EPA Issues Final SNUR for Certain Multi-Walled Carbon Nanotubes
On May 6, 2011, the U.S. Environmental Protection Agency (EPA) promulgated a final significant new use rule (SNUR) under Section 5(a)(2) of the Toxic Substances Control Act (TSCA) for the chemical substance identified generically as multi-walled carbon nanotubes (MWCNT), which was the subject of premanufacture notice (PMN) P-08-199. Under the final SNUR, persons intending to manufacture, import, or process MWCNT for a use that is designated as a significant new use by the final rule must notify EPA at least 90 days before commencing that activity. The EPA states that it believes the final rule is necessary “because the chemical substance may be hazardous to human health,” and the required notification would provide EPA with the opportunity to evaluate the intended use and, if necessary, to prohibit or limit that activity before it occurs. The final rule will be effective June 6, 2011.
The EPA issued a proposed SNUR on February 3, 2010, and then on July 28, 2010, it reopened the comment period for 30 days to address public comment and add information to the docket. In the May 6, 2011, Federal Register notice, EPA states that, in response to comments on the basis for the proposed SNUR, EPA developed a revised summary document entitled “Summary of EPA’s Current Assessments of Health and Environmental Effects of Carbon Nanotubes,” which specifies EPA’s current hazard concerns as supported by available information and data. This document is available online. According to the May 6, 2011, notice, EPA considered comments on the proposed SNUR, and the final SNUR:
- Retains the proposed workplace protection and specific use provisions as significant new uses;
- Adds exclusions from applicability of the SNUR uses identified as ongoing; and
- Identifies those forms of the subject PMN substance that are exempt from the provisions of the SNUR. These exemptions apply to quantities of the PMN substance:
- After they have been completely reacted (cured);
- Incorporated or embedded into a polymer matrix that itself has been reacted (cured); or
- Embedded in a permanent solid polymer form that is not intended to undergo further processing except for mechanical processing.
The EPA provides the following rationale:
As discussed in the proposed rule, EPA identified concerns for lung effects, immunotoxicity, and mutagenicity from exposure to the PMN substance during its review of the chemical substance, which was the subject of P-08-199. These concerns were based on test data on analogous respirable, poorly soluble particulates and on other carbon nanotubes (CNTs).
To determine what would constitute a significant new use for the MWCNTs subject to the final SNUR, EPA considered relevant information about the toxicity of the chemical substance, and likely human exposures and environmental releases associated with possible uses. For the MWCNTs described in P-08-199, EPA “believes that certain changes from the use scenario described in the PMN could result in increased exposures.”Responses to Comments on the Proposed SNUR
The final SNUR includes the following comments and EPA’s responses:
Comment: The proposed SNUR did not contain a no-release-to-water restriction and other consent orders and SNURs for CNTs do contain a no-release-to-water restriction. This difference “was inappropriate and that it should not be allowed to persist.”
Response: Because the release to water is an ongoing use, EPA is unable to issue a SNUR that includes a no release to water provision.
Comment: The PMN submitter commented that significant new uses must not be ongoing and should be consistent with the existing uses identified in its comments. The PMN submitter also outlined its understanding of how the rule would apply in practice to particular existing uses and requested that EPA clarify that understanding.
Response: After reviewing the PMN and the PMN submitter’s outline of how the SNUR would apply in practice to its existing uses, EPA confirms that the significant new uses in the rule are not ongoing and that the commenter’s outline of how the rule would apply to existing uses is correct. In its March 5, 2010, comments on the proposed SNUR, however, the PMN submitter identified specific use(s) other than as an additive/filler for polymer composites and support media for industrial catalysts. The company claimed these specific uses as confidential business information (CBI). As described in the proposed SNUR, persons who begin, after the date of the proposed rule, commercial manufacture, import, or processing of the MWCNTs that were the subject of P-08-199 for a use preliminarily designated as a “significant new use” in the proposed rule must cease any such activity before the effective date of the final rule. After the final SNUR is effective, any person intending to manufacture, import, or process the substance for a use other than as an additive/filler for polymer composites and support media for industrial catalysts must submit a significant new use notice (SNUN) at least 90 days before commencing such use.
Comment: The PMN submitter asked EPA to clarify the meaning of uses as described in the PMN. The uses described in the PMN were additive/filler for polymer composites and support media for industrial catalysts. The PMN submitter asked whether notification would be required for each specific polymer composite or for different equipment used to manufacture or process the PMN substance.
Response: If a manufacturer or processor is using the PMN substance as either an additive/filler for polymer composites, or support media for industrial catalysts, they may change processes to include new equipment or new polymer composites. If there is any question as to whether a specific use or application is not the use described in the PMN, a manufacturer or processor may contact EPA or submit a SNUN.
Comment: The PMN submitter commented that there should be an exemption for bound forms of the PMN substance when the SNUR would not apply, for example, when the PMN substance is embedded or incorporated into plastic resin pellets.
Response: The EPA agrees that, consistent with other SNURs and consent orders for CNTs, (e.g., the MWCNT that was the subject of PMN P-08-177), and the existing uses of the PMN substance, there should be an exemption from the final SNUR requirements once the PMN substance has been fixed to a substrate or encapsulated within a plastic or other polymer matrix. The EPA has included language in the final SNUR to exempt from SNUR requirements persons that manufacture, import, or process the PMN substance when the substance has been incorporated or embedded into a polymer matrix that itself has been reacted (cured) or embedded in a permanent solid polymer form that is not intended to undergo further processing except for mechanical processing.
Comment: The PMN submitter asked EPA to specify the identity of the PMN substance specifically in relation to other MWCNTs, explaining how EPA is describing the PMN substance as a unique chemical type.
Response: Because of a lack of established nomenclature for CNTs, EPA has allowed PMN submitters to represent their CNTs using a generic name “such as carbon nanotube (CNT), multi-walled carbon nanotube (MWCNT), or single-walled carbon nanotube (SWCNT) while submitting a detailed description of the CNT using specific structural characteristics.” All submitters of new chemical notices for CNTs, including the submitter for the MWCNT described in P-08-199, have claimed those specific structural characteristics as CBI. The EPA states that it is publishing the generic chemical name along with the PMN number to identify that a distinct chemical substance was the subject of the PMN without revealing the confidential chemical identity of the PMN substance. Confidentiality claims preclude a more detailed description of the identity of this MWCNT. Manufacturers may submit a bona fide intent to manufacture or import to determine whether a specific CNT is on the TSCA Inventory.
Comment: The PMN submitter commented on the document entitled, “Material Characterization of Carbon Nanotubes for Molecular Identity (MI) Determination & Nomenclature” (docket ID number EPA-HQ-OPPT-2009-0686-0015, available online) that identifies a list of chemical structural features, chemical particle properties, and manufacturing methods that may be important for making CNT molecular identity determinations and naming them for TSCA purposes. The PMN submitter stated it was difficult to comment on the document, as the record does not identify either its particular provenance, or how EPA is using, or plans to use it. The commenter also noted that many of the features may be impractical to observe, measure, or characterize with any consistency or statistical certainty, and others may be altered simply by the act of measuring. The commenter stated that several of the criteria refer only to properties of a CNT material (i.e., a collection of molecules rather than a single molecule), then asserted that these characteristics may be relevant to management considerations, but they are not relevant to defining molecular identity for TSCA purposes.
Response: The EPA does not agree that these characteristics are not relevant to defining the molecular identity of a CNT. Because of a lack of established nomenclature for CNTs, EPA is currently representing CNTs using a generic chemical name along with the PMN number to identify them as distinct chemical substances. The EPA included this list of physical features that may be important to demonstrate that it is considering additional characteristics when reviewing and identifying CNTs. The EPA has used a wide variety of characteristics to identify chemical substances of unknown or variable composition, complex reaction products, and biological materials (UVCB) for TSCA purposes. As noted by the commenter, some of these characteristics may not be suitable for unambiguously determining molecular identity. As EPA learns more about the structures of CNTs, it will develop a set of characteristics to identify systematically CNTs.
Comment: A commenter noted that recent signed and draft consent orders for other CNTs contain additional updated hazard assessment information for both health and environmental concerns. The commenter suggested this language should be referenced in the final SNUR so that all of EPA’s concerns are described in a similar manner for all SNURs pertaining to CNTs. The PMN submitter stated that while EPA did place data in the public docket supporting the finding from inhalation exposure, there are no data in the public docket supporting the finding from dermal exposures.
Response: The EPA states that it “is continually refining and adding to its risk assessment and risk management approaches, especially for new chemical substances such as CNTs that have limited available hazard, exposure, and fate data.” Recent consent orders for CNTs cite additional data that were not referenced in the proposed SNUR for this PMN substance. The EPA placed in the public docket a document entitled “Summary of EPA’s Current Assessment of Health and Environmental Effects of Carbon Nanotubes” (docket ID number EPA-HQ-OPPT-2009-0686-0016), in support of the health effects findings and significant new use designations made in the proposed rule. This document identifies those references available at the time of assessment of the chemical substance in this final rule. The EPA also reopened the comment period on July 28, 2010, to allow interested parties to comment on the additional information that was the basis for the SNUR.
Comment: The PMN submitter expressed concerns with respect to the cited inhalation (or simulated inhalation) studies. The commenter questioned the validity of the studies as several of the cited studies exist only as abstracts of unpublished presentations. The commenter stated there is no assessment of the doses involved in these studies, or the studies underlying the poorly soluble particles chemical categories report. The commenter also noted a Bayer Material Science study for CNTs and detailed results of the inhalation studies that have been recently published in the peer-reviewed journals, Inhalation Toxicology, Toxicological Sciences, andToxicology that EPA should take into account in connection with the rulemaking. Finally, the commenter states that EPA does not explain how these studies satisfy the regulatory concern criteria on which EPA relies.
Response: The EPA has found that the substance meets the decisional criteria in Section 721.170(b)(3)(ii). The decisional criteria state: “The substance may cause serious chronic effects, serious acute effects, or developmentally toxic effects under reasonably anticipated conditions of exposure because the substance is closely analogous, based on toxicologically relevant similarities in molecular structure and physical properties, to another chemical substance that has been shown by valid test data to cause serious chronic effects, serious acute effects, or developmentally toxic effects in humans or in at least one species of laboratory animal at dose levels that could be of concern under reasonably anticipated conditions of exposure.” The EPA states that it “is not required to conduct a quantitative risk assessment or establish safe dose levels. The EPA must only establish that effects could occur under reasonably anticipated conditions of exposure.” The papers referenced in the docket, the Bayer Material Science study, and other data cited by the PMN submitter, and data that are the basis for the poorly soluble respirable particulates category, “demonstrate the potential chronic pulmonary and cardiovascular effects (including pulmonary toxicity, fibrosis, carcinogenicity, mutagenicity, and immunotoxicity, and cardiovascular toxicity) of carbon nanotubes, including the PMN substance, at various dose levels.” The EPA considered this information in the review of the MWCNTs described in PMN P-08-199, and concluded that the specified significant new uses of the PMN substance “could result in inhalation exposures at levels where health effects were observed in the papers referenced in the docket.”
Comment: The PMN submitter stated that the company supports minimizing dermal and inhalation exposures to the extent reasonably practicable on a voluntary basis, and that controls should be used where warranted, but they should not be required to prevent particular exposures for which EPA has no reasoned basis to believe may cause significant effects. The commenter asserted that the materials in the public docket only address the potential direct and indirect effects of inhalation exposures. Further, in summary, the commenter stated that the proposal appears to lack any reasoned basis for the particular dermal controls proposed in the SNUR and does not appear to meet the decisional criteria in Section 721.170(b)(3)(ii) as the basis for establishing controls. The commenter stated that one cannot assess the basis and extent for EPA’s concern, making it impossible to comment on whether the suggested controls are reasonably tailored to those concerns.
Response: The EPA believes it has demonstrated that the subject substance meets the decisional criteria, including the significant new use of manufacturing, importing, or processing of the PMN substance without dermal protection where workers are reasonably likely to be exposed. As noted above, EPA has established that CNTs, including the PMN substance, may cause pulmonary toxicity, fibrosis, carcinogenicity, mutagenicity, and immunotoxicity, and cardiovascular toxicity. The “Summary of EPA’s Current Assessment of Health and Environmental Effects of Carbon Nanotubes” (docket ID number EPA-HQ-OPPT-2009-0686-0016) states that “absorption is expected to be poor for all routes,” which includes dermal exposure. This suggests that some dermal absorption could occur. The EPA considered this information in the review of the MWCNTs described in PMN P-08-199, and concluded that the specified significant new uses of the PMN substance could also result in dermal exposures at levels where health effects were observed in the papers referenced in the docket.
Test Data and Other Information
In the final SNUR, EPA states that it “recognizes that TSCA section 5 does not require the development of any particular test data before submission of a SNUN,” with two exceptions:
- Development of test data is required where the chemical substance subject to the SNUR is also subject to a test rule under TSCA Section 4 (see TSCA Section 5(b)(1)); or
- Development of test data may be necessary where the chemical substance has been listed under TSCA Section 5(b)(4) (see TSCA Section 5(b)(2)). In the absence of a TSCA Section 4 test rule or a TSCA Section 5(b)(4) listing covering the chemical substance, persons are required only to submit test data in their possession or control and to describe any other data known to or reasonably ascertainable by them. Upon review of PMNs and SNUNs, however, EPA has the authority to require appropriate testing. In this case, EPA recommends persons, before performing any testing, to consult with EPA pertaining to protocol selection.
The EPA states that, while the recommended testing described in the proposed rule “may not be the only means of addressing the potential risks of the chemical substance…, SNUNs submitted without any test data may increase the likelihood that EPA will respond by taking action under TSCA section 5(e), particularly if satisfactory test results have not been obtained from a prior PMN or SNUN submitter. The EPA recommends that potential SNUN submitters contact EPA early enough so that they will be able to conduct the appropriate tests prior to submitting a SNUN.” The EPA notes that SNUN submitters “should be aware” that EPA will be better able to evaluate SNUNs that provide detailed information on the following:
- Human exposure and environmental release that may result from the significant new use of the chemical substance;
- Potential benefits of the chemical substance; and
- Information on risks posed by the chemical substance compared to risks posed by potential substitutes.