Respiratory Health Effects of Organophosphate Ester Exposure: From Toxicological Mechanisms to Epidemiological Associations

Abstract

Organophosphate esters (OPEs), particularly organophosphate flame retardants (OPFRs), have become ubiquitous environmental contaminants since the phase-out of brominated flame retardants. As additives that are not chemically bound, OPFRs migrate into dust and air and are detected in over 90% of the general population, with the highest intakes in young children. This review integrates toxicological and epidemiological evidence linking OPFR exposure to respiratory health, presenting the mechanistic findings first. In population studies, prenatal and early-life exposure is associated with childhood asthma and wheeze; the highest household-dust quartile of tris(2-butoxyethyl) phosphate (TBOEP) carried nearly 4-fold higher asthma odds (odds ratio 3.85, 95% confidence interval 1.92–7.74), whereas chlorinated OPFRs show the most consistent associations with reduced lung function. These associations are constrained by exposure misclassification, co-pollutant confounding, and reverse causation in cross-sectional designs, and the available meta-analysis rates the overall evidence as low. Toxicologically, OPFR exposure is associated with oxidative stress, inflammation, and allergic sensitization, with chlorinated and aryl compounds most cytotoxic and alkyl compounds acting as immune adjuvants at the human tolerable daily intake. This convergence, reinforced by detection of OPFRs in human lung tissue, strengthens biological plausibility without proving causality. Major gaps regarding chronic obstructive pulmonary disease (COPD), occupational exposure, and long-term trajectories warrant precautionary regulation and prospective study.