Non-carcinogenic Health Outcomes Associated with Polycyclic Aromatic Hydrocarbons (PAHs) Exposure in Humans: An Umbrella Review

Abstract

Several polycyclic aromatic hydrocarbons (PAHs) are suspected as human carcinogens and have been associated with various types of cancer. However, less is known for their non-carcinogenic health effects and available evidence is often inconsistent. We conducted this umbrella review to synthesize the findings of selected eligible reviews on the non-carcinogenic health outcomes associated with PAH exposures in human populations. PubMed and Scopus were searched to identify eligible reviews according to the inclusion and exclusion criteria developed a priori. Following the quality assessment of each identified review, their findings were categorized by the type of the health outcomes and synthesized. A total of 29 review papers were determined eligible for this study, and these included 4 meta-analysis papers, 7 systematic reviews, 16 literature reviews, and 2 scoping reviews. Key non-carcinogenic health outcomes of humans associated with PAH exposure could be grouped as neurodevelopment, respiratory diseases, cardiovascular diseases (CVDs), reproduction related effects, and endocrine outcomes. Overall, the selected reviews supported the associations of PAH exposure with lowered IQ, impaired cognitive development, decreased pulmonary function, hypertension, preterm birth, and delayed fetal growth. However, association was either null or inconsistent for attention-deficit/hyperactivity disorder (ADHD), behavioral problems, asthma, and hypertension (only in occupational setting). For other health effects such as some respiratory diseases (bronchitis, allergic reactions), CVDs (myocardial infarction, ischemic heart disease, atherosclerosis, peripheral arterial disease, heart rate variation, cardiac autonomic dysfunction), obesity, and infertility, only least amount of information is available, and more evidence are warranted. Several challenges were identified: many primary studies were based on the exposure to mixtures with other chemical groups and hence did not represent the outcomes associated with PAHs alone. Moreover, exposure assessment based on biomonitoring data failed to include many PAHs that have been frequently found in food and other major sources. Therefore, exposure is likely to be underestimated and the conclusion could be biased. This definitive, comprehensive analysis of the reported evidence showed clear associations of PAHs with some adverse reproduction and neurodevelopmental outcomes in humans. Knowledge gaps in exposure assessment, e.g., difficulties in interpreting mixture exposure and limited coverage of biomonitoring data, were identified and should be considered for design and interpretation of the association studies.