Oncogenicity studies of methyl tertiary‐butyl ether (MTBE) vapor were conducted in CD‐1 mice and Fischer 344 rats. Fifty animals of each sex per species per group were exposed for 6 h a day, 5 days per week to 0 (control), 400, 3000 and 8000 ppm MTBE vapor in air for 18 months (mice) and 24 months (rats). Both species showed reversible central nervous system depression at 8000 ppm for the first week of exposure, which continued for mice for the study duration. For the 8000 ppm mice, reduced body weight gain and early mortality prior to terminal euthanasia were exposure related. In the males, these deaths appear to be due to exacerbation of uropathy or dysuria, which occurs spontaneously in this strain. Increases in absolute and relative liver (both sexes) and kidney weight (males only) were seen at 3000 and 8000 ppm and decreases in brain and spleen weights were also noted (the latter decreases were without microscopic lesions and occurred at 8000 ppm only). An increase in hepatocellular hypertrophy occurred in both sexes at the two highest concentrations. The only neoplastic lesion found in this study in mice was an increased incidence of hepatocellular adenomas in females at the 8000 ppm exposure. In a follow‐up study, a statistically significant elevation of cell proliferation in female mouse liver has been shown to occur following 5 days, but not 28 days, of exposure to 8000 ppm MTBE, suggesting that MTBE induces mitogenesis. For male rats, early euthanasia was required at week 82 and week 97 for the 8000 and 3000 ppm groups, respectively, due to excessive mortality from a severe progressive nephrosis. The end stage of this process appeared earlier in the male rats of all MTBE exposure groups; the incidence of this lesion and mortality for exposed females was comparable to control females. No exposure‐related changes in hematological parameters were observed for any group at any time point, but a decrease in corticosterone levels was seen for male rats from the 8000 ppm group. Absolute and relative kidney and liver weight increases occurred in 3000 and 8000 ppm exposure groups, but the liver weight change was not accompanied by histopathological change. At study termination, increases in the incidence and severity of a chronic nephropathy in males from all exposure groups and in females exposed to 3000 and 8000 ppm was associated with secondary lesions of hyperplasia of the parathyroid and mineralization of tissues. Renal tubular cell tumors were increased in male rats exposed to 3000 and 8000 ppm. This may be associated with an accumulation of a protein (stainable by Mallory's Heidenhain) in kidney tubular epithelial cells after 4 weeks of exposure. An increased incidence of interstitial cell adenomas of the testes was seen in males exposed to 3000 and 8000 ppm but was believed to be an artefact of an unusually low control incidence and not considered to be exposure related. Based on the above effects, the no‐observed‐effect level (NOEL) for chronic toxicity is 400 ppm, and the NOEL for carcinogenic...

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Biomonitoring uses analytic methods that permit the accurate measurement of low levels of environmental chemicals in human tissues. However, depending on the intended use, biomonitoring, like all exposure tools, may not be a stand-alone exposure assessment tool for some of its environmental public health uses. Although biomonitoring data demonstrate that many environmental chemicals are absorbed in human tissues, uncertainty exists regarding if and at what concentrations many of these chemicals cause adverse health outcomes. Moreover, without exposure pathway information, it is difficult to relate biomonitoring results to sources and routes of exposure and develop effective health risk management strategies. In September 2004, the Health and Environmental Sciences Institute, U.S. Environmental Protection Agency, Centers for Disease Control and Prevention, Agency for Toxic Substances and Disease Registry, and International Council of Chemical Associations co-sponsored the International Biomonitoring Workshop, which explored the processes and information needed for placing biomonitoring data into perspective for risk assessment purposes, with special emphasis on integrating biomarker measurements of exposure, internal dose, and potential health outcome. Scientists from international governments, academia, and industry recommended criteria for applying biomonitoring data for various uses. Six case studies, which are part of this mini-monograph, were examined: inorganic arsenic, methyl eugenol, organophosphorus pesticides, perfluorooctanesulfonate, phthalates, and polybrominated diphenyl ethers. Based on the workshop and follow-up discussions, this overview article summarizes lessons learned, identifies data gaps, outlines research needs, and offers guidance for designing and conducting biomonitoring studies, as well as interpreting biomonitoring data in the context of risk assessment and risk management.

Biomonitoring programs in the United States and Europe demonstrate the vast array of data that are publicly available for the evaluation of exposure trends, identification of susceptible populations, detection of emerging chemical risks, the conduct of epidemiology studies, and evaluation of risk reduction strategies. To cultivate international discussion on these issues, the ILSI Health and Environmental Sciences Institute convened a scientific session at its annual meeting in January 2006 on "Integration of Biomonitoring Exposure Data into the Risk Assessment Process." This Forum paper presents perspectives from session speakers on the biomonitoring activities of the Centers for Disease Control and Prevention, the U.S. Environmental Protection Agency, the National Research Council Committee on Human Biomonitoring for Environmental Toxicants, the German Commission on Human Biomonitoring, and the Health and Environmental Sciences Institute Biomonitoring Technical Committee. Speakers noted that better estimates of biological concentrations of substances in the tissues of human populations can be combined with other exposure indices, as well as epidemiological and toxicologic data, to improve risk estimates. With this type of combined data, the potential also exists to define exposure levels at which hazard and risk are of minimal concern. Limitations in interpreting biomonitoring data were discussed, including the need for different criteria for applying biomonitoring data for exposure assessment, risk assessment, risk management, or disease prevention purposes. As efforts and resources are expended to improve the ability to apply biomonitoring exposure data in the risk assessment process, it is equally important to communicate the significance of such data to the public.

Groups of 110 Fischer 344 rats/sex were fed diisononyl phthalate (DINP) at dietary levels of 0, 0.03, 0.3, and 0.6 wt% for periods up to 2 years. Interim sacrifices of 10 predesignated rats/sex/dose were at 6, 12, and 18 months with surviving animals sacrificed at 24 months. At study termination, survival was in excess of 60% for every group. At the mid or high dose, the following biological effects were noted: slight decreases in food consumption and body weight; slight increase in mortality; a dose-related increase in relative organ weights of liver and kidney; and some slight effects on urinalysis, hematologic, and clinical chemistry parameters. No peroxisome induction was observed in livers of treated rats compared with controls. No clear treatment-related nonneoplastic or neoplastic lesions were found. However, mononuclear cell leukemia (MNCL) and changes known to be associated with an increased incidence of MNCL were seen in the mid-dose and high-dose groups. A literature review suggests that MNCL is a common finding in aging F344 rats and that this increased incidence in rats treated with DINP is not relevant to man. A clear no-observed-effect level was demonstrated for all biological end points at a dietary level of 0. 03 wt% or approximately 17 mg/kg/day of DINP.

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