Urinary Diphenyl Phosphate and Thyroid Function in Adults

Introduction: Triphenyl phosphate (TPHP) is an organophosphate flame retardant and plasticizer with widespread human exposure. Data on health effects of TPHP are limited. Recent toxicological studies suggest that TPHP may disrupt thyroid function. We examined the relationships between urinary concentrations of the TPHP metabolite, diphenyl phosphate (DPHP), and serum thyroid hormone levels in adults. Methods: We sampled 51 adults at months 1, 6, and 12 from 2010-2011. Urine was analyzed for DPHP and iodide (UIC). Serum was analyzed for polybrominated diphenyl ethers (PBDEs), free and total thyroxine (fT4, TT4), total triiodothyronine (TT3), and thyroid stimulating hormone (TSH). We used linear mixed effects models to estimate associations of specific gravity-corrected DPHP concentrations with each hormone, adjusting for UIC, PBDEs, and other potential confounders. We stratified by sex to explore effect measure modification. Results: DPHP was detected in 95% of samples. The DPHP geometric mean (geometric s...