[Federal Register: May 30, 2007 (Volume 72, Number 103)] [Rules and Regulations] [Page 30141-30167] From the Federal Register Online via GPO Access [wais.access.gpo.gov] [DOCID:fr30my07-17] [[Page 30141]] ----------------------------------------------------------------------- Part III Environmental Protection Agency ----------------------------------------------------------------------- 40 CFR Part 82 Protection of Stratospheric Ozone: Listing of Substitutes for Ozone- Depleting Substances-n-Propyl Bromide in Solvent Cleaning; Protection of Stratospheric Ozone: Listing of Substitutes for Ozone- DepletingSubstances-n-Propyl Bromide in Adhesives, Coatings, and Aerosols; Final Rule and Proposed Rule [[Page 30142]] ----------------------------------------------------------------------- ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 82 [EPA-HQ-OAR-2002-0064; FRL-8316-8] RIN 2060-AO10 Protection of Stratospheric Ozone: Listing of Substitutes for Ozone-Depleting Substances-n-Propyl Bromide in Solvent Cleaning AGENCY: Environmental Protection Agency. ACTION: Final Rule. ----------------------------------------------------------------------- SUMMARY: The Environmental Protection Agency (EPA) determines that n- propyl bromide (nPB) is an acceptable substitute for methyl chloroform and chlorofluorocarbon (CFC)-113 in the solvent cleaning sector under the Significant New Alternatives Policy (SNAP) program under section 612 of the Clean Air Act. The SNAP program reviews alternatives to Class I and Class II ozone depleting substances and approves use of alternatives which do not present a substantially greater risk to public health and the environment than the substance they replace or than other available substitutes. DATES: This final rule is effective on July 30, 2007. ADDRESSES: EPA has established a docket for this action under Docket ID No. EPA-HQ-OAR-2002-0064. All documents in the docket are listed on the http://www.regulations.gov Web site. Although listed in the index, some information is not publicly available, i.e., Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy form. Publicly available docket materials are available either electronically in http://www.regulations.gov or in hard copy at the Air and Radiation Docket, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. This docket facility is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the Air and Radiation Docket is (202) 566-1742. FOR FURTHER INFORMATION CONTACT: Margaret Sheppard, Stratospheric Protection Division, Office of Atmospheric Programs, Mail Code 6205J, Environmental Protection Agency, 1200 Pennsylvania Ave., NW., Washington, DC 20460; telephone number (202) 343-9163; fax number (202) 343-2362, e-mail address: sheppard.margaret@epa.gov. Notices and rulemakings under the SNAP program are available on EPA's Stratospheric Ozone World Wide Web site at http://www.epa.gov/ozone/snap/regs. SUPPLEMENTARY INFORMATION: Table of Contents: This action is divided into eight sections: I. General Information A. Does this action apply to me? B. What is n-propyl bromide? C. What acronyms and abbreviations are used in the preamble? II. How does the Significant New Alternatives Policy (SNAP) Program work? A. What are the statutory requirements and authority for the SNAP Program? B. How do the regulations for the SNAP Program work? C. How does the SNAP Program list our decisions? D. Where can I get additional information about the SNAP Program? III. What is EPA's final listing decision on nPB in solvent cleaning? IV. What criteria did EPA use in making this Final Decision? A. Availability of alternatives to ozone-depleting substances B. Impacts on the Atmosphere and Local Air Quality C. Ecosystem and Other Environmental Impacts D. Flammability and Fire Safety E. Impact on Human Health V. How is EPA responding to comments on the June 2003 Notice of Proposed Rulemaking? A. EPA's Acceptability Decision B. Toxicity C. Ozone Depletion Potential D. Other Environmental Impacts E. Flammability F. Legal Authority to Set Exposure Limits VI. How can I use nPB as safely as possible? VII. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planning and Review B. Paperwork Reduction Act C. Regulatory Flexibility Act D. Unfunded Mandates Reform Act E. Executive Order 13132: Federalism F. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments G. Executive Order 13045: Protection of Children from Environmental Health and Safety Risks H. Executive Order 13211: Actions That Significantly Affect Energy Supply, Distribution, or Use I. National Technology Transfer and Advancement Act J. Congressional Review Act VIII. References I. General Information A. Does this action apply to me? This final rule lists n-propyl bromide (nPB) as an acceptable substitute when used as a solvent in industrial equipment for metals cleaning, electronics cleaning, or precision cleaning. General metals, precision, and electronics cleaning includes cleaning with industrial cleaning equipment such as vapor degreasers, in-line cleaning systems, or automated equipment used for cleaning below the boiling point. We understand that nPB is used primarily for cleaning in vapor degreasers. Manual cleaning, such as pail-and-brush, hand wipe, recirculating over- spray (``sink-on-a-drum'') parts washers, immersion cleaning into dip tanks with manual parts handling, and use of squirt bottles, is not currently regulated under the SNAP program. EPA also does not regulate the use of solvents as carriers for flame retardants, dry cleaning, or paint stripping under the SNAP program. This final action does not address the use of n-propyl bromide as an aerosol solvent or as a carrier solvent in adhesives or coatings. We are issuing a proposed rule addressing these end uses in a separate Federal Register action. Neither this final nor the proposed rule issue a decision on other end uses in which nPB was submitted as an ozone- depleting substance (ODS) substitute, such as fire suppression or foam blowing, because of insufficient information. Affected users under this final rule could include: Businesses that clean metal parts, such as automotive manufacturers, machine shops, machinery manufacturers, and electroplaters. Businesses that manufacture electronics or computer equipment. Businesses that require a high level of cleanliness in removing oil, grease, or wax, such as for aerospace applications or for manufacture of optical equipment. [[Page 30143]] Table 1.--Potentially Regulated Entities, by North American Industrial Classification System (NAICS) Code or Subsector ------------------------------------------------------------------------ NAICS code Category or Description of regulated subsector entities ------------------------------------------------------------------------ Industry......................... 331 Primary Metal Manufacturing. Industry......................... 332 Fabricated Metal Product Manufacturing. Industry......................... 333 Machinery Manufacturing. Industry......................... 334 Computer and Electronic Product Manufacturing. Industry......................... 335 Equipment Appliance, and Component Manufacturing. Industry......................... 336 Transportation Equipment Manufacturing. Industry......................... 337 Furniture and Related Product Manufacturing. Industry......................... 339 Miscellaneous Manufacturing. ------------------------------------------------------------------------ This table is not intended to be exhaustive, but rather a guide regarding entities likely to be regulated by this action. If you have any questions about whether this action applies to a particular entity, consult the person listed in the preceding section, FOR FURTHER INFORMATION CONTACT. B. What is n-propyl bromide? n-propyl bromide (nPB), also called 1-bromopropane, is a non- flammable organic solvent with a strong odor. Its chemical formula is C3H7Br. Its identification number in Chemical Abstracts Service's registry (CAS Reg. No.) is 106-94-5. nPB is used to remove wax, oil, and grease from electronics, metal, and other materials. It also is used as a carrier solvent in adhesives. Some brand names of products using nPB are: Abzol[supreg], EnSolv[supreg], and Solvon[supreg] cleaners; Pow-R-Wash[supreg] NR Contact Cleaner, Superkleen Flux Remover 2311 and LPS NoFlash NU Electro Contact Cleaner aerosols; and Whisper Spray and Fire Retardant Soft Seam 6460 adhesives. C. What acronyms and abbreviations are used in the preamble? Below is a list of acronyms and abbreviations used in this document. 8-hr--eight hour ACGIH--American Conference of Governmental Industrial Hygienists AEL--acceptable exposure limit ASTM--American Society for Testing and Materials BMD--benchmark dose BMDL--benchmark dose lowerbound, the lower 95%-confidence level bound on the dose/exposure associated with the benchmark response BSOC--Brominated Solvents Consortium CAA--Clean Air Act CAS Reg. No.--Chemical Abstracts Service Registry Identification Number CBI--Confidential Business Information CEG--community exposure guideline CERHR--Center for the Evaluation of Risks to Human Reproduction CFC-113--the ozone-depleting chemical 1,1,2-trifluoro-1,2,2- trichloroethane, C2Cl3F3, CAS Reg. No. 76-13-1 CFC--chlorofluorocarbon cfm--cubic feet per minute CFR--Code of Federal Regulations CNS--central nervous system DNA--deoxyribonucleic acid EDSTAC--The Endocrine Disruptor Screening and Testing Advisory Committee EPA--the United States Environmental Protection Agency FR--Federal Register GWP--global warming potential HCFC-123--the ozone-depleting chemical 1,2-dichloro-1,1,2- trifluoroethane, CAS Reg. No. 306-83-2 HCFC-141b--the ozone-depleting chemical 1,1-dichloro-1-fluoroethane, CAS Reg. No. 1717-00-6 HCFC-225ca/cb--the commercial mixture of the two ozone-depleting chemicals 3,3-dichloro-1,1,1,2,2-pentafluoropropane, CAS Reg. No. 422-56-0 and 1,3-dichloro-1,1,2,2,3-pentafluoropropane, CAS Reg. No. 507-55-1 HCFC--hydrochlorofluorocarbon HEC--human equivalent concentration HFC-245fa--the chemical 1,1,3,3,3-pentafluoropropane, CAS Reg. No. 460-73-1 HFC-365mfc--the chemical 1,1,1,3,3-pentafluorobutane, CAS Reg. No. 405-58-6 HFC-4310mee--the chemical 1,1,1,2,3,4,4,5,5,5-decafluoropentane, CAS Reg. No. 138495-42-8 HFC--hydrofluorocarbon HFE--hydrofluoroether HHE--health hazard evaluation ICF--ICF Consulting ICR--Information Collection Request iPB--isopropyl bromide, C3H7Br, CAS Reg. No. 75-26-3, an isomer of n-propyl bromide; also called 2-bromopropane or 2-BP Koc--organic carbon partition coefficient, for determining the tendency of a chemical to bind to organic carbon in soil LC50--the concentration at which 50% of test animals die LOAEL--Lowest Observed Adverse Effect Level Log Kow--logarithm of the octanol-water partition coefficient, for determining the tendency of a chemical to accumulate in lipids or fats instead of remaining dissolved in water mg/l--milligrams per liter MSDS--Material Safety Data Sheet NAICS--North American Industrial Classification System NESHAP--National Emission Standard for Hazardous Air Pollutants NIOSH--National Institute for Occupational Safety and Health NOAEL--No Observed Adverse Effect Level NOEL--No Observed Effect Level nPB-n-propyl bromide, C3H7Br, CAS Reg. No. 106-94-5; also called 1-bromopropane or 1-BP NPRM--Notice of Proposed Rulemaking NTP--National Toxicology Program NTTAA--National Technology Transfer and Advancement Act ODP--ozone depletion potential ODS--ozone-depleting substance OEHHA--Office of Environmental Health Hazard Assessment of the California Environmental Protection Agency OMB--U.S. Office of Management and Budget OSHA--the United States Occupational Safety and Health Administration PCBTF--parachlorobenzotrifluoride, CAS Reg. No. 98-56-6 PEL--Permissible Exposure Limit ppm--parts per million RCRA--Resource Conservation and Recovery Act RFA--Regulatory Flexibility Act RfC--reference concentration SIP--state implementation plan SNAP--Significant New Alternatives Policy STEL--Short term exposure limit TCA--the ozone-depleting chemical 1,1,1-trichloroethane, CAS Reg. No. 71-55-6; also called methyl chloroform, MCF, or 1,1,1 TCE--the chemical 1,1,2-trichloroethene, CAS Reg. No. 79-01-6, C2Cl3H; also call trichloroethylene TERA--Toxicological Excellence for Risk Assessment TLV--Threshold Limit Value\TM\ TSCA--Toxic Substances Control Act TWA--time-weighted average UMRA--Unfunded Mandates Reform Act U.S.C.--United States Code VMSs--volatile methyl siloxanes VOC--volatile organic compound WEL--workplace exposure limit II. How does the Significant New Alternatives Policy (SNAP) program work? A. What are the statutory requirements and authority for the SNAP program? Section 612 of the Clean Air Act (CAA) authorizes EPA to develop a [[Page 30144]] program for evaluating alternatives to ozone-depleting substances, referred to as the Significant New Alternatives Policy (SNAP) program. The major provisions of section 612 are: Rulemaking--Section 612(c) requires EPA to promulgate rules making it unlawful to replace any class I (chlorofluorocarbon, halon, carbon tetrachloride, methyl chloroform, and hydrobromofluorocarbon) or class II (hydrochlorofluorocarbon) substance with any substitute that the Administrator determines may present adverse effects to human health or the environment where the Administrator has identified an alternative that (1) reduces the overall risk to human health and the environment, and (2) is currently or potentially available. Listing of Unacceptable/Acceptable Substitutes--Section 612(c) also requires EPA to publish a list of the substitutes unacceptable for specific uses. We must publish a corresponding list of acceptable alternatives for specific uses. Petition Process--Section 612(d) grants the right to any person to petition EPA to add a substitute to or delete a substitute from the lists published in accordance with section 612(c). EPA has 90 days to grant or deny a petition. Where the Agency grants the petition, we must publish the revised lists within an additional six months. 90-day Notification--Section 612(e) requires EPA to require any person who produces a chemical substitute for a class I substance to notify the Agency not less than 90 days before new or existing chemicals are introduced into interstate commerce for significant new uses as substitutes for a class I substance. The producer must also provide the Agency with the producer's health and safety studies on such substitutes. Outreach--Section 612(b)(1) states that the Administrator shall seek to maximize the use of federal research facilities and resources to assist users of class I and II substances in identifying and developing alternatives to the use of such substances in key commercial applications. Clearinghouse--Section 612(b)(4) requires the Agency to set up a public clearinghouse of alternative chemicals, product substitutes, and alternative manufacturing processes that are available for products and manufacturing processes which use class I and II substances. B. How do the regulations for the SNAP program work? On March 18, 1994, EPA published the original rulemaking (59 FR 13044) that described the process for administering the SNAP program and issued the first acceptability lists for substitutes in the major industrial use sectors. These sectors include: Refrigeration and air conditioning; foam blowing; solvents cleaning; fire suppression and explosion protection; sterilants; aerosols; adhesives, coatings and inks; and tobacco expansion. These sectors comprise the principal industrial sectors that historically consumed large volumes of ozone- depleting substances. Anyone who plans to market or produce a substitute for an ODS in one of the eight major industrial use sectors must provide the Agency with health and safety studies on the substitute at least 90 days before introducing it into interstate commerce for significant new use as an alternative. This requirement applies to the person planning to introduce the substitute into interstate commerce, typically chemical manufacturers, but may also include importers, formulators or end-users when they are responsible for introducing a substitute into commerce. C. How does the SNAP program list our decisions? The Agency has identified four possible decision categories for substitutes: Acceptable; acceptable subject to use conditions; acceptable subject to narrowed use limits; and unacceptable. Use conditions and narrowed use limits are both considered ``use restrictions'' and are explained below. Substitutes that are deemed acceptable with no use restrictions (no use conditions or narrowed use limits) can be used for all applications within the relevant sector end-use. Substitutes that are acceptable subject to use restrictions may be used only in accordance with those restrictions. It is illegal to replace an ODS with a substitute listed as unacceptable. After reviewing a substitute, the Agency may make a determination that a substitute is acceptable only if certain conditions of use are met to minimize risks to human health and the environment. We describe such substitutes as ``acceptable subject to use conditions.'' If you use these substitutes without meeting the associated use conditions, you use these substitutes in an unacceptable manner and you could be subject to enforcement for violation of section 612 of the Clean Air Act. For some substitutes, the Agency may permit a narrowed range of use within a sector. For example, we may limit the use of a substitute to certain end-uses or specific applications within an industry sector or may require a user to demonstrate that no other acceptable end uses are available for their specific application. We describe these substitutes as ``acceptable subject to narrowed use limits.'' If you use a substitute that is acceptable subject to narrowed use limits, but use it in applications and end-uses which are not consistent with the narrowed use limit, you are using these substitutes in an unacceptable manner and you could be subject to enforcement for violation of section 612 of the Clean Air Act. The Agency publishes its SNAP program decisions in the Federal Register. For those substitutes that are deemed acceptable subject to use restrictions (use conditions and/or narrowed use limits), or for substitutes deemed unacceptable, we first publish these decisions as proposals to allow the public opportunity to comment, and we publish final decisions as final rulemakings. In contrast, we publish substitutes that are deemed acceptable with no restrictions in ``notices of acceptability,'' rather than as proposed and final rules. As described in the rule implementing the SNAP program (59 FR 13044), we do not believe that rulemaking procedures are necessary to list alternatives that are acceptable without restrictions because such listings neither impose any sanction nor prevent anyone from using a substitute. Many SNAP listings include ``comments'' or ``further information.'' These statements provide additional information on substitutes that we determine are either unacceptable, acceptable subject to narrowed use limits, or acceptable subject to use conditions. Since this additional information is not part of the regulatory decision, these statements are not binding for use of the substitute under the SNAP program. However, regulatory requirements listed in this column are binding under other programs. The further information does not necessarily include all other legal obligations pertaining to the use of the substitute. However, we encourage users of substitutes to apply all statements in the FURTHER INFORMATION column in their use of these substitutes. In many instances, the information simply refers to sound operating practices that have already been identified in existing industry and/or building-code standards. Thus, many of the comments, if adopted, would not require the affected industry to make significant changes in existing operating practices. D. Where can I get additional information about the SNAP program? For copies of the comprehensive SNAP lists of substitutes or additional information on SNAP, look at EPA's [[Page 30145]] Ozone Depletion World Wide Web site at http://www.epa.gov/ozone/snap/lists/index.html. For more information on the Agency's process for administering the SNAP program or criteria for evaluation of substitutes, refer to the SNAP final rulemaking published in the Federal Register on March 18, 1994 (59 FR 13044), codified at Code of Federal Regulations at 40 CFR part 82, subpart G. You can find a complete chronology of SNAP decisions and the appropriate Federal Register citations at http://www.epa.gov/ozone/snap/chron.html. III. What is EPA's final listing decision on nPB in solvent cleaning? The Agency is listing nPB as an acceptable substitute in metals, precision and electronics cleaning end uses. Based on the available information, we find that nPB can be used with no substantial increase in overall risks to human health and the environment, compared to other available or potentially available substitutes for ozone-depleting substances in these end uses. EPA is issuing today's listing in the form of a final rule, rather than in a notice of acceptability, in order to respond to the public comments received on a Notice of Proposed Rulemaking (NPRM) that we issued on June 3, 2003 (68 FR 33284). In that rule, we proposed listing n-propyl bromide (nPB) as an acceptable substitute for use in metals, precision, and electronics cleaning, and in aerosols and adhesives end- uses, subject to the use condition that nPB used in these applications contains no more than 0.05% by weight of isopropyl bromide. In addition, in that proposed rule, EPA indicated that we also would recommend that users adhere to a voluntary acceptable exposure limit (AEL) of 25 parts per million averaged over an eight-hour time-weighted average (TWA). Based on new information received after the close of the comment period on the June 2003 NPRM relevant to our proposed determinations for adhesive and aerosol solvent end uses in that same proposal, the Agency is issuing a new proposal for those end uses in a separate Federal Register action. The Agency is not including a recommended AEL in this final rule. Table 2 contains the text pertaining to nPB use in solvent cleaning end-uses that will be added to EPA's list of acceptable substitutes located on the SNAP Web site at http://www.epa.gov/ozone/snap/lists/index.html. This and other listings for substitutes that are acceptable without restriction are not included in the Code of Federal Regulations because they are not regulatory requirements. The information contained in the ``Further Information'' column of those tables are non-binding recommendations on the safe use of substitutes. Table 2.--Solvent Cleaning Acceptable Substitute ---------------------------------------------------------------------------------------------------------------- End use Substitute Decision Further information ---------------------------------------------------------------------------------------------------------------- Metals cleaning, electronics n-propyl bromide (nPB) Acceptable............ EPA recommends the use of cleaning, and precision cleaning. as a substitute for personal protective CFC-113 and methyl equipment, including chloroform. chemical goggles, flexible laminate protective gloves and chemical-resistant clothing. EPA expects that all users of nPB would comply with any final Permissible Exposure Limit that the Occupational Safety and Health Administration issues in the future under 42 U.S.C. 7610(a). nPB, also known as 1- bromopropane, is Number 106-94-5 in the Chemical Abstracts Service (CAS) Registry. ---------------------------------------------------------------------------------------------------------------- IV. What criteria did EPA consider in making this final determination? In the original rule implementing the SNAP program (March 18, 1994; 59 FR 13044, at 40 CFR 82.180(a)(7)), the Agency identified the criteria we use in determining whether a substitute is acceptable or unacceptable as a replacement for class I or II compounds: (i) Atmospheric effects and related health and environmental impacts; [e.g., ozone depletion potential] (ii) General population risks from ambient exposure to compounds with direct toxicity and to increased ground-level ozone; (iii) Ecosystem risks [e.g., bioaccumulation, impacts on surface and groundwater]; (iv) Occupational risks; (v) Consumer risks; (vi) Flammability; and (vii) Cost and availability of the substitute. In this review, EPA considered all the criteria above. However, n- propyl bromide is used in industrial applications such as electronics cleaning. In those consumer products made using nPB, such as a computer, the nPB would have evaporated long before a consumer would purchase the item. Therefore, we believe there is no consumer exposure risk in the end uses we evaluated for this rule. Section 612(c) of the Clean Air Act directs EPA to publish a list of replacement substances (``substitutes'') for class I and class II ozone depleting substances based on whether the Administrator determines they are safe (when compared with other currently or potentially available substitutes) for specific uses or are to be prohibited for specific uses. EPA must compare the risks to human health and the environment of a substitute to the risks associated with other substitutes that are currently or potentially available. In addition, EPA also considers whether the substitute for class I and class II ODSs ``reduces the overall risk to human health and the environment'' compared to the ODSs being replaced. Our evaluation is based on the end use; for example, we compared nPB as a metal cleaning solvent against other available or potentially available metal cleaning alternatives. Although EPA does not judge the effectiveness of an alternative for purposes of determining whether it is acceptable, we consider effectiveness when determining whether alternatives that pose less risk are available in a particular application within an end use. There are a wide variety of acceptable alternatives listed for solvent cleaning, but not all are appropriate for a specific application because of differences in soils, materials compatibility, degree of cleanliness required, local environmental requirements, and other factors. For example, aqueous cleaners are effective cleaners in many situations and are the substitute of choice for many in the metal cleaning end use. However, in some specific precision cleaning applications that require a high degree of cleanliness and that have narrow [[Page 30146]] spaces that may trap water used in rinsing, aqueous cleaners may not be appropriate and thus are not available in those specific applications. EPA evaluated each of the criteria separately and then considered overall risk to human health and the environment in comparison to other available or potentially available alternatives. We concluded that overall, while there are a number of alternatives that reduce the risks from ozone depletion or from smog production \1\ slightly more than nPB when used in industrial solvent cleaning equipment, we found no single alternative that could work in all applications that clearly would reduce overall risks to human health and the environment in metals cleaning, electronics cleaning, and precision cleaning. Balancing the different criteria discussed below, nPB used in solvent cleaning end- uses does not pose a significantly greater risk than other substitutes or than the ODS it is replacing in these end uses. Thus, we are listing nPB as acceptable in metals cleaning, electronics cleaning, and precision cleaning. --------------------------------------------------------------------------- \1\ Smog, also known as ground-level ozone, is produced from emissions of volatile organic compounds that react under certain conditions of temperature and light. --------------------------------------------------------------------------- A. Availability of Alternatives to Ozone-Depleting Substances Other alternatives to methyl chloroform and CFC-113 are available for metals, electronics, and precision cleaning that have already been found acceptable or acceptable subject to use conditions under the SNAP program including: Aqueous cleaners, semi-aqueous cleaners, alcohols, ketones, esters, ethers, terpenes, HCFC-225ca/cb, hydrofluoroethers (HFEs), hydrofluorocarbon (HFC)-4310mee, HFC-365mfc, heptafluorocyclopentane, hydrocarbons, volatile methyl siloxanes (VMSs), trans-1,2-dichloroethylene, methylene chloride, trichloroethylene \2\ (TCE), perchloroethylene,\3\ parachlorobenzotrifluoride (PCBTF), and alternative technologies like supercritical fluids, plasma cleaning, and ultraviolet/ozone cleaning. Some alternatives are unlikely to be used in particular end uses because of constraints such as cleaning performance, materials compatibility, cost, workplace exposure requirements, or flammability. For example, no-clean technology is used in electronics cleaning and not in precision cleaning because of the need for a high degree of cleanliness in precision cleaning. Of the available substitutes, aqueous cleaners or solvents for vapor degreasing such as TCE, blends of alcohols or trans-1,2-dichloroethylene and HFCs or HFEs, and HCFC- 225ca/cb are most likely to be used in the same applications as nPB. nPB is already commercially available in solvent cleaning, and is used mostly for vapor degreasing in the electronics and precision cleaning end uses (IBSA, 2002). --------------------------------------------------------------------------- \2\ Also called trichlorethene or TCE, C2Cl3H, CAS Reg. No. 79-01-6. \3\ Also called PERC, tetrachloroethylene, or tetrachloroethene, C2Cl4, CAS Reg. No. 172-18-4. --------------------------------------------------------------------------- B. Impacts on the Atmosphere and Local Air Quality As discussed in the June 2003 proposal, nPB emissions from the continental United States are estimated to have an ozone depletion potential (ODP) of approximately 0.013-0.018, (Wuebbles, 2002) \4\, lower than that of the ozone depletion potential of the substances that nPB would replace--CFC-113 (ODP=1.0), and methyl chloroform and HCFC- 141b (ODPs = 0.12) (WMO, 2002). Some other acceptable alternatives for these ODSs also have low ODPs. For example, HCFC-225ca/cb has an ODP of 0.02-0.03 (WMO, 2002) and is acceptable in metals cleaning and aerosol solvents, and acceptable subject to use conditions in precision cleaning and electronics cleaning. HCFC-123 has an ODP of 0.02 (WMO, 2002), and is an acceptable substitute in precision cleaning. There are other acceptable cleaners that essentially have no ODP--aqueous cleaners, HFEs, HFC-4310mee, HFC-365mfc, HFC-245fa, hydrocarbons, VMSs, methylene chloride, TCE, perchloroethylene, and PCBTF. --------------------------------------------------------------------------- \4\ nPB emissions in the tropics have an ODP of 0.071 to 0.100; the portions of the U.S. outside the continental U.S., such as Alaska, Hawaii, Guam, and the U.S. Virgin Islands, contain less than 1 percent of the U.S.'s businesses in industries that could use nPB. Thus, their potential impact on the ozone layer must be significantly less than that of the already low impact from nPB emissions in the continental U.S. (U.S. Economic Census, 2002a through f). --------------------------------------------------------------------------- The global warming potential (GWP) index is a means of quantifying the potential integrated climate forcing of various greenhouse gases relative to carbon dioxide. Earlier data found a direct 100-year integrated GWP (100yr GWP) for nPB of 0.31 (Atmospheric and Environmental Research, Inc., 1995). More recent analysis that considers both the direct and the indirect GWP of nPB found a 100-yr GWP of 1.57 (ICF, 2003a; ICF, 2006a). In either case, the GWP for nPB is comparable to or below that of previously approved substitutes in these end uses. Use of nPB may be controlled as a volatile organic compound (VOC) under state implementation plans (SIPs) developed to attain the National Ambient Air Quality Standards for ground-level ozone, which is a respiratory irritant. Users located in ozone non-attainment areas may need to consider using a substitute for cleaning that is not a VOC or if they choose to use a substitute that is a VOC, they may need to control emissions in accordance with the SIP. Companies have petitioned EPA, requesting that we exempt nPB from regulation as a VOC. However, unless and until EPA issues a final rulemaking exempting a compound from the definition of VOC and states change their SIPs to exclude such a compound from regulation, that compound is still regulated as a VOC. Other acceptable ODS-substitute solvents that are VOCs for state air quality planning purposes include most oxygenated solvents such as alcohols, ketones, esters, and ethers; hydrocarbons and terpenes; trichloroethylene; trans-1,2-dichloroethylene; monochlorotoluenes; and benzotrifluoride. Some VOC-exempt solvents that are acceptable ODS substitutes include HFC-245fa for aerosol solvents; HCFC-225ca/cb, HFC- 365mfc and HFC-4310mee for metals electronics, and precision cleaning and aerosol solvents; and methylene chloride, perchloroethylene, HFE- 7100, HFE-7200, PCBTF, acetone, and methyl acetate for metals, electronics, and precision cleaning, aerosol solvents, adhesives, and coatings. C. Ecosystem and Other Environmental Impacts EPA considered the possible impacts of nPB if it were to pollute soil or water as a waste and compared these impacts to screening criteria developed by the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC, 1998) (see Table 3). Available data on the organic carbon partition coefficient (Koc), the breakdown processes in water and hydrolysis half-life, and the volatilization half-life indicate that nPB is less persistent in the environment than many solvents and would be of low to moderate concern for movement in soil. Based on the LC50, the acute concentration at which 50% of tested animals die, nPB's toxicity to aquatic life is moderate, being less than that for some acceptable cleaners (for example, trichloroethylene, hexane, d-limonene, and possibly some aqueous cleaners) and greater than that for some others (methylene chloride, acetone, isopropyl alcohol, and some other aqueous cleaners). The LC50 for nPB is 67 mg/l, which is greater than 10 mg/l. Based on EPA's criteria for listing under the Toxics Release Inventory (U.S. EPA, [[Page 30147]] 1992), we believe that nPB would not be sufficiently toxic to aquatic life to warrant listing under the Toxics Release Inventory. Based on its relatively low bioconcentration factor and log Kow value, nPB is not prone to bioaccumulation. Table 3 summarizes information on environmental impacts of nPB; trans-1,2- dichloroethylene, a commonly-used solvent in blends for aerosol solvents, precision cleaning, and electronics cleaning; trichloroethylene, a solvent used for metals, electronics, and precision cleaning; and methyl chloroform, an ODS that nPB would replace. Table 3.--Ecosystem and Other Environmental Properties of nPB and Other Solvents -------------------------------------------------------------------------------------------------------------------------------------------------------- Description of Value for trans-1,2- Value for Value for methyl Property environmental property Value for nPB dichloro-ethylene trichloroethylene chloroform -------------------------------------------------------------------------------------------------------------------------------------------------------- Koc, organic-carbon partition Degree to which a 330 (Source: ICF, 32 to 49 (Source: 106 to 460 (Source: 152 (Source: U.S. coefficient. substance tends to stick 2004a). ATSDR, 1996). ATSDR, 1997). EPA, 1994a). to soil or move in soil. Lower values (< 300)* indicate great soil mobility; values of 300 to 500 indicate moderate mobility in soil. Break down in water............... Mechanism and speed with Hydrolysis is Photolytic Volatilization and Volatilization most which a compound breaks significant. decomposition, biodegradation most significant; down in the environment. Hydrolysis half- dechlorination and significant, with biodegradation and (Hydrolysis half-life life of 26 days biodegradation are hydrolysis relatively hydrolysis also values > 25 weeks* are of (Source: ICF, significant; insignificant. occur (Source: concern.) 2004a). hydrolysis not Hydrolysis half-life ATSDR, 2004). significant of 10.7 to 30 months (Source: ATSDR, (Source: ATSDR, 1997). 1996). Volatilization half-life from Tendency to volatilize and 3.4 hours-4.4 days 3 to 6.2 hours 3.4 hours to 18 days Hours to weeks surface waters. pass from water into the (Source: ICF, (Source: ATSDR, (Source: ATSDR, 1997). (Source: U.S. EPA, air. 2004a). 1996). 1994a). LC50 (96 hours) for fathead Concentration at which 50% 67 mg/L (Source: 108 mg/L (Source: 40.7 to 66.8 mg/L 52.8 to 105 mg/L minnows. of animals die from Geiger, 1988). U.S. EPA, 1980). (Source: NPS, 1997). (Source: U.S. EPA, toxicity after exposure 1994a). for 4 days. log Kow........................... Logarithm of the octanol/ 2.10 (Source: ICF, -0.48 (Source: 2.38 (Source: LaGrega 2.50 (Source: water partition 2004a). LaGrega et al., et al., 2001, p. LaGrega et al., coefficient, a measure of 2001, p. 1119). 1127). 2001, p. 1127). tendency to accumulate in fat. Log Kow values >3* indicate high tendency to accumulate. Bioconcentration factor........... High factors (>1000)* 23 (Source: HSDB, 5 to 23 (Source: 10 to 100 (Source: <9 (Source: U.S. indicate strong tendency 2004). ATSDR, 1996). ATSDR, 1997). EPA, 1994a). for fish to absorb the chemical from water into body tissues. -------------------------------------------------------------------------------------------------------------------------------------------------------- *Criteria from EDSTAC, 1998. nPB is not currently regulated as a hazardous air pollutant and is not listed as a hazardous waste under the Resource Conservation and Recovery Act (RCRA). nPB is not required to be reported as part of the Toxic Release Inventory under Title III of the Superfund Amendments and Reauthorization Act. Despite this, large amounts of nPB might be harmful if disposed of in water. We recommend that users dispose of nPB as they would dispose of any spent halogenated solvent (F001 waste under RCRA). Users should not dump nPB into water, and should dispose of it by incineration. D. Flammability and Fire Safety A number of commenters on the June 2003 proposal provided additional information on the flammability of nPB using standard test methods for determining flash point, such as the American Society for Testing and Materials (ASTM) D 92 open cup, ASTM D56 Tag closed cup, and ASTM D93 Pensky-Martens closed cup methods (BSOC, 2000; Miller, 2003; Morford, 2003a, b and c; Shubkin, 2003; Weiss Cohen, 2003). We agree with the commenters that by these standard test methods, nPB displayed no flash point. Thus under standard test conditions, nPB is not flammable, and it should not be flammable under normal use conditions. With its low potential for flammability, nPB is comparable to chlorinated solvents, HCFCs, HFEs, HFC-245fa, HFC-4310mee, and aqueous cleaners, and is less flammable than many acceptable substitutes, such as ketones, alcohols, terpenes, and hydrocarbons. nPB exhibits lower and upper flammability limits of approximately 3% to 8% (BSOC, 2000). A number of other solvents that are typically considered to be non-flammable also have flammability limits (for example, methylene chloride, HCFC-141b, and methyl chloroform). If the concentration of vapor of such a solvent falls between the upper and lower flammability limits, it could catch fire in presence of a flame. Such a situation is unusual, but users should take appropriate precautions in cases where the concentration of vapor could fall between the flammability limits. E. Impact on Human Health In evaluating potential human health impacts of nPB, EPA considered impacts on both exposed workers and on the general population because we identified these groups of people as the ones likely to be exposed to nPB when it is used as a substitute for ozone-depleting substances. EPA evaluated the available toxicity data using EPA guidelines to develop health-based criteria to characterize human health risks (U.S. EPA, 1994b. RfC Guidelines; U.S. EPA, 1991. Guidelines for Developmental Toxicity Risk Assessment; U.S. EPA, 1995b. Benchmark Dose guidelines; U.S. EPA, 1996. Guidelines for Reproductive Toxicity Risk Assessment). [[Page 30148]] In the June 2003 NPRM, EPA proposed that an exposure limit of 25 ppm would be protective of a range of effects observed in animal and human studies, including reproductive and developmental toxicity, neurotoxicity, and hepatotoxicity. Reduction of sperm motility in rats, noted across multiple studies at relatively low exposures, was determined to be the most sensitive effect. The Agency derived an exposure limit of 18 ppm from a dose response relationship in male rat offspring (``F1 generation'') whose parents were exposed to nPB from prior to mating through birth and weaning of the litters (WIL Research Laboratories, 2001). We then proposed to adjust this value upwards to 25 ppm based on principles of risk management consistent with one of the original ``Guiding Principles'' of the SNAP program (59 FR 13046, March 18, 1994). As we discussed in the June 2003 NPRM, EPA noted that adhesives users should be able to achieve an AEL of 25 ppm and that 25 ppm was between the level based on the most sensitive endpoint (sperm motility in the F1 offspring generation) and the second most sensitive endpoint (sperm motility in the F0 parental generation). Following SNAP program principles, we noted that ``a slight adjustment of the AEL may be warranted after applying judgment based on the available data and after considering alternative derivations'' (69 FR 33295). We stated further that ``18 ppm is a reasonable but possibly conservative starting point, and that exposure to 25 ppm would not pose substantially greater risks, while still falling below an upper bound on the occupation[al] exposure limit.'' As part of this final rulemaking, the Agency has reviewed both information available at the time of the 2003 NPRM related to the health risks associated with nPB use, as well as more recent case studies of nPB exposures and effects in the workplace, newly published toxicological studies, comments to the NPRM, new risk assessments on nPB, and a new threshold limit value (TLV) issued by the American Council of Government and Industrial Hygienists (ACGIH). The new information is reviewed in greater detail in EPA's proposal specific to the use of nPB in aerosol solvents, adhesives, and coatings. Some general conclusions we draw from the new studies include: New data from toxicological studies on nervous system effects remain inconsistent and equivocal concerning the level at which nervous system effects occur (Fueta et al., 2002; Fueta et al., 2004; Honma et al., 2003; Ishidao et al., 2002, NTP, 2003; Sohn et al. 2002, Wang et al., 2003). Case reports of nPB exposure in the workplace indicate that severe, possibly irreversible, neurological effects may occur at sustained concentrations of approximately 100 ppm or greater (Beck and Caravati, 2003; Majersik et al., 2004; Majersik et al., 2005; Ichihara et al., 2002; Miller, 2005; Raymond and Ford, 2005). In other cases, similar or higher concentrations up to 170 ppm caused less severe nervous system effects (Nemhauser, 2005; NIOSH, 2003a; Ichihara, 2004a). Some neurological effects occurred in workers at levels of less than 50 ppm (Ichihara et al., 2004b). Because of design and methodological limitations, such as small numbers of subjects and limited exposure information, these studies do not provide a sufficient quantitative basis to derive an acceptable exposure limit. Data on female rats indicate that nPB affects the maturation of ovarian follicles and the ovarian cycle (Yamada et al., 2003), consistent with previously reviewed data (WIL, 2001; Sekiguchi et al., 2002). Some data on occupation exposure suggest that workers exposed to nPB may have experienced menstrual disorders (Ichihara et al., 2002; Ichihara et al., 2004b). However, the data are not statistically significant and are not sufficient to conclude that nPB exposure caused these female reproductive effects. Data on DNA damage in workers exposed to nPB was not statistically significant (Toraason et al., 2006). Metabolic data on mice and rats indicate some species differences. Metabolism of nPB appears to be primarily through cytochrome P450 enzymes, particularly in mice; glutathione conjugation also plays a role, and a bigger role for rats than for mice (RTI, 2005). These more recent studies do not cause us to change our acceptability determination for solvent cleaning. In addition, we considered new evaluations of the toxicity of nPB from Stelljes and Wood (2004), Toxicological Excellence in Risk Assessment (TERA, 2004), ICF (2004a, 2006a), and the TLV documentation from the ACGIH (ACGIH, 2005). Stelljes and Wood (2004) is similar in its results to SLR International (2001), a study by the same authors. EPA previously reviewed SLR International, 2001 in developing the June 2003 NPRM. Both these studies concluded with a recommended AEL of 156 ppm, based on male reproductive effects and uncertainty factors of 1 in driving the AEL. These documents assigned uncertainty factors in a manner inconsistent with EPA's guidance. This would result in a higher AEL than we would determine following the approach EPA has used on other chemicals, as well as an AEL that in our view would not sufficiently protect human health from nPB's effects because of multiple sources of uncertainty in available data (i.e., variability within the working population and differences between animals and humans in how nPB affects the reproductive system). TERA (2004) reviews other AEL derivations for nPB, performs a benchmark dose (BMD) analysis, and recommends an AEL of 20 ppm based on live litter size. This document is consistent with EPA guidance for BMD modeling and for assigning uncertainty factors. A review of this document is available in the public docket (ICF, 2004b). ICF (2004c, 2006b) derived an AEL for nPB based upon female reproductive effects. ICF (2004c, 2006b) discussed the relevant literature (Ichihara et al., 1999, 2002, 2004a, 2004b; Sekiguchi, 2002; Yamada et al., 2003; WIL, 2001) and calculated mean estrous cycle length and the mean number of estrous cycles occurring during a three- week period at different exposure levels in the WIL, 2001 2-generation study. ICF (2004c, 2006a) found statistically significant reductions in the number of estrous cycles in a three-week period, both including and excluding females that had stopped their estrous cycles, at 250, 500, and 750 ppm in the F0 parental generation and at 500 and 750 ppm in the F1 generation. ICF (2004c, 2006a) conducted BMD modeling and calculated benchmark dose lowerbound (BMDL) values of the number of estrous cycles in a three-week period that varied from 102 to 208 ppm, depending upon the model used and the benchmark criteria selected. All data were calculated based on the mean reductions in estrous cycle number calculated from the WIL, 2001 study. Values were calculated for the F0 generation; the number of data for the F1 generation was too small for statistical analysis. The BMDLs that ICF calculated for the number of estrous cycles in a three-week period were 162 ppm and 208 ppm, depending on the benchmark response criteria (10% change in response vs. one standard deviation) and using a linear-heterogeneous model. The ACGIH issued a recommended TLV of 10 ppm (time- weighted average) for nPB (ACGIH, 2005). ACGIH summarized numerous studies showing [[Page 30149]] different effects of nPB and identified no observed effect levels (NOELs) of 200 ppm for hepatotoxicity (ClinTrials, 1997b) and less than 100 ppm for developmental toxicity, as evidenced by decreased fetal weight (Huntingdon Life Sciences, 2001). The Occupational Safety and Health Administration (OSHA) has not developed a permissible exposure limit (PEL) for nPB that EPA could use to evaluate toxicity risks \5\ from workplace exposure. In prior SNAP reviews, EPA has used ACGIH TLVs where available in assessing a chemical's risks and determining its acceptability if OSHA has not set a PEL. ACGIH is recognized as an independent, scientifically knowledgeable organization with expertise in issues of toxicity and industrial hygiene. However, in this case, EPA believes that ACGIH's TLV for nPB of 10 ppm has significant limitations as a reliable basis for an acceptable exposure limit, especially given the availability of other, more comprehensive analyses described in this preamble. First, according to the authors of the Huntingdon Life Sciences study, the decrease in fetal weight was an artifact of sampling procedure that biased the data (test animals were only sacrificed at the end of the day rather than at random). The Center for the Evaluation of Risks to Human Reproduction (CERHR) expert panel excluded ``aberrantly low'' fetal weights from one litter in this study and calculated a BMDL greater than 300 ppm for this endpoint after removing those outlier data (CERHR, 2002a, 2003a, and 2004a). TERA calculated a BMDL similar to that of the CERHR expert panel when analyzing the same data set (TERA, 2004). Further, the reference list in the documentation on the TLV indicates that ACGIH did not review and evaluate all the studies available prior to the development of the recommended exposure limit. For example, key supporting articles that reported disruption of estrous cycles (Yamada et al., 2003 and Sekiguchi et al., 2002) were not discussed in the TLV documentation. Further, ACGIH did not provide sufficient reasoning for the selection of the chosen endpoint over others (e.g., reproductive toxicity and/or neurotoxicity). The lack of discussion of applied uncertainty factors also prevents a determination of how ACGIH arrived at a TLV of 10 ppm. In summary, EPA is not basing its proposed acceptability determination for nPB on the ACGIH TLV because: (1) Other scientists evaluating the database for nPB did not find the reduced pup weight to be the most sensitive endpoint; (2) BMD analysis of the reduced pup weight data (CERHR, 2002a; TERA, 2004) results in a higher BMDL (roughly 300 ppm) than those for sperm effects and estrous cycle changes; and (3) ACGIH may not have reviewed the complete body of literature as several studies discussing neurotoxicity and female reproductive effects were omitted from the list of references. A number of reviews of this document are available in the public docket (ICF, 2004d; O'Malley, 2004). Despite some flaws in its derivation, the TLV of 10 ppm is less than two-fold lower than the low end of the range of acceptable exposure levels based on the most sensitive reproductive endpoints (see below). This small difference is well within the uncertainty we see when extrapolating a benchmark dose from an experimental study in rats to an occupational exposure limit in humans. --------------------------------------------------------------------------- \5\ Vendors of nPB-based products have recommended a wide range of exposure limits, from 5 ppm to 100 ppm (Albemarle, 2003; Chemtura, 2006; Docket A-2001-07, item II-D-19; Enviro Tech International, 2006; Farr, 2003; Great Lakes Chemical Company, 2001). --------------------------------------------------------------------------- We summarize the data for a number of end points found in these analyses in Table 4 below. We examined these data to assess the acceptability of nPB use in the metals, electronics, and precision cleaning end uses reviewed in this final rule. These data indicate that, once uncertainty factors are applied consistent with EPA guidelines, the lowest levels for acceptable exposures would be derived for reproductive effects.\6\ The data also indicate that a level sufficient to protect against male reproductive effects (e.g., reduced sperm motility) would be in a range from 18 to 30 ppm, in the range of 17 to 22 ppm to protect against female reproductive effects (e.g., estrous cycle length), and at approximately 20 ppm for effects related to reproductive success (live litter size). --------------------------------------------------------------------------- \6\ By EPA guidelines, we would apply an uncertainty factor of [radic]10, or approximately 3, for differences between species for all health effects. We would also apply an uncertainty factor of [radic]10 (3) for variability within the working population for reproductive and developmental effects, because, among other reasons, these conditions would not necessarily screen out an individual from being able to work, unlike for liver or nervous system effects. Therefore, for reproductive and developmental effects, we use a composite uncertainty factor of 10. See further discussion of uncertainty factors in section V.B.3 below. Table 4.--Summary of Endpoints Using Benchmark Response Modeling ---------------------------------------------------------------------------------------------------------------- Human equivalent Endpoint \a\ Study BMDL\b\ concentration (ppm) (HEC)\c\ (ppm) ---------------------------------------------------------------------------------------------------------------- Liver Effects \d\ ---------------------------------------------------------------------------------------------------------------- Liver vacuolation in males (F1 offspring WIL, 2001 as analyzed in ICF, 2002... 110 116 generation). Liver vacuolation in males (F0 parent WIL, 2001 as analyzed in ICF, 2002... 143 150 generation). Liver vacuolation............................ ClinTrials, 1997b as analyzed in ICF, 226 170 2002 and Stelljes & Wood, 2004. ---------------------------------------------------------------------------------------------------------------- Reproductive Effects--Male ---------------------------------------------------------------------------------------------------------------- Sperm motility (F1 offspring generation)..... WIL, 2001 as analyzed in ICF, 2002... 169 177 WIL, 2001 as analyzed in Stelljes & 156 164 Wood, 2004. Sperm motility (F0 parent generation)........ WIL, 2001 as analyzed in ICF, 2002... 282 296 WIL, 2001 as analyzed in Stelljes & 263 276 Wood, 2004. Prostate weight (F0 parent generation)....... WIL, 2001 as analyzed in TERA, 2004.. 190 200 Sperm count.................................. Ichihara et al., 2000b as analyzed in 232 325 Stelljes & Wood, 2004. [[Page 30150]] Sperm deformities (F0 parent generation)..... WIL, 2001 as analyzed in Stelljes & 296 311 Wood, 2004. ---------------------------------------------------------------------------------------------------------------- Reproductive Effects--Female ---------------------------------------------------------------------------------------------------------------- Number of estrus cycles during a 3 week WIL, 2001 as analyzed in ICF, 2006a.. 162 170 period (F0 parent generation). WIL, 2001 as analyzed in ICF, 2006a.. 208 218 Estrous cycle length (F1 offspring WIL, 2001 as analyzed in TERA, 2004.. 400 420 generation) \d\. Estrous cycle length (F0 parent generation) WIL, 2001 as analyzed in TERA, 2004.. 210 220 \e\. No estrous cycle incidence (F1 offspring WIL, 2001 as analyzed in TERA, 2004.. 180 189 generation). No estrous cycle incidence (F0 parent WIL, 2001 as analyzed in TERA, 2004.. 480 504 generation). ---------------------------------------------------------------------------------------------------------------- Reproductive Effects--Reproductive Success ---------------------------------------------------------------------------------------------------------------- Decreased live litter size (F1 offspring WIL, 2001 as analyzed in TERA, 2004.. 190 200 generation). Decreased live litter size (F2 offspring WIL, 2001 as analyzed in TERA, 2004.. 170 179 generation). Pup weight gain, post-natal days 21 to 28 (F1 WIL, 2001 as analyzed in TERA, 2004.. 180 189 offspring generation). ---------------------------------------------------------------------------------------------------------------- Developmental Effects ---------------------------------------------------------------------------------------------------------------- Fetal body weight............................ WIL, 2001 as analyzed in TERA, 2004.. 310 326 Fetal body weight............................ WIL, 2001 as analyzed in CERHR, 2002a 305 320 ---------------------------------------------------------------------------------------------------------------- Nervous System Effects ---------------------------------------------------------------------------------------------------------------- Hindlimb strength............................ Ichihara et. al., 2000a as analyzed 214 300 in Stelljes and Wood, 2004. ---------------------------------------------------------------------------------------------------------------- \a\ Unless explicitly stated, data are from a parental generation. Of the studies analyzed, only the WIL, 2001 study has multiple generations to be analyzed. \b\ The benchmark response value represents a specified level of excess risk above a control response. \c\ When considering workplace exposures, the human equivalent concentration is the BMDL, adjusted to apply to a 40-hour work week in which workers are exposed for 8 hours a day for five days per week. Animals in the WIL, 2001 study were exposed for 6 hours a day, 7 days a week. Animals in the Ichihara, 2000a and 2000b studies were exposed for 8 hours a day, 7 days a week. Animals in the ClinTrials, 1997b study were exposed for 6 hours a day, 5 days a week. \d\ After applying an uncertainty factor of 3 for animal to human extrapolation, acceptable levels of exposure to protect against liver effects would be in the range of 39 to 57 ppm. \e\ Omits data from those animals that have stopped estrous cycling altogether (TERA, 2004). These more recent evaluations do not change EPA's acceptability determination for solvent cleaning. As discussed below, users of solvent cleaning equipment are reliably able to achieve exposure levels well below our proposed AEL of 25 ppm in the June 2003 NPRM and therefore we expect nPB users in the metals, electronics, and precision cleaning end uses to be able to achieve acceptable exposure levels. Concentrations of nPB emitted from industrial solvent cleaning equipment were found to be below 25 ppm in roughly 88% of 500 samples on an 8-hr time-weighted average, below 18 ppm in 81% of these samples, and below 10 ppm in roughly 70% of these samples (U.S. EPA, 2003). Based on review of the previously available information and information submitted in comments to the NPRM, the Agency believes that its derivation of 18 ppm as a starting point in the development of a recommended acceptable exposure level is still valid. For purposes of assessing the acceptability of nPB use in solvent cleaning applications, the Agency evaluated whether exposure levels expected to result from solvent cleaning would approach either the 2003 proposed recommended AEL of 25 ppm, or the more conservative starting point of 18 ppm which was derived from the Agency's original risk analysis. We also evaluated any potential risks to the general population associated with nPB use as a solvent. 1. Workplace Risks EPA believes that the great majority of users of nPB in metals cleaning, electronics cleaning, and precision cleaning have been able to attain exposure levels of well below 25 ppm, the proposed AEL in the 2003 NPRM, with their existing equipment. Recently measured exposure levels for nPB are much lower than histori