An evidence mapping approach to support hazard identification for polychlorinated biphenyl (PCB) mixture exposure and developmental endpoints
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Background: Systematic evidence maps (SEMs) facilitate the organization and review of complex databases. SEMs can be helpful in identifying when epidemiological data may be sufficient to determine associations between exposures and health effects, and where animal or other data can address research gaps in the human database. We use SEM methods to survey human and animal studies on polychlorinated biphenyls (PCBs) exposure and developmental effects and determine if the database is likely to support human health hazard identification.
Methods: We developed a Population, Exposures, Comparators, and Outcomes (PECO) statement to direct the literature search, screening (through Sept 2021), and categorization. Data were extracted into literature inventory tables. To identify outcomes promising for human health hazard identification, we considered: database size, study design, biological significance of the outcome, and exposure characterization.
Results: We identified >300 studies evaluating PCB exposures and developmental effects. Most human studies focused on birth weight or other aspects of fetal growth. Body size in early life also had an abundance of animal data. Similarly, human studies of pregnancy loss are supplemented by many animal studies that assessed offspring viability. Birth defects were investigated in few human studies and tended to have few cases, but 24 studies investigated PCBs and structural alterations in animals.
Conclusion: We used SEM methods to identify developmental outcomes evaluated in PCB-exposed humans and animals. Database strength is high for birth weight and other indicators of size and growth in early life. The strength of the human evidence for other developmental effects is limited by few studies, small sample sizes or case numbers, and variations in study design. However, animal studies can provide additional information for evaluating potential hazards of PCB exposure.