Review of the Environmental Protection Agency's Draft IRIS Assessment of Tetrachloroethylene (2010) / Chapter Skim
Currently Skimming:
3 Neurotoxicity
3 Neurotoxicity
Pages 30-41
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 30... ...
assessment of the effects of tetrachloroethylene on the nervous system. It considers first the human evidence, including an evaluation of EPA's selection of the most critical study on which to base its reference values, and then the evidence from experimental animal studies.
|
From page 31... ...
Exposure assessment ranged from biologic measurements of tetrachloroethylene exposure to environmental exposure assessments. Studies that included measurements and analyses of exposure at the individual level were given greater weight.
|
From page 32... ...
The reference group included employees of the Public Health Office or the Medical Institution of Environmental Hygiene, none of whom resided at their place of employment and who may have lived outside the commercial city center. Personal characteristics as well as differences in exposures in the ambient environment may have confounded the analyses of exposure and neurobehavioral outcomes.
|
From page 33... ...
The absence of norms makes it especially important to have standardized measures of intellectual function that can be used to characterize the native intellectual capacity of the two groups. Examples of such tests are the NES Vocabulary subtest, the Wide Range Achievement Test Reading subtest, and the Wechsler Adult Intelligence Scale Information subtest.
|
From page 34... ...
After adjustment for the covariates, performance on tests for Wechsler Memory Scale Visual Reproduction, NES Pattern Memory, and NES Pattern Recognition was significantly poorer in workers who had a high index of lifetime tetrachloroethylene exposure than in workers who had a low index of lifetime tetrachloroethylene exposure (Table 3-1)
|
From page 35... ...
. The statistically significant relationship between TWA of tetrachloroethylene exposure and CCI depended on two extreme values.
|
From page 36... ...
showed improvement at the low and intermediate spatial frequencies in the 10-ppm group but loss in the 50-ppm group. Brainstem auditory evoked potentials were not associated with tetrachloroethylene exposure.
|
From page 37... ...
The animal studies entail known histories and living conditions and controlled exposure conditions, usually over a range of doses or concentrations; this allows assessment of dose-effect relationships under conditions that are less influenced by the covariates and biases that hamper the interpretation of human exposures. The literature describing controlled acute and subchronic inhalation exposures of laboratory animals is summarized in the EPA document.
|
From page 38... ...
Incorporating their results into a risk assessment must entail the application of uncertainty factors to identify hazard at environmentally, or even occupationally, relevant concentrations. In addition, the dependent measures in most studies differed from those identified in the human literature as particularly sensitive to tetrachloroethylene exposure.
|
From page 39... ...
EPA also reviewed animal studies conducted with intraperitoneal or oral exposure. The studies of exposure of adults included functional observational batteries (Moser et al.
|
From page 40... ...
described changes in brain fatty acids of neonatal guinea pigs exposed to tetrachloroethylene at 160 ppm during gestation, but the samples were very small, and many important details were lacking. As noted in the draft IRIS assessment, there was evidence of litter effects in this study, and EPA correctly notes that there are concerns about the absence of a dose-effect relationship and of important methodologic considerations, such as use of non-blinded observers on end points that involved subjective observations and difficulty in relating intraperitoneal routes of administration to oral or inhalation routes.
|
From page 41... ...
While the draft IRIS assessment notes that tetrachloroethylene enters the developing brain, it appears to dismiss the potential for developmental neurotoxicity independent of reproductive or maternal toxicity. Additional research may help to fill gaps in the evidence.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.