OAR Box 1830 

Prepped by Ollie Stewart 

Document Number: 

7) IV-B-3 

Docket Number: 

A-87-11 

Printed 11/13/2008 7:20:51 AM Sheet 7 of 232 

p.1 
P.2 

lg afjm \ UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

I^W^Z ? WASHINGTON, D.C. 20460 

DEC 2 ? ,rr"

r

 OFFICE OF 

fc W : ^ ' RESEARCH AND DEVELOPMENT 

MEMORANDUM 

SUBJECT: Review of MVMA comments on Gasoline Vapor Risk 

Assessment 

FROM: William Pepelko, Ph.D. 'Jv*'-'->-•-

 ,Jf-c J;" 

Toxicologist 

Carcinogen Assessment Group (RD-689) 

TO: Charles L. Gray, Jr. 

Director 

Emission Control Technology Division 

Ann Arbor, Michigan 

THRU: William H. Farland, Ph.D. 

Acting Director 

Office of Health and Environmental 

Assessment (RD-689) 

I have reviewed the July 6, 1987 letter from the Motor Vehicle Manufacturers 

Association concerning the EPA Health Risk Assessment of Gasoline Vapors. They 

pointed out that kidney cell proliferation in the male rat is induced only by a 

high concentration of wholly vaporized gasoline, that the degree of proliferation correlates well with the induction of renal tumors, that the proliferative 

reponse is causally related to the presence of specific hydrocarbons in gasoline, and that the cell proliferation and increased DNA synthesis caused by 

these compounds is the result of binding to a specific protein only found to 

date in the male rat. This protein (alpha-2-microglobulin) is filtered 

through the glomerulus of the kidney, absorbed by the proximal tubule cells 

and metabolized. Binding of the hydrocarbons to the protein evidently inhibits 

catabolism, resulting in accumulation in the tubular cells as hyaline droplets, 

leading to cellular death and subsequent regeneration. Since only the male rat 

has been shown to produce the specific protein linked to the histopathologic 

response, the MVMA feels that the rat is a uniquely sensitive and therefore inappropriate model for assessing the earcinogenicity of gasoline vapors in humans. 

In support of this argument is evidence that a variety of other organic 

chemicals also induce kidney pathology to a significant degree only in the male 

rat. Three of these hydrocarbons, hydrogenated dimers of norbornadiene, extratetrahydro (cyclopentadiene) and para-dichlorobenzene, have been tested in long 

term bioassays and have also been shown to induce kidney tumors in male rats. 
P.3 

ENVIRONMENTAL PROTECTION 

AOFwr.v 

APR / 2 1988 

CENTRAL DOCKET 

SECTION 
P.4 

If the male rat is determined to be inappropriate for assessing the carcinogenic risk of exposure to gasoline vapors, then the only biologically and statisti' 

cally significant tumorigenic response found in animals is an increase in liver 

tumors in mice. If this were the case then a strong argument could be made for 

downgrading the qualitative assessment of carcinogenicity for unleaded gasoline 

from category B2 to C. 

Although the letter does not mention quantitative analysis of cancer 

risk, that would also require change if the premise of the letter were 

accepted. If the nephrotoxicity, originating as described above, is 

a precursor of tumon'genicity, then the tumor induction can be considered 

the result of only the C6-C9 branched chain hydrocarbon components of the 

vapor, which are present at only about 1/5 of their concentration in the 

aerosolized gasoline used in the animal experiments. Secondly, it has 

been hypothesized that the tumorigenicity in rats is the result of promoting action. In this hypothesis lysozyme leakage in cells overloaded with 

hyaline droplets may cause physical damage to chromosomes. These effects 

would be enhanced by a much more rapid rate of cell turnover. Implicit in 

this hypothesis is the presence of a threshold, rendering a linear nonthreshold model inappropriate. 

We agree that consideration of the newer data does strengthen the 

argument that the male rat may be unique in its response to gasoline 

vapors. Nevertheless, we feel the evidence is not conclusive and that 

a cautious approach is prudent. Some of the reasons for the continuing 

uncertainty regarding the uniqueness of the rat tumorigenic response are 

listed below. 

First of all, while the tumors occur in the general area of nephropathy, 

the exact site of tumorigenesis has not been defined. Thus, it is not known 

for certain if the tumors arise from the proximal tubule cell.s, the site of 

cell turnover. Secondly, old rats normally develop kidney nephropathy, yet 

kidney tumors are very rare in untreated animals. Finally, in the only 

chronic study carried out to date using animals exposed to aerosolized 

whole unleaded gasoline, a renal sarcoma was reported in a female rat, 

while an adenoma and a carcinoma were reported to have occurred in the 

kidneys of two mice. Although these were not statistically significant 

effects, such tumors are only rarely seen in unexposed animals. Taken 

together, this evidence tends to cast some doubt on the hypothesis 

linking kidney tumor induction to chronic nephropathy. 

In a study recently published (Toxicology and Applied Pharmacology, 

90: 43-51, 1987) study^ Olson, et al. found that there is not a one-to-one 

correspondence between cells with hyaline droplets and cells staining for 

alpha-2-microglobulin. Some cells with hyaline droplets did not have 

alpha-2-microglobulin, and they stated that it is not known whether the 

accumulation of this protein in the proximal tubule cells was the cause 
P.5 

•*i 

,M 

or the result of the nephropathy. Their findings leave open the possibility 

that other proteins which are not necessarily unique to male F 344 rats could 

cause hyaline droplet formation and subsequent nephrotoxicity. Therefore, 

even if the hypothesis linking kidney cancer to the development of nephrotoxicity is accepted, it is possible that kidney tumors could be induced by 

gasoline vapors in other species. 

Significant increases in cancer incidence have been reported in several 

human epidemiology studies of occupational exposure to gasoline vapors and 

other refinery products. Because of weaknesses in the design of these 

studies and uncertainty regarding the nature of exposure, these studies 

are generally considered inadequate to make conclusions regarding the 

carcinogenicity of gasoline alone in humans. Collectively, however, 

they do provide, at least, some suggestive evidence that gasoline 

and or related hydrocarbons may be carcinogenic in humans. 

Continuing uncertainty, regarding the relationship between kidney 

nephropathy and tumor induction, the possibility that hydrocarbon 

nephropathy may be induced in other species, the significant increase 

of liver tumors in female mice, and the suggestive evidence for a 

carcinogenic effects of gasoline and/or refinery products in humans, 

collectively indicate a concern that gasoline vapors could be carcinogenic. For this reason we prefer to maintain a conservative stance and 

retain the B2 classification. We recognize, however, the evidence is 

not clearcut and that new data may result in a reconsideration of the 

classification.