In Ovo Effects of Two Organophosphate Flame Retardants-TCPP and TDCPP-on Pipping Success, Development, mRNA Expression, and Thyroid Hormone Levels in Chicken Embryos

Tris(1-chloro-2-propyl) phosphate (TCPP) and tris(1,3-dichloro-2-propyl) phosphate (TDCPP) are organic flame retardants detected in the environment and biota for which avian toxicological data are limited. In this study, domestic chicken eggs were injected with TCPP or TDCPP (maximum dose = 51,600 and 45,000 ng/g egg, respectively) to determine dose-dependent effects on pipping success, development, hepatic messenger RNA (mRNA) expression levels of genes associated with xenobiotic metabolism and the thyroid hormone (TH) pathway, and TH levels following 20-22 days of incubation. Neither compound reduced pipping success; however, TCPP significantly delayed pipping at 9240 and 51,600 ng/g and reduced tarsus length at 51,600 ng/g. TDCPP exposure resulted in significant decreases in head plus bill length, embryo mass, and gallbladder size at 45,000 ng/g and reduced plasma free T-4 levels at 7640 ng/g. Type I deiodinase, liver fatty acid-binding protein, and cytochrome P450 (CYP) 3A37 mRNA levels were significantly induced by TCPP, whereas TDCPP induced CYP3A37 and CYP2H1. Chemical analysis of egg contents at incubation days 0, 5, 11, 18, and 19 revealed that > 92% of the injected TCPP or TDCPP concentration was detectable up to day 5; however, < 1% was detected by day 19. The observed phenotypic responses to TCPP and TDCPP exposure may be associated with disruption of the TH axis, which is critical for normal growth and development in birds. The effects of TDCPP on the gallbladder indicate that the disturbance of lipid metabolism is a likely mechanism of toxicity.