Organophosphate esters (OPEs), used as plasticizers and flame retardants, are major emerging environmental contaminants in the Arctic. OPEs of environmental interest include triphenyl phosphate (TPHP) and a growing array of alkyl-substituted TPHP analogues. Using a microsomal assay of the liver tissue of polar bears and their ringed seal prey, the comparative in vitro metabolism of TPHP was investigated relative to the analogues of isodecyl diphenyl phosphate (IDDPP), (p-tert-butylphenyl) diphenyl phosphate (TBPDPP), tris(p-tert-butylphenyl) phosphate (TTBPP), and two tris(isopropylphenyl) phosphate isomers (T2IPPP and T4IPPP). Polar bear metabolism of the p-tert-butylphenyl-substituted OPEs, TBPDPP and TTBPP, had a substantially slower rate and percent metabolic depletion compared to those with TPHP. Isodecyl- and isopropyl-substituted OPEs, IDDPP, T2IPPP, and T4IPPP, were also more slowly depleted by polar bears than TPHP was. TPHP, IDDPP, T2IPPP, TBPDPP, TTBPP, and T4IPPP were all slowly metabolized by ringed seals. Overall, TPHP in vitro metabolism was clearly affected by o- and p-alkyl substitution that generally hindered the depletion rate. This information is important in understanding the accumulation, biotransformation, and magnification of TPHP and other OPEs in top predator polar bears and their ringed seal prey as well as transfer of OPEs between trophic levels, i.e., ringed seal to polar bears.

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Journal Environmental Science and Technology Letters
Strobel, A. (Adelle), Letcher, R.J, Willmore, W, Sonne, C. (Christian), & Dietz, R. (Rune). (2018). Structure-Dependent in Vitro Metabolism of Alkyl-Substituted Analogues of Triphenyl Phosphate in East Greenland Polar Bears and Ringed Seals. Environmental Science and Technology Letters, 5(4), 214–219. doi:10.1021/acs.estlett.8b00064