[Federal Register Volume 61, Number 65 (Wednesday, April 3, 1996)]
[Notices]
[Pages 14773-14778]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-8008]



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ENVIRONMENTAL PROTECTION AGENCY
[OPPTS-42186A; FRL-5359-3]


Request for Proposals for Enforceable Consent Agreements; Dermal 
Absorption Rate Testing of Eighty OSHA Chemicals; Solicitation of 
Interested Parties; Text of Test Protocol

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice.

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SUMMARY: This notice addresses all manufacturers and processors of 
eighty chemical substances of interest to the Occupational Safety and 
Health Administration of the Department of Labor (OSHA) which were 
designated for dermal absorption testing in the 31st, 32nd and 35th 
Reports of the TSCA section 4 Interagency Testing Committee (ITC). 
These persons are invited to submit to EPA proposals for enforceable 
consent agreement (ECA) consideration for dermal absorption rate 
testing of the 80 chemicals. The protocol set forth in this notice is 
recommended as the test protocol for these proposals. In addition, EPA 
is soliciting ``interested parties'' to participate in or monitor any 
ECA negotiations initiated in response to this solicitation.

DATES: Written proposals for ECAs and written requests to be designated 
an interested party must be received by July 2, 1996. EPA may extend 
the deadline for receipt of testing proposals upon request and a 
showing of good faith efforts on the part of potential submitters to 
develop testing proposals by the deadline.

ADDRESSEES: Send written submissions, identified by the document 
control number (OPPTS-42186A) (FRL-5359-3), in triplicate to: TSCA 
Document Control Office (7407), Rm. ET-G099, Office of Pollution 
Prevention and Toxics, U.S. Environmental Protection Agency, 401 M St., 
SW., Washington, DC 20460, Attn: TSCA section 4. The public record 
supporting this action, including comments, is available for public 
inspection from Noon to 4 p.m., Mondays through Fridays, except legal 
holidays. The public record is located in the TSCA Nonconfidential 
Information Center, Rm. NE-B607, U.S. Environmental Protection Agency, 
401 M St., SW., Washington, DC 20460.
    Persons submitting information any portion of which they believe is 
entitled to treatment as confidential business information (CBI) by EPA 
must assert a business confidentiality claim in accordance with 40 CFR 
2.203(b) for each such portion. This claim must be made at the time 
that the information is submitted to EPA. If a submitter does not 
assert a confidentiality claim at the time of submission, EPA will 
consider this waiver of any confidentiality claim, and the information 
may be made available to the public by EPA without further notice to 
the submitter.
    Proposals may be submitted electronically by sending electronic 
mail (e-mail) to: [email protected]. Proposals in electronic form 
must be submitted as ASCII files and must avoid the use of special 
characters and any form of encryption. Proposals will also be accepted 
on disks in WordPerfect 5.1 (DOS) file format or ASCII file format. All 
proposals in electronic form must be identified by docket number OPPTS-
42186A (FRL-5359-3). Information claimed as CBI should not be submitted 
via e-mail. Proposals in electronic form may be filed on-line at many 
Federal depository libraries. Additional information on submissions in 
electronic form may be found in Unit VI of this notice.

FOR FURTHER INFORMATION CONTACT: Susan B. Hazen, Director, 
Environmental Assistance Division (7408), Rm. ET-543B, Office of 
Pollution Prevention and Toxics, U.S. Environmental Protection Agency, 
401 M St., SW., Washington, DC 20460; telephone: (202) 554-1404; TDD: 
(202) 554-0551; e-mail: TSCA-H[email protected]. For specific 
information regarding this solicitation or related matters, contact 
Roger A. Nelson, Project Manager, Chemical Testing and Information 
Branch (7405), Rm. ET-729A, Office of Pollution Prevention and Toxics, 
U.S. Environmental Protection Agency, 401 M St., SW., Washington, DC 
20460; telephone: (202) 260-8163; e-mail: [email protected].

SUPPLEMENTARY INFORMATION:

I. Introduction

    The ITC has reviewed 658 chemical substances that were presented to 
the ITC by OSHA in 1991 (58 FR 26898, 26900, May 5, 1993 and 58 FR 
38490,

[[Page 14774]]

38492-38493, July 16, 1993). OSHA requested the ITC to assess the 
availability of dermal absorption data for these chemical substances 
and to determine the need for further testing. (See 58 FR 26898, 26900, 
May 5, 1993.) The ITC indicated that OSHA needs quantitative measures 
of dermal absorption in order to evaluate the potential hazard of these 
chemicals to workers (58 FR 38490, 38492, July 16, 1993).
    In its 31st, 32nd, and 35th Reports to the EPA Administrator 
(published at 58 FR 26898, May 5, 1993; 58 FR 38490, July 16, 1993; and 
59 FR 67596, December 29, 1994, respectively) (FRL-4583-4, FRL-4630-2, 
and FRL-4923-2, respectively), the ITC designated for dermal absorption 
testing a total of 83 of the chemical substances nominated by OSHA. 
These chemicals are listed in Table 1.--``Chemicals Designated by the 
ITC for Dermal Absorption Testing'' in Unit II of this notice. After 
reviewing additional information, in its 34th and 36th Reports 
(published at 59 FR 35720, July 13, 1994 and 60 FR 42982, August 17, 
1995, respectively) (FRL-4870-4 and FRL-4965-6, respectively), the ITC 
withdrew the designation for three of the chemicals (noted in table 1 
in Unit II of this notice). Eighty of the chemical substances nominated 
by OSHA are thus currently designated by the ITC for dermal absorption 
testing.
    In the Federal Register notices containing the 31st, 32nd and 35th 
ITC Reports, EPA solicited proposals for ECAs for dermal absorption 
testing of the subject chemical substances. In the notices of the 31st, 
32nd and 35th Reports, EPA referenced a proposed dermal absorption test 
protocol for review by potential submitters in developing their 
submissions (Ref. 1). Public comments on the protocol were received by 
EPA and were entered into the docket for the 31st, 32nd, or 35th ITC 
Report, as appropriate (docket nos. OPPTS-41038, OPPTS-41039, and 
OPPTS-41042, respectively). In addition, the Chemical Manufacturers 
Association (CMA) submitted a proposal outlining an alternative 
protocol (Ref. 2). Scientists from EPA and a number of agencies 
represented on the ITC (including OSHA) reviewed the public comments 
and the CMA proposal. Based on this review, a protocol entitled 
``Recommended Protocol for In Vitro Percutaneous Absorption Rate 
Studies'' was developed, and is set forth in Unit V of this notice.
    EPA received no proposals for ECAs for dermal absorption testing of 
any of the subject chemical substances in response to the above-
mentioned solicitations. In today's notice, EPA is soliciting proposals 
for ECAs which address the chemical substances listed in table 1 in 
Unit II of this notice and through which dermal absorption rate data 
would be developed to meet OSHA's needs.

II. Response to Submissions to EPA

A. Response to Public Comments on the ITC Reports

    Comments were received on the 31st, 32nd and 35th ITC Reports and 
were entered into the docket for the corresponding ITC Report. Comments 
received on these ITC Reports addressing the proposed test protocol 
were reviewed as part of the protocol development process, as discussed 
in Unit I of this notice. EPA and the ITC have reviewed all other 
comments received on these ITC Reports. The analysis of these comments 
by EPA and the ITC follows.
    In its comments on the 31st ITC Report, Mobil (Ref. 3) asserted 
that acute dermal toxicity studies would be cheaper and faster than 
skin penetration studies. EPA and the ITC believe that acute dermal 
toxicity studies would not meet OSHA's needs since such studies would 
not provide data on absorption rates.
    BASF (Ref. 4) stated that it has been established that 
tetrahydrofuran (32nd ITC Report) can be rapidly absorbed in lethal 
amounts through the skin of rats and rabbits. OSHA needs data related 
to the real measured rate of the absorption of tetrahydrofuran by the 
skin. The needed data are not provided in the comment.
    Aristech (Ref. 5) commented that there is no specific need to test 
diphenylamine (32nd ITC Report) since this chemical is no different 
from other regulated substances for which dermal penetration data are 
not available. EPA and the ITC believe that such data are needed to 
make determinations concerning the need to alert industrial hygienists, 
employers, and workers to the potential adverse health effects of 
dermal exposure to diphenylamine, as explained in Unit III of this 
notice.
    DuPont (32nd ITC Report) and the CMA Propylene Glycol Ethers Panel 
(35th ITC Report) (Refs. 6 and 7, respectively) questioned how OSHA 
planned to use these data. The uses to which the data will be put are 
explained in Unit III of this notice. Dow (31st ITC Report) (Ref. 8) 
questioned the appropriateness of the grouping of the subject chemical 
substances for testing purposes. EPA believes that the identity of 
testing needs (dermal absorption rate) for these eighty chemicals is 
sufficient reason for grouping them together in one notice.
    The CMA Ketones Panel (Ref. 9) commented on the request contained 
in the Federal Register notice announcing the 31st ITC Report for a 
testing consortium to develop ECAs for all designated chemicals. The 
Panel expressed its belief that such a consortium would not be feasible 
in light of the number of chemicals designated and the number of 
companies that would have to participate in ECA negotiations. EPA 
acknowledges that multiple ECAs may present a feasible approach. (See 
Unit III of this notice).
    Angus Chemicals submitted two dermal absorption studies (Refs. 10 
and 11)--one on 1-nitropropane (31st ITC Report) and the other on 2-
nitropropane (32nd ITC Report). These studies were submitted by Angus 
to support its claims that additional testing of these chemicals is not 
needed. EPA and the ITC have ascertained that the submitted studies are 
deficient because the recovered amounts (0.5%) of test material 
rendered the studies inadequate to determine dermal absorption rates 
for these chemicals.
    DuPont (Ref. 6) submitted comments on 14 chemical substances in the 
32nd ITC Report claiming that dermal toxicity data for these chemicals 
(referenced in the comments) are available. EPA and the ITC have 
determined that the references cited by DuPont do not address the issue 
of dermal absorption rate.
    The CMA Dinitrotoluenes Panel (32nd ITC Report) (Ref. 12) submitted 
comments on 2,4-dinitrotoluene (2,4-DNT), including literature 
describing studies of 2,6-DNT and technical grade DNT, a mixture of 
2,4-DNT and 2,6-DNT. (The literature on 2,6-DNT was offered on the 
basis that 2,6-DNT was an acceptable surrogate for 2,4-DNT.) The Panel 
claimed that existing dermal absorption data are adequate for 2,4-DNT. 
EPA and the ITC reviewed the literature and determined that since it 
does not address dermal absorption rates, the literature is not 
adequate to meet OSHA's data needs.
    The CMA Propylene Glycol Ethers Panel (Ref. 13) commented that 
dermal toxicity data already exist on dipropylene glycol methyl ether 
(DPGME) (35th ITC Report). EPA and the ITC ascertained that no dermal 
absorption rate studies were cited by CMA.
    SOCMA (Ref. 14) questioned the designation of biphenyl (35th ITC 
Report), stating that dermal exposure to biphenyl is limited and animal 
studies indicate that biphenyl does not produce

[[Page 14775]]
adverse health effects following dermal application. EPA and the ITC 
determined that none of the studies cited by SOCMA relate to dermal 
absorption rate.
    Union Carbide (Ref. 15) asserted that the ITC should not have 
designated isophorone (35th ITC Report) for dermal absorption testing. 
OSHA needs data related to the dermal absorption rate of isophorone. 
These needed data are not provided in the comment.

B. Response to TSCA Section 8(d) Studies

    EPA has screened the health and safety studies on the subject 
chemical substances that have been submitted to the Agency pursuant to 
section 8(d) of the Toxic Substances Control Act (TSCA). None of these 
submitted studies was determined to be relevant to dermal absorption 
rate.

 Table 1.--Chemicals Designated by the ITC for Dermal Absorption Testing
------------------------------------------------------------------------
                  CAS No.                           Chemical Name       
------------------------------------------------------------------------
31st ITC Report:                                                        
                                                                        
  60-29-7.................................  Ethyl ether                 
  75-65-0.................................  tert-Butyl alcohol          
  76-22-2.................................  Camphor                     
  78-92-2.................................  sec-Butyl alcohol           
  79-20-9.................................  Methyl acetate              
  97-77-8.................................  Disulfiram                  
  100-25-4................................  p-Dinitrobenzene            
  105-46-4................................  sec-Butyl acetate           
  106-42-3................................  p-Xylene                    
  107-31-3................................  Methyl formate              
  107-66-4................................  Dibutyl phosphate           
  108-03-2................................  1-Nitropropane              
  108-87-2................................  Methylcyclohexane           
  109-66-0................................  Pentane                     
  110-83-8................................  Cyclohexene                 
  111-84-2................................  Nonane                      
  123-92-2................................  Isoamyl acetate             
  142-82-5................................  n-Heptane                   
  287-92-3................................  Cyclopentane                
  532-27-4................................  a-Chloroaceto-    phenone   
  540-88-5................................  tert-Butyl acetate          
  628-63-7................................  n-Amyl acetate              
  7631-90-5...............................  Sodium bisulfite            
  7681-57-4...............................  Sodium metabisulfite        
                                                                        
32nd ITC Report:                                                        
                                                                        
  61-82-5.................................  Amitrole                    
  74-96-4.................................  Ethyl bromide               
  75-15-0.................................  Carbon disulfide            
  75-25-2.................................  Bromoform                   
  75-34-3.................................  1,1-Dichloroethane          
  77-78-1.................................  Dimethyl sulfate            
  79-46-9.................................  2-Nitropropane              
  80-62-6.................................  Methyl methacrylate\1\      
  84-66-2.................................  Diethyl phthalate\1\        
  88-72-2.................................  o-Nitrotoluene              
  89-72-5.................................  o-sec-Butylphenol           
  90-04-0.................................  o-Anisidine                 
  95-13-6.................................  Indene                      
  95-49-8.................................  o-Chlorotoluene             
  99-65-0.................................  m-Dinitrobenzene            
  100-00-5................................  p-Nitrochlorobenzene        
  100-01-6................................  p-Nitroaniline              
  100-44-7................................  Benzyl chloride             
  100-63-0................................  Phenylhydrazine             
  106-49-0................................  p-Toluidine                 
  108-44-1................................  m-Toluidine                 
  108-90-7................................  Chlorobenzene               
  109-99-9................................  Tetrahydrofuran             
  121-14-2................................  2,4-Dinitrotoluene          
  122-39-4................................  Diphenylamine               
  126-99-8................................  beta-Chloroprene            
  150-76-5................................  p-Methoxyphenol             
  528-29-0................................  o-Dinitrobenzene            
  540-59-0................................  1,2-Dichloroethylene        
  626-17-5................................  m-Phthalodinitrile          
  768-52-5................................  N-Isopropylaniline          
  1300-73-8...............................  Xylidine                    
  6423-43-4...............................  Propylene glycol dinitrate  
  25013-15-4..............................  Vinyl toluene               
                                                                        
35th ITC Report:                                                        
                                                                        
  75-05-8.................................  Acetonitrile                
  75-12-7.................................  Formamide                   
  75-35-4.................................  Vinylidene chloride         
  77-73-6.................................  Dicyclopentadiene           
  78-59-1.................................  Isophorone                  
  78-83-1.................................  Isobutyl alcohol            
  78-87-5.................................  Propylene dichloride        
  91-20-3.................................  Naphthalene                 
  92-52-4.................................  Biphenyl                    
  95-50-1.................................  o-Dichlorobenzene           
  96-18-4.................................  1,2,3-trichloropropane      
  98-29-3.................................  t-Butylcatechol             
  99-08-1.................................  m-Nitrotoluene              
  99-99-0.................................  p-Nitrotoluene              
  106-46-7................................  p-Dichlorobenzene           
  107-06-2................................  Ethylene dichloride         
  108-93-0................................  Cyclohexanol                
  108-94-1................................  Cyclohexanone\2\            
  110-12-3................................  Methyl isoamyl     ketone   
  120-80-9................................  Catechol                    
  121-69-7................................  Dimethylaniline             
  123-42-2................................  Diacetone alcohol           
  127-19-5................................  Dimethyl acetamide          
  542-92-7................................  Cyclopentadiene             
  34590-94-8..............................  Dipropylene glycol methyl   
                                             ether                      
------------------------------------------------------------------------
\1\ Removed by the ITC in its 34th Report.                              
\2\ Removed by the ITC in its 36th Report.                              

III. Request for Proposals

    No proposals for ECAs for dermal absorption testing of any of the 
subject chemical substances were received by EPA as a result of the 
solicitations in the Federal Register notices containing the 31st, 32nd 
and 35th ITC Reports. EPA has revised the test protocol and is now 
seeking proposals that will provide for the development of dermal 
absorption rate data on the eighty chemical substances listed in table 
1 in Unit II of this notice. EPA has reason to believe that industry 
now has an interest in proposing dermal absorption rate testing schemes 
for at least some of these chemical substances.
    EPA encourages submitters to work together to develop proposals for 
ECAs that address all eighty subject chemical substances or significant 
subsets thereof. The Agency, however, will also accept proposals for 
ECAs providing for the testing of individual chemicals. All proposals 
should set forth offers to test specific chemicals for the endpoint of 
interest (dermal absorption rate); expressions of interest in ECA 
negotiations do not, in and of themselves, constitute proposals.
    The dermal absorption rate data obtained under this testing program 
will be used to support development of OSHA's ``skin designations'' for 
the subject chemical substances. Skin designations for specific 
chemicals alert industrial hygienists, employers, and workers to 
potential adverse health effects resulting from dermal exposure to 
these chemicals in the workplace. OSHA assigns a skin designation to a 
chemical if it determines that cutaneous exposure (through the skin, 
eyes, and mucous membranes) to that chemical in the workplace 
represents a potential significant contribution to overall workplace 
exposure. Cutaneous exposure is a function of, among other things, the 
rate of absorption of the chemical substance. One methodology under 
consideration for developing and assigning skin designations is 
discussed in Walker et al. (Ref. 17).
    EPA has developed a protocol, set forth in Unit V of this notice, 
that is recommended as the test protocol for all proposals for ECAs. 
The Agency believes that testing conducted in accordance with the 
protocol will provide data of use to OSHA, is consistent with EPA and 
OSHA testing policies, and provides the most economical approach to 
address a large number of diverse chemical substances. If a submitter 
chooses not to use the recommended protocol but instead submits an 
alternative protocol, an explanation should be given as to how this 
alternative protocol will provide comparable data and achieve the same 
goals as the recommended protocol.

IV. Solicitation of Interested Parties

    Negotiations on ECAs for dermal absorption rate testing of the 
subject chemical substances will be conducted pursuant to the 
procedures described in 40 CFR 790.22. All persons who respond to this 
notice on or before July 2, 1996 will be given the status of interested 
parties and will be afforded an opportunity to monitor or participate

[[Page 14776]]
in the negotiations. All such persons should indicate the chemical 
substance(s), by name and CAS number, in which they are interested. 
Those persons who have already given notice in their response(s) to the 
31st, 32nd, or 35th ITC Report that they wish to be designated 
interested parties with regard to ECA negotiations on specific chemical 
substances will be considered automatically to be interested parties on 
such chemicals. Interested parties do not incur any obligation by being 
so designated.
    Upon making the appropriate findings under section 4 of the Toxic 
Substances Control Act (TSCA), EPA has the authority to require dermal 
absorption rate testing of some or all of these chemical substances 
through formal rulemaking. If an ECA-based approach does not prove 
viable, EPA will proceed with rulemaking to require industry to conduct 
the needed testing.

V. Recommended Protocol for In Vitro Percutaneous Absorption Rate 
Studies

A. Introduction

    This recommended protocol was developed to provide percutaneous 
absorption rate data for the Occupational Safety and Health 
Administration (OSHA) chemicals designated in the 31st, 32nd and 35th 
Reports (published at 58 FR 26898, May 5, 1993; 58 FR 38490, July 16, 
1993; and 59 FR 67596, December 29, 1994, respectively) of the TSCA 
section 4 Interagency Testing Committee (ITC), as modified by the 34th 
and 36th ITC Reports (published at 59 FR 35720, July 13, 1994 and 60 FR 
42982, August 17, 1995, respectively). The protocol was developed by a 
group of scientists from agencies represented on the ITC (the Consumer 
Product Safety Commission, the Department of Defense, EPA, the Food and 
Drug Administration, the National Institute for Occupational Safety and 
Health, and OSHA) based on the methods of Bronaugh and Collier (Ref. 
16), and modified in response to comments.
    The protocol outlines procedures for measuring a permeability 
constant (Kp) and a short-term absorption rate for chemicals in liquid 
form. Measurement of short-term absorption rates is only required when 
a Kp cannot be obtained using the protocol described. For most 
chemicals, a Kp is most useful in estimating skin permeation. However, 
for harsh chemicals that may damage the skin more severely with 
prolonged contact, a short-term absorption rate is more relevant. The 
permeability constants and short-term absorption rates measured will be 
used by OSHA to give more specific guidance to employers on whether a 
chemical used in a particular process warrants changes in engineering 
controls or use of personal protective equipment to reduce the hazard 
of systemic toxicity after dermal absorption of the chemical.
    OSHA expects that this would be accomplished by using a semi-
quantitative procedure such as estimating time required to absorb a 
toxic dose compared to the inhalation permissible exposure limits (Ref. 
17). It is not contemplated that the values developed using this 
protocol would be used for quantitative risk assessment because of the 
limitations of the methods used to collect the data and the variability 
of individual exposure scenarios present in workplaces.
    The protocol utilizes established in vitro diffusion cell 
techniques which allow absorption studies to be conducted with human 
skin. The in vitro method is chosen for practical considerations. It is 
efficient in terms of labor and materials and can be easily performed 
using a standard method by different laboratories. In vitro diffusion 
cell studies are necessary for measuring a Kp.
    Although maintaining the viability of skin more closely simulates 
in vivo conditions, this protocol allows use of static diffusion cells 
and cadaver skin. This protocol also requires the use of radiolabeled 
chemicals unless it can be demonstrated that alternative, non-
radiolabeled methods provide sufficient sensitivity to detect the 
parent chemical (and its major skin metabolites in those cases where 
skin viability is maintained). The first five protocol parameters that 
are discussed (choice of membrane, preparation of membrane, diffusion 
cell design, testing hydrophobic chemicals and vehicle) are similar for 
determination of either of the two percutaneous absorption values. In 
contrast, the remaining two protocol parameters (i.e., dose and study 
duration) are different for the two percutaneous absorption values.

B. Conduct of Test

1. Choice of Membrane
    i. Skin selection. The most accurate absorption data for regulatory 
concerns related to human health would be obtained with human skin. 
Since this protocol allows use of the static cell, maintenance of 
viability of skin is not necessary. Human cadaver skin is required for 
these studies.
    ii. Number of subjects. Data from a total of at least six samples 
obtained from at least three human subjects should be averaged to allow 
for biological variation between subjects. Replicates are not required. 
The variability can be up to 5-fold in different samples of normal 
human skin.
    iii. Regional variability. Variability in skin permeation is well 
known to occur in different anatomical regions. The trunk and the 
extremities have reasonably similar barrier properties (less than 2-
fold differences). Enhanced absorption can be observed in regions of 
the face (4-fold) and the scrotum (20-fold). Small differences in 
regional absorption may not be significant compared to intersubject 
variability. However, to minimize the variability in skin absorption 
measurements, for these tests all samples of human skin shall be 
obtained from the abdominal region of human subjects of known source 
and disease state. The time elapsed between death and harvest of tissue 
shall be reported.
    iv. Validation of human skin barrier. Barrier properties of human 
skin shall be pretested with a standard compound such as tritiated 
water prior to conducting an experiment with the test chemical because 
barrier alteration can result from surgery or topical scrubbing (Ref. 
18).
2. Preparation of Membrane
    Full thickness skin should not be used. Since absorbed chemicals 
are taken up by blood vessels directly beneath the epidermis in vivo, 
an in vitro study should use a membrane with most of the dermis 
removed. This is particularly important for hydrophobic chemicals that 
would diffuse slowly through the dermis. A suitable membrane shall be 
prepared from fresh skin with a dermatome at a thickness of 200 to 500 
mm. The microtomed skin samples can be stored frozen for up to two 
weeks, if necessary, if they are frozen quickly and the barrier 
properties of the samples are confirmed.
3. Diffusion Cell Design
    Flow cells or static diffusion cells shall be used in these 
studies. Flow cells are useful for maintaining the viability of the 
skin (in the case that live skin is used) because nutrient media must 
be continually replaced. Also, these cells are preferable for studies 
requiring round-the-clock sampling since samples can be collected 
automatically in a fraction collector. Flow cells of adequate design 
will have only small exposed areas of skin for applying test chemicals 
because the receptor volume must be small so that the cell contents can 
be rapidly exchanged (Ref. 19). If flow cells are used, the draft ITC 
protocol describing their use shall be followed. The draft

[[Page 14777]]
ITC protocol was first made publicly available with the 31st ITC 
Report.
    If static cells are used, the testing laboratory must verify that 
there is not an increase in concentration of the test compound in the 
receptor fluid that would change the penetration rate. Specifically, 
the concentration difference across the membrane must not decrease by 
more than 10% during the experiment. Concentration of the neat liquid 
should be taken as the density of the compound.
4. Temperature
    Skin shall be maintained at a physiological temperature which is 
about 32 deg.C.
5. Testing Hydrophobic Test Chemicals
    Chemicals with water solubility less than about 10 mg/L do not 
freely partition from skin into aqueous receptor fluid. To increase the 
water solubility of such hydrophobic chemicals, polyethoxyoleate (PEG 
20 oleyl ether) shall be added to the receptor fluid at a concentration 
of 6 percent. To ensure that an increase in concentration of the 
chemical in the receptor fluid does not alter the penetration rate, the 
concentration difference across the membrane must not decrease by more 
than 10% during the experiment.
6. Vehicle
    If the test chemical is a liquid at room temperature and does not 
damage the skin during the determination of Kp, it shall be applied 
neat. If the chemical cannot be applied neat because it is a solid at 
room temperature or because it damages the skin when applied neat, it 
should be dissolved in water. If the concentration of a hydrophobic 
chemical in water is not high enough so that a steady-state absorption 
can be obtained, the chemical shall be dissolved in isopropyl 
myristate. In vitro percutaneous absorption experiments with other 
vehicles of interest may be required for selected test chemicals in 
order to meet the data needs of individual Federal agencies. A 
sufficient volume of liquid shall be used to completely cover the skin 
and provide the amount of test chemical needed as described in section 
B.7. ``Dose'' of this protocol below. The volume should be sufficient 
so that the skin surface remains covered by the vehicle during the 
determination of Kp.
7. Dose
    i. Permeability constant. An ``infinite dose'' of the test chemical 
shall be applied to the skin to achieve the steady-state rate of 
absorption necessary for calculation of a Kp. The actual concentration 
required to give an undepletable reservoir on the surface of the skin 
depends on the rate of penetration of the test chemical. Preliminary 
studies may be necessary to determine this concentration. If necessary 
to generate a reliable Kp, the diffusion cell tops should be covered 
with a stopper or with Parafilm7 to prevent evaporation of the vehicle 
or test chemical. If damage to the skin is likely due to the nature of 
the test chemical, the skin barrier integrity shall be verified at the 
end of the experiment by measuring the absorption of a standard 
compound such as tritiated water (Ref. 18).
    ii. Short-term absorption rates. Short-term absorption rates shall 
be determined for those chemicals for which a Kp cannot be measured. 
The dose of test chemical applied to the skin shall be sufficient to 
completely cover the exposed skin surface. Four to six diffusion cells 
shall be set up using skin from a single subject and two to three of 
these will be terminated at 10 minutes and at 60 minutes. Skin 
absorption at each sampling time is the sum of the receptor fluid 
levels and the absorbed chemical that remains in the skin (Ref. 20). 
Unabsorbed chemical is removed from the skin surface by washing gently 
with soap and water. This experiment shall be repeated with skin from 
two additional subjects. If necessary to generate reliable short-term 
absorption rates, the diffusion cell tops should be covered with a 
stopper or with Parafilm7 to prevent evaporation of the test chemical.
8. Study Duration
    i. Permeability constant. The percutaneous absorption study shall 
be performed until at least four absorption measurements are obtained 
during the steady state absorption portion of the experiment. A 
preliminary study may be useful to establish time points for sampling. 
The required absorption measurements can be accomplished in an hour or 
two with fast penetrating chemicals but can require 24 hours or longer 
for slow-penetrating chemicals. Unabsorbed material need not be removed 
from the surface of the skin.
    ii. Short-term exposure rate. The test chemical shall be applied to 
skin for at least durations of 10 and 60 minutes. At the end of the 
study, the unabsorbed material shall be removed from the surface of the 
skin with soap and water and the amount absorbed into the skin and 
receptor fluid shall be determined (Ref. 20).

C. Expression of Results

1. Permeability Constant
    The Kp shall be calculated by dividing the steady-state rate of 
penetration (measured in g  x  hr-1  x  cm-2) by the 
concentration of test chemical (measured in g  x  cm-3) 
applied to the skin. For example, if the steady-state rate is 1 
g  x  hr-1  x  cm-2 and the concentration applied to 
the skin is 1000 g  x  cm-3, then the Kp value is 
calculated to be 0.001 cm  x  hr-1.
2. Short-Term Exposure Rate
    The rates of penetration (g  x  hr-1  x  cm-2) 
shall be determined from the total amount of test chemical found in the 
receptor fluid and skin after the 10- and 60-minute exposures.

D. Recordkeeping and Reporting Requirements

    In addition to compliance with TSCA Good Laboratory Practice (GLP) 
Standards at 40 CFR part 792, the following specific information shall 
be collected and reported:
1. Description of Test Systems and Test Methods
    The report shall include where and when the test was performed, who 
performed it, a good laboratory practice statement, and where the 
records of the test are stored. All of this must be certified by the 
signatures of the individuals performing the work and their 
supervisors.
    The source, identity and purity of the test chemical shall be 
reported. The source, identity and handling of the test skin shall be 
described. There shall be a detailed description of the test procedure 
and all materials, devices used and doses tested. There shall be a 
detailed description and illustration of flow cell design. There shall 
be a description of the skin preparation method including measurements 
of the skin membrane thickness.
    The analytical techniques to be used including their accuracy, 
precision and detection limits (in particular for non-radiolabelled 
tests) shall be described and if a radiolabel is used, there shall be a 
description of the radiolabel (e.g., type, location of and 
radiochemical purity of the label).
    All data collected in the course of the experiment must clearly be 
identified as to dose and specimen. Derived values (means, permeability 
coefficient, graphs, charts, etc.) are not sufficient.
2. Conduct of Study
    Data shall be collected and reported on the following:
    1. Monitoring of testing parameters.
    
[[Page 14778]]

    2. Temperature of chamber.
    3. Receptor fluid pH.
    4. Barrier property validation.
    5. Maintenance of glucose utilization (if using viable skin).
    6. Analysis of receptor fluid for radioactivity or test chemical 
and metabolites (if using viable skin).
3. Results
    The permeability constant (Kp) or short-term absorption rate shall 
be presented. In addition, all raw data from each individual diffusion 
cell shall be maintained to support the calculations of permeability 
constants and short-term exposure rates. When radiolabelled compounds 
are used, a full balance of the radioactivity shall be presented, 
including cell rinsings and stability of the test substance in the 
donor compartment.

VI. Public Docket

A. Materials Contained in the Docket

    EPA has established a docket for this action (to include paper 
versions of comments in electronic form) under docket control number 
OPPTS-42186A (FRL-5359-3). The public record is available for 
inspection from Noon to 4 p.m., Mondays through Fridays, except legal 
holidays, in the TSCA Nonconfidential Information Center, Rm. NE-B607, 
U.S. Environmental Protection Agency, 401 M St., SW., Washington, DC 
20460. Information claimed as CBI, while part of the record, is not 
available for public review. The docket includes the following:

    1. USEPA. Proposed Protocol for In Vitro Percutaneous Absorption 
Studies. (May 5, 1993).

    2. Chemical Manufacturers Association (CMA). Letter to Charles 
M. Auer, USEPA. (October 21, 1994).

    3. Mobil Oil Corporation. Comments on the 31st TSCA Interagency 
Testing Committee Report. Submitted to the TSCA Docket Receipts 
Office, USEPA. (July 6, 1993).

    4. BASF Corporation. Comments on the 32nd TSCA Interagency 
Testing Committee Report. Submitted to the TSCA Docket Receipts 
Office, USEPA. (September 13, 1993).

    5. Aristech Chemical Corporation. Comments on the 32nd TSCA 
Interagency Testing Committee Report. Submitted to the TSCA Docket 
Receipts Office, USEPA. (September 29, 1993).

    6. DuPont. Comments on the 32nd TSCA Interagency Testing 
Committee Report. Submitted to the TSCA Docket Receipts Office, 
USEPA. (September 15, 1993).

    7. The CMA Propylene Glycol Ethers Panel. Comments on the 35th 
TSCA Interagency Testing Committee Report. Submitted to the TSCA 
Nonconfidential Information Center, USEPA. (February 27, 1995).

    8. The Dow Chemical Company. Comments on the 31st TSCA 
Interagency Testing Committee Report. Submitted to the TSCA Docket 
Receipts Office, USEPA. (June 3, 1993).

    9. The CMA Ketones Panel. Comments on the 31st TSCA Interagency 
Testing Committee Report. Submitted to the TSCA Docket Receipts 
Office, USEPA. (July 2, 1993).

    10. Angus Chemical Company. Letter from Allen F. Bollmeier, Jr. 
to Roger Nelson, USEPA, enclosing study entitled: ``Skin Absorption 
and Metabolism/Toxicokinetic Study of 14C-1-Nitropropane in 
Female Rhesus Monkeys''. (June 16, 1993).

    11. Angus Chemical Company. Letter from Allen F. Bollmeier, Jr. 
to John D. Walker, ITC, enclosing study entitled: ``Skin Absorption 
and Metabolism/Toxicokinetic Study of 14C-2-Nitropropane in 
Female Rhesus Monkeys''. (June 21, 1993).

    12. The CMA Dintrotoluenes Panel. Comments on the 32nd TSCA 
Interagency Testing Committee Report. Submitted to the TSCA Docket 
Receipts Office, USEPA. (September 30, 1993).

    13. The CMA Propylene Glycol Ethers Panel. Comment letter on the 
35th TSCA Interagency Testing Committee Report from Langley Spurlock 
to Charles M. Auer, USEPA. (March 31, 1995).

    14. Synthetic Organic Chemical Manufacturers Association, Inc. 
(SOCMA). Comments on the 35th TSCA Interagency Testing Committee 
Report. Submitted to the TSCA Nonconfidential Information Center, 
USEPA. (January 30, 1995).

    15. Union Carbide Corp. Comments on the 35th TSCA Interagency 
Testing Committee Report. Submitted to the TSCA Nonconfidential 
Information Center, USEPA. (February 24, 1995).

    16. Bronaugh, R.L. and Collier, S.W. Protocol for In Vitro 
Percutaneous Absorption Studies, in In Vitro Percutaneous 
Absorption: Principles, Fundamentals, and Applications, (R.L. 
Bronaugh and H.I. Maibach, Eds.), CRC Press, Boca Raton, 1991, pp. 
237-241.

    17. Walker, J.D., Whittaker, C. and McDougal, J.N. Role of the 
TSCA Interagency Testing Committee in Meeting the U.S. Government's 
Data Needs: Designating Chemicals for Percutaneous Absorption 
Testing. In: F. Marzulli and H. Maibach (eds.) Dermatotoxicology. 
Taylor Francis, Washington, DC. (In press).

    18. Bronaugh, R.L., Stewart, R.F., and Simon, M. Methods for In 
Vitro Percutaneous Absorption VII: Use of Excised Human Skin, J. 
Pharm. Sci., vol. 75, pp. 1094-1097, 1986.

    19. Bronaugh, R.L. and Stewart, R.F. Methods for In Vitro 
Percutaneous Absorption Studies IV: The Flow-Through Diffusion Cell, 
J. Pharm. Sci., vol. 74, pp. 64-67, 1985.

    20. Bronaugh, R.L., Stewart, R.F., and Storm, J.E. Extent of 
Cutaneous Metabolism during Percutaneous Absorption of Xenobiotics, 
Toxicol. Appl. Pharmacol., vol. 99, pp. 534-543, 1989.

B. Submissions to the Docket in Electronic Form

    Proposals in electronic form may be sent directly to EPA at:
    [email protected]
    Proposals in electronic form must be submitted as ASCII files and 
must avoid the use of special characters and any form of encryption.
    The official record of this action, as well as the public version, 
will be maintained in paper form. Accordingly, EPA will transfer all 
proposals received electronically into paper form as they are received 
and will place the paper copies in the official record which will also 
include all proposals submitted directly in writing. The official 
record is the paper record maintained at the address in ``ADDRESSES'' 
at the beginning of this document.

    Authority: 15 U.S.C. 2603.

    Dated: March 26, 1996.

Charles M. Auer,
Director, Chemical Control Division, Office of Pollution Prevention and 
Toxics.
[FR Doc. 96-8008 Filed 4-2-96; 8:45 am]
BILLING CODE 6560-50-F