Toxicokinetics of tetrabromoethylcyclohexane (TBECH) in juvenile brown trout (Salmo trutta) and effects on plasma sex hormones

Technical 1,2-dibromo-4-(1,2 dibromoethyl)cyclohexane or tetrabromoethylcyclohexane (TBECH) used primarily as an additive flame retardant in polystyrene foams, contains two diastereoisomers, alpha- and beta-present in equimolar amounts. At temperatures in excess of 125 degrees C, isomerization to two other isoforms, delta- and gamma- is possible. The recent detection of TBECH in the environment and studies suggesting that isomers are androgenic prompted us to examine the toxicokinetics and biochemical effects of one of the isomers, beta-, in a controlled laboratory environment. juvenile brown trout (Salmo trutta) were exposed to three different amounts of the beta-isomer (low, medium and high) via the food followed by a period in which they were exposed to unfortified food. A fourth group of fish was exposed to unfortified food for the duration of the experiment. On days 0, 7, 14, 21, 35, 49, 56, 63, 77, 91, 105, and 133, eight fish from each treatment group were euthanized and liver, plasma, lower jaw (i.e., thyroid tissue) and gonad were collected and the remaining tissue ('whole-fish') was retained. beta-Isomer content was measured in whole-fish and in liver while estradiol (E2), 11-ketotestosterone (11-KT) and testosterone (T) were measured in plasma. Based on liver and gonad somatic indices, no apparent effects on liver or gonad development in fish from any of the treatment groups were observed. The bioaccumulation of beta-isomer was similar in fish from all treatment groups with steady-state occurring before the end of the uptake phase. Depuration of the beta-isomer from fish obeyed first order kinetics and there were no statistically significant differences in the depuration half life (t(1/2)) among the treatment groups: 22.5 +/- 10.4 (low), 13.5 +/- 5.9 (med) and 13.8 +/- 2.2 (high) days. Steady-state biomagnification factors were much smaller than 1 for fish in all treatment groups. Debrominated metabolites were not detected in composite liver or whole-fish extracts and there was no evidence of isomerization of the beta-isomer to other isoforms in vivo. While there were occasional differences among treatment groups in circulating plasma E2, T and 11-KT levels there was no clear, temporal trend or dose-response. (C) 2010 Elsevier B.V. All rights reserved.