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Toxicological Profile for Bromodichloromethane. Atlanta (GA): Agency for Toxic Substances and Disease Registry (US); 2020 Mar.
Toxicological Profile for Bromodichloromethane.
Show detailsTo increase the transparency of ATSDR’s process of identifying, evaluating, synthesizing, and interpreting the scientific evidence on the health effects associated with exposure to bromodichloromethane, ATSDR utilized a slight modification of NTP’s Office of Health Assessment and Translation (OHAT) systematic review methodology (NTP 2013, 2015; Rooney et al. 2014). ATSDR’s framework is an eight-step process for systematic review with the goal of identifying the potential health hazards of exposure to bromodichloromethane:
- Step 1. Problem Formulation
- Step 2. Literature Search and Screen for Health Effects Studies
- Step 3. Extract Data from Health Effects Studies
- Step 4. Identify Potential Health Effect Outcomes of Concern
- Step 5. Assess the Risk of Bias for Individual Studies
- Step 6. Rate the Confidence in the Body of Evidence for Each Relevant Outcome
- Step 7. Translate Confidence Rating into Level of Evidence of Health Effects
- Step 8. Integrate Evidence to Develop Hazard Identification Conclusions
C.1. PROBLEM FORMULATION
The objective of the toxicological profile and this systematic review was to identify the potential health hazards associated with inhalation, oral, or dermal/ocular exposure to bromodichloromethane. The inclusion criteria used to identify relevant studies examining the health effects of bromodichloromethane are presented in Table C-1.
Data from human and laboratory animal studies were considered relevant for addressing this objective. Human studies were divided into two broad categories: observational epidemiology studies and controlled exposure studies. The observational epidemiology studies were further divided: cohort studies (retrospective and prospective studies), population studies (with individual data or aggregate data), and case-control studies.
Table C-1Inclusion Criteria for Identifying Health Effects Studies
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C.2. LITERATURE SEARCH AND SCREEN FOR HEALTH EFFECTS STUDIES
A literature search and screen was conducted to identify studies examining the health effects of bromodichloromethane. The literature search framework for the toxicological profile is discussed in detail in Appendix B.
C.2.1. Literature Search
As noted in Appendix B, the current literature search was intended to update the draft toxicological profile for bromodichloromethane released for public comment in 2018. See Appendix B for the databases searched and the search strategy.
A total of 209 records relevant to all sections of the toxicological profile were identified (after duplicate removal).
C.2.2. Literature Screening
As described in Appendix B, a two-step process was used to screen the literature search to identify relevant studies examining the health effects of bromodichloromethane.
Title and Abstract Screen. In the Title and Abstract Screen step, 236 records were reviewed; 12 documents were considered to meet the health effects inclusion criteria in Table C-1 and were moved to the next step in the process.
Full Text Screen. In the second step in the literature screening process for the systematic review, a full text review of the 12 health effects documents identified in the update literature was performed. From those 12 documents, 8 studies were included in the qualitative review. Additionally, 77 studies cited in the LSE tables for the existing profile were included in the full study screen bringing the total number of studies for the qualitative review to 85.
C.3. EXTRACT DATA FROM HEALTH EFFECTS STUDIES
Relevant data extracted from the individual studies selected for inclusion in the systematic review were collected in customized data forms. A summary of the type of data extracted from each study is presented in Table C-2. For references that included more than one experiment or species, data extraction records were created for each experiment or species.
Table C-2Data Extracted From Individual Studies
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A summary of the extracted data for each study is presented in the Supplemental Document for Bromodichloromethane and overviews of the results of the inhalation and oral exposure studies (no dermal exposure studies were identified) are presented in Sections 2.2–2.18 of the profile and in the Levels Significant Exposures tables in Section 2.1 of the profile (Tables 2-2 and 2-3, respectively).
C.4. IDENTIFY POTENTIAL HEALTH EFFECT OUTCOMES OF CONCERN
Overviews of the potential health effect outcomes for bromodichloromethane identified in human and animal studies are presented in Tables C-3 and C-4, respectively. The available human studies examined a limited number of endpoints (hepatic, immunological, reproductive, and developmental effects) and reported immunological, reproductive, and developmental effects. Animal studies examined a number of endpoints following inhalation or oral exposure. These studies examined most endpoints and reported body weight, gastrointestinal, hematological, hepatic, renal, ocular, endocrine, immunological, reproductive, developmental, and other noncancer (alterations in blood glucose) effects. Hepatic, renal, immunological, reproductive, and developmental effects were considered sensitive outcomes (i.e., effects were observed at low concentrations or doses). Studies examining these potential outcomes were carried through to Steps 4–8 of the systematic review. Eighty-five studies (published in 54 documents) examining these potential outcomes were carried through to Steps 4–8 of the systematic review.
Table C-3Overview of the Health Outcomes for Bromodichloromethane Evaluated In Human Studies
Body weight | Respiratory | Cardiovascular | Gastrointestinal | Hematological | Musculoskeletal | Hepatic | Renal | Dermal | Ocular | Endocrine | Immunological | Neurological | Reproductive | Developmental | Other Noncancer | Caner | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Inhalation studies | |||||||||||||||||
Cohort | |||||||||||||||||
Case control | |||||||||||||||||
Population | |||||||||||||||||
Case series | |||||||||||||||||
Oral studies | |||||||||||||||||
Cohort | 2 | 9 | 1 | ||||||||||||||
2 | 8 | 1 | |||||||||||||||
Case control | 4 | 1 | |||||||||||||||
2 | 1 | ||||||||||||||||
Population | 1 | 1 | 1 | 1 | |||||||||||||
0 | 1 | 0 | 0 | ||||||||||||||
Case series | |||||||||||||||||
Dermal studies | |||||||||||||||||
Cohort | |||||||||||||||||
Case control | |||||||||||||||||
Population | |||||||||||||||||
Case series | |||||||||||||||||
Number of studies examining endpoint | 0 | 1 | 2 | 3 | 4 | 5-9 | ≥10 | ||||||||||
Number of studies reporting outcome | 0 | 1 | 2 | 3 | 4 | 5-9 | ≥10 |
Table C-4Overview of the Health Outcomes for Bromodichloromethane Evaluated in Experimental Animal Studies
Body weight | Respiratory | Cardiovascular | Gastrointestinal | Hematological | Musculoskeletal | Hepatic | Renal | Dermal | Ocular | Endocrine | Immunologicala | Neurologicala | Reproductivea | Developmental | Other Noncancer | Caner | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Inhalation studies | |||||||||||||||||
Acute-duration | 2 | 2 | 2 | 2 | 2 | ||||||||||||
2 | 2 | 2 | 2 | 0 | |||||||||||||
Intermediate-duration | 3 | 2 | 2 | 3 | |||||||||||||
0 | 0 | 2 | 0 | ||||||||||||||
Chronic-duration | |||||||||||||||||
Oral studies | |||||||||||||||||
Acute-duration | 16 | 1 | 1 | 1 | 3 | 1 | 9 | 8 | 1 | 3 | 3 | 4 | 7 | 5 | |||
12 | 0 | 0 | 0 | 2 | 0 | 7 | 6 | 0 | 2 | 2 | 3 | 7 | 1 | ||||
Intermediate-duration | 11 | 7 | 7 | 9 | 6 | 9 | 11 | 7 | 2 | 8 | 6 | 3 | 2 | ||||
5 | 0 | 0 | 1 | 0 | 6 | 2 | 0 | 1 | 1 | 2 | 1 | 1 | |||||
Chronic-duration | 8 | 7 | 7 | 7 | 1 | 8 | 7 | 7 | 1 | 6 | 1 | 8 | |||||
4 | 0 | 0 | 0 | 0 | 4 | 3 | 1 | 0 | 1 | 1 | 3 | ||||||
Dermal studies | |||||||||||||||||
Acute-duration | |||||||||||||||||
Intermediate-duration | |||||||||||||||||
Chronic-duration | |||||||||||||||||
Number of studies examining endpoint | 0 | 1 | 2 | 3 | 4 | 5-9 | ≥10 | ||||||||||
Number of studies reporting outcome | 0 | 1 | 2 | 3 | 4 | 5-9 | ≥10 |
- a
Number of studies examining endpoint includes study evaluating histopathology, but not evaluating function
C.5. ASSESS THE RISK OF BIAS FOR INDIVIDUAL STUDIES
C.5.1. Risk of Bias Assessment
The risk of bias of individual studies was assessed using OHAT’s Risk of Bias Tool (NTP 2015). The risk of bias questions for observational epidemiology studies, human-controlled exposure studies, and animal experimental studies are presented in Tables C-5, C-6, and C-7, respectively. Each risk of bias question was answered on a four-point scale:
- Definitely low risk of bias (++)
- Probably low risk of bias (+)
- Probably high risk of bias (−)
- Definitely high risk of bias (− −)
In general, “definitely low risk of bias” or “definitely high risk of bias” was used if the question could be answered with information explicitly stated in the study report. If the response to the question could be inferred, then “probably low risk of bias” or “probably high risk of bias” response was typically used.
Table C-5Risk of Bias Questionnaire for Observational Epidemiology Studies
Selection bias
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Confounding bias
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Attrition/exclusion bias
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Detection bias
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Selective reporting bias
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Table C-6Risk of Bias Questionnaire for Human-Controlled Exposure Studies
Selection bias
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Performance bias
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Attrition/exclusion bias
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Detection bias
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Selective reporting bias
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Table C-7Risk of Bias Questionnaire for Experimental Animal Studies
Selection bias
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Performance bias
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Attrition/exclusion bias
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Detection bias
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Selective reporting bias
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After the risk of bias questionnaires were completed for the health effects studies, the studies were assigned to one of three risk of bias tiers based on the responses to the key questions listed below and the responses to the remaining questions.
- Is there confidence in the exposure characterization? (only relevant for observational studies)
- Is there confidence in the outcome assessment?
- Does the study design or analysis account for important confounding and modifying variables? (only relevant for observational studies)
First Tier. Studies placed in the first tier received ratings of “definitely low” or “probably low” risk of bias on the key questions AND received a rating of “definitely low” or “probably low” risk of bias on the responses to at least 50% of the other applicable questions.
Second Tier. A study was placed in the second tier if it did not meet the criteria for the first or third tiers.
Third Tier. Studies placed in the third tier received ratings of “definitely high” or “probably high” risk of bias for the key questions AND received a rating of “definitely high” or “probably high” risk of bias on the response to at least 50% of the other applicable questions.
The results of the risk of bias assessment for the different types of bromodichloromethane health effects studies (observational epidemiology and animal experimental studies) are presented in Tables C-8 and C-9, respectively.
Table C-8Summary of Risk of Bias Assessment for Bromodichloromethane—Observational Epidemiology Studies
Reference | Risk of bias criteria and ratings | Risk of bias tier | |||||
---|---|---|---|---|---|---|---|
Selection bias | Confounding bias | Attrition / exclusion bias | Detection bias | Selective reporting bias | |||
Comparison groups appropriate? | Study design or analysis account for important confounding and modifying variables?* | Outcome data complete without attrition or exclusion from analysis? | Confidence in exposure characterization?* | Confidence in outcome assessment?* | All measured outcomes reported? | ||
Outcome: Hepatic Effects | |||||||
Cross-sectional studies | |||||||
Burch et al. 2015 | ++ | − | + | + | + | + | Third |
Outcome: Immunological Effects | |||||||
Cohort studies | |||||||
Vlaanderen et al. 2017 | ++ | − | + | + | + | + | Third |
Outcome: Reproductive Effects | |||||||
Cohort studies | |||||||
MacLehose et al. 2008 | ++ | − | + | − | + | + | Third |
Windham et al. 2003 | ++ | − | + | − | + | + | Third |
Cross-sectional studies | |||||||
Zeng et al. 2013 | ++ | − | + | + | + | + | Third |
Outcome: Developmental Effects | |||||||
Cohort studies | |||||||
Cao et al. 2016 | ++ | − | + | + | + | + | Third |
Chen et al. 2019 | ++ | − | + | + | + | + | Third |
Dodds and King 2001 | ++ | − | + | − | + | + | Third |
Grazuleviciene et al. 2013 | ++ | − | + | − | + | + | Third |
King et al. 2000 | ++ | − | + | − | + | + | Third |
Rivera-Núñez and Wright 2013 | ++ | − | + | − | + | + | Third |
Summerhayes et al. 2012 | ++ | − | + | − | + | + | Third |
Waller et al. 1998 | ++ | − | + | − | + | + | Third |
Wright et al. 2004 | ++ | − | + | − | + | + | Third |
Case-control Studies | |||||||
Danileviciute et al. 2012 | ++ | − | + | − | + | + | Third |
Iszatt et al. 2011 | ++ | − | + | − | + | + | Third |
Rivera-Núñez et al. 2018 | ++ | − | + | − | + | + | Third |
Wright et al. 2017 | ++ | − | + | − | + | + | Third |
++ = definitely low risk of bias; + = probably low risk of bias; − = probably high risk of bias; − − = definitely high risk of bias; na = not applicable
- *
Key question used to assign risk of bias tier
Table C-9Summary of Risk of Bias Assessment for Bromodichloromethane—Experimental Animal Studies
Reference | Risk of bias criteria and ratings | Risk of bias tier | |||||||
---|---|---|---|---|---|---|---|---|---|
Selection bias | Performance bias | Attrition/exclusion bias | Detection bias | Selective reporting bias | |||||
Administered dose or exposure level adequately randomized? | Allocation to study groups adequately concealed? | Experimental conditions identical across study groups? | Research personnel blinded to the study group during the study? | Outcome data complete without attrition or exclusion from analysis? | Confidence in exposure characterization? | Confidence in outcome assessment?* | All measured outcomes reported? | ||
Outcome: Hepatic Effects | |||||||||
Inhalation acute exposure | |||||||||
Torti et al. 2001 (C57BL/6 mouse) | ++ | + | ++ | + | + | + | + | + | First |
Torti et al. 2001 (FVN mouse) | ++ | + | ++ | + | + | + | + | + | First |
Inhalation intermediate exposure | |||||||||
Torti et al. 2001 (C57BL/6 mouse) | ++ | + | ++ | + | + | + | + | + | First |
Torti et al. 2001 (FVN mouse | ++ | + | ++ | + | + | + | + | + | First |
Oral acute exposure | |||||||||
Condie et al. 1983 (mouse) | − | + | + | + | + | − | + | + | First |
Keegan et al. 1998 (rat) | − | + | + | + | + | + | + | + | First |
Lilly et al. 1994 (rat, GW) | + | + | + | + | + | + | + | + | First |
Lilly et al. 1994 (rat, GO) | + | + | + | + | + | + | + | + | First |
Lilly et al. 1996 (rat) | + | + | + | + | + | + | + | + | First |
Munson et al. 1982 (mouse) | − | + | + | + | + | + | + | + | First |
Ruddick et al. 1983 (rat) | + | + | + | + | + | + | + | + | First |
Thornton-Manning et al. 1994 (rat) | + | + | + | + | + | + | + | + | First |
Thornton-Manning et al. 1994 (mouse) | + | + | + | + | + | + | + | + | First |
Oral intermediate exposure | |||||||||
Aida et al. 1989 (rat, F) | − | + | + | + | + | + | + | + | First |
Aida et al. 1989 (rat, W) | − | + | + | + | + | + | + | + | First |
Aida et al. 1992 (rat) | + | + | + | + | + | + | + | + | First |
Chu et al. 1982 (rat) | − | + | + | + | + | − | + | + | First |
Hooth et al. 2002 (rat) | + | + | + | + | + | + | + | + | First |
NTP 1987 (rat) | ++ | + | + | + | + | ++ | + | + | First |
NTP 1987 (mouse) | ++ | + | + | + | + | ++ | + | + | First |
NTP 2006 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
Oral chronic exposure | |||||||||
Aida et al. 1992 (rat) | + | + | + | + | + | + | + | + | First |
George et al. 2002 (rat) | + | + | + | + | + | + | + | + | First |
George et al. 2002 (mouse) | + | + | + | + | + | + | + | + | First |
NTP 1987 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 1987 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
Tumasonis et al. 1985 (rat) | − | + | + | + | + | + | + | + | First |
Outcome: Renal Effects | |||||||||
Inhalation acute exposure | |||||||||
Torti et al. 2001 (C57BL/6 mouse) | ++ | + | ++ | + | + | + | + | + | First |
Torti et al. 2001 (FVN mouse) | ++ | + | ++ | + | + | + | + | + | First |
Inhalation intermediate exposure | |||||||||
Torti et al. 2001 (C57BL/6 mouse) | ++ | + | ++ | + | + | + | + | + | First |
Torti et al. 2001 (FVN mouse) | ++ | + | ++ | + | + | + | + | + | First |
Oral acute exposure | |||||||||
Condie et al. 1983 (mouse) | − | + | + | + | + | − | + | + | First |
Lilly et al. 1994 (rat, GW) | + | + | + | + | + | + | + | + | First |
Lilly et al. 1994 (rat, GO) | + | + | + | + | + | + | + | + | First |
Lilly et al. 1996 (rat) | + | + | + | + | + | + | + | + | First |
Munson et al. 1982 (mouse) | − | + | + | + | + | + | + | + | First |
Ruddick et al. 1983 (rat) | + | + | + | + | + | + | + | + | First |
Thornton-Manning et al. 1994 (rat) | + | + | + | + | + | + | + | + | First |
Thornton-Manning et al. 1994 (mouse) | + | + | + | + | + | + | + | + | First |
Oral intermediate exposure | |||||||||
Aida et al. 1989 (rat, F) | − | + | + | + | + | + | + | + | First |
Aida et al. 1989 (rat, W) | − | + | + | + | + | + | + | + | First |
Aida et al. 1992 (rat) | + | + | + | + | + | + | + | + | First |
Chu et al. 1982 (rat) | − | + | + | + | + | − | + | + | First |
Lipsky et al. 1993 (rat) | − | + | + | + | + | − | + | + | First |
Lock et al. 2004 (rat) | − | + | + | + | + | + | + | + | First |
Lock et al. 2004 (mouse) | − | + | + | + | + | + | + | + | First |
NTP 1987 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 1987 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
Oral chronic exposure | |||||||||
Aida et al. 1992 (rat) | + | + | + | + | + | + | + | + | First |
George et al. 2002 (rat) | + | + | + | + | + | + | + | + | First |
George et al. 2002 (mouse) | + | + | + | + | + | + | + | + | First |
NTP 1987 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 1987 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
Outcome: Immunological Effects | |||||||||
Oral acute exposure | |||||||||
French et al. 1999 (rat, 5 days) | − | + | + | + | + | + | + | + | First |
French et al. 1999 (rat, 14 days) | − | + | + | + | + | + | + | + | First |
Munson et al. 1982 | − | + | + | + | + | + | + | + | First |
Oral intermediate exposure | |||||||||
French et al. 1999 (mouse, 16 days; GW) | − | + | + | + | + | + | + | + | First |
French et al. 1999 (rat, 26 weeks; W) | − | + | + | + | + | + | + | + | First |
Outcome: Reproductive Effects | |||||||||
Oral acute exposure | |||||||||
Bielmeier et al. 2001 (rat, GDs 8–9) | − | + | + | + | + | + | + | ++ | First |
Bielmeier et al. 2004 (rat) | − | + | + | + | + | + | + | ++ | First |
Bielmeier et al. 2007 (rat) | − | + | + | + | + | + | + | ++ | First |
Ruddick et al. 1983 (rat) | + | + | + | + | + | + | + | + | First |
Oral intermediate exposure | |||||||||
Aida et al. 1992 (rat) | + | + | + | + | + | + | + | + | First |
Christian et al. 2001b | ++ | + | + | + | + | + | + | + | First |
NTP 1987 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 1987 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
Oral chronic exposure | |||||||||
Aida et al. 1992 (rat) | + | + | + | + | + | + | + | + | First |
Klinefelter et al. 1995 (rat) | − | + | + | + | + | + | + | + | First |
NTP 1987 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 1987 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (rat) | ++ | + | + | + | + | ++ | + | ++ | First |
NTP 2006 (mouse) | ++ | + | + | + | + | ++ | + | ++ | First |
Outcome: Developmental Effects | |||||||||
Oral Acute Exposure | |||||||||
Bielmeier et al. 2001 (rat, GDs 6–10) | − | + | + | + | + | + | + | ++ | First |
Bielmeier et al. 2001 (Sprague-Dawley rat, GDs 6–10) | − | + | + | + | + | + | + | ++ | First |
Bielmeier et al. 2001 (rat, GDs 8–9) | − | + | + | + | + | + | + | ++ | First |
Bielmeier et al. 2001 (rat, GDs 6–10 or 6–15) | − | + | + | + | + | + | + | ++ | First |
Bielmeier et al. 2004 (rat) | − | + | + | + | + | + | + | ++ | First |
Narotsky et al. 1997 (rat) | ++ | + | + | + | + | + | + | ++ | First |
Ruddick et al. 1983 (rat) | + | + | + | + | + | + | + | + | First |
Oral intermediate exposure | |||||||||
Christian et al. 2001a (rat) | ++ | + | + | + | + | + | + | + | First |
Christian et al. 2001a (rabbit) | ++ | + | + | + | + | + | + | + | First |
Christian et al. 2001b (rat) | ++ | + | + | + | + | + | + | + | First |
++ = definitely low risk of bias; + = probably low risk of bias; − = probably high risk of bias; − − = definitely high risk of bias; na = not applicable
- *
Key question used to assign risk of bias tier
C.6. RATE THE CONFIDENCE IN THE BODY OF EVIDENCE FOR EACH RELEVANT OUTCOME
Confidences in the bodies of human and animal evidence were evaluated independently for each potential outcome. ATSDR did not evaluate the confidence in the body of evidence for carcinogenicity; rather, the Agency defaulted to the cancer weight-of-evidence assessment of other agencies including DHHS, EPA, and IARC. The confidence in the body of evidence for an association or no association between exposure to bromodichloromethane and a particular outcome was based on the strengths and weaknesses of individual studies. Four descriptors were used to describe the confidence in the body of evidence for effects or when no effect was found:
- High confidence: the true effect is highly likely to be reflected in the apparent relationship
- Moderate confidence: the true effect may be reflected in the apparent relationship
- Low confidence: the true effect may be different from the apparent relationship
- Very low confidence: the true effect is highly likely to be different from the apparent relationship
Confidence in the body of evidence for a particular outcome was rated for each type of study: case-control, case series, cohort, population, human-controlled exposure, and experimental animal. In the absence of data to the contrary, data for a particular outcome were collapsed across animal species, routes of exposure, and exposure durations. If species (or strain), route, or exposure duration differences were noted, then the data were treated as separate outcomes.
C.6.1. Initial Confidence Rating
In ATSDR’s modification to the OHAT approach, the body of evidence for an association (or no association) between exposure to bromodichloromethane and a particular outcome was given an initial confidence rating based on the key features of the individual studies examining that outcome. The presence of these key features of study design was determined for individual studies using four “yes or no” questions, which were customized for epidemiology, human controlled exposure, or experimental animal study designs. Separate questionnaires were completed for each outcome assessed in a study. The key features for observational epidemiology (cohort, population, and case-control) studies, human controlled exposure, and experimental animal studies are presented in Tables C-10, C-11, and C-12, respectively. The initial confidence in the study was determined based on the number of key features present in the study design:
- High Initial Confidence: Studies in which the responses to the four questions were “yes”.
- Moderate Initial Confidence: Studies in which the responses to only three of the questions were “yes”.
- Low Initial Confidence: Studies in which the responses to only two of the questions were “yes”.
- Very Low Initial Confidence: Studies in which the response to one or none of the questions was “yes”.
Table C-10Key Features of Study Design for Observational Epidemiology Studies
Exposure was experimentally controlled |
Exposure occurred prior to the outcome |
Outcome was assessed on individual level rather than at the population level |
A comparison group was used |
Table C-11Key Features of Study Design for Human-Controlled Exposure Studies
A comparison group was used or the subjects served as their own control |
A sufficient number of subjects were tested |
Appropriate methods were used to measure outcomes (i.e., clinically-confirmed outcome versus self-reported) |
Appropriate statistical analyses were performed and reported or the data were reported in such a way to allow independent statistical analysis |
Table C-12Key Features of Study Design for Experimental Animal Studies
A concurrent control group was used |
A sufficient number of animals per group were tested |
Appropriate parameters were used to assess a potential adverse effect |
Appropriate statistical analyses were performed and reported or the data were reported in such a way to allow independent statistical analysis |
The presence or absence of the key features and the initial confidence levels for studies examining hepatic, renal, immunological, reproductive, and developmental effects observed in the observational epidemiology and animal experimental studies are presented in Tables C-13 and C-14, respectively.
Table C-13Presence of Key Features of Study Design for Bromodichloromethane—Observational Epidemiology Studies
Reference | Key features | Initial study confidence | |||
---|---|---|---|---|---|
Controlled exposure | Exposure prior to outcome | Outcomes assessed on an individual level | Comparison group | ||
Outcome: Hepatic effects | |||||
Cross-sectional studies | |||||
Burch et al. 2015 | No | No | Yes | Yes | Low |
Outcome: Immunological effects | |||||
Cohort studies | |||||
Vlaanderen et al. 2017 | No | Yes | Yes | Yes | Moderate |
Outcome: Reproductive effects | |||||
Cohort studies | |||||
MacLehose et al. 2008 | No | No | Yes | Yes | Low |
Windham et al. 2003 | No | No | Yes | Yes | Low |
Cross-sectional studies | |||||
Zeng et al. 2013 | No | No | Yes | Yes | Low |
Outcome: Developmental effects | |||||
Cohort studies | |||||
Cao et al. 2016 | No | No | Yes | Yes | Low |
Chen et al. 2019 | No | No | Yes | Yes | Low |
Dodds and King 2001 | No | No | Yes | Yes | Low |
Grazuleviciene et al. 2013 | No | No | Yes | Yes | Low |
King et al. 2000 | No | No | Yes | Yes | Low |
Rivera-Núñez and Wright 2013 | No | No | Yes | Yes | Low |
Summerhayes et al. 2012 | No | No | Yes | Yes | Low |
Waller et al. 1998 | No | No | Yes | Yes | Low |
Wright et al. 2004 | No | No | Yes | Yes | Low |
Case-control studies | |||||
Danileviciute et al. 2012 | No | No | Yes | Yes | Low |
Iszatt et al. 2011 | No | No | Yes | Yes | Low |
Rivera-Núñez et al. 2018 | No | No | Yes | Yes | Low |
Wright et al. 2017 | No | No | Yes | Yes | Low |
Table C-14Presence of Key Features of Study Design for Bromodichloromethane—Experimental Animal Studies
Reference | Key features | Initial study confidence | |||
---|---|---|---|---|---|
Concurrent control group | Sufficient number of animals per group | Appropriate parameters to assess potential effect | Adequate data for statistical analysis | ||
Outcome: Hepatic Effects | |||||
Inhalation acute exposure | |||||
Torti et al. 2001 (C57BL/6 mouse) | Yes | No | Yes | Yes | Moderate |
Torti et al. 2001 (FVN mouse) | Yes | No | Yes | Yes | Moderate |
Inhalation intermediate exposure | |||||
Torti et al. 2001 (C57BL/6 mouse) | Yes | No | Yes | Yes | Moderate |
Torti et al. 2001 (FVN mouse) | Yes | No | Yes | Yes | Moderate |
Oral acute exposure | |||||
Condie et al. 1983 (mouse) | Yes | No | Yes | Yes | Moderate |
Keegan et al. 1998 (rat) | Yes | No | No | Yes | Low |
Lilly et al. 1994 (rat, GW) | Yes | No | Yes | Yes | Moderate |
Lilly et al. 1994 (rat, GO) | Yes | No | Yes | Yes | Moderate |
Lilly et al. 1996 (rat) | Yes | No | Yes | Yes | Moderate |
Munson et al. 1982 (mouse) | Yes | No | No | Yes | Low |
Ruddick et al. 1983 (rat) | Yes | No | Yes | Yes | Moderate |
Thornton-Manning et al. 1994 (rat) | Yes | No | Yes | Yes | Moderate |
Thornton-Manning et al. 1994 (mouse) | Yes | No | Yes | Yes | Moderate |
Oral intermediate exposure | |||||
Aida et al. 1989 (rat, F) | Yes | No | Yes | Yes | Moderate |
Aida et al. 1989 (rat, W) | Yes | No | Yes | Yes | Moderate |
Aida et al. 1992 (rat) | Yes | Yes | Yes | Yes | High |
Chu et al. 1982 (rat) | Yes | No | Yes | Yes | Moderate |
Hooth et al. 2002 (rat) | Yes | No | Yes | Yes | Moderate |
NTP 1987 (rat) | Yes | Yes | Yes | Yes | High |
NTP 1987 (mouse) | Yes | Yes | Yes | Yes | High |
NTP 2006 (rat) | Yes | No | Yes | Yes | Moderate |
NTP 2006 (mouse) | Yes | No | Yes | Yes | Moderate |
Oral chronic exposure | |||||
Aida et al. 1992 (rat) | Yes | Yes | Yes | Yes | High |
George et al. 2002 (rat) | Yes | No | Yes | Yes | Moderate |
George et al. 2002 (mouse) | Yes | No | Yes | Yes | Moderate |
NTP 1987 (rat) | Yes | Yes | Yes | Yes | High |
NTP 1987 (mouse) | Yes | Yes | Yes | Yes | High |
NTP 2006 (rat) | Yes | No | Yes | Yes | Moderate |
NTP 2006 (mouse) | Yes | No | Yes | Yes | Moderate |
Tumasonis et al. 1985 (rat) | Yes | Yes | Yes | Yes | High |
Outcome: Renal Effects | |||||
Inhalation acute exposure | |||||
Torti et al. 2001 (C57BL/6 mouse) | Yes | No | Yes | Yes | Moderate |
Torti et al. 2001 (FVN mouse) | Yes | No | Yes | Yes | Moderate |
Inhalation intermediate exposure | |||||
Torti et al. 2001 (C57BL/6 mouse) | Yes | No | Yes | Yes | Moderate |
Torti et al. 2001 (FVN mouse) | Yes | No | Yes | Yes | Moderate |
Oral acute exposure | |||||
Condie et al. 1983 (mouse) | Yes | No | Yes | Yes | Moderate |
Lilly et al. 1994 (rat, GW) | Yes | No | Yes | Yes | Moderate |
Lilly et al. 1994 (rat, GO) | Yes | No | Yes | Yes | Moderate |
Lilly et al. 1996 (rat) | Yes | No | Yes | Yes | Moderate |
Munson et al. 1982 (mouse) | Yes | No | No | Yes | Low |
Ruddick et al. 1983 (rat) | Yes | No | Yes | Yes | Moderate |
Thornton-Manning et al. 1994 (rat) | Yes | No | Yes | Yes | Moderate |
Thornton-Manning et al. 1994 (mouse) | Yes | No | Yes | Yes | Moderate |
Oral intermediate exposure | |||||
Aida et al. 1989 (rat, F) | Yes | No | Yes | Yes | Moderate |
Aida et al. 1989 (rat, W) | Yes | No | Yes | Yes | Moderate |
Aida et al. 1992 (rat) | Yes | Yes | Yes | Yes | High |
Chu et al. 1982 (rat) | Yes | No | Yes | Yes | Moderate |
Lipsky et al. 1993 (rat) | Yes | No | Yes | Yes | Moderate |
Lock et al. 2004 (rat) | Yes | No | Yes | Yes | Moderate |
Lock et al. 2004 (mouse) | Yes | No | Yes | Yes | Moderate |
NTP 1987 (rat) | Yes | Yes | Yes | Yes | High |
NTP 1987 (mouse) | Yes | Yes | Yes | Yes | High |
NTP 2006 (rat) | Yes | No | Yes | Yes | Moderate |
NTP 2006 (mouse) | Yes | No | Yes | Yes | Moderate |
Oral chronic exposure | |||||
Aida et al. 1992 (rat) | Yes | Yes | Yes | Yes | High |
George et al. 2002 (rat) | Yes | No | Yes | Yes | Moderate |
George et al. 2002 (mouse) | Yes | No | Yes | Yes | Moderate |
NTP 1987 (rat) | Yes | Yes | Yes | Yes | High |
NTP 1987 (mouse) | Yes | Yes | Yes | Yes | High |
NTP 2006 (rat) | Yes | No | Yes | Yes | Moderate |
NTP 2006 (mouse) | Yes | No | Yes | Yes | Moderate |
Outcome: Immunological Effects | |||||
Oral acute exposure | |||||
French et al. 1999 (rat, 5 days) | Yes | No | Yes | Yes | Moderate |
French et al. 1999 (rat, 14 days) | Yes | No | Yes | Yes | Moderate |
Munson et al. 1982 (mouse) | Yes | No | No | Yes | Low |
Oral intermediate exposure | |||||
French et al. 1999 (mouse, 16 days; GW) | Yes | No | Yes | Yes | Moderate |
French et al. 1999 (rat, 26 weeks, W) | Yes | No | Yes | Yes | Moderate |
Outcome: Reproductive Effects | |||||
Oral acute exposure | |||||
Bielmeier et al. 2001 (rat, GDs 8–9) | Yes | Yes | No | Yes | Moderate |
Bielmeier et al. 2004 (rat) | Yes | Yes | No | Yes | Moderate |
Bielmeier et al. 2007 (rat) | Yes | No | No | Yes | Low |
Ruddick et al. 1983 (rat) | Yes | Yes | No | Yes | Moderate |
Oral intermediate exposure | |||||
Aida et al. 1992 (rat) | Yes | Yes | No | Yes | Moderate |
Christian et al. 2001b | Yes | Yes | Yes | Yes | High |
NTP 1987 (rat) | Yes | Yes | No | Yes | Moderate |
NTP 1987 (mouse) | Yes | Yes | No | Yes | Moderate |
NTP 2006 (rat) | Yes | Yes | No | Yes | Moderate |
NTP 2006 (mouse) | Yes | Yes | No | Yes | Moderate |
Oral chronic exposure | |||||
Aida et al. 1992 (rat) | Yes | Yes | No | Yes | Moderate |
Klinefelter et al. 1995 (rat) | Yes | Yes | Yes | Yes | High |
NTP 1987 (rat) | Yes | Yes | No | Yes | Moderate |
NTP 1987 (mouse) | Yes | Yes | No | Yes | Moderate |
NTP 2006 (rat) | Yes | Yes | No | Yes | Moderate |
NTP 2006 (mouse) | Yes | Yes | No | Yes | Moderate |
Outcome: Developmental Effects | |||||
Oral Acute Exposure | |||||
Bielmeier et al. 2001 (rat, GDs 6–10) | Yes | Yes | No | Yes | Moderate |
Bielmeier et al. 2001 (Sprague-Dawley rat, GDs 6–10) | Yes | Yes | No | Yes | Moderate |
Bielmeier et al. 2001 (rat, GDs 8–9) | Yes | Yes | No | Yes | Moderate |
Bielmeier et al. 2001 (rat, GDs 6–10 or 6–15) | Yes | Yes | No | Yes | Moderate |
Bielmeier et al. 2004 (rat) | Yes | Yes | No | Yes | Moderate |
Narotsky et al. 1997 (rat) | Yes | Yes | No | Yes | Moderate |
Ruddick et al. 1983 (rat) | Yes | Yes | Yes | No | Moderate |
Oral intermediate exposure | |||||
Christian et al. 2001a (rat) | Yes | Yes | Yes | Yes | High |
Christian et al. 2001a (rabbit) | Yes | Yes | Yes | Yes | High |
Christian et al. 2001b (rat) | Yes | Yes | No | Yes | Moderate |
A summary of the initial confidence ratings for each outcome is presented in Table C-15. If individual studies for a particular outcome and study type had different study quality ratings, then the highest confidence rating for the group of studies was used to determine the initial confidence rating for the body of evidence; any exceptions were noted in Table C-15.
Table C-15Initial Confidence Rating for Bromodichloromethane Health Effects Studies
Initial study confidence | Initial confidence rating | |
---|---|---|
Outcome: Hepatic Effects | ||
Inhalation acute exposure | ||
Animal studies | ||
Torti et al. 2001 (C57BL/6 mouse) | Moderate | Moderate |
Torti et al. 2001 (FVN mouse) | Moderate | |
Inhalation intermediate exposure | ||
Animal studies | ||
Torti et al. 2001 (C57BL/6 mouse) | Moderate | Moderate |
Torti et al. 2001 (FVN mouse) | Moderate | |
Oral acute exposure | ||
Animal studies | ||
Condie et al. 1983 (mouse) | Moderate | Moderate |
Keegan et al. 1998 (rat) | Low | |
Lilly et al. 1994 (rat, GW) | Moderate | |
Lilly et al. 1994 (rat, GO) | Moderate | |
Lilly et al. 1996 (rat) | Moderate | |
Munson et al. 1982 (mouse) | Low | |
Ruddick et al. 1983 (rat) | Moderate | |
Thornton-Manning et al. 1994 (rat) | Moderate | |
Thornton-Manning et al. 1994 (mouse) | Moderate | |
Oral intermediate exposure | ||
Animal studies | ||
Aida et al. 1989 (rat, F) | Moderate | High |
Aida et al. 1989 (rat, W) | Moderate | |
Aida et al. 1992 (rat) | High | |
Chu et al. 1982 (rat) | Moderate | |
Hooth et al. 2002 (rat) | Moderate | |
NTP 1987 (rat) | High | |
NTP 1987 (mouse) | High | |
NTP 2006 (rat) | Moderate | |
NTP 2006 (mouse) | Moderate | |
Oral chronic exposure | ||
Human studies | ||
Burch et al. 2015 | Low | Low |
Animal studies | ||
Aida et al. 1992 (rat) | High | High |
George et al. 2002 (rat) | Moderate | |
George et al. 2002 (mouse) | Moderate | |
NTP 1987 (rat) | High | |
NTP 1987 (mouse) | High | |
NTP 2006 (rat) | Moderate | |
NTP 2006 (mouse) | Moderate | |
Tumasonis et al. 1985 (rat) | High | |
Outcome: Renal Effects | ||
Inhalation acute exposure | ||
Animal studies | ||
Torti et al. 2001 (C57BL/6 mouse) | Moderate | Moderate |
Torti et al. 2001 (FVN mouse) | Moderate | |
Inhalation intermediate exposure | ||
Animal studies | ||
Torti et al. 2001 (C57BL/6 mouse) | Moderate | Moderate |
Torti et al. 2001 (FVN mouse) | Moderate | |
Oral acute exposure | ||
Animal studies | ||
Condie et al. 1983 (mouse) | Moderate | Moderate |
Lilly et al. 1994 (rat, GW) | Moderate | |
Lilly et al. 1994 (rat, GO) | Moderate | |
Lilly et al. 1996 (rat) | Moderate | |
Munson et al. 1982 (mouse) | Low | |
Ruddick et al. 1983 (rat) | Moderate | |
Thornton-Manning et al. 1994 (rat) | Moderate | |
Thornton-Manning et al. 1994 (mouse) | Moderate | |
Oral intermediate exposure | ||
Animal studies | ||
Aida et al. 1989 (rat, F) | Moderate | High |
Aida et al. 1989 (rat, W) | Moderate | |
Aida et al. 1992 (rat) | High | |
Chu et al. 1982 (rat) | Moderate | |
Lipsky et al. 1993 (rat) | Moderate | |
Lock et al. 2004 (rat) | Moderate | |
Lock et al. 2004 (mouse) | Moderate | |
NTP 1987 (rat) | High | |
NTP 1987 (mouse) | High | |
NTP 2006 (rat) | Moderate | |
NTP 2006 (mouse) | Moderate | |
Oral chronic exposure | ||
Animal studies | ||
Aida et al. 1992 (rat) | High | High |
George et al. 2002 (rat) | Moderate | |
George et al. 2002 (mouse) | Moderate | |
NTP 1987 (rat) | High | |
NTP 1987 (mouse) | High | |
NTP 2006 (rat) | Moderate | |
NTP 2006 (mouse) | Moderate | |
Outcome: Immunological Effects | ||
Oral acute exposure | ||
Animal studies | ||
French et al. 1999 (rat, 5 days) | Moderate | Moderate |
French et al. 1999 (rat, 14 days) | Moderate | |
Munson et al. 1982 (mouse) | Low | |
Oral intermediate exposure | ||
Animal studies | ||
French et al. 1999 (mouse, 16 days; GW) | Moderate | Moderate |
French et al. 1999 (rat, 26 weeks; W) | Moderate | |
Acute dermal exposure | ||
Human studies | ||
Vlaanderen et al. 2017 | Moderate | Moderate |
Outcome: Reproductive Effects | ||
Oral acute exposure | ||
Animal studies | ||
Bielmeier et al. 2001 (rat, GDs 8–9) | Moderate | Moderate |
Bielmeier et al. 2004 (rat) | Moderate | |
Bielmeier et al. 2007 (rat) | Low | |
Ruddick et al. 1983 (rat) | Moderate | |
Oral intermediate exposure | ||
Animal studies | ||
Aida et al. 1992 (rat) | Moderate | High |
Christian et al. 2001b | High | |
NTP 1987 (rat) | Moderate | |
NTP 1987 (mouse) | Moderate | |
NTP 2006 (rat) | Moderate | |
NTP 2006 (mouse) | Moderate | |
Oral chronic exposure | ||
Human studies | ||
MacLehose et al. 2008 | Low | Low |
Windham et al. 2003 | Low | |
Zeng et al. 2013 | Low | |
Animal studies | ||
Aida et al. 1992 (rat) | Moderate | High |
Klinefelter et al. 1995 (rat) | High | |
NTP 1987 (rat) | Moderate | |
NTP 1987 (mouse) | Moderate | |
NTP 2006 (rat) | Moderate | |
NTP 2006 (mouse) | Moderate | |
Outcome: Developmental Effects | ||
Oral acute exposure | ||
Animal studies | ||
Bielmeier et al. 2001 (F344 rat, GDs 6–10) | Moderate | Moderate |
Bielmeier et al. 2001 (Sprague-Dawley rat, GDs 6–10) | Moderate | |
Bielmeier et al. 2001 (rat, GDs 8–9) | Moderate | |
Bielmeier et al. 2001 (rat, GDs 6–10 or 6–15) | Moderate | |
Bielmeier et al. 2004 (rat) | Moderate | |
Narotsky et al. 1997 (rat) | Moderate | |
Ruddick et al. 1983 (rat) | Moderate | |
Oral intermediate exposure | ||
Animal studies | ||
Christian et al. 2001a (rat) | High | High |
Christian et al. 2001b (rat) | Moderate | |
Christian et al. 2001a (rabbit) | High | |
Oral chronic exposure | ||
Human studies | ||
Cao et al. 2016 | Low | Low |
Chen et al. 2019 | Low | |
Danileviciute et al. 2012 | Low | |
Dodds and King 2001 | Low | |
Grazuleviciene et al. 2013 | Low | |
Iszatt et al. 2011 | Low | |
King et al. 2000 | Low | |
Rivera-Núñez et al. 2018 | Low | |
Rivera-Núñez and Wright 2013 | Low | |
Summerhayes et al. 2012 | Low | |
Waller et al. 1998 | Low | |
Wright et al. 2004 | Low | |
Wright et al. 2017 | Low |
C.6.2. Adjustment of the Confidence Rating
The initial confidence rating was then downgraded or upgraded depending on whether there were substantial issues that would decrease or increase confidence in the body of evidence. The nine properties of the body of evidence that were considered are listed below. The summaries of the assessment of the confidence in the body of evidence for hepatic, renal, immunological, reproductive, and developmental effects are presented in Table C-16. If the confidence ratings for a particular outcome were based on more than one type of human study, then the highest confidence rating was used for subsequent analyses. An overview of the confidence in the body of evidence for all health effects associated with bromodichloromethane exposure is presented in Table C-17.
Five properties of the body of evidence were considered to determine whether the confidence rating should be downgraded:
- Risk of bias. Evaluation of whether there is substantial risk of bias across most of the studies examining the outcome. This evaluation used the risk of bias tier groupings for individual studies examining a particular outcome (Tables C-8 and C-9). Below are the criteria used to determine whether the initial confidence in the body of evidence for each outcome should be downgraded for risk of bias:
- No downgrade if most studies are in the risk of bias first tier
- Downgrade one confidence level if most studies are in the risk of bias second tier
- Downgrade two confidence levels if most studies are in the risk of bias third tier
- Unexplained inconsistency. Evaluation of whether there is inconsistency or large variability in the magnitude or direction of estimates of effect across studies that cannot be explained. Below are the criteria used to determine whether the initial confidence in the body of evidence for each outcome should be downgraded for unexplained inconsistency:
- No downgrade if there is little inconsistency across studies or if only one study evaluated the outcome
- Downgrade one confidence level if there is variability across studies in the magnitude or direction of the effect
- Downgrade two confidence levels if there is substantial variability across studies in the magnitude or direct of the effect
- Indirectness. Evaluation of four factors that can affect the applicability, generalizability, and relevance of the studies:
- Relevance of the animal model to human health—unless otherwise indicated, studies in rats, mice, and other mammalian species are considered relevant to humans
- Directness of the endpoints to the primary health outcome—examples of secondary outcomes or nonspecific outcomes include organ weight in the absence of histopathology or clinical chemistry findings in the absence of target tissue effects
- Nature of the exposure in human studies and route of administration in animal studies—inhalation, oral, and dermal exposure routes are considered relevant unless there are compelling data to the contrary
- Duration of treatment in animal studies and length of time between exposure and outcome assessment in animal and prospective human studies—this should be considered on an outcome-specific basis
- No downgrade if none of the factors are considered indirect
- Downgrade one confidence level if one of the factors is considered indirect
- Downgrade two confidence levels if two or more of the factors are considered indirect
- Imprecision. Evaluation of the narrowness of the effect size estimates and whether the studies have adequate statistical power. Data are considered imprecise when the ratio of the upper to lower 95% CIs for most studies is ≥10 for tests of ratio measures (e.g., odds ratios) and ≥100 for absolute measures (e.g., percent control response). Adequate statistical power is determined if the study can detect a potentially biologically meaningful difference between groups (20% change from control response for categorical data or risk ratio of 1.5 for continuous data). Below are the criteria used to determine whether the initial confidence in the body of evidence for each outcome should be downgraded for imprecision:
- No downgrade if there are no serious imprecisions
- Downgrade one confidence level for serious imprecisions
- Downgrade two confidence levels for very serious imprecisions
- Publication bias. Evaluation of the concern that studies with statistically significant results are more likely to be published than studies without statistically significant results.
- Downgrade one level of confidence for cases where there is serious concern with publication bias
Table C-16Adjustments to the Initial Confidence in the Body of Evidence
Initial confidence | Adjustments to the initial confidence rating | Final confidence | |
---|---|---|---|
Outcome: Hepatic Effects | |||
Human studies | Low | −2 risk of bias | Very Low |
Animal studies | High | +1 large magnitude of effect | High |
Outcome: Renal Effects | |||
Animal studies | High | −1 inconsistency | Moderate |
Outcome: Immunological Effects | |||
Human studies | Moderate | −2 risk of bias, −1 imprecision | Very Low |
Animal studies | Moderate | None | Moderate |
Outcome: Reproductive Effects | |||
Human studies | Low | −2 risk of bias | Very Low |
Animal studies | High | −1 inconsistency. −1 imprecision | Low |
Outcome: Developmental Effects | |||
Human studies | Low | −2 risk of bias | Very Low |
Animal studies | High | +1 large magnitude of effect | High |
Table C-17Confidence in the Body of Evidence for Bromodichloromethane
Outcome | Confidence in body of evidence | |
---|---|---|
Human studies | Animal studies | |
Hepatic effects | Very Low | High |
Renal effects | No data | Moderate |
Immunological effects | Very Low | Moderate |
Reproductive effects | Very Low | Low |
Developmental effects | Very Low | High |
Four properties of the body of evidence were considered to determine whether the confidence rating should be upgraded:
- Large magnitude of effect. Evaluation of whether the magnitude of effect is sufficiently large so that it is unlikely to have occurred as a result of bias from potential confounding factors.
- Upgrade one confidence level if there is evidence of a large magnitude of effect in a few studies, provided that the studies have an overall low risk of bias and there is no serious unexplained inconsistency among the studies of similar dose or exposure levels; confidence can also be upgraded if there is one study examining the outcome, provided that the study has an overall low risk of bias
- Dose response. Evaluation of the dose-response relationships measured within a study and across studies. Below are the criteria used to determine whether the initial confidence in the body of evidence for each outcome should be upgraded:
- Upgrade one confidence level for evidence of a monotonic dose-response gradient
- Upgrade one confidence level for evidence of a non-monotonic dose-response gradient where there is prior knowledge that supports a non-monotonic dose-response and a non-monotonic dose-response gradient is observed across studies
- Plausible confounding or other residual biases. This factor primarily applies to human studies and is an evaluation of unmeasured determinants of an outcome such as residual bias towards the null (e.g., “healthy worker” effect) or residual bias suggesting a spurious effect (e.g., recall bias). Below is the criterion used to determine whether the initial confidence in the body of evidence for each outcome should be upgraded:
- Upgrade one confidence level for evidence that residual confounding or bias would underestimate an apparent association or treatment effect (i.e., bias toward the null) or suggest a spurious effect when results suggest no effect
- Consistency in the body of evidence. Evaluation of consistency across animal models and species, consistency across independent studies of different human populations and exposure scenarios, and consistency across human study types. Below is the criterion used to determine whether the initial confidence in the body of evidence for each outcome should be upgraded:
- Upgrade one confidence level if there is a high degree of consistency in the database
C.7. TRANSLATE CONFIDENCE RATING INTO LEVEL OF EVIDENCE OF HEALTH EFFECTS
In the seventh step of the systematic review of the health effects data for bromodichloromethane, the confidence in the body of evidence for specific outcomes was translated to a level of evidence rating. The level of evidence rating reflected the confidence in the body of evidence and the direction of the effect (i.e., toxicity or no toxicity); route-specific differences were noted. The level of evidence for health effects was rated on a five-point scale:
- High level of evidence: High confidence in the body of evidence for an association between exposure to the substance and the health outcome
- Moderate level of evidence: Moderate confidence in the body of evidence for an association between exposure to the substance and the health outcome
- Low level of evidence: Low confidence in the body of evidence for an association between exposure to the substance and the health outcome
- Evidence of no health effect: High confidence in the body of evidence that exposure to the substance is not associated with the health outcome
- Inadequate evidence: Low or moderate confidence in the body of evidence that exposure to the substance is not associated with the health outcome OR very low confidence in the body of evidence for an association between exposure to the substance and the health outcome
A summary of the level of evidence of health effects for bromodichloromethane is presented in Table C-18.
Table C-18Level of Evidence of Health Effects for Bromodichloromethane
Outcome | Confidence in body of evidence | Direction of health effect | Level of evidence for health effect |
---|---|---|---|
Human studies | |||
Hepatic effects | Very Low | Health effect | Inadequate |
Renal effects | No data | No data | |
Immunological effects | Very Low | Health effect | Inadequate |
Reproductive effects | Very Low | Health effect | Inadequate |
Developmental effect | Very Low | Health effect | Inadequate |
Animal studies | |||
Hepatic effects | High | Health effect | High |
Renal effects | Moderate | Health effect | Moderate |
Immunological effects | Moderate | Health effect | Moderate |
Reproductive effects | Low | Health effect | Low |
Developmental effect | High | Health effect | High |
C.8. INTEGRATE EVIDENCE TO DEVELOP HAZARD IDENTIFICATION CONCLUSIONS
The final step involved the integration of the evidence streams for the human studies and animal studies to allow for a determination of hazard identification conclusions. For health effects, there were four hazard identification conclusion categories:
- Known to be a hazard to humans
- Presumed to be a hazard to humans
- Suspected to be a hazard to humans
- Not classifiable as to the hazard to humans
The initial hazard identification was based on the highest level of evidence in the human studies and the level of evidence in the animal studies; if there were no data for one evidence stream (human or animal), then the hazard identification was based on the one data stream (equivalent to treating the missing evidence stream as having low level of evidence). The hazard identification scheme is presented in Figure C-1 and described below:
- Known: A health effect in this category would have:
- High level of evidence for health effects in human studies AND a high, moderate, or low level of evidence in animal studies.
- Presumed: A health effect in this category would have:
- Moderate level of evidence in human studies AND high or moderate level of evidence in animal studies OR
- Low level of evidence in human studies AND high level of evidence in animal studies
- Suspected: A health effect in this category would have:
- Moderate level of evidence in human studies AND low level of evidence in animal studies OR
- Low level of evidence in human studies AND moderate level of evidence in animal studies
- Not classifiable: A health effect in this category would have:
- Low level of evidence in human studies AND low level of evidence in animal studies
Other relevant data such as mechanistic or mode-of-action data were considered to raise or lower the level of the hazard identification conclusion by providing information that supported or opposed biological plausibility.
Two hazard identification conclusion categories were used when the data indicated that there may be no health effect in humans:
- Not identified to be a hazard in humans
- Inadequate to determine hazard to humans
If the human level of evidence conclusion of no health effect was supported by the animal evidence of no health effect, then the hazard identification conclusion category of “not identified” was used. If the human or animal level of evidence was considered inadequate, then a hazard identification conclusion category of “inadequate” was used. As with the hazard identification for health effects, the impact of other relevant data was also considered for no health effect data.
The hazard identification conclusions for bromodichloromethane are listed below and summarized in Table C-19.
Presumed Health Effects
- Hepatic effects
- Inadequate evidence from a cross-sectional study (Burch et al. 2015) examining the association between serum bromodichloromethane levels and alanine aminotransferase levels.
- High level of evidence in mice following acute inhalation exposure (Torti et al. 2001) and in rats and mice following acute (Condie et al. 1983; Keegan et al. 1998; Lilly et al. 1994, 1996; Munson et al. 1982; Thornton-Manning et al. 1994), intermediate (Aida et al. 1992; Hooth et al. 2002; NTP 1987), and chronic (Aida et al. 1992; NTP 1987) oral exposure.
- Developmental effects
- Although a number of epidemiology studies found associations between exposure to bromodichloromethane and developmental effects, the human data were considered inadequate for evaluating the potential hazard due to the low initial confidence in these studies and the high risk of bias.
- High level of evidence from acute (Bielmeier et al. 2001, 2004; Narotsky et al. 1997) and intermediate (Christian et al. 2001a) oral exposure in rats. The most sensitive developmental endpoint was full-litter resorption in F344 rats, but not in Sprague-Dawley rats (Bielmeier et al. 2001, 2004; Narotsky et al. 1997).
Suspected Health Effects
- Renal effects
- No human data are available on the potential renal toxicity of bromodichloromethane.
- Moderate evidence of renal toxicity in mice following acute or intermediate inhalation exposure and in rats and mice following acute (Condie et al. 1983; Lilly et al. 1994, 1996; Munson et al. 1982; Thornton-Manning et al. (1994), intermediate (NTP 1987), and chronic (George et al. 2002; NTP 1987) oral exposure.
- Immunological effects
- Very low evidence in an epidemiological study that evaluated immune markers in subjects swimming in chlorinated water for 40 minutes (Vlaanderen et al. 2017). No data are available on whether inhalation, oral, or dermal exposure to bromodichloromethane impairs immune function.
- Moderate evidence in animal studies based on two studies that found altered responses to immune stimulants after acute gavage administration (French et al. 1999; Munson et al. 1982) or intermediate oral exposure in rats (French et al. 1999).
Not Classifiable Effects
- Reproductive effects
- Inadequate evidence in cohort and cross-sectional studies that examined sperm parameters (Zeng et al. 2013), menstrual cycle (Windham et al. 2003), and time to pregnancy (MacLehose et al. 2008).
- Low evidence in animal studies (Aida et al. 1992; Bielmeier et al. 2001, 2004, 2007; Christian et al. 2001b; Klinefelter et al. 1995; NTP 1987, 2006; Ruddick et al. 1983). Studies evaluating the histopathology of the reproductive system have not found alterations at nonlethal doses (Aida et al. 1992; NTP 1987, 2006). Bielmeier et al. (2001, 2004, 2007) reported significant alterations in reproductive hormone levels in pregnant rats, and Klinefelter et al. (1995) reported decreases in sperm velocity, but no changes in sperm motility. No alterations in reproductive function were observed in a 2-generation study in rats (Christian et al. 2001b). The lack of consistency across studies and the indirectness of the observed effects decreased the initial confidence in these studies.
Table C-19Hazard Identification Conclusions for Bromodichloromethane
Outcome | Hazard identification |
---|---|
Hepatic effects | Presumed health effect |
Renal effects | Suspected health effect |
Immunological effects | Suspected health effect |
Reproductive effects | Not classifiable |
Developmental effects | Presumed health effect |
- PROBLEM FORMULATION
- LITERATURE SEARCH AND SCREEN FOR HEALTH EFFECTS STUDIES
- EXTRACT DATA FROM HEALTH EFFECTS STUDIES
- IDENTIFY POTENTIAL HEALTH EFFECT OUTCOMES OF CONCERN
- ASSESS THE RISK OF BIAS FOR INDIVIDUAL STUDIES
- RATE THE CONFIDENCE IN THE BODY OF EVIDENCE FOR EACH RELEVANT OUTCOME
- TRANSLATE CONFIDENCE RATING INTO LEVEL OF EVIDENCE OF HEALTH EFFECTS
- INTEGRATE EVIDENCE TO DEVELOP HAZARD IDENTIFICATION CONCLUSIONS
- FRAMEWORK FOR ATSDR’S SYSTEMATIC REVIEW OF HEALTH EFFECTS DATA FOR BROMODICHLORO...FRAMEWORK FOR ATSDR’S SYSTEMATIC REVIEW OF HEALTH EFFECTS DATA FOR BROMODICHLOROMETHANE - Toxicological Profile for Bromodichloromethane
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