Update: Spring 2000
Current Massachusetts Regulatory Limit
ORSGL = 0.14 mg/L.
Federal Regulatory Limit
The U.S. EPA has not published an MCL for naphthalene.
Basis for Criteria
The ORSGL is based on an updated oral reference dose for naphthalene. The ORSGL is derived based on the RfD presented below and assumes that a 70 kg adult ingests 2 L/day of water. A relative source contribution of 20% is incorporated into the final value.
RfD: 2 x 10-2 mg/kg/day
UF: 3000 (10 = intraspecies; 10 = interspecies; 10 = subchronic to chronic; 3 = database deficiencies including the lack of chronic oral exposure studies and 2-generation reproductive toxicity studies)
(U.S. EPA, 1998)
Non-cancer effects produced in laboratory animals orally exposed to high doses of naphthalene for acute or subchronic periods of time include hemolytic anemia (in dogs) and cataracts (in rats and rabbits). Effects noted at lower doses included decreased body weight, central nervous system depression and organ weight changes. In developmental studies in which pregnant female rats were exposed via gavage, maternal toxicity was produced in the absence of fetal developmental toxicity (U.S. EPA, 2000).
In a 3-week study, Fischer 344 rats were exposed at dose levels of 0, 25, 50, 100 200 or 400 mg/kg for 5 days/week for 13 weeks. Decreased body weight was the most sensitive effect noted in this study. A NOAEL identified from this study (for a greater than 10% decrease in body weight) is 100 mg/kg/day (duration adjusted for 5/7 days to 71 mg/kg/day). This NOAEL for this critical effect was used for development of the RfD referenced above (U.S. EPA, 1998).
Cancer Assessment: The U.S. EPA has classified naphthalene as a C carcinogen (possible human carcinogen) under the 1986 Carcinogen Risk Assessment Guidelines, based on the inadequate data of carcinogenicity in humans exposed to naphthalene via the oral and inhalation routes, and the limited evidence of carcinogenicity in animals via the inhalation route (U.S. EPA, 2000). Benign respiratory tumors and one carcinoma were observed in female mice only exposed to naphthalene by inhalation (NTP, 1992). The fact that exposure to 1-methylnaphthalene produced an increase in respiratory tumors provides supportive evidence of carcinogenicity (U.S. EPA, 2000). Although the mechanism of carcinogenicity has not currently been fully determined, based on the many negative results obtained in mutagenicity tests, a genotoxic mechanism of action is probably not likely (U.S. EPA, 2000).
Polycyclic Aromatic Hydrocarbon
U.S. EPA Methods 502.2; 524.2; 550; 550.1; 610
PQLs and analytical methods may have been updated since this guidance value was last revised. Updated analytical methods for drinking water and their associated PQLs may be found at http://www.epa.gov/safewater/methods/methods.html.
Other Regulatory Data
Any Health Advisories, Reference Doses (RfDs), cancer assessments or Cancer Potency Factors (CPFs) referenced in this document pertain to the derivation of the current guidance value. Updated information may be obtained from the following sources:
Health Advisories - The U.S. EPA provides guidance for shorter-term exposures for chemicals based on their non-cancer effects. Current health advisories may be more current than those used to derive MCLs and may be found at http://www.epa.gov/safewater/methods/methods.html.
RfDs, cancer assessments and CPFs - For specific information pertaining to derivation of drinking water criteria, consult the Federal Register notice that announces the availability of the most current guidance for that chemical. In addition, information on other current RfDs and CPFs as well as cancer assessments for specific chemicals may be found in the U.S. EPA Integrated Risk Information System (IRIS) at http://www.epa.gov/iris/. Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.
U.S. EPA (U.S. Environmental Protection Agency). August 1998. Toxicological Review of Naphthalene (CAS No. 91-20-3) in Support of Summary Information on the Integrated Risk Information System (IRIS).
U.S. EPA (U.S. Environmental Protection Agency). 2000. Integrated Risk Information System (IRIS). Washington, D.C.. http://cfpub.epa.gov/ncea/iris/index.cfm.
NTP (National Toxicology Program). 1992. Technical Report on the Toxicology and Carcinogenesis Studies of Naphthalene (CAS No. 91-20-3) in B6C3F1 Mice. (Inhalation Studies). DHHS, PHS, NIH, Rockville, MD.