Organophosphate flame retardants and their metabolites in paired dog food and urine: Pet exposure through food consumption

Companion dogs are exposed to various chemicals. However, our understanding of the sources and pathways of chemical exposure in pets remains limited. In this study, we collected urine samples from 47 dogs and corresponding samples of the food they consumed to analyze the concentrations and dietary exposure to organophosphate flame retardants (OPFRs) and their metabolites (mOPFRs). Triphenyl phosphate (TPHP) and its metabolite, diphenyl phosphate (DHPH), were the predominant compounds detected in dog food and urine samples. The concentration of mOPFRs in urine decreased as body weight increased; however, neither sex nor age significantly influenced mOPFR levels in dog urine. The estimated daily intake of OPFRs (343 ng/kg bw/day) through food consumption (EDI_food) was comparable to the previously reported levels of polycyclic aromatic hydrocarbons (324 ng/kg bw/day) and higher than those of pesticides (214 ng/kg bw/day), parabens (120 ng/kg bw/day), and polychlorinated biphenyls (103 ng/kg bw/day). By calculating the ratio of EDI_food to the cumulative daily intake based on urinary mOPFR concentrations, it was found that dietary sources contributed to 66% of the total TPHP exposure in dogs. This finding was further supported by Spearman's correlation analysis between parent OPFR concentrations in dog food and mOPFR levels in urine (p < 0.01), indicating that dietary intake may be one of the most significant exposure pathways for OPFRs in dogs. To the best of our knowledge, this is the first study to investigate the levels of OPFR exposure in paired dog food and urine samples.