Relationship between flame retardants and respiratory health – A Systematic review and meta-analysis of observational studies

Chronic respiratory diseases are a dealing cause of death and disability worldwide. Their prevalence is steadily increasing and the exposure to environmental contaminants, in which Flame Retardants (FR) are included, is being considered as a possible risk factor. Despite the widespread and continuous exposure to FRs, the role of these contaminants in chronic respiratory diseases is yet not clear. This study aims to systematically review the association between the exposure to FR and chronic respiratory diseases. Searches were performed using the Cochrane Library, MEDLINE, EMBASE, PUBMED, SCOPUS, ISI Web of Science (Science and Social Science Index), WHO Global Health Library and CINAHL EBSCO. Analytical, observational, and epidemiological studies (cohort, case-control, and cross-sectional studies) reporting associations between chronic respiratory diseases and different types of FR or their metabolites quantified in environmental or biological matrices were included. Random-effects meta-analysis were used to summarise the numerical effect estimates. Among the initial 351 articles found, only 7 fulfilled the inclusion criteria and were included (5 cross-sectional and 2 cohort studies). No statistically significant increase in the risk for chronic respiratory diseases with exposure to FR was found and therefore there is not enough evidence to support that FRs pose a significantly higher risk for the development or worsening of respiratory diseases. However, a non-significant trend for potential hazard was found for asthma and rhinitis/rhinoconjunctivitis, particularly considering urinary organophosphorus FRs (PFR) including TNBP, TPHP, TCEP and TCIPP congeners/compounds. Most studies showed a predominance of moderate risk of bias, therefore the global strength of the evidence is low. The limitations of the studies here reviewed, and the potential hazardous effects herein identified highlights the need for good quality large-scale cohort studies in which biomarkers of exposure should be quantified in biological samples.