High Molecular Weight Polymers in the New Chemicals Program
There are three categories or types of High Molecular Weight (HMW, >10,000 daltons) polymers typically reviewed by the New Chemicals Program:
- Insoluble/non-water absorbing ("non-swellable"),
- Water absorbing ("swellable").
EPA has a concern for potential fibrosis of the lung or other pulmonary effects that may be caused by inhalation of respirable particles of water-insoluble HMW polymers. The toxicity may be a result of "overloading" the clearance mechanisms of the lung. EPA also has concerns for water absorbing polymers, based on data showing that cancer was observed in a two-year inhalation study in rats on a HMW water-absorbing polyacrylate polymer. Each of the three types is treated differently as indicated below:
EPA does not expect water-soluble polymers to exhibit lung toxicity because they are expected to rapidly clear the respiratory tract and therefore not cause an overloading effect. However, where there is substantial production volume, exposure and release, the Agency will require testing on PMN substances of this type under its exposure-based authority.
Insoluble: non-water absorbing (non-swellable) polymers
Although exempt from reporting by the 1995 PMN rule amendments under the polymer exemption criteria, the Agency has concerns for this class of HMW polymers. This concern is based on a study, designated TSCA 8(e)-0668, which reported irreversible lung damage linked with inhalation of respirable particles of water-insoluble polymers (toner used in copy machines) of MW 70,000 or greater.
There is a data gap for polymers with MW between 10,000 and 70,000. If a company chooses to submit a PMN for this type of HMW polymer (rather than take advantage of the polymer exemption option), and the PMN substance meets the program's exposure-based criteria (in particular, production volume and inhalation exposure), EPA may regulate under its exposure-based policy with a modified testing scheme. A 90-day subchronic toxicity test via inhalation with a 60-day holding period (absent neurotoxic components and other organ effects) will be triggered under a TSCA section 5(e) consent order. Data from such a study will be compared to the results from 8(e)-0668.
Other references are:
- Pulmonary Response to Toner Upon Chronic Inhalation Exposure in Rats. H. Muhle, B. Bellmann, 0. Creutzenberg, C. Dasenbrock, H. Ernst, R. Kilpper, J.C. MacKenzie, P. Morrow, U. Mohr, S. Takenaka, and R. Mermelstein. Fundam. Appl. Toxicol. 17, 280-299(1991).
- Lung Clearance and Retention of Toner, Utilizing a Tracer Technique During a Long-term Inhalation Study in Rats. B. Bellmann, H. Muhle, 0. Creutzenberg, C. Dasenbrock, R. Kilpper, J.C. MacKenzie, P. Morrow, and R. Mermelstein. Fundam. Appl. Toxicol. 17, 300-313(1991).
- Chronic Inhalation Study Findings as a Basis for Proposing a New Occupational Dust Exposure Limit. P. Morrow, H. Muhle, and R. Mermelstein. J. American College of Toxicology, 10, No. 2, 279-290(1991).
- Abstract-Hamster Response to Chronic Test Toner Inhalation. R. Mermelstein, 0. Creutzenberg, C. Dasenbrock, H. Ernst, M. Kuschner, U. Mohr, and H. Muhle. presented at the 1992 Annual Society of Toxicology (SOT) Meeting, Seattle, WA, The Toxicologist (1992).
Insoluble: non-water swellable, highly respirable
Also exempt from reporting under the new polymer exemption. In addition to lung overload described above, these substances raise serious, yet less predictive concerns for potential lung effects associated with their highly respirable size -- where a significant percentage of the particles are <10 microns -- and lack of absorption potential; the physical effect is deposition to the deep lung and inability to dislodge the particles.
For these cases, current Agency policy is to not pursue regulation of the chemical, but to send a letter to the submitter that mentions the basic overload issue from above -- with the toner data references--and stresses the heightened concern based on the substance's highly respirable nature -- with additional references on "ultrafines," highly respirable particles that are much more toxic to lungs than larger particles of the same material. Such a letter typically will recommend use of a NIOSH-approved respirator or appropriate engineering controls.
General Note on the Insoluble HMW Polymers and the Polymer Exemption
EPA recognizes that there is a different hurdle for placing PMN chemical substances on the TSCA (Toxic Substances Control Act) Inventory than for permitting exemptions for polymers, specified at 40 CFR 723.250. In promulgating this exemption for polymers, EPA generally concluded that "there is an exceedingly low probability that potential exposure to high molecular weight water-insoluble polymers, as a class, will result in unreasonable risk or injury to human health or the environment."
Within the context of individual PMN chemical substances, however, EPA continues to have a concern for the potential for irreversible lung damage when respirable insoluble dusts are inhaled at levels that also produce "lung overloading" and impaired clearance by the lungs. As a result, EPA will assess polymers submitted as PMNs on a case-by-case basis. This concern is based on the above mentioned photocopy toner data (TSCA 8(e)-0668). Based on this concern, EPA reserves the right to require testing under its TSCA exposure-based authority, warranted by high exposures and production volume.
In promulgating the polymer exemption in 40 CFR 723.250, EPA did not impose conditions on this category of insoluble high MW polymers as part of the final rule. At the time, EPA stated that, "the Agency believes that manufacturers and users of polymers and chemical substances, in general, where feasible should take appropriate action to mitigate exposure to all respirable particles as part of good industrial hygiene practices."
Accordingly, EPA may send a "letter of concern" to a PMN submitter, as a restatement of this last point. EPA believes such a letter is an appropriate action which fulfills EPA's responsibility to communicate a potential for adverse effects based on the TSCA Section 8(e) photocopy toner data. Note that EPA, in promulgating the 1995 amendments to the Polymer Exemption Rule, elected not to establish an exposure limit for respirable particles, agreeing with public comments that consistency among Federal regulations (i.e., between TSCA new chemicals regulation and OSHA nuisance dust standards) regarding workplace exposure is desirable.
Water absorbing (swellable) polymers
For these substances the Agency makes the "may present an unreasonable risk" determination with concerns for fibrosis and cancer, based upon water absorption properties. Concerns are associated with substances that absorb their weight (or greater) in water. The primary reference for Agency concerns for this class of polymers is TSCA 8(e)-1795, submitted by the Institute for Polyacrylate Absorbents (IPA), which indicated that high molecular weight polyacrylate polymers caused lung neoplasms in animal studies. EPA has also reviewed data on modified starches submitted by the Corn Refiners Association, comparing the structures of the test substances with the structures of twelve modified starch PMN substances.
Based on the submitted data, EPA was unable to support concerns for the water retentive capacity of these PMN substances as potentially leading to lung cancer. EPA will review future PMNs for modified starches on a case-by-case basis to determine the applicability of these test results to the future PMNs. High molecular weight polymers that swell to twice their weight are not eligible for the polymer exemption. EPA will assess on a case-by-case basis whether these substances pose a risk and whether testing is warranted, and if they are made in substantial amounts and demonstrate potential for acute or chronic worker inhalation exposure.