Impacts of Unregulated Novel Brominated Flame Retardants on Human Liver Thyroid Deiodination and Sulfotransferation.

The inhibitory effects of five novel brominated flame retardants, 1,2-bis(2,4,5-tribromophenoxy)ethane (BTBPE), decabromodiphenylethane (DBDPE), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), bis(2-ethylhexyl)tetrabromophthalate (BEH-TEBP), and ß-tetrabromoethylcyclohexane (ß-TBECH), on thyroid hormone deiodinase (DIO) and sulfotransferase (SULT) activity were investigated using human in vitro liver microsomal and cytosolic bioassays. Enzymatic activity was measured by incubating active human liver subcellular fractions with thyroid hormones (T4 and rT3 separately) and measuring changes in thyroid hormone (T4, T3, rT3, and 3,3'-T2) concentrations. Only DBDPE showed inhibition of both outer and inner ring deiodination (O and IRD) of T3 and 3,3'-T2 formation from T4, respectively, with an estimated IC50 of 160 nM; no statistically significant inhibition of SULT activity was observed. ORD inhibition of 3,3'-T2 formation from rT3 was also observed (IC50 ∼ 100 nM). The kinetics of T4 O and IRD were also investigated, although a definitive mechanism could not be identified as the Michaelis-Menten parameters and maximal rate constants were not significantly different. Concentrations tested were intentionally above expected environmental levels, and this study suggests that these NBFRs are not potent human liver DIO and SULT inhibitors. To our knowledge, DBDPE is the first example of a nonhydroxylated contaminant inhibiting DIO activity, and further study of the mechanism of action is warranted.

Polycyclic aromatic hydrocarbon metabolites in Arctic cod (Boreogadus saida) from the Beaufort Sea and associative fish health effects.

In 2012, Arctic cod (Boreogadus saida) were collected from offshore regions of the Beaufort Sea to determine the concentrations of CYP1A1 phase I metabolites of polycyclic aromatic hydrocarbons (OH-PAHs) in liver and to correlate measured concentrations with (i) morphometric measurements that are known to be indicative of fish health and, (ii) biochemical end points of health including vitamin A/E and metabolites and hepatic deiodinase activity (DI). Four ring OH-PAHs were detected in 90% of our samples with a mean liver concentration of 1829.2 ± 159.2 ng/g (ww). Total (∑) concentrations of 5/6-membered ring OH-PAHs in liver were smaller [mean of 931.6 ± 104.3 ng/g, (ww)] and detected less frequently (75%) than the 4-ring OH-PAHs. Fish length and liver weight were both negatively correlated to ∑ concentrations of 4-ringed OH-PAHs (p < 0.001). Liver somatic index was also negatively correlated to ∑4-OH-PAHs (p < 0.05) but not for ∑5/6-OH-PAHs (p > 0.1). There was a significant positive relationship between DI and 4-ring OH-PAHs (p < 0.05) in liver, suggesting an induction of this enzyme. No such correlation was observed for the 5/6-ring OH-PAHs. Retinyl palmitate (RP) was the only vitamin that could be measured in liver ranging from 0.230 to 26.3 ug/g (ww). No associations between RP and levels of the 4- or 5/6-ringed OH-PAHs were observed. Continued baseline studies are clearly warranted to further understand effects of OH-PAHs on fish health before planned exploration activities begin in this region.

Corrigendum: A survey of Fusarium species and ADON genotype on Canadian wheat grain.

[This corrects the article DOI: 10.3389/ffunb.2022.1062444.].

A survey of Fusarium species and ADON genotype on Canadian wheat grain.

Introduction: Wheat is a staple food that is important to global food security, but in epidemic years, fungal pathogens can threaten production, quality, and safety of wheat grain. Globally, one of the most important fungal diseases of wheat is Fusarium head blight (FHB). This disease can be caused by several different Fusarium species with known differences in aggressiveness and mycotoxin-production potential, with the trichothecene toxin deoxynivalenol (DON) and its derivatives being of particular concern. In North America, the most predominant species causing FHB is F. graminearum, which has two distinct sub-populations that are commonly classified into two main chemotypes/genotypes based on their propensity to form trichothecene derivatives, namely 15-acetyldeoxynivalenol (15-ADON) and 3-acetyldeoxynivalenol (3-ADON). Materials and methods: We used a panel of 13 DNA markers to perform species and ADON genotype identification for 55, 444 wheat kernels from 7, 783 samples originating from across Canada from 2014 to 2020. Results and discussion: Based on single-seed analyses, we demonstrate the relationships between Fusarium species and trichothecene chemotype with sample year, sample location, wheat species (hexaploid and durum wheat), severity of Fusarium damaged kernels (FDK), and accumulation of DON. Results indicate that various Fusarium species are present across wheat growing regions in Canada; however, F. graminearum is the most common species and 3-ADON the most common genotype. We observed an increase in the occurrence of the 3-ADON genotype, particularly in the western Prairie regions. Our data provides important information on special-temporal trends in Fusarium species and chemotypes that can aid with the implementation of integrated disease management strategies to control the detrimental effects of this devastating disease.

A multi-year survey of mycotoxins and ergosterol in Canadian oats.

Canadian oat harvest samples, deliveries to processors, and train shipments from primary elevators were collected from mid-2014 through mid-2017 and analyzed for 26 mycotoxins and the fungal biomarker ergosterol. Of the 26 mycotoxins, 7 were not detected in any sample. The most frequently measured mycotoxins were beauvericin (in over 95% of samples analyzed), followed by tentoxin, culmorin, alternariol, alternariol methyl ether, and deoxynivalenol. Median concentrations of the Fusarium-produced mycotoxins ranged from 68 to 1142 µg/kg for deoxynivalenol, 39 to 188 µg/kg for HT-2 and T-2 toxins, 66 to 232 µg/kg for nivalenol, and less than 35 µg/kg for beauvericin. Median concentrations of the sum of Alternaria-produced mycotoxins were all less than 250 µg/kg. Concentrations of analytes varied among years, as well as among growing areas, for the harvest samples. Ergosterol, Fusarium, and Alternaria mycotoxin concentrations appeared to increase from the west toward the eastern Prairies and the province of Quebec; the differences were not statistically significant though. Ochratoxin A in deliveries and train shipments showed annual cyclic increases in the late summer. The results of the survey demonstrate the general compliance of Canadian oats with existing maximum levels for mycotoxins and indicate that in late summer and in years with increased Fusarium infection, there can be a need for monitoring of ochratoxin A and deoxynivalenol, respectively, to mitigate risks of noncompliant grain.

Brominated and chlorinated flame retardants in Lake Ontario, Canada, lake trout (Salvelinus namaycush) between 1979 and 2004 and possible influences of food-web changes.

Concentrations of non-polybrominated diphenyl ether (PBDE) brominated (hexabromocyclododecane [HBCD], 1,2-bis[2,4,6-tribromophenoxy]ethane [BTBPE], and pentabromoethylbenzene [PEB]) and chlorinated (Dechlorane Plus [DP] as well as short- and medium-chain chlorinated paraffins [SCCP and MCCP, respectively]) flame retardants were evaluated in archived Lake Ontario, Canada, lake trout (Salvelinus namaycush) samples collected between 1979 and 2004. Polybrominated diphenyl ethers also were analyzed to provide a point of reference for comparison to previous studies. Concentrations of the dominant PBDE congeners (BDEs 28, 47, 99, 100, 153, and 154) increased significantly from 1979 until the mid-1990s, then either leveled off or decreased significantly between 1998 and 2004, a result that corresponds to those of previous studies. In contrast, BDE 209 increased approximately fourfold between 1998 and 2004. The temporal trends of the non-PBDE flame retardants varied, with sum (sigma) HBCD and DP showing significant overall decreases; BTBPE, sigmaSCCP, and sigmaMCCP showing parabolic trends; and PEB showing no overall change during the study period. Because many of the non-PBDE chemicals may be used as replacements for penta- and octa-BDE mixtures, these results will provide a baseline to evaluate future usage patterns. Possible changes in food-web structure, evaluated through stable nitrogen isotopes (delta15N), may be influencing our interpretations of contaminant trends in lake trout and are hypothesized to be partially responsible for the observed decrease in concentrations of BDEs 28, 47, 99, 100, 153, and 154 between 1998 and 2004. Retrospective analyses evaluating temporal trends in stable isotope values at the base of the food web, however, are recommended to test this hypothesis further.

Deoxynivalenol-3-Glucoside Content Is Highly Associated with Deoxynivalenol Levels in Two-Row Barley Genotypes of Importance to Canadian Barley Breeding Programs.

Barley (Hordeum vulgare L.) is a multipurpose crop that can be harvested as grain or cut prior to maturity for use as forage. Fusarium head blight (FHB) is a devastating disease of barley that reduces quality of grain. FHB can also result in the accumulation of mycotoxins such as deoxynivalenol (DON). Breeding FHB resistant varieties has been a long-term goal of many barley-producing countries, including Canada. While the genetic basis of DON detoxification via production of less-phytotoxic conjugates such as DON-3-glucoside (DON3G) is well documented in barley, little information exists in reference to varietal response. Over two years, 16 spring, two-row barley genotypes, of importance to western Canadian barley breeding programs, were grown as short-rows and inoculated following spike emergence with a Fusarium graminearum conidia suspension. Half of the plots were harvested at soft dough stage and then dissected into rachis and grain components, whereas the remainder was harvested at maturity. Multiple Fusarium-mycotoxins were assayed using liquid chromatography-mass spectrometry. Mycotoxin content was elevated at the earlier harvest point, especially in the rachis tissue. DON3G constituted a significant percentage (26%) of total trichothecene content and thus its co-occurrence with DON should be considered by barley industries. DON3G was highly correlated with DON and 3-acetyl-deoxynivalenol (3ADON). The ratio of D3G/DON exhibited consistency across genotypes, however more-resistant genotypes were characterized by a higher ratio at the soft-dough stage followed by a decrease at maturity. Plant breeding practices that use DON content as a biomarker for resistance would likely result in the development of barley cultivars with lower total DON-like compounds.

Structure characterization and thermal stabilities of the isomers of the brominated flame retardant 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane.

1,2-Dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) is used primarily as an additive flame retardant. 1H NMR spectroscopy and an X-ray structure determination have revealed that a technical mixture consists largely of two (of the four possible) diastereomers, rac-(1R,2R)-1,2-dibromo-(4S)-4-((1S)-1,2-dibromoethyl)cyclohexane (alpha-TBECH) and rac-(1R,2R)-1,2-dibromo-(4S)-4-((1R)-1,2-dibromoethyl)cyclohexane (beta-TBECH), in a mole ratio of approximately 1:1. The two other possible isomers, gamma- and delta-TBECH, were not detected in a technical mixture. The TBECH isomers are thermally sensitive and can easily interconvert at temperatures of 125 degrees C. A thermal equilibrium mixture of alpha-, beta-, gamma- and delta-TBECH consists of approximately 33%, 33%, 17% and 17% of these isomers, respectively. Separation of all four TBECH diastereomers, with minimal thermal interconversion of the isomers, was achieved by careful selection of GC-capillary column length and injector temperature. Although technical TBECH does not contain the gamma- and delta-isomers, they may still be relevant environmental contaminants since manufacturing processes utilize thermal processes which may induce their formation.

Effect of nanosilver on cortisol release and morphometrics in rainbow trout (Oncorhynchus mykiss).

Nanosilver (nAg) is a nanoparticle commonly incorporated into consumer products for its antimicrobial properties that has been detected in aquatic environments. Toxic effects of nAg on fish have been observed, and nAg may induce a stress response in fish in the form of increased blood plasma cortisol. Effects of nAg exposure on rainbow trout (Oncorhynchus mykiss) were investigated over a 28-d period using blood plasma cortisol concentrations as an indicator of stress. Several morphometric measures (growth, Fulton's condition factor, and hepatosomatic index [HSI]) were also taken during the experiment to investigate potential whole-body effects of exposure, and concentrations of nAg in fish muscle tissue were measured. Fish were exposed to environmentally relevant (average 0.28 µg/L) and higher (average 47.60 µg/L) exposure concentrations of nAg. The results showed a significant increase in blood plasma cortisol for both exposure treatments. A significant effect on HSI by treatment dependent on exposure time was also observed, although no obvious trend was detected, whereas other morphometric measures were not affected by nAg exposure. In addition, Ag was detected in fish muscle tissue. The results indicate that although nAg did engage the stress response in fish, it did not affect growth or condition under the experimental conditions and time frame investigated. Environ Toxicol Chem 2017;36:1606-1613. © 2016 SETAC.

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, α- and ß- present in equimolar amounts. At temperatures in excess of 125°C, isomerization to two other isoforms, δ- and γ- 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, ß-, in a controlled laboratory environment. Juvenile brown trout (Salmo trutta) were exposed to three different amounts of the ß-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. ß-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 ß-isomer was similar in fish from all treatment groups with steady-state occurring before the end of the uptake phase. Depuration of the ß-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 ß-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.

Altered thyroxine metabolism in rainbow trout (Oncorhynchus mykiss) exposed to hexabromocyclododecane (HBCD).

Hexabromocyclododecane (HBCD) is an additive flame retardant used in consumer and industrial applications. Our earlier work suggested that fish exposed to HBCD exhibited an increase in the rate of turnover of thyroxine (T4), the precursor molecule to the active thyroid hormone triiodothyronine (T3). To examine this further, juvenile rainbow trout were held in the laboratory and fed diets containing environmentally relevant concentrations of the individual alpha, beta or gamma isomers. Thirty-two days after feeding began, 20 fish from each group were gavaged with gelatin containing 1microCi [(125)I]-T4. Uptake of [(125)I]-T4 from the gut was low and recoveries of the initial [(125)I]-T4 were <10% after 2d and <3% and <2% after 6 and 14d respectively, with no differences among groups. However, measurements of the labeled T4 in tissues 2, 4, 6 and 14d after gavage showed that tissue disposition and elimination rates of the hormone were altered by HBCD. In particular, on day 14 after gavage feeding, there was significantly lower radioactivity in the thyroid of fish exposed to the HBCD isomers relative to the reference group. This implies that either there was lower iodide uptake by the gland in fish exposed to HBCD or that the rate of thyroid hormone turnover in HBCD treated fish was elevated. There was also a significantly higher type II outer ring deiodinase enzyme activity in livers of fish exposed to the beta and gamma isomers. Taken together, these results indicate that HBCD can potentially impact the thyroid system of fish.

Trophodynamics of some PFCs and BFRs in a western Canadian Arctic marine food web.

The trophodynamics of per- and polyfluorinated compounds and bromine-based flame retardants were examined in components of a marine food web from the western Canadian Arctic. The animals studied and their relative trophic status in the food web, established using stable isotopes of nitrogen (delta15N), were beluga (Delphinapterus leucas) > ringed seal (Phoca hispida) > Arctic cod (Boreogadus saida) > Pacific herring (Clupea pallasi) approximately equal to Arctic cisco (Coregonus autumnalis) > pelagic amphipod (Themisto libellula) > Arctic copepod (Calanus hyperboreus). For the brominated diphenyl ethers, the lipid adjusted concentrations of the seven congeners analyzed (Sigma7BDEs: -47, -85, -99, -100, -153, -154, and -209) ranged from 205.4 +/- 52.7 ng/g in Arctic cod to 2.6 +/- 0.4 ng/g in ringed seals. Mean Sigma7BDEs concentrations in Arctic copepods, 16.4 ng/g (n = 2, composite sample), were greater than those in the top trophic level (TL) marine mammals and suggests that (i) Arctic copepods are an important dietary component that delivers BDEs to the food web and (ii) because these compounds are bioaccumulative, metabolism and depletion of BDE congeners in top TL mammals is an important biological process. There were differences in the concentration profiles of the isomers of hexabromocyclododecane (HBCD) in the food web. The most notable difference was observed for beluga, where the alpha-isomer was enriched (accounting for approximately 90% of the SigmaHBCD body burden), relative to its primary prey species, Arctic cod, where the alpha-isomer accounted for only 20% of the SigmaHBCD body burden (beta: 4% and gamma: 78%). For the C8-C11 perfluorinated carboxylic acids, the trophic magnification factors (TMFs) were all greater than unity and increased with increasing carbon chain length. PFOS and its neutral precursor, PFOSA, also had TMF values greater than one. There were also pronounced differences in the PFOSA to PFOS ratio in ringed seal (0.04) and in beluga (1.4) and suggests that, in part, there are differences in the efficacy of biotransforming PFOSA by whale and seal top predators that both preferentially feed on Arctic cod.

Identilication of the novel cycloaliphatic brominated flame retardant 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane in Canadian Arctic beluga (Delphinapterus leucas).

1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) is used primarily as an additive flame retardant. Technical grade TBECH consists of near equimolar amounts of two (of a possible four) diastereoisomers: rac-(1R,2R)-1,2-dibromo-(4S)-4-((1S)-1,2-dibromoethyl)cyclohexane ((alpha-TBECH) and rac-(1R,2R)-1,2-dibromo-(4S)-4-((1R)-1,2-dibromoethyl)cyclohexane (beta-TBECH). The two other possible isomers, gamma- and delta-TBECH, appear in the technical mixture when heated at temperatures above 120 degrees C. Careful selection of GC-capillary column length was critical in resolution of the two main diastereoisomers. Column lengths of 60 or 30 m (0.25 microm film thickness) resulted in incomplete separation of the alpha- and beta-isomers, while on a 10 m column, the isomers were baseline separated. The gamma- and delta-isomers could not be resolved on any column length in this study. Increased injector port temperature induced thermal conversion of the alpha- and beta-isomers to gamma- and delta-TBECH. Electron impact ionization (EI) was used to provide specificity because no characteristic ions in the electron capture negative ionization (ECNI) mass spectrum of TBECH were evident. In EI, the dominant ions in the mass spectrum corresponded to a concomitant loss of HBr and Br from the molecular ion; the biggest peak in this ion cluster (m/z 266.9208) was used for quantitation and the second biggest peak (m/z 264.9227) was used for confirmation. Beluga (Delphinapterus leucas) blubber extracts of animals from the Canadian Arctic (n=29) were analyzed using low resolution (LR) MS and high resolution (HR) MS run at a resolving power of 10,000. beta-TBECH was the only isomer observed in the samples and was detected in 17 samples. The LRMS technique appeared to overestimate beta-TBECH concentrations compared to HRMS, suggesting a small interference arose at the nominal mass monitored. This potential interference also led to some false positive and negative values (n=7) based on the expected ion ratio of the quantitation and confirmation ions. Observed concentrations of the beta-isomer as measured by HRMS ranged from 1.1 to 9.3 ng/g (lipid weight).

Enantioselective bioaccumulation of hexabromocyclododecane and congener-specific accumulation of brominated diphenyl ethers in an eastern Canadian Arctic marine food web.

The extent of trophic transfer of the three diastereoisomers of hexabromocyclododecane (HBCD) and seven brominated diphenyl ether (BDE) congeners was examined in components of an Arctic marine food web from eastern Canada. Alpha and gamma-HBCD diastereoisomers were detected in all species and total (sigma) HBCD concentrations ranged from 0.6 +/- 0.2 pg/g (geometric mean +/- 1 x standard error (SE), lipid weight (lw)) in arctic cod to 3.9 +/- 0.9 ng/g (lw) in narwhal. beta-HBCD was below method detection limits in all the samples. Mean sigmaBDE (sum of seven congeners) concentrations ranged from 0.4 +/- 0.2 ng/g (lw) in walrus to 73 +/- 10 ng/g (lw) in zooplankton. The relative trophic status of biota was determined by nitrogen stable isotopes (delta15N), and results indicated clear differences in HBCD isomer and BDE congener profiles with trophic level (TL). Trophic magnification was observed for the alpha-diastereoisomer and BDE-47 as concentrations increased with increasing TL in the food web, whereas there was trophic dilution of gamma-HBCD and BDE-209 through the food web. Only the (-)alpha-enantiomer showed a strong positive relationship between concentration and TL (p < 0.01) with a trophic magnification factor (TMF) value of 2.2. A small but significant increase in the enantiomeric fraction value of the alpha-enantiomers with TL was also observed (r2 = 0.22, p < 0.005), implying that there is an overall preferential enrichment of the (-)alpha-enantiomer relative to the (+)alpha-enantiomer likely due to the greater bioaccumulation potential of the (-)alpha-enantiomer and/or to the greater susceptibility of the (+)alpha-enantiomer to metabolism.

Examination of isomer specific bioaccumulation parameters and potential in vivo hepatic metabolites of syn- and anti-Dechlorane Plus isomers in juvenile rainbow trout (Oncorhynchus mykiss).

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed in the laboratory to elevated doses of syn- and anti-isomers of Dechlorane Plus (DP) via their diet for 49 days (uptake phase), followed by 112 days of untreated food (depuration phase) to examine bioaccumulation parameters and possible metabolic products. Three groups of 60 fish were used in the study. Two groups were exposed separately to food fortified with known concentrations of syn- (0.79 +/- 0.03 microg/g, lipid weight) and anti-DP (1.17 +/- 0.12 microg/g, lipid weight) while a third control group was fed unfortified food. Neither isomer reached steady-state after 49 days of exposure. Only the syn-isomer accumulated linearly in the fish (whole-body minus liver) during the dosing phase with a calculated uptake rate constant of 0.045 +/- 0.005 (arithmetic mean +/- 1 x standard error) nmoles per day. A similar uptake rate was also observed for this isomer in the liver. The elimination of both isomers from the whole fish (minus liver) obeyed first order depuration kinetics (syn-: r2 = 0.6427, p < 0.001, anti-: r2 = 0.5350, p < 0.005) with calculated half-lives (t1/2) of 53.3 +/- 13.1 (syn-) and 30.4 +/- 5.7 (anti-) days. Elimination of the isomers from the liver was difficult to interpret because of suspected enterohepatic circulation and redistribution of the isomers in the liver during clearance from other tissues. The biomagnification factor (BMF, determined in whole fish minus liver) of the syn-isomer (5.2) was greater than the anti-isomer (1.9) suggesting that the former isomer is more bioavailable. A suite of metabolites were screened for in the liver including dechlorinated, hydroxylated, methoxylated and methyl sulfone degradates. Even with the purposely high dose used in the uptake phase, none of these degradates could be detected in the extracts. This suggests that if metabolites of DP are detected in fish from aquatic food webs their presence is likely not from in vivo biotransformation of the parent compound.

Biotransformation enzymes and thyroid axis disruption in juvenile rainbow trout (Oncorhynchus mykiss) exposed to hexabromocyclododecane diastereoisomers.

Juvenile rainbow trout (Oncorhynchus mykiss) were fed either a reference diet or one of three diets enriched with alpha, beta, or gamma diastereoisomers of hexabromocyclododecane (HBCD, C12H18Br6) for 56 days. This exposure period was followed by 112 days during which all fish were fed the reference diet. Potential effects of HBCD on phase I and II biotransformation enzyme activities and thyroid axis disruption were examined. Disruption of the thyroid axis was most evident in the gamma-HBCD exposed group, as indicated by lower circular FT4 and higher FT3 as well as an increase in thyroid epithelial cell height. However, fish fed the alpha-HBCD enriched diet also exhibited altered glucuronyltransferase activity and thyroid epithelial cell heights and the beta-HBCD group had altered FT4 and FT3 and glucuronyltransferase activity. T4ORD activity was not affected after 14 days, but was significantly lower among all HBCD exposed fish compared to the reference fish after 56 days. Results from these experiments indicate that all isomers have the potential to disrupt thyroid homeostasis.

Isomers of dechlorane plus in Lake Winnipeg and Lake Ontario food webs.

The extent of bioaccumulation of the syn- and anti-isomers of Dechlorane Plus (DP) is assessed in archived food web samples from Lake Winnipeg and Lake Ontario. Concentrations of the isomers were determined using purified analytical solutions of individual isomers as opposed to the technical mixture. The syn-isomer was consistently detected in all samples from both lakes; the anti-isomer was detected in all Lake Ontario samples, but only 45% of the samples from Lake Winnipeg. The pattern of bioaccumulation was different for the isomers in Lake Winnipeg. The anti-isomer was dominant in higher trophic level (TL) organisms like walleye [arithmetic mean +/- 1 x standard error: 730 +/- 120 pg/g, lipid weight (1w)] and goldeye (760 +/- 170 pg/g, Iw) while the syn-isomer dominated the lower TL organisms like zooplankton (550 +/- 40 pg/g, Iw) and mussels (430 +/- 140 pg/g, Iw). In Lake Ontario, the extent of bioaccumulation of the isomers and concentrations was greatest in the lower TL benthic organism, Diporeia (syn, 1307 +/- 554; and anti, 3108 +/- 898 pg/g Iw) and also high in zooplankton (syn, 719; and anti, 1332 pg/g Iw). This suggests that the isomers are bioavailable in sediment and that, despite their molecular size, diffusion from the water column into zooplankton can occur. Differences in the mean fractional abundance of the anti-isomer (mean fanti = mean concentration of the anti-isomer divided by sum of mean syn- and anti-concentrations) were pronounced in sediments between lakes (Lake Winnipeg mean fanti = 0.610, Lake Ontario mean fanti = 0.860) and the extent of enrichment (anti-) and depletion (syn-) of the isomers were more marked in Lake Winnipeg biota. There were also differences in the biomagnification potentials, as measured bythe trophic magnification factor (TMF), between the isomers in the Lake Winnipeg food web; no statistically significant TMFs for either isomer were found for the

Dietary exposure of juvenile rainbow trout (Oncorhynchus mykiss) to 1,2-bis(2,4,6-tribromophenoxy)ethane: bioaccumulation parameters, biochemical effects, and metabolism.

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed in the laboratory to an environmentally relevant dose of 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) via their diet for 49 days, followed by 154 days of untreated food to examine bioaccumulation parameters, potential biochemical effects, and metabolic products. There was a linear increase in the amount of BTBPE in fish during the uptake phase of the experiment, and an uptake rate constant of 0.0069 +/- 0.0012 (arithmetic mean +/- 1 x standard error) nmoles per day was calculated. The elimination of BTBPE from the fish obeyed first-order depuration kinetics (r2 = 0.6427, p < 0.001) with a calculated half-life of 54.1 +/- 8.5 days. The derived biomagnification factor of 2.3 +/- 0.9 suggests that this chemical has a high potential for biomagnification in aquatic food webs. Debrominated and hydroxylated metabolites were not detected in liver extracts and suggest that either biotransformation or storage of BTBPE-metabolites in the hepatic system of fish is minor or that our exposure time frame was too short. Similar concentrations of circulating thyroid hormones, liver deiodinase enzyme activity, and thyroid glandular histology suggest that BTBPE is not a potent thyroid axis disruptor.