Smaller Than the Rules Anticipated: Exposure Assessment for Engineered Nanomaterials
By Paul E. Rosenfeld, M.S., Ph.D., Principal Environmental Chemist, RoseyFields LLC, Santa Monica, California
A litigation theme that is still being written
Nanoparticle exposure represents one of the more genuinely novel areas within RoseyFields LLC’s environmental exposure practice, addressing engineered nanomaterials, particles with at least one dimension smaller than 100 nanometers, whose exposure and toxicological science remains considerably less mature than that of conventional chemical contaminants, and whose regulatory framework is still substantially under development.
Why conventional exposure assessment tools do not simply transfer
Standard air sampling and risk assessment methodology was developed around mass-based concentration measurements, micrograms per cubic meter, but a growing body of toxicological research suggests that for some engineered nanomaterials, particle number concentration and surface area, rather than mass alone, may better predict biological effect, meaning nanomaterial exposure assessment cannot simply apply conventional particulate matter methodology without adaptation (NIOSH, Current Intelligence Bulletin 63).
NIOSH’s occupational exposure guidance for specific nanomaterials
NIOSH has published recommended exposure limits for specific engineered nanomaterials, including carbon nanotubes and nanofibers and nanoscale titanium dioxide, reflecting the agency’s determination that sufficient toxicological evidence exists for these specific materials to warrant quantitative occupational guidance even though a comprehensive regulatory framework for the broader nanomaterial category remains under development (NIOSH, Current Intelligence Bulletins 63 and 65).
Why particle size itself changes toxicological behavior
Nanoscale particles can penetrate biological barriers, including deep lung tissue and potentially the blood-brain barrier, more readily than larger particles of the same chemical composition, meaning a nanomaterial’s health effects cannot necessarily be predicted from the toxicological literature for the same chemical substance at conventional particle sizes, a scientific reality that has significant implications for how existing chemical-specific toxicity values apply, or fail to apply, to a nanoscale exposure claim.
Occupational settings where nanomaterial exposure is most relevant
Manufacturing facilities producing engineered nanomaterials, downstream users incorporating nanomaterials into consumer products, and research and development laboratories represent the primary occupational settings where nanomaterial exposure reconstruction is currently most relevant, generally preceding any established environmental release or community exposure scenario given the industry’s current scale and maturity.
The evidentiary challenge of limited historical monitoring
Because commercially available nanomaterial-specific air monitoring instrumentation and analytical methods have only become widely accessible in the past decade or two, historical nanomaterial exposure reconstruction faces an even more acute missing-data problem than most legacy chemical contamination matters, often requiring reliance on facility production records, material safety data, and published exposure studies from comparable manufacturing processes rather than any site-specific historical air monitoring data.
Distinguishing nanomaterial-specific toxicology from bulk-material toxicology
A rigorous nanomaterial exposure and risk assessment must explicitly address whether the relevant toxicological evidence concerns the specific engineered nanomaterial at issue or is being extrapolated from bulk-material studies of the same base chemical, a distinction of particular importance given the accumulating evidence that nanoscale physical dimensions can independently drive toxicological effects beyond what chemical composition alone would predict.
Regulatory developments still in progress
EPA’s Toxic Substances Control Act reporting requirements for certain nanoscale materials, and the agency’s ongoing evaluation of specific nanomaterials under its chemical risk evaluation framework, reflect regulatory efforts still actively developing rather than a mature, settled regulatory structure comparable to that governing benzene, lead, or asbestos (US EPA, TSCA Nanomaterials Reporting Rule).
Why this remains a genuinely emerging litigation theme
Given the combination of limited historical exposure monitoring, still-developing toxicological consensus for many specific nanomaterials, and an incomplete regulatory framework, nanomaterial exposure litigation currently occupies a position analogous to where PFAS litigation stood roughly fifteen to twenty years ago, before the accumulated scientific and regulatory record reached its current, far more developed state.
Why early, careful scientific grounding matters especially here
Because nanomaterial exposure science remains genuinely unsettled in important respects, an exposure assessment addressing this emerging area should be unusually explicit about which specific claims rest on well-established science, which rest on reasonable extrapolation from related materials, and which remain areas of open scientific inquiry, a level of transparency that matters for any exposure assessment but is especially important where the underlying science itself continues to evolve. More on this area of Dr. Rosenfeld’s practice, emerging contaminant exposure assessment work, is posted at RoseyFields.com.
References
1. National Institute for Occupational Safety and Health. Occupational Exposure to Carbon Nanotubes and Nanofibers. Current Intelligence Bulletin 65. Cincinnati, OH: CDC/NIOSH; 2013.
2. National Institute for Occupational Safety and Health. Occupational Exposure to Titanium Dioxide. Current Intelligence Bulletin 63. Cincinnati, OH: CDC/NIOSH; 2011.
3. US Environmental Protection Agency. Chemical Substances When Manufactured or Processed as Nanoscale Materials: TSCA Reporting and Recordkeeping Requirements. 40 CFR Part 704, Subpart B.
4. National Institute for Occupational Safety and Health. Approaches to Safe Nanotechnology: Managing the Health and Safety Concerns Associated with Engineered Nanomaterials. Cincinnati, OH: CDC/NIOSH; 2009.
5. Oberdörster G, Oberdörster E, Oberdörster J. Nanotoxicology: an emerging discipline evolving from studies of ultrafine particles. Environ Health Perspect. 2005;113(7):823-839.
6. Donaldson K, Poland CA. Nanotoxicity: challenging the myth of nano-specific toxicity. Curr Opin Biotechnol. 2013;24(4):724-734.
7. Agency for Toxic Substances and Disease Registry. Nanomaterials and Health. Atlanta, GA: US Department of Health and Human Services.
8. US Environmental Protection Agency. Nanomaterial Case Studies. Washington, DC: US EPA.
9. International Organization for Standardization. ISO/TR 12885: Nanotechnologies — Health and Safety Practices in Occupational Settings Relevant to Nanotechnologies.
10. Poland CA, Duffin R, Kinloch I, et al. Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study. Nat Nanotechnol. 2008;3(7):423-428.
11. National Institute for Occupational Safety and Health. General Safe Practices for Working with Engineered Nanomaterials in Research Laboratories. Cincinnati, OH: CDC/NIOSH; 2012.
12. US Environmental Protection Agency. TSCA Risk Evaluations for Existing Chemicals, Including Nanoscale Forms. Washington, DC: US EPA.
13. Rosenfeld PE. RoseyFields LLC: Emerging Contaminant and Nanomaterial Exposure Assessment. Santa Monica, CA: RoseyFields LLC; 2026.
14. US Environmental Protection Agency. Revisions to the Guideline on Air Quality Models. 40 CFR Part 51, Appendix W. Fed Regist. 2017;82(10):5182-5235.