Guidance for Air
The following guidance was developed by the Minnesota Department of Health (MDH) at the request of the Minnesota Pollution Control Agency (MPCA). For more information, contact the Health Risk Assessment Unit.
Naphthalene: Acute and Chronic Health-Based Values
Updated July 6, 2004
CAS number: 91-20-3
Endpoint(s): Respiratory System
Acute Value: 200 ug/m3
Chronic Value: 9 ug/m3
Sources: NTP (1992, 2000) for chronic value
The Minnesota Department of Health (MDH) has derived both an acute Health-Based Value (HBV) of 200 ug/m3 and a chronic HBV of 9 ug/m3 for inhalation exposures to naphthalene. A description of the techniques, assumptions and caveats used in developing these numbers follows.
Note: MDH has less confidence in the acute value and recommends that it be considered a site-specific screening number to be used to trigger remedial action, where appropriate.
Acute: There are limited data addressing the impacts of acute exposures of experimental animals to naphthalene. However, because there are a number of anecdotal reports of naphthalene toxicity in humans (nausea, vomiting, abdominal pain, and hemolytic anemia) at concentrations above those that trigger an odor (200 — 440 ug/m3) MDH recommends the use of an acute HBV (one hour exposure) of 200 ug/m3 as a reasonable maximum exposure level.
The use of this number is supported by results from a study on rats that reported respiratory changes (cell swelling and sloughing) following four hours of exposure to 380 mg/m3 of naphthalene (Buckpitt, 1982). In this study 204 mg/m3 was a No Observed Adverse Effect Level (NOAEL). Applying an uncertainty factor of 1000 (10 for intraspecies variability, 10 for interspecies variability, and 10 for database deficiencies) gives an acute value of 200 ug/m3 for a four-hour exposure. As an additional precaution, MDH recommends that this number be applied using a 1 hour averaging time.
Chronic: Two chronic rodent bioassays, one in mice (NTP, 1992) and one in rats (NTP, 2000) are the basis for MDH's chronic HBV of 9 ug/m3. Both of these studies involved the administration of naphthalene for 6 hours per day, five days per week for two years. Both studies produced a Lowest Observed Adverse Effect Level (LOAEL) of 10 ppm naphthalene with fairly marked respiratory and nasal impacts as adverse endpoints.
Manipulating this exposure to allow for a 24 hour/day and a seven day/week exposure yields an adjusted LOAEL of 1.78 ppm which converts to a value of 9.3 mg naphthalene/m3. Applying an uncertainty factor of 1000 (10 for intraspecies variability, 10 for interspecies variability, and 10 for the use of a LOAEL rather than a NOAEL) results in a final chronic HBV for naphthalene of 9 µg/m3. Although by definition MDH considers a chronic exposure to be one that occurs on a daily basis over a 70-year lifetime, MDH recommends that exposures that take place for more than 10 percent of an individual's lifetime be assessed using chronic values. MDH anticipates that chronic HBVs will be applied using annual emission estimates.
Please be advised that although MDH has a reasonable level of confidence in the chronic naphthalene number, and in fact intends to propose this value as a HRV during the next rule revision, available data do not address two additional toxic endpoints reported in humans — cataracts, and the blood disorder, hemolytic anemia. MDH is therefore less certain about the conservative nature of the naphthalene number for these endpoints.
Buckpitt, A.R. (1982). Comparative biochemistry and metabolism. Part 2: Naphthalene lung toxicity. AFAMRL-TR-82-52, pg 25-30. Air Force Aerospace Medical Research Laboratory, Wright-Patterson Air Force Base, Ohio.
NTP (1992). National Toxicology Program. Toxicology and carcinogenesis studies of naphthalene (CAS No. 91-20-3) in B6C3F1 mice (inhalation studies). NTP Technical Report Series No. 410. NIH publication no. 92-3141. U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, Research Triangle Park, N.C.
NTP (2000). National Toxicology Program. Toxicology and carcinogenesis studies of naphthalene (CAS No. 91-20-3) in F344/N rats (inhalation studies). NTP Technical Report Series No. 500. NIH publication no. 01-4434. U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, Research Triangle Park, N.C.