S6: biochemical effects of organophosphate flame retardants
Bioaccumulation, biotransformation and biochemical effects of organophosphate flame retardants in the tissues of adult zebrafish (Danio rerio)
School of the Environment, Nanjing University
Ph D, Professor
Organophosphate flame retardants (OPFRs) have been used in varieties of industrial and consumer products as additive flame retardants. Many of these OPFRs are easily released to water ecosystems via weathering, erosion, leaching and/or abrasion. Although OPFRs have been detected in many aquatic organisms, relatively little is known regarding their potential accumulation, metabolism, and adverse health effects on aquatic life. The main objective of this research was to determine the tissue specific accumulation, transformation, and potential biochemical effects of seven typical OPFRs (tripropyl phosphate (TPP), tributyl phosphate (TNBP), tris (2-butoxyethyl) phosphate (TBOEP), tris(2-chloroethyl) phosphate (TCEP), tris(1,3-dichloro-2-propyl) phosphate (TDCPP), triphenyl phosphate (TPHP), and tricresyl phosphate (TCP)) in fish.
Zebrafish (Danio rerio) were exposed to three concentrations (0, 1/150 LC50 (environmentally relevant level), and 1/30 LC50 per OPFRs congener) of the 7 OPFR mixtures in the laboratory for 19 days, followed by 3 day depuration, to examine the tissue specific accumulation parameters and potential biotransformation of OPFRs in fish. Half-lives (t1/2’s) of the OPFR congeners (e.g., TPHP and TCP) were much lower than that estimated on their Kow, which was likely due to biotransformation via hydrolysis and oxidative hydroxylation. Both bioconcentration factor (BCF) with wet weight (ww) and normalized with lipid weight (lw) showed significant correlation with the octanol-water partition coefficient (Kow). The BCF values were significantly affected by the lipid content of the tissues and the metabolism in liver. A physiologically based toxicokinetic (PBTK) mode was used to analyze the bioaccumulation data in zebrafish, which showed obvious effects of transformation on the accumulation of OPFRs in liver. The metabolism pathways of OPFRs in zebrafish were elucidated, which included hydrolysis, hydroxylation, and hydroxylation followed by glucuronic acid conjugation. Quantification of the main metabolites in the selected tissues showed that higher amounts of metabolites, even 1.0 to 2.2 times of parent OPFRs (eg., TDCPP and TPHP), were detected in liver and intestine.
Acetyl cholinesterase activity (AchE) in brain and carboxylesterase activity (CesE), glutathione transferase (GST), CYP 1A enzyme activity (measured as ECOD) and phosphotriesterase (measured with ethyl paraoxon) in liver were varied significantly among diffident OPFR exposure groups throughout the experiment. Significant inhibition on the CesE was shown in all the OPFRs-exposed fish, and significant up regulation of the ECOD and GST activities were observed in TBOEP and TDCPP exposed fish after 12 days in 1/10 LC50 concentration, suggesting that OPFRs may influence lipid metabolism and physiological activity at levels higher than what is normally found in the environment. These results provided important information for the understanding of the metabolism, disposition, and toxicology of OPFRs in aquatic life. This research was supported by the National Natural Science Foundation of China (21377050).