included a 
provision for exposure determination for general industry, shipyards 
and construction in the final rule. In order to provide additional 
flexibility in characterizing employee exposures, OSHA is allowing 
employers to choose between a scheduled monitoring option and a 
performance-based option for making exposure determinations.
    Methods of Compliance. Under the proposed rule employers were to 
use engineering and work practice controls to achieve the proposed PEL 
unless the employer could demonstrate such controls are not feasible. 
In the final rule, OSHA has retained this exception but has added a 
provision that only requires employers to use engineering and work 
practice controls to reduce or maintain employee exposures to 25 [mu]g/
m\3\ when painting aircraft or large aircraft parts in the aerospace 
industry to the extent such controls are feasible. The employer must 
then supplement those engineering controls with respiratory protection 
to achieve the PEL. As discussed more fully in the Summary of the Final 
Economic Analysis and Regulatory Flexibility Analysis (Section VIII) 
and the Summary and Explanation (Section XV) OSHA has determined that 
this is the lowest level achievable through the use of engineering and 
work practice controls alone for these limited operations.
    Housekeeping. In the proposed rule, cleaning methods such as 
shoveling, sweeping, and brushing were prohibited unless they were the 
only effective means available to clean surfaces contaminated with 
Cr(VI). The final standard has modified this prohibition to make clear 
only dry shoveling, sweeping and brushing are prohibited so that 
effective wet shoveling, sweeping, and brushing would be allowed. OSHA 
is also adding a provision that allows the use of compressed air to 
remove Cr(VI) when no alternative method is feasible.
    Medical Surveillance. As proposed and continued in these final 
standards, medical surveillance is required to be provided to employees 
experiencing signs or symptoms of the adverse health effects associated 
with Cr(VI) exposure or exposed in an emergency. In addition, for 
general industry, employees exposed above the PEL for 30 or more days a 
year were to be provided medical surveillance. In the final standard, 
OSHA has changed the trigger for medical surveillance to exposure above 
the action level (instead of the PEL) for 30 days a year to take into 
account the existing risks at the new PEL. This provision has also been 
extended to the standards for shipyards and construction since those 
employers now will be required to perform an exposure determination and 
thus will be able to determine which employees are exposed above the 
action level 30 or more days a year.

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    Communication of Hazards. In the proposed standard, OSHA specified 
the sign for the demarcation of regulated areas in general industry and 
the label for contaminated work clothing or equipment and Cr(VI) 
contaminated waste and debris. The proposed standard also listed the 
various elements to be covered for employee training. In order to 
simplify requirements under this section of the final standard and 
reduce confusion between this standard and the Hazard Communication 
Standard, OSHA has removed the requirement for special signs and labels 
and the specification of employee training elements. Instead, the final 
standard requires that signs, labels and training be in accordance with 
the Hazard Communication Standard (29 CFR 1910.1200). The only 
additional training elements required in the final rule are those 
related specifically to the contents of the final Cr(VI) standards. 
While the final standards have removed language in the communication of 
hazards provisions to make them more consistent with OSHA's existing 
Hazard Communication Standard, the employers obligation to mark 
regulated areas (where regulated areas are required), to label Cr(VI) 
contaminated clothing and wastes, and to train on the hazards of Cr(VI) 
have not changed.
    Recordkeeping. In the proposed standards for shipyards and 
construction there were no recordkeeping requirements for exposure 
records since there was not a requirement for exposure determination. 
The final standard now requires exposure determination for shipyards 
and construction and therefore, OSHA has also added provisions for 
exposure records to be maintained in these final standards. In keeping 
with its intent to be consistent with the Hazard Communication 
Standard, OSHA has removed the requirement for training records in the 
final standards.
    Dates. In the proposed standard, the effective date of the standard 
was 60 days after the publication date; the start-up date for all 
provisions except engineering controls was 90 days after the effective 
date; and the start-up date for engineering controls was two years 
after the effective date. OSHA believes that it is appropriate to allow 
additional time for employers, particularly small employers, to meet 
the requirements of the final rule. The effective and start-up dates 
have been extended as follows: the effective date for the final rule is 
changed to 90 days after the publication date; the start-up date for 
all provisions except engineering controls is changed to 180 days after 
the effective date for employers with 20 or more employees; the start-
up date for all provisions except engineering controls is changed to 
one year after the effective date for employers with 19 or fewer 
employees; and the start-up date for engineering controls is changed to 
four years after the effective date for all employers.

II. Pertinent Legal Authority

    The purpose of the Occupational Safety and Health Act, 29 U.S.C. 
651 et seq. (``the Act'') is to,

* * * assure so far as possible every working man and woman in the 
nation safe and healthful working conditions and to preserve our 
human resources. 29 U.S.C. 651(b).

    To achieve this goal Congress authorized the Secretary of Labor 
(the Secretary) to promulgate and enforce occupational safety and 
health standards. 29 U.S.C. 654(b) (requiring employers to comply with 
OSHA standards), 655(a) (authorizing summary adoption of existing 
consensus and federal standards within two years of the Act's 
enactment), and 655(b) (authorizing promulgation, modification or 
revocation of standards pursuant to notice and comment).
    The Act provides that in promulgating health standards dealing with 
toxic materials or harmful physical agents, such as this standard 
regulating occupational exposure to Cr(VI), the Secretary,

* * * shall set the standard which most adequately assures, to the 
extent feasible, on the basis of the best available evidence that no 
employee will suffer material impairment of health or functional 
capacity even if such employee has regular exposure to the hazard 
dealt with by such standard for the period of his working life. 29 
U.S.C. Sec.  655(b)(5).

    The Supreme Court has held that before the Secretary can promulgate 
any permanent health or safety standard, she must make a threshold 
finding that significant risk is present and that such risk can be 
eliminated or lessened by a change in practices. Industrial Union 
Dept., AFL-CIO v. American Petroleum Institute, 448 U.S. 607, 641-42 
(1980) (plurality opinion) (``The Benzene case''). The Court further 
observed that what constitutes ``significant risk'' is ``not a 
mathematical straitjacket'' and must be ``based largely on policy 
considerations.'' The Benzene case, 448 U.S. at 655. The Court gave the 
example that if,

* * * the odds are one in a billion that a person will die from 
cancer * * * the risk clearly could not be considered significant. 
On the other hand, if the odds are one in one thousand that regular 
inhalation of gasoline vapors that are 2% benzene will be fatal, a 
reasonable person might well consider the risk significant. * * * 
Id.

    OSHA standards must be both technologically and economically 
feasible. United Steelworkers v. Marshall, 647 F.2d 1189, 1264 (D.C. 
Cir. 1980) (``The Lead I case''). The Supreme Court has defined 
feasibility as ``capable of being done.'' American Textile Mfrs. Inst. 
v. Donovan, 425 U.S. 490, 509 (1981) (``The Cotton dust case''). The 
courts have further clarified that a standard is technologically 
feasible if OSHA proves a reasonable possibility,

* * * within the limits of the best available evidence * * * that 
the typical firm will be able to develop and install engineering and 
work practice controls that can meet the PEL in most of its 
operations. See The Lead I case, 647 F.2d at 1272.

    With respect to economic feasibility, the courts have held that a 
standard is feasible if it does not threaten massive dislocation to or 
imperil the existence of the industry. See The Lead case, 647 F.2d at 
1265. A court must examine the cost of compliance with an OSHA standard 
``in relation to the financial health and profitability of the industry 
and the likely effect of such costs on unit consumer prices.'' Id.

    [The] practical question is whether the standard threatens the 
competitive stability of an industry, * * * or whether any intra-
industry or inter-industry discrimination in the standard might 
wreck such stability or lead to undue concentration. Id. (citing 
Industrial Union Dept., AFL-CIO v. Hodgson, 499 F.2d 467 (D.C. Cir. 
1974)).

    The courts have further observed that granting companies reasonable 
time to comply with new PEL's may enhance economic feasibility. Id. 
While a standard must be economically feasible, the Supreme Court has 
held that a cost-benefit analysis of health standards is not required 
by the Act because a feasibility analysis is. The Cotton dust case, 453 
U.S. at 509. Finally, unlike safety standards, health standards must 
eliminate risk or reduce it to the maximum extent that is 
technologically and economically feasible. See International Union, 
United Automobile, Aerospace & Agricultural Implement Workers of 
America, UAW v. OSHA, 938 F.2d 1310, 1313 (D.C. Cir. 1991); Control of 
Hazardous Energy Sources (Lockout/Tagout), Final rule; supplemental 
statement of reasons, (58 FR 16612, March 30, 1993).

III. Events Leading to the Final Standard

    OSHA's previous standards for workplace exposure to Cr(VI) were 
adopted in 1971, pursuant to section 6(a) of the Act, from a 1943 
American National Standards Institute (ANSI) recommendation originally 
established to control irritation and damage to nasal

[[Page 10103]]

tissues (36 FR at 10466, 5/29/71; Ex. 20-3). OSHA's general industry 
standard set a permissible exposure limit (PEL) of 1 mg chromium 
trioxide per 10 m\3\ air in the workplace (1 mg/10 m\3\ 
CrO3) as a ceiling concentration, which corresponds to a 
concentration of 52 [mu]g/m\3\ Cr(VI). A separate rule promulgated for 
the construction industry set an eight-hour time-weighted-average PEL 
of 1 mg/10 m3 CrO3, also equivalent to 52 [mu]g/
m\3\ Cr(VI), adopted from the American Conference of Governmental 
Industrial Hygienists (ACGIH) 1970 Threshold Limit Value (TLV) (36 FR 
at 7340, 4/17/71).
    Following the ANSI standard of 1943, other occupational and public 
health organizations evaluated Cr(VI) as a workplace and environmental 
hazard and formulated recommendations to control exposure. The ACGIH 
first recommended control of workplace exposures to chromium in 1946, 
recommending a time-weighted average Maximum Allowable Concentration 
(later called a Threshold Limit Value) of 100 [mu]g/m\3\ for chromic 
acid and chromates as Cr2O3 (Ex. 5-37), and later 
classified certain Cr(VI) compounds as class A1 (confirmed human) 
carcinogens in 1974. In 1975, the NIOSH Criteria for a Recommended 
Standard recommended that occupational exposure to Cr(VI) compounds 
should be limited to a 10-hour TWA of 1 [mu]g/m\3\, except for some 
forms of Cr(VI) then believed to be noncarcinogenic (Ex. 3-92). The 
National Toxicology Program's First Annual Report on Carcinogens 
identified calcium chromate, chromium chromate, strontium chromate, and 
zinc chromate as carcinogens in 1980 (Ex. 35-157).
    During the 1980s, regulatory and standards organizations came to 
recognize Cr(VI) compounds in general as carcinogens. The Environmental 
Protection Agency (EPA) Health Assessment Document of 1984 stated that,

* * * using the IARC [International Agency for Research on Cancer] 
classification scheme, the level of evidence available for the 
combined animal and human data would place hexavalent chromium (Cr 
VI) compounds into Group 1, meaning that there is decisive evidence 
for the carcinogenicity of those compounds in humans (Ex. 19-1, p. 
7-107).

    In 1988 IARC evaluated the available evidence regarding Cr(VI) 
carcinogenicity, concluding in 1990 that

* * * [t]here is sufficient evidence in humans for the 
carcinogenicity of chromium[VI] compounds as encountered in the 
chromate production, chromate pigment production and chromium 
plating industries, [and] sufficient evidence in experimental 
animals for the carcinogenicity of calcium chromate, zinc chromates, 
strontium chromate and lead chromates (Ex. 18-3, p. 213).

    In September 1988, NIOSH advised OSHA to consider all Cr(VI) 
compounds as potential occupational carcinogens (Ex. 31-22-22). ACGIH 
now classifies water-insoluble and water-soluble Cr(IV) compounds as 
class A1 carcinogens (Ex. 35-207). Current ACGIH standards include 
specific 8-hour time-weighted average TLVs for calcium chromate (1 
[mu]g/m3), lead chromate (12 [mu]g/m3), strontium 
chromate (0.5 [mu]g/m3), and zinc chromates (10 [mu]g/
m3), and generic TLVs for water soluble (50 [mu]g/
m3) and insoluble (10 [mu]g/m3) forms of 
hexavalent chromium not otherwise classified, all measured as chromium 
(Ex. 35-207).
    In July 1993, OSHA was petitioned for an emergency temporary 
standard to reduce occupational exposures to Cr(VI) compounds (Ex. 1). 
The Oil, Chemical, and Atomic Workers International Union (OCAW) and 
Public Citizen's Health Research Group (Public Citizen), citing 
evidence that occupational exposure to Cr(VI) increases workers' risk 
of lung cancer, petitioned OSHA to promulgate an emergency temporary 
standard to lower the PEL for Cr(VI) compounds to 0.5 [mu]g/
m3 as an eight-hour time-weighted average (TWA). Upon review 
of the petition, OSHA agreed that there was evidence of increased 
cancer risk from exposure to Cr(VI) at the existing PEL, but found that 
the available data did not show the ``grave danger'' required to 
support an emergency temporary standard (Ex. 1-C). The Agency therefore 
denied the request for an emergency temporary standard, but initiated 
Section 6(b)(5) rulemaking and began performing preliminary analyses 
relevant to the rule.
    In 1997, Public Citizen petitioned the United States Court of 
Appeals for the Third Circuit to compel OSHA to complete rulemaking 
lowering the standard for occupational exposure to Cr(VI). The Court 
denied Public Citizen's request, concluding that there was no 
unreasonable delay and dismissed the suit. Oil, Chemical and Atomic 
Workers Union and Public Citizen Health Research Group v. OSHA, 145 
F.3d 120 (3rd Cir. 1998). Afterwards, the Agency continued its data 
collection and analytic efforts on Cr(VI) (Ex. 35-208, p. 3). In 2002, 
Public Citizen again petitioned the Court to compel OSHA to commence 
rulemaking to lower the Cr(VI) standard (Ex. 31-24-1). Meanwhile on 
August 22, 2002, OSHA published a Request for Information on Cr(VI) to 
solicit additional information on key issues related to controlling 
exposures to Cr(VI) (FR 67 at 54389), and on December 4, 2002 announced 
its intent to proceed with developing a proposed standard (Ex. 35-306). 
On December 24, 2002, the Court granted Public Citizen's petition, and 
ordered the Agency to proceed expeditiously with a Cr(VI) standard. See 
Public Citizen Health Research Group v. Chao, 314 F.3d 143 (3rd Cir. 
2002)). In a subsequent order, the Court established a compressed 
schedule for completion of the rulemaking, with deadlines of October 4, 
2004 for publication of a proposed standard and January 18, 2006 for 
publication of a final standard (Ex. 35-304).
    In 2003, as required by the Small Business Regulatory Enforcement 
Act (SBREFA), OSHA initiated SBREFA proceedings, seeking the advice of 
small business representatives on the proposed rule. The SBREFA panel, 
including representatives from OSHA, the Small Business Administration 
(SBA), and the Office of Management and Budget (OMB), was convened on 
December 23, 2003. The panel conferred with representatives from small 
entities in chemical, alloy, and pigment manufacturing, electroplating, 
welding, aerospace, concrete, shipbuilding, masonry, and construction 
on March 16-17, 2004, and delivered its final report to OSHA on April 
20, 2004. The Panel's report, including comments from the small entity 
representatives (SERS) and recommendations to OSHA for the proposed 
rule, is available in the Cr(VI) rulemaking docket (Ex. 34). The SBREFA 
Panel made recommendations on a variety of subjects. The most important 
recommendations with respect to alternatives that OSHA should consider 
included: A higher PEL than the PEL of 1; excluding cement from the 
scope of the standard; the use of SECALs for some industries; different 
PELS for different Hexavalent chromium compounds; a multi-year phase-in 
to the standards; and further consideration to approaches suited to the 
special conditions of the maritime and construction industries. OSHA 
has adapted many of these recommendations: The PEL is now 5; cement has 
been excluded from the scope of the standard; a compliance alternative, 
similar to a SECAL, has been used in aerospace industry; the standard 
allows four years to phase in engineering controls; and a new 
performance based monitoring approach for all industries, among other 
changes, all of which should make it easier for all

[[Page 10104]]

industries with changing work place conditions to meet the standard in 
a cost effective way. A full discussion of all of the recommendations, 
and OSHA's responses to them, is provided in Section VIII of this 
Preamble.
    In addition to undertaking SBREFA proceedings, in early 2004, OSHA 
provided the Advisory Committee on Construction Safety and Health 
(ACCSH) and the Maritime Advisory Committee on Occupational Safety and 
Health (MACOSH) with copies of the draft proposed rule for review. OSHA 
representatives met with ACCSH in February 2004 and May 2004 to discuss 
the rulemaking and receive their comments and recommendations. On 
February 13, 2004, ACCSH recommended that portland cement should be 
included within the scope of the proposed standard (Ex. 35-307, pp. 
288-293) and that identical PELs should be set for construction, 
maritime, and general industry (Ex. 35-307, pp. 293-297). On May 18, 
2004, ACCSH recommended that the construction industry should be 
included in the current rulemaking, and affirmed its earlier 
recommendation regarding portland cement. OSHA representatives met with 
MACOSH in March 2004. On March 3, 2004, MACOSH collected and forwarded 
additional exposure monitoring data to OSHA to help the Agency better 
evaluate exposures to Cr(VI) in shipyards (Ex. 35-309, p. 208). MACOSH 
also recommended a separate Cr(VI) standard for the maritime industry, 
arguing that maritime involves different exposures and requires 
different means of exposure control than general industry and 
construction (Ex. 35-309, p. 227).
    In accordance with the Court's rulemaking schedule, OSHA published 
the proposed standard for hexavalent chromium on October 4, 2004 (69 FR 
at 59306). The proposal included a notice of public hearing in 
Washington, DC (69 FR at 59306, 59445-59446). The notice also invited 
interested persons to submit comments on the proposal until January 3, 
2005. In the proposal, OSHA solicited public input on 65 issues 
regarding the human health risks of Cr(VI) exposure, the impact of the 
proposed rule on Cr(VI) users, and other issues of particular interest 
to the Agency (69 FR at 59306-59312).
    OSHA convened the public hearing on February 1, 2005, with 
Administrative Law Judges John M. Vittone and Thomas M. Burke 
presiding. At the conclusion of the hearing on February 15, 2005, Judge 
Burke set a deadline of March 21, 2005, for the submission of post 
hearing comments, additional information and data relevant to the 
rulemaking, and a deadline of April 20, 2005, for the submission of 
additional written comments, arguments, summations, and briefs. A wide 
range of employees, employers, union representatives, trade 
associations, government agencies and other interested parties 
participated in the public hearing or contributed written comments. 
Issues raised in their comments and testimony are addressed in the 
relevant sections of this preamble (e.g., comments on the risk 
assessment are discussed in section VI; comments on the benefits 
analysis in section VIII). On December 22, 2005, OSHA filed a motion 
with the U.S. Court of Appeals for the Third Circuit requesting an 
extension of the court-mandated deadline for the publication of the 
final rule by six weeks, to February 28, 2006 (Ex. 48-13). The Court 
granted the request on January 17, 2006 (Ex. 48-15).
    As mandated by the Act, the final standard on occupational exposure 
to hexavalent chromium is based on careful consideration of the entire 
record of this proceeding, including materials discussed or relied upon 
in the proposal, the record of the hearing, and all written comments 
and exhibits received.
    OSHA has developed separate final standards for general industry, 
shipyards, and the construction industry. The Agency has concluded that 
excess exposure to Cr(VI) in any form poses a significant risk of 
material impairment to the health of workers, by causing or 
contributing to adverse health effects including lung cancer, non-
cancer respiratory effects, and dermal effects. OSHA determined that 
the TWA PEL should not be set above 5 [mu]g/m3 based on the 
evidence in the record and its own quantitative risk assessment. The 
TWA PEL of 5 [mu]g/m3 reduces the significant risk posed to 
workers by occupational exposure to Cr(VI) to the maximum extent that 
is technologically and economically feasible. (See discussion of the 
PEL in Section XV below.)

IV. Chemical Properties and Industrial Uses

    Chromium is a metal that exists in several oxidation or valence 
states, ranging from chromium (-II) to chromium (+VI). The elemental 
valence state, chromium (0), does not occur in nature. Chromium 
compounds are very stable in the trivalent state and occur naturally in 
this state in ores such as ferrochromite, or chromite ore 
(FeCr2O4). The hexavalent, Cr(VI) or chromate, is 
the second most stable state. It rarely occurs naturally; most Cr(VI) 
compounds are man made.
    Chromium compounds in higher valence states are able to undergo 
``reduction'' to lower valence states; chromium compounds in lower 
valence states are able to undergo ``oxidation'' to higher valence 
states. Thus, Cr(VI) compounds can be reduced to Cr(III) in the 
presence of oxidizable organic matter. Chromium can also be reduced in 
the presence of inorganic chemicals such as iron.
    Chromium does exist in less stable oxidation (valence) states such 
as Cr(II), Cr(IV), and Cr(V). Anhydrous Cr(II) salts are relatively 
stable, but the divalent state (II, or chromous) is generally 
relatively unstable and is readily oxidized to the trivalent (III or 
chromic) state. Compounds in valence states such as (IV) and (V) 
usually require special handling procedures as a result of their 
instability. Cr(IV) oxide (CrO2) is used in magnetic 
recording and storage devices, but very few other Cr(IV) compounds have 
industrial use. Evidence exists that both Cr(IV) and Cr(V) are formed 
as transient intermediates in the reduction of Cr(VI) to Cr(III) in the 
body.
    Chromium (III) is also an essential nutrient that plays a role in 
glucose, fat, and protein metabolism by causing the action of insulin 
to be more effective. Chromium picolinate, a trivalent form of chromium 
combined with picolinic acid, is used as a dietary supplement, because 
it is claimed to speed metabolism.
    Elemental chromium and the chromium compounds in their different 
valence states have various physical and chemical properties, including 
differing solubilities. Most chromium species are solid. Elemental 
chromium is a steel gray solid, with high melting and boiling points 
(1857 [deg]C and 2672 [deg]C, respectively), and is insoluble in water 
and common organic solvents. Chromium (III) chloride is a violet or 
purple solid, with high melting and sublimation points (1150 [deg]C and 
1300 [deg]C, respectively), and is slightly soluble in hot water and 
insoluble in common organic solvents. Ferrochromite is a brown-black 
solid; chromium (III) oxide is a green solid; and chromium (III) 
sulfate is a violet or red solid, insoluble in water and slightly 
soluble in ethanol. Chromium (III) picolinate is a ruby red crystal 
soluble in water (1 part per million at 25 [deg]C). Chromium (IV) oxide 
is a brown-black solid that decomposes at 300 [deg]C and is insoluble 
in water.
    Cr(VI) compounds have mostly lemon yellow to orange to dark red 
hues. They are typically crystalline, granular, or powdery although one 
compound (chromyl chloride) exists in liquid form. For example, chromyl 
chloride is a dark

[[Page 10105]]

red liquid that decomposes into chromate ion and hydrochloric acid in 
water. Chromic acids are dark red crystals that are very soluble in 
water. Other examples of soluble chromates are sodium chromate (yellow 
crystals) and sodium dichromate (reddish to bright orange crystals). 
Lead chromate oxide is typically a red crystalline powder. Zinc 
chromate is typically seen as lemon yellow crystals which decompose in 
hot water and are soluble in acids and liquid ammonia. Other chromates 
such as barium, calcium, lead, strontium, and zinc chromates vary in 
color from light yellow to greenish yellow to orange-yellow and exist 
in solid form as crystals or powder.
    The Color Pigments Manufacturers Association (CPMA) provided 
additional information on lead chromate and some other chromates used 
in their pigments (Ex. 38-205, pp. 12-13). CPMA describes two main lead 
chromate color groups: the chrome yellow pigments and the orange to red 
varieties known as molybdate orange pigments. The chrome yellow 
pigments are solid solution crystal compositions of lead chromate and 
lead sulfate. Molybdate orange pigments are solid solution crystal 
compositions of lead chromate, lead sulfate, and lead molybdate (Ex. 
38-205, p. 12). CPMA also describes a basic lead chromate called 
``chrome orange,'' and a lead chromate precipitated ``onto a core'' of 
silica (Ex. 38-205, p. 13).
    OSHA re-examined available information on solubility values in 
light of comments from the CPMA and Dominion Color Corporation (DCC) on 
qualitative solubility designations and CPMA's claim of low 
bioavailability of lead chromate due to its extremely low solubility 
(Exs. 38-201-1, p. 4; 38-205, p. 95). There was not always agreement or 
consistency with the qualitative assignments of solubilities. 
Quantitative values for the same compound also differ depending on the 
source of information.
    The Table IV-1 is the result of OSHA's re-examination of 
quantitative water solubility values and qualitative designations. 
Qualitative designations as well as quantitative values are listed as 
they were provided by the source. As can be seen by the Table IV-1, 
qualitative descriptions vary by the descriptive terminology chosen by 
the source.
BILLING CODE 4510-26-P

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[GRAPHIC] [TIFF OMITTED] TR28FE06.000


[[Page 10107]]


[GRAPHIC] [TIFF OMITTED] TR28FE06.001

BILLING CODE 4510-26-C
    OSHA has made some generalizations to describe the water 
solubilities of chromates in subsequent sections of this Federal 
Register notice. OSHA has divided Cr(VI) compounds and mixtures into 
three categories based on solubility values. Compounds and mixtures 
with water solubilities less than 0.01 g/l are referred to as water 
insoluble. Compounds and mixtures between 0.01 g/l and 500 g/l are 
referred to as slightly

[[Page 10108]]

soluble. Compounds and mixtures with water solubility values of 500 g/l 
or greater are referred to as highly water soluble. It should be noted 
that these boundaries for insoluble, slightly soluble, and highly 
soluble are arbitrary designations for the sake of further description 
elsewhere in this document. Quantitative values take precedence over 
qualitative designations. For example, zinc chromates would be slightly 
soluble where their solubility values exceed 0.01 g/l.
    Some major users of chromium are the metallurgical, refractory, and 
chemical industries. Chromium is used by the metallurgical industry to 
produce stainless steel, alloy steel, and nonferrous alloys. Chromium 
is alloyed with other metals and plated on metal and plastic substrates 
to improve corrosion resistance and provide protective coatings for 
automotive and equipment accessories. Welders use stainless steel 
welding rods when joining metal parts.
    Cr(VI) compounds are widely used in the chemical industry in 
pigments, metal plating, and chemical synthesis as ingredients and 
catalysts. Chromates are used as high quality pigments for textile 
dyes, paints, inks, glass, and plastics. Cr(VI) can be produced during 
welding operations even if the chromium was originally present in 
another valence state. While Cr(VI) is not intentionally added to 
portland cement, it is often present as an impurity.
    Occupational exposures to Cr(VI) can occur from inhalation of mists 
(e.g., chrome plating, painting), dusts (e.g., inorganic pigments), or 
fumes (e.g., stainless steel welding), and from dermal contact (e.g., 
cement workers).
    There are about thirty major industries and processes where Cr(VI) 
is used. These include producers of chromates and related chemicals 
from chromite ore, electroplating, welding, painting, chromate pigment 
production and use, steel mills, and iron and steel foundries. A 
detailed discussion of the uses of Cr(VI) in industry is found in 
Section VIII of this preamble.

V. Health Effects

    This section summarizes key studies of adverse health effects 
resulting from exposure to hexavalent chromium (Cr(VI)) in humans and 
experimental animals, as well as information on the fate of Cr(VI) in 
the body and laboratory research that relates to its toxic mode of 
action. The primary health impairments from workplace exposure to 
Cr(VI) are lung cancer, asthma, and damage to the nasal epithelia and 
skin. While this chapter on health effects does not describe all of the 
many studies that have been conducted on Cr(VI) toxicity, it includes a 
selection of those that are relevant to the rulemaking and 
representative of the scientific literature on Cr(VI) health effects.

A. Absorption, Distribution, Metabolic Reduction and Elimination

    Although chromium can exist in a number of different valence 
states, Cr(VI) is the form considered to be the greatest health risk. 
Cr(VI) enters the body by inhalation, ingestion, or absorption through 
the skin. For occupational exposure, the airways and skin are the 
primary routes of uptake. The following discussion summarizes key 
aspects of Cr(VI) uptake, distribution, metabolism, and elimination.

1. Deposition and Clearance of Inhaled Cr(VI) From the Respiratory 
Tract

    Various anatomical, physical and physiological factors determine 
both the fractional and regional deposition of inhaled particulate 
matter. Due to the airflow patterns in the lung, more particles tend to 
deposit at certain preferred regions in the lung. It is therefore 
possible to have a buildup of chromium at certain sites in the 
bronchial tree that could create areas of very high chromium 
concentration. A high degree of correspondence between the efficiency 
of particle deposition and the frequency of bronchial tumors at sites 
in the upper bronchial tree was reported in research by Schlesinger and 
Lippman that compared the distribution of cancer sites in published 
reports of primary bronchogenic tumors with experimentally determined 
particle deposition patterns (Ex. 35-102).
    Large inhaled particles (>5 [mu]m) are efficiently removed from the 
air-stream in the extrathoracic region (Ex. 35-175). Particles greater 
than 2.5 [mu]m are generally deposited in the tracheobronchial regions, 
whereas particles less than 2.5 [mu]m are generally deposited in the 
pulmonary region. Some larger particles (>2.5 [mu]m) can reach the 
pulmonary region. The mucociliary escalator predominantly clears 
particles that deposit in the extrathoracic and the tracheobronchial 
region of the lung. Individuals exposed to high particulate levels of 
Cr(VI) may also have altered respiratory mucociliary clearance. 
Particulates that reach the alveoli can be absorbed into the 
bloodstream or cleared by phagocytosis.
2. Absorption of Inhaled Cr(VI) Into the Bloodstream
    The absorption of inhaled chromium compounds depends on a number of 
factors, including physical and chemical properties of the particles 
(oxidation state, size, solubility) and the activity of alveolar 
macrophages (Ex. 35-41). The hexavalent chromate anions 
(CrO4)2- enter cells via facilitated diffusion 
through non-specific anion channels (similar to phosphate and sulfate 
anions). As demonstrated in research by Suzuki et al., a portion of 
water soluble Cr(VI) is rapidly transported to the bloodstream in rats 
(Ex. 35-97). Rats were exposed to 7.3-15.9 mg Cr(VI)/m\3\ as potassium 
dichromate for 2-6 hours. Following exposure to Cr(VI), the ratio of 
blood chromium/lung chromium was 1.440.30 at 0.5 hours, 
0.810.10 at 18 hours, 0.850.20 at 48 hours, and 
0.960.22 at 168 hours after exposure.
    Once the Cr(VI) particles reach the alveoli, absorption into the 
bloodstream is greatly dependent on solubility. More soluble chromates 
are absorbed faster than water insoluble chromates, while insoluble 
chromates are poorly absorbed and therefore have longer resident time 
in the lungs. This effect has been demonstrated in research by Bragt 
and van Dura on the kinetics of three Cr(VI) compounds: highly soluble 
sodium chromate, slightly soluble zinc chromate and water insoluble 
lead chromate (Ex. 35-56). They instilled \51\chromium-labeled 
compounds (0.38 mg Cr(VI)/kg as sodium chromate, 0.36 mg Cr(VI)/kg as 
zinc chromate, or 0.21 mg Cr(VI)/kg as lead chromate) intratracheally 
in rats. Peak blood levels of \51\chromium were reached after 30 
minutes for sodium chromate (0.35 [mu]g chromium/ml), and after 24 
hours for zinc chromate (0.60 [mu]g chromium/ml) and lead chromate 
(0.007 [mu]g chromium/ml). At 30 minutes after administration, the 
lungs contained 36, 25, and 81% of the respective dose of the sodium, 
zinc, and lead chromate. On day six, >80% of the dose of all three 
compounds had been cleared from the lungs, during which time the 
disappearance from lungs followed linear first-order kinetics. The 
residual amount left in the lungs on day 50 or 51 was 3.0, 3.9, and 
13.9%, respectively. From these results authors concluded that zinc 
chromate, which is less soluble than sodium chromate, is more slowly 
absorbed from the lungs. Lead chromate was more poorly and slowly 
absorbed, as indicated by very low levels in blood and greater 
retention in the lungs. The authors also noted that the kinetics of 
sodium and zinc chromates were very similar. Zinc chromate, which is 
less soluble than sodium chromate, was slowly absorbed from the lung, 
but the maximal blood levels were higher than those resulting from an 
equivalent dose of sodium chromate. The authors

[[Page 10109]]

believe that this was probably the result of hemorrhages 
macroscopically visible in the lungs of zinc chromate-treated rats 24 
hours following intratracheal administration. Boeing Corporation 
commented that this study does not show that the highly water soluble 
sodium chromate is cleared more rapidly or retained in the lung for 
shorter periods than the less soluble zinc chromate (Ex. 38-106-2, p. 
18-19). This comment is addressed in the Carcinogenic Effects 
Conclusion Section V.B.9 dealing with the carcinogenicity of slightly 
soluble Cr(VI) compounds.
    Studies by Langard et al. and Adachi et al. provide further 
evidence of absorption of chromates from the lungs (Exs. 35-93; 189). 
In Langard et al., rats exposed to 2.1 mg Cr(VI)/m\3\ as zinc chromate 
for 6 hours/day achieved steady state concentrations in the blood after 
4 days of exposure (Ex. 35-93). Adachi et al. studied rats that were 
subject to a single inhalation exposure to chromic acid mist generated 
from electroplating at a concentration of 3.18 mg Cr(VI)/m\3\ for 30 
minutes which was then rapidly absorbed from the lungs (Ex. 189). The 
amount of chromium in the lungs of these rats declined from 13.0 mg 
immediately after exposure to 1.1 mg after 4 weeks, with an overall 
half-life of five days.
    Several other studies have reported absorption of chromium from the 
lungs after intratracheal instillation (Exs. 7-9; 9-81; Visek et al. 
1953 as cited in Ex. 35-41). These studies indicated that 53-85% of 
Cr(VI) compounds (particle size <5 [mu]m) were cleared from the lungs 
by absorption into the bloodstream or by mucociliary clearance in the 
pharynx; the rest remained in the lungs. Absorption of Cr(VI) from the 
respiratory tract of workers has been shown in several studies that 
identified chromium in the urine, serum and red blood cells following 
occupational exposure (Exs. 5-12; 35-294; 35-84).
    Evidence indicates that even chromates encapsulated in a paint 
matrix may be released in the lungs (Ex. 31-15, p. 2). In a study of 
chromates in aircraft spray paint, LaPuma et al. measured the mass of 
Cr(VI) released from particles into water originating from three types 
of paint particles: solvent-borne epoxy (25% strontium chromate 
(SrCrO4)), water-borne epoxy (30% SrCrO4) and 
polyurethane (20% SrCrO4) (Ex. 31-2-1). The mean fraction of 
Cr(VI) released into the water after one and 24 hours for each primer 
averaged: 70% and 85% (solvent epoxy), 74% and 84% (water epoxy), and 
94% and 95% (polyurethane). Correlations between particle size and the 
fraction of Cr(VI) released indicated that smaller particles (<5 [mu]m) 
release a larger fraction of Cr(VI) versus larger particles (>5 [mu]m). 
This study demonstrates that the paint matrix only modestly hinders 
Cr(VI) release into a fluid, especially with smaller particles. Larger 
particles, which contain the majority of Cr(VI) due to their size, 
appear to release proportionally less Cr(VI) (as a percent of total 
Cr(VI)) than smaller particles. Some commenters suggested that the 
above research shows that the slightly soluble Cr(VI) from aircraft 
spray paint is less likely to reach and be absorbed in the 
bronchoalveolar region of the lung than a highly soluble Cr(VI) form, 
such as chromic acid aerosol (Exs. 38-106-2; 39-43, 44-33). This issue 
is further discussed in the Carcinogenic Effects Conclusion Section 
V.B.9.a and in the Quantitative Risk Assessment Section VI.G.4.a.
    A number of questions remain unanswered regarding encapsulated 
Cr(VI) and bioavailability from the lung. There is a lack of detailed 
information on the efficiency of encapsulation and whether all of the 
chromate molecules are encapsulated. The stability of the encapsulated 
product in physiological and environmental conditions over time has not 
been demonstrated. Finally, the fate of inhaled encapsulated Cr(VI) in 
the respiratory tract and the extent of distribution in systemic 
tissues has not been thoroughly studied.
3. Dermal Absorption of Cr(VI)
    Both human and animal studies demonstrate that Cr(VI) compounds are 
absorbed after dermal exposure. Dermal absorption depends on the 
oxidation state of chromium, the vehicle and the integrity of the skin. 
Cr(VI) readily traverses the epidermis to the dermis (Exs. 9-49; 309). 
The histological distribution of Cr(VI) within intact human skin was 
studied by Liden and Lundberg (Ex. 35-80). They applied test solutions 
of potassium dichromate in petrolatum or in water as occluded circular 
patches of filter paper to the skin. Results with potassium dichromate 
in water revealed that Cr(VI) penetrated beyond the dermis and 
penetration reached steady state with resorption by the lymph and blood 
vessels by 5 hours. About 10 times more chromium penetrated when 
potassium dichromate was applied in petrolatum than when applied in 
water, indicating that organic solvents facilitate the absorption of 
Cr(VI) from the skin. Research by Baranowska-Dutkiewicz also 
demonstrated that the absorption rates of sodium chromate solutions 
from the occluded forearm skin of volunteers increase with increasing 
concentration (Ex. 35-75). The rates were 1.1 [mu]g Cr(VI)/cm\2\/hour 
for a 0.01 molar solution, 6.4 [mu]g Cr(VI)/cm\2\/hour for a 0.1 molar 
solution, and 10 [mu]g Cr(VI)/cm\2\/hour for a 0.2 molar solution.
    Additional studies have demonstrated that the absorption of Cr(VI) 
compounds can take place through the dermal route. Using volunteers, 
Mali found that potassium dichromate penetrates the intact epidermis 
(Exs. 9-49; 35-41). Wahlberg and Skog demonstrated the presence of 
chromium in the blood, spleen, bone marrow, lymph glands, urine and 
kidneys of guinea pigs dermally exposed to \51\chromium labeled Cr(VI) 
compounds (Ex. 35-81).
4. Absorption of Cr(VI) by the Oral Route
    Inhaled Cr(VI) can enter the digestive tract as a result of 
mucocilliary clearance and swallowing. Studies indicate Cr(VI) is 
absorbed from the gastrointestinal tract. For example, in a study by 
Donaldson and Barreras, the six-day fecal and 24-hour urinary excretion 
patterns of radioactivity in groups of six volunteers given Cr(VI) as 
sodium chromate labeled with \51\chromium indicated that at least 2.1% 
of the Cr(VI) was absorbed. After intraduodenal administration at least 
10% of the Cr(VI) compound was absorbed. These studies also 
demonstrated that Cr(VI) compounds are reduced to Cr(III) compounds in 
the stomach, thereby accounting for the relatively poor 
gastrointestinal absorption of orally administered Cr(VI) compounds 
(Exs. 35-96; 35-41). In the gastrointestinal tract, Cr(VI) can be 
reduced to Cr(III) by gastric juices, which is then poorly absorbed 
(Underwood, 1971 as cited in Ex. 19-1; Ex. 35-85).
    In a study conducted by Clapp et al., treatment of rats by gavage 
with an unencapsulated lead chromate pigment or with a silica-
encapsulated lead chromate pigment resulted in no measurable blood 
levels of chromium (measured as Cr(III), detection limit = 10 [mu]g/L) 
after two or four weeks of treatment or after a two-week recovery 
period. However, kidney levels of chromium (measured as Cr(III)) were 
significantly higher in the rats that received the unencapsulated 
pigment when compared to the rats that received the encapsulated 
pigment, indicating that silica encapsulation may reduce the 
gastrointestinal bioavailability of chromium from lead chromate 
pigments (Ex. 11-5). This study does not address the bioavailability of 
encapsulated chromate pigments from the lung where residence time could 
be different.

[[Page 10110]]

5. Distribution of Cr(VI) in the Body
    Once in the bloodstream, Cr(VI) is taken up into erythrocytes, 
where it is reduced to lower oxidation states and forms chromium 
protein complexes during reduction (Ex. 35-41). Once complexed with 
protein, chromium cannot leave the cell and chromium ions are unable to 
repenetrate the membrane and move back into the plasma (Exs. 7-6; 7-7; 
19-1; 35-41; 35-52). Once inside the blood cell, the intracellular 
Cr(VI) reduction to Cr(III) depletes Cr(VI) concentration in the red 
blood cell (Ex. 35-89). This serves to enhance diffusion of Cr(VI) from 
the plasma into the erythrocyte resulting in very low plasma levels of 
Cr(VI). It is also believed that the rate of uptake of Cr(VI) by red 
blood cells may not exceed the rate at which they reduce Cr(VI) to 
Cr(III) (Ex. 35-99). The higher tissue levels of chromium after 
administration of Cr(VI) than after administration of Cr(III) reflect 
the greater tendency of Cr(VI) to traverse plasma membranes and bind to 
intracellular proteins in the various tissues, which may explain the 
greater degree of toxicity associated with Cr(VI) (MacKenzie et al. 
1958 as cited in 35-52; Maruyama 1982 as cited in 35-41; Ex. 35-71).
    Examination of autopsy tissues from chromate workers who were 
occupationally exposed to Cr(VI) showed that the highest chromium 
levels were in the lungs. The liver, bladder, and bone also had 
chromium levels above background. Mancuso examined tissues from three 
individuals with lung cancer who were exposed to chromium in the 
workplace (Ex. 124). One was employed for 15 years as a welder, the 
second and third worked for 10.2 years and 31.8 years, respectively, in 
ore milling and preparations and boiler operations. The cumulative 
chromium exposures for the three workers were estimated to be 3.45, 
4.59, and 11.38 mg/m\3\-years, respectively. Tissues from the first 
worker were analyzed 3.5 years after last exposure, the second worker 
18 years after last exposure, and the third worker 0.6 years after last 
exposure. All tissues from the three workers had elevated levels of 
chromium, with the possible exception of neural tissues. Levels were 
orders of magnitude higher in the lungs when compared to other tissues. 
Similar results were also reported in autopsy studies of people who may 
have been exposed to chromium in the workplace as well as chrome 
platers and chromate refining workers (Exs. 35-92; 21-1; 35-74; 35-88).
    Animal studies have shown similar distribution patterns after 
inhalation exposure. For example, a study by Baetjer et al. 
investigated the distribution of Cr(VI) in guinea pigs after 
intratracheal instillation of slightly soluble potassium dichromate 
(Ex. 7-8). At 24 hours after instillation, 11% of the original dose of 
chromium from potassium dichromate remained in the lungs, 8% in the 
erythrocytes, 1% in plasma, 3% in the kidney, and 4% in the liver. The 
muscle, skin, and adrenal glands contained only a trace. All tissue 
concentrations of chromium declined to low or nondetectable levels in 
140 days, with the exception of the lungs and spleen.
6. Metabolic Reduction of Cr(VI)
    Cr(VI) is reduced to Cr(III) in the lungs by a variety of reducing 
agents. This serves to limit uptake into lung cells and absorption into 
the bloodstream. Cr(V) and Cr(IV) are transient intermediates in this 
process. The genotoxic effects produced by the Cr(VI) are related to 
the reduction process and are further discussed in the section V.B.8 on 
Mechanistic Considerations.
    In vivo and in vitro experiments in rats indicated that, in the 
lungs, Cr(VI) can be reduced to Cr(III) by ascorbate and glutathione. A 
study by Suzuki and Fukuda showed that the reduction of Cr(VI) by 
glutathione is slower than the reduction by ascorbate (Ex. 35-65). 
Other studies have reported the reduction of Cr(VI) to Cr(III) by 
epithelial lining fluid (ELF) obtained from the lungs of 15 individuals 
by bronchial lavage. The average overall reduction capacity was 0.6 
[mu]g Cr(VI)/mg of ELF protein. In addition, cell extracts made from 
pulmonary alveolar macrophages derived from five healthy male 
volunteers were able to reduce an average of 4.8 [mu]g Cr(VI)/10\6\ 
cells or 14.4 [mu]g Cr(VI)/mg protein (Ex. 35-83). Postmitochondrial 
(S12) preparations of human lung cells (peripheral lung parenchyma and 
bronchial preparations) were also able to reduce Cr(VI) to Cr(III) (De 
Flora et al. 1984 as cited in Ex. 35-41).
7. Elimination of Cr(VI) From the Body
    Excretion of chromium from Cr(VI) compounds is predominantly in the 
urine, although there is some biliary excretion into the feces. In both 
urine and feces, the chromium is present as low molecular weight 
Cr(III) complexes. Absorbed chromium is excreted from the body in a 
rapid phase representing clearance from the blood and at least two 
slower phases representing clearance from tissues. Urinary excretion 
accounts for over 50% of eliminated chromium (Ex. 35-41). Although 
chromium is excreted in urine and feces, the intestine plays only a 
minor part in chromium elimination, representing only about 5% of 
elimination from the blood (Ex. 19-1). Normal urinary levels of 
chromium in humans have been reported to range from 0.24-1.8 [mu]g/L 
with a median level of 0.4 [mu]g/L (Ex. 35-79). Humans exposed to 0.01-
0.1 mg Cr(VI)/m\3\ as potassium dichromate (8-hour time-weighted 
average) had urinary excretion levels from 0.0247 to 0.037 mg Cr(III)/
L. Workers exposed mainly to Cr(VI) compounds had higher urinary 
chromium levels than workers exposed primarily to Cr(III) compounds. An 
analysis of the urine did not detect Cr(VI), indicating that Cr(VI) was 
rapidly reduced before excretion (Exs. 35-294; 5-48).
    A half-life of 15-41 hours has been estimated for chromium in urine 
for four welders using a linear one-compartment kinetic model (Exs. 35-
73; 5-52; 5-53). Limited work on modeling the absorption and deposition 
of chromium indicates that adipose and muscle tissue retain chromium at 
a moderate level for about two weeks, while the liver and spleen store 
chromium for up to 12 months. The estimated half-life for whole body 
chromium retention is 22 days for Cr(VI) (Ex. 19-1). The half-life of 
chromium in the human lung is 616 days, which is similar to the half-
life in rats (Ex. 7-5).
    Elimination of chromium was shown to be very slow in rats exposed 
to 2.1 mg Cr(VI)/m\3\ as zinc chromate six hours/day for four days. 
Urinary levels of chromium remained almost constant for four days after 
exposure and then decreased (Ex. 35-93). After intratracheal 
administration of sodium dichromate to rats, peak urinary chromium 
concentrations were observed at six hours, after which the urinary 
concentrations declined rapidly (Ex. 35-94). The more prolonged 
elimination of the moderately soluble zinc chromate as compared to the 
more soluble sodium dichromate is consistent with the influence of 
Cr(VI) solubility on absorption from the respiratory tract discussed 
earlier.
    Information regarding the excretion of chromium in humans after 
dermal exposure to chromium or its compounds is limited. Fourteen days 
after application of a salve containing water soluble potassium 
chromate, which resulted in skin necrosis and sloughing at the 
application site, chromium was found at 8 mg/L in the urine and 0.61 
mg/100 g in the feces of one individual (Brieger 1920 as cited in Ex. 
19-1). A slight increase over background levels of urinary chromium was 
observed in four

[[Page 10111]]

subjects submersed in a tub of chlorinated water containing 22 mg 
Cr(VI)/L as potassium dichromate for three hours (Ex. 31-22-6). For 
three of the four subjects, the increase in urinary chromium excretion 
was less than 1 [mu]g/day over the five-day collection period. Chromium 
was detected in the urine of guinea pigs after radiolabeled sodium 
chromate solution was applied to the skin (Ex. 35-81).
8. Physiologically-Based Pharmacokinetic Modeling
    Physiologically-based pharmacokinetic (PBPK) models have been 
developed that simulate absorption, distribution, metabolism, and 
excretion of Cr(VI) and Cr(III) compounds in humans (Ex. 35-95) and 
rats (Exs. 35-86; 35-70). The original model (Ex. 35-86) evolved from a 
similar model for lead, and contained compartments for the lung, GI 
tract, skin, blood, liver, kidney, bone, well-perfused tissues, and 
slowly perfused tissues. The model was refined to include two lung 
subcompartments for chromium, one of which allowed inhaled chromium to 
enter the blood and GI tract and the other only allowed chromium to 
enter the GI tract (Ex. 35-70). Reduction of Cr(VI) to Cr(III) was 
considered to occur in every tissue compartment except bone.
    The model was developed from several data sets in which rats were 
dosed with Cr(VI) or Cr(III) intravenously, orally or by intratracheal 
instillation, because different distribution and excretion patterns 
occur depending on the route of administration. In most cases, the 
model parameters (e.g., tissue partitioning, absorption, reduction 
rates) were