Review of DOD's Approach to Deriving an Occupational Exposure Level for Trichloroethylene (2019) / Chapter Skim
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6 Conclusions
6 Conclusions
Pages 50-61
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PROPOSED OEL FOR INHALED TCE DOD derived candidate OELs for six noncancer end points, including neurological, liver, kidney, immunological, reproductive, and developmental effects. DOD then selected the lowest candidate OEL, which was based on immunological effects, as the overall OEL of 0.9 parts per million (ppm)
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When compared with other occupational exposure guidelines, DOD's proposed OEL for noncancer effects has the potential to be more health protective than existing guidelines for DOD workers. DOD APPROACH FOR DERIVING AN OEL Chapters 3 through 5 provide the committee's detailed discussion of the approach used by DOD to derive the OEL for TCE.
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. This rating is driven by several factors including the lack of a systematic review protocol, inadequate methods to assess risk of bias, and incomplete description of individual studies.
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For example, weaknesses found in the IRIS assessment of formaldehyde included incomplete documentation of assessment methods, lack of clear inclusion and exclusion criteria, insufficient use of evidence tables, and a lack of uniform approaches to evaluate the strengths and weaknesses of critical studies 3This caveat would apply to all narrative reviews that do not meet accepted standards for a systematic review. 4The committee acknowledges uncertainty as to whether this was indeed DOD's goal.
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DOD Study Applicability Tool As discussed in Chapter 4, DOD created a study applicability tool to evaluate individual animal studies (Sussan et al.
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The committee recommends that DOD abandon the use of this study applicability tool in favor of established tools to assess risk of bias of animal and human studies (e.g., NTP 2019)
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. Use of Human Studies in the Assessment DOD developed a PECO statement that included human studies, and the associated literature search yielded 58 human studies published since 2010 that met the inclusion criteria (Sussan et al.
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(2003) study did not receive an applicability score, suggesting that it was not evaluated using DOD's study applicability tool but was excluded from consideration earlier in the process.
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While the overall conclusion drawn by DOD about the human studies related to TCE and CHD might be appropriate, the assessment would be improved if all relevant human studies were assessed for risk of bias using an appropriate tool. The committee's evaluation of the presented CHD data also revealed some additional inconsistencies with respect to how DOD's systematic review was performed.
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Thus, DOD could consider using the proposed OEL as an interim value while these improvements occur. In the short term, DOD could focus efforts on the recurring concerns that touched on nearly all steps in DOD's approach, namely a lack of transparency that arises from incomplete description of the methods used and inconsistent application of the methods across different data streams (e.g., animal versus human studies, oral versus inhalation studies, noncancer versus cancer effects)
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2003. Threshold of trichloro ethylene contamination in maternal drinking waters affecting fetal heart develop ment in the rat.
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2018. Role of risk of bias in systematic review for chemical risk assessment: A case study in understanding the relationship between congenital heart defects and exposures to trichloroethylene.
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