Supplemental Information on Human Health Hazard
Total Page：16
File Type：pdf, Size：1020Kb
United States Office of Chemical Safety and Environmental Protection Agency Pollution Prevention Final Risk Evaluation for Cyclic Aliphatic Bromides Cluster (HBCD) Supplemental Information File: Supplemental Information on Human Health Hazard CASRN: 25637-99-4 CASRN: 3194-55-6 CASRN: 3194-57-8 Br Br Br Br Br Br September 2020 TABLE OF CONTENTS 1 DETAILED HAZARD OVERVIEW ...................................................................................3 1.1 Thyroid Effects ..................................................................................................................3 Human Evidence ...........................................................................................................3 Animal Evidence ..........................................................................................................4 Thyroid Hormones ........................................................................................................4 Thyroid Histopathology ................................................................................................5 Thyroid Weight .............................................................................................................5 Mechanistic Evidence .................................................................................................17 1.2 Liver Effects ....................................................................................................................21 Human Evidence .........................................................................................................21 Animal Evidence ........................................................................................................21 Mechanistic Evidence .................................................................................................31 1.3 Reproductive Effects .......................................................................................................33 Female Reproductive Effects ......................................................................................33 Male Reproductive Effects .........................................................................................41 1.4 Developmental Effects ....................................................................................................50 Human Evidence .........................................................................................................50 Animal Evidence ........................................................................................................50 Mechanistic Evidence .................................................................................................57 1.5 Nervous System Effects ..................................................................................................59 Human Evidence .........................................................................................................59 Animal Evidence ........................................................................................................59 Mechanistic Evidence .................................................................................................71 1.6 Immune System Effects ..................................................................................................73 Human Evidence .........................................................................................................73 Animal Evidence ........................................................................................................73 Mechanistic Evidence .................................................................................................86 1.7 Genotoxicity ....................................................................................................................86 2 DOSE-RESPONSE ANALYSIS .........................................................................................91 2.1 Supplemental Information on Non-Cancer Dose Response Analysis .............................91 Additional Considerations for Selection of Studies for Dose-Response Analysis .....91 BMR Selection ............................................................................................................94 3 DOSE-RESPONSE MODELING FOR THE DERIVATION OF POINTS OF DEPARTURE ...............................................................................................................................98 3.1 Noncancer Endpoints for BMD Modeling ......................................................................98 3.2 Dose-Response Modeling of Non-Cancer Endpoints ...................................................101 Evaluation of Model Fit ............................................................................................101 Model Selection ........................................................................................................101 Modeling Results ......................................................................................................102 4 REFERENCES ...................................................................................................................190 Page 2 of 202 1 Detailed Hazard Overview 1.1 Thyroid Effects Human Evidence The association between HBCD exposure and alterations of thyroid hormones was investigated in populations at different lifestages. Specifically, investigations of the potential effects of HBCD on the thyroid in humans have been conducted in infants and children participating in birth cohort studies in the Netherlands (Roze et al., 2009) and Norway (Eggesbø et al., 2011), adolescents participating in a cross-sectional general population study in areas around industrial sites in Belgium (Kiciński et al., 2012), and adult men attending an infertility clinic in the United States (cross-sectional study) (Johnson et al., 2013). In addition, there is one case-control study of hypothyroidism in Korean mother and infant pairs (Kim and Oh, 2014). Of these five studies, only two were large scale (>500 participants) (Kiciński et al., 2012; Eggesbø et al., 2011), and only one included an analysis that allowed for the examination of exposure-response patterns (Eggesbø et al., 2011). Quantitative methods used by several of the studies resulted in 25−75% of samples below stated detection limits (Kim and Oh, 2014; Kiciński et al., 2012; Eggesbø et al., 2011). While some of the available studies included consideration of other suspected thyroid- disrupting chemicals, none considered known thyroid antagonists such as perchlorate, thiocyanate, or nitrate (Steinmaus et al., 2013; Tonacchera et al., 2004). Other study limitations and a summary of overall confidence in the results are noted in Table 1-1. Studies are ordered by the age at outcome evaluation, and then by overall confidence in the study. A Norwegian birth cohort did not find a statistically significant association between the levels of HBCD measured in breast milk and thyroid-stimulating hormone (TSH) levels in newborns (Eggesbø et al., 2011). Elevated, but non-statistically significant, odds ratios (range: 1.3−1.6) were reported for increased TSH in relation to increasing HBCD levels in breast milk that are suggestive of a potential association; however, confidence intervals (CIs) around each of the point estimates were relatively wide (based on approximately 30 individuals per group) and a clear dose-response was not observed. This analysis controlled for several potential mediators of normal thyroid hormone variability and several thyroid disruptors (e.g., polychlorinated biphenyls [PCBs], polybrominated diphenyl ethers [PBDEs], and hexachlorobenzene). Adjustments for iodine deficiency were not made; however, the study authors noted that this condition is rare in Norway (Eggesbø et al., 2011). A study in adolescents ages 13−17 years who lived in areas around industrial sites in Belgium (n = 515) did not find an association between serum concentrations of HBCD and concurrent measures of TSH, thyroxine (T4), or triiodothyronine (T3) (Kiciński et al., 2012). Since approximately 75% of serum concentrations were below the limit of quantitation (LOQ), analyses were dichotomized to compare effects associated with HBCD concentrations above and below the LOQ. The three remaining studies (Kim and Oh, 2014; Johnson et al., 2013; Roze et al., 2009) had reporting deficiencies that limit the ability to interpret results from these studies (Table 1-2). In studies of infants (Roze et al., 2009) and adult men (Johnson et al., 2013), the Page 3 of 202 authors did not identify a statistically significant relationship between HBCD and a specific thyroid hormone; quantitative results pertaining to the magnitude or direction of association between HBCD and thyroid hormones were not reported. Kim and Oh (2014) found no significant correlations between α-, β-, or γ-HBCD and any thyroid hormones in infants with congenital hypothyroidism; however, reporting limitations of this case-control study (, no information on participant recruitment) and analysis (i.e., 25% of samples were below the limit of detection [LOD]) were noted. The human database for HBCD is inadequate to support conclusions regarding the relationship between HBCD exposure and thyroid effects. The studies of HBCD exposure in relation to variation in thyroid hormone levels or thyroid disease (congenital hypothyroidism) do not provide a basis for assessing a causal association at any lifestage. Animal Evidence Several short-term and subchronic rodent studies evaluated the effects of HBCD on the