Species-specific differences and structure-activity relationships in the debromination of PBDE congeners in three fish species

Brominated and chlorinated flame retardants in San Francisco Bay sediments and wildlife

Restrictions on the use of polybrominated diphenyl ethers (PBDEs) have resulted in the use of alternative flame retardants in consumer products to comply with flammability standards. In contrast to PBDEs, information on the occurrence and fate of these alternative compounds in the environment is limited, particularly in the United States. In this study, a survey of flame retardants in San Francisco Bay was conducted to evaluate whether PBDE replacement chemicals and other current use flame retardants were accumulating in the Bay food web. In addition to PBDEs, brominated and chlorinated flame retardants (hexabromocyclododecane (HBCD) and Dechlorane Plus (DP)) were detected in Bay sediments and wildlife. Median concentrations of PBDEs, HBCD, and DP, respectively, were 4.3, 0.3, and 0.2 ng g⁻¹ dry weight (dw) in sediments; 1670, <6.0, and 0.5 ng g⁻¹ lipid weight (lw) in white croaker (Genyonemus lineatus); 1860, 6.5, and 1.3 ng g⁻¹ lw in shiner surfperch (Cymatogaster aggregata); 5500, 37.4, and 0.9 ng g⁻¹ lw in eggs of double-crested cormorant (Phalacrocorax auritus); 770, 7.1, and 0.9 ng g⁻¹ lw in harbor seal (Phoca vitulina) adults; and 330, 3.5, and <0.1 ng g⁻¹ lw in harbor seal (P. vitulina) pups. Two additional flame retardants, pentabromoethylbenzene (PBEB) and 1,2-bis(2,4,6 tribromophenoxy)ethane (BTBPE) were detected in sediments but with less frequency and at lower concentrations (median concentrations of 0.01 and 0.02 ng g⁻¹ dw, respectively) compared to the other flame retardants. PBEB was also detected in each of the adult harbor seals and in 83% of the pups (median concentrations 0.2 and 0.07 ng g⁻¹ lw, respectively). The flame retardants hexabromobenzene (HBB), decabromodiphenyl ethane (DBDPE), bis(2-ethylhexyl) tetrabromophthalate (TBPH), and 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB), were not detected in sediments and BTBPE, HBB and TBB were not detected in wildlife samples. Elevated concentrations of some flame retardants were likely associated with urbanization and Bay hydrodynamics. Compared to other locations, concentrations of PBDEs in Bay wildlife were comparable or higher, while concentrations of the alternatives were generally lower. This study is the first to determine concentrations of PBDE replacement products and other flame retardants in San Francisco Bay, providing some of the first data on the food web occurrence of these flame retardants in a North American urbanized estuary.

Relationship between BDE 209 metabolites and thyroid hormone levels in rainbow trout (Oncorhynchus mykiss)

Decabromodiphenyl ether (BDE 209), the primary component in a commonly used flame retardants, has recently been shown to be metabolized by organisms. In the present study, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to BDE 209 at five nominal gradient concentrations from 50 to 1000 ng/g wet weight for 21 days via a single intraperitoneal injection. Then the liver, kidney and blood samples were collected to analyze for its debrominated, hydroxylated and methoxylated metabolites. The relationships between levels of BDE 209 metabolites in different tissues and thyroid hormone (TH) levels in plasma were evaluated. The results showed that BDE 209 could be metabolized into debrominated BDEs, methoxylated BDEs (MeO-BDEs) and hydroxylated BDEs (OH-BDEs). Levels of these three metabolites were tissue-dependent. The TH levels, including total thyroxine (TT(4)), free thyroxine (FT(4)), total triiodothyronine (TT(3)) and free triiodothyronine (FT(3)) in plasma, were significantly affected by BDE 209 metabolism. However, only FT(4) levels showed a negative correlation with MeO-BDE and OH-BDE metabolites, among which the correlation between FT(4) and OH-BDEs was the most significant.

Alpha and beta isomers of tetrabromoethylcyclohexane (TBECH) flame retardant: depletion and metabolite formation in vitro using a model rat microsomal assay

The metabolism of α- and β-isomers of the flame retardant chemical tetrabromoethylcyclohexane (TBECH) was investigated using a model in vitro enzyme-mediated biotransformation assay based on rat liver microsomes. In enzymatically active assays, concentrations of both α- and β-TBECH isomers were equally depleted by about 40% and in a time-dependent fashion over a 60-min assay incubation period, and determined by GC-MS(ECNI) analysis. No such depletion was observed in nonenzymatically active control assays. After the full 60-min assay incubation period, debrominated TBECH metabolites were not detected by GC-MS(ECNI), and suggested that enzyme-mediated debromination of TBECH did not occur via cyctochrome P450 enzyme-mediated catalysis or that the rate of TBECH metabolism in vitro was too slow. In the enzymatically active assays, but not in the nonezymatically active control assays, α- and β-monohydroxy-TBECH (OH-TBECH), dihydroxy-TBECH ((OH)(2)-TBECH), and some additional compounds with molecular formulas of C(8)H(13)Br(3)O(2) and C(8)H(11)Br(3)O(2) were identified by LC-Q-ToF-MS. Two unique sets of OH-TBECH and (OH)(2)-TBECH metabolites were derived from both α- and β-TBECH isomers. The LC-ESI(-)-MS/MS peak areas of all four OH-TBECH and (OH)(2)-TBECH metabolites increased at a comparable rate in a time-dependent manner over a 60-min assay incubation period. This study demonstrated that metabolism via hydroxylation can occur in vitro for α- and β-TBECH. These results underscore the importance of understanding the biological fate of TBECH and the possible implications on the health and TBECH levels in exposed wildlife and in the environment.

Hydrodebromination of decabromodiphenyl ether (BDE-209) in cooking experiments with salmon fillet

Polybrominated diphenyl ethers (PBDEs) are environmental contaminants regularly detected in biota and food. Seafood has been identified as the major dietary source for human uptake. Fish is predominantly consumed after cooking, and this process may alter the actual human intake of contaminants. This study thus aimed to investigate the fate of PBDEs in this cooking process. Heating of fish fortified with 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE-209) at typical cooking conditions (200 °C, in plant oil) resulted in a decrease of its concentration in favor of the formation of lower brominated congeners. After 15 min, ∼25% of BDE-209 was transformed into nona- to octabrominated congeners. The major transformation route was BDE-209 → BDE-206 → BDE-196 and BDE-199. Low amounts of heptabrominated congeners as well as one hexabromodibenzofuran and a heptabromodibenzofuran isomer were also detected. However, penta- and tetrabrominated diphenyl ethers were not observed, and heating of BDE-47 did not produce new transformation products.

Bioaccumulation of polybrominated diphenyl ethers (PBDEs) in flounder (Platichthys flesus) in the southern Baltic Sea

Concentrations of seven polybrominated diphenyl ether (PBDE) congeners were examined in flounder (Platichthys flesus) and sediment in three southern Baltic Sea sites, representing a range of exposure conditions, in order to evaluate spatial differences in PBDE contamination. Additionally, PBDEs were measured in muscle, liver, and gonads of flounder from one of the sites in order to examine inter-tissue distribution. Mean muscle Σ(7)PBDE levels, in the range of 10-21 ng g(-1) lipid, showed inter-site differences attributed to the distance from the Gulf of Gdańsk, and were overall lower than reported earlier in herring, sprat, and salmon. Biota sediment accumulation factors (BSAFs) for Σ(7)PBDE and individual BDE congeners, in the range of 0.5-24.5, were generally consistent with predicted models for persistent hydrophobic halogenated contaminants. Wet weight (wet wt) PBDE levels in muscle and liver, but not in gonads, were related to tissue lipid content and did not correlate with the fish length and weight. These tissues differed in PBDE levels and profiles as a result of varying lipid content and presumably lipid composition and congener-specific physico-chemical properties.

Polybrominated diphenyl ethers disrupt molting in neonatal Daphnia magna

Polybrominated diphenyl ethers (PBDEs) are flame-retardants which can bioaccumulate and biomagnify and are found worldwide despite their banned usage in some countries. In recent years, the possibility that PBDEs may disrupt endocrine functions in vertebrates has been well investigated, but little attention has been paid to the endocrine disrupting potential in aquatic invertebrates. The current study aimed to investigate whether PBDEs affect molting in neonatal Daphnia magna. Prior to molting studies, 48 h LC50 values were tested for several environmentally prevalent PBDEs: PBDEs-28, -47, -99, -100 and -209. The 48 h LC50s determined were 110.7, 7.9, 2.6, and 11.1 μg/L for PBDEs-28, -47, -99, and -100, respectively, but the highest concentration of PBDEs-209 tested (2.5 mg/L) did not affect survival at 48 h. Sublethal concentrations of these were used to investigate their potential effects on molting, assessed by the time taken to reach 4 molts. Molting studies found that PBDE-28 at 12 μg/L significantly increased the time it took to complete 4 molts. PBDE-47 at 20 μg/L inhibited daphnid molting initially but such an inhibitory effect disappeared with the prolongation of exposure due to the death of sensitive individuals. No other PBDEs affected molting at the concentrations tested, while still maintaining relatively high survival rates. In conclusion, this study found that PBDEs-28 and -47 can delay molting at μg/L concentrations, which raises concern for disrupted molting in crustaceans exposed to PBDEs.

Bioaccumulation of polybrominated diphenyl ethers by the freshwater benthic amphipod Gammarus pulex

This study reports on the relationship between polybrominated diphenyl ether (PBDE) levels in water, sediment, and the benthic macroinvertebrate Gammarus pulex, which plays a major ecological role in freshwater ecosystems. Samples were taken in a periurban watershed (near Paris, France), and PBDEs were systematically detected in sediment (≤727 ng g(-1) OC) and G. pulex (≤264 ng g(-1) lipids). PBDEs were also occasionally detected in the water column at low levels (∑ PBDEs < 1.5 ng L(-1)). The log values of bioaccumulation factors were in the range 7.8 ± 0.1-8.3 ± 0.4 L kg(-1) for tetra- and penta-BDEs, which were the only ones quantified in the dissolved phase of river water. Meanwhile, levels of individual tri- to hepta-PBDE congeners in G. pulex generally positively correlated with sediment levels, suggesting an equilibrium situation. Biota-to-sediment accumulation factors (BSAFs) of tri-hepta BDEs were congener specific and were in the range 0.5 ± 0.3-2.6 ± 1.2. For several PBDEs, BSAF values deviated from the expected range, likely because of in vivo metabolism.

Glutathione, glutathione S-transferase, and glutathione conjugates, complementary markers of oxidative stress in aquatic biota

Contaminants are ubiquitous in the environment and their impacts are of increasing concern due to human population expansion and the generation of deleterious effects in aquatic species. Oxidative stress can result from the presence of persistent organic pollutants, metals, pesticides, toxins, pharmaceuticals, and nanomaterials, as well as changes in temperature or oxygen in water, the examined species, with differences in age, sex, or reproductive cycle of an individual. The antioxidant role of glutathione (GSH), accompanied by the formation of its disulfide dimer, GSSG, and metabolites in response to chemical stress, are highlighted in this review along with, to some extent, that of glutathione S-transferase (GST). The available literature concerning the use and analysis of these markers will be discussed, focusing on studies of aquatic organisms. The inclusion of GST within the suite of biomarkers used to assess the effects of xenobiotics is recommended to complement that of lipid peroxidation and mixed function oxygenation. Combining the analysis of GSH, GSSG, and conjugates would be beneficial in pinpointing the role of contaminants within the plethora of causes that could lead to the toxic effects of reactive oxygen species.

Multi-species comparison of the mechanism of biotransformation of MeO-BDEs to OH-BDEs in fish

Polybrominated diphenyl ethers (PBDEs) and their methoxylated- (MeO-) and hydroxylated- (OH-) analogs are ubiquitously distributed in the environment worldwide. The OH-BDEs have greater potency than PBDEs and can be produced from the transformation of MeO-BDEs. The objectives of the current study were to (1) identify the enzyme(s) that catalyze biotransformation of 6-MeO-BDE-47 to 6-OH-BDE-47 in livers from rainbow trout, and (2) compare biotransformation of 6-MeO-BDE-47 to 6-OH-BDE-47 among rainbow trout, white sturgeon and goldfish. Cytochrome P450 1A (CYP1A) enzymes did not catalyze the biotransformation reaction. However, biotransformation was significantly inhibited by the CYP inhibitors clotrimazole and 1-benzylimidazole but not gestodene. Therefore, the reaction is likely catalyzed by CYP2 enzymes. When biotransformation was compared among species, concentrations of 6-OH-BDE-47 were significantly 3.4- and 9.1-fold greater in microsomes from rainbow trout compared to goldfish or white sturgeon, respectively. Concentrations of 6-OH-BDE-47 in microsomes from goldfish were non-significantly 2.7-fold greater than in sturgeon. The initial rate of biotransformation in microsomes from livers of rainbow trout was significantly 2.0- and 6.2-fold greater than the initial rate of biotransformation in microsomes from livers of goldfish or sturgeon, respectively, while the initial rate in goldfish was significantly 3.1-fold greater than in sturgeon. It is hypothesized that differences in CYP-mediated biotransformation of MeO-BDEs to OH-BDEs could influence concentrations of OH-BDEs in different species of fish.

In situ accumulation of HBCD, PBDEs, and several alternative flame-retardants in the bivalve (Corbicula fluminea) and gastropod (Elimia proxima)

Alternative brominated flame-retardants (BFRs), 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB), 2-ethylhexyl 2,3,4,5-tetrabromophthalate (TBPH), 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE) and decabromodiphenyl ethane (DBDPE), are now being detected in the environment. However, contaminant bioavailability is influenced by the organisms' ecology (i.e., route of uptake) and in situ environmental factors. We observed that the filter-feeding bivalve (Corbicula fluminea) and grazing gastropod (Elimia proxima), collected downstream from a textile manufacturing outfall, exhibited TBB, TBPH, and BTBPE concentrations from 152 to 2230 ng g(-1) lipid weight (lw). These species also contained additional BFRs. Maximum levels of total hexabromocyclododecane diastereomers (∑HBCDs) in these species were 363,000 and 151,000 ng g(-1) lw, and those of polybrominated diphenyl ethers (∑PBDEs) were 64,900 and 47,200 ng g(-1) lw, respectively. These concentrations are among the highest reported to date worldwide. While BDE-209 was once thought to be nonbioavailable and resistant to degradation, it was the dominant BFR present and likely debromination products were detected. Contributions of α- and β-HBCD were higher in tissues than sediments, consistent with γ-HBCD bioisomerization. Mollusk bioaccumulation factors were similar between HBCD and PBDEs with 4 to 6 bromines, but factors for TBB, TBPH, and BTBPE were lower. Despite different feeding strategies, the bivalves and gastropods exhibited similar BFR water and sediment accumulation factors.

In vitro metabolism of the brominated flame retardants 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB) and bis(2-ethylhexyl) 2,3,4,5-tetrabromophthalate (TBPH) in human and rat tissues

Due to the phaseout of polybrominated diphenyl ether (PBDE) flame retardants, new chemicals, such as 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB) and bis(2-ethylhexyl) 2,3,4,5-tetrabromophthalate (TBPH), have been used as replacements in some commercial flame retardant mixtures. Both chemicals have been detected in indoor dust at concentrations approaching the concentrations of PBDEs; however, little is known about their fate, metabolism, or toxicity. The goal of this study was to investigate the potential metabolism of these two brominated flame retardants in human and rat tissues by conducting in vitro experiments with liver and intestinal subcellular fractions. In all the experiments, TBB was consistently metabolized to 2,3,4,5-tetrabromobenzoic acid (TBBA) via cleavage of the 2-ethylhexyl chain without requiring any added cofactors. TBBA was also formed in purified porcine carboxylesterase but at a much faster rate of 6.29 ± 0.58 nmol min(-1) mg protein(-1). The estimated K(m) and V(max) values for TBB metabolism in human microsomes were 11.1 ± 3.9 μM and 0.644 ± 0.144 nmol min(-1) mg protein(-1), respectively. A similar K(m) of 9.3 ± 2.2 μM was calculated for porcine carboxylesterase, indicating similar enzyme specificity. While the rapid formation of TBBA may reduce the bioaccumulation potential of TBB in mammals and may be useful as a biomarker of TBB exposure, the toxicity of this brominated benzoic acid is unknown and may be a concern based on its structural similarity to other toxic pollutants. In contrast to TBB, no metabolites of TBPH were detected in human or rat subcellular fractions. However, a metabolic product of TBPH, mono(2-ethylhexyl) tetrabromophthalate (TBMEHP), was formed in purified porcine carboxylesterase at an approximate rate of 1.08 pmol min(-1) mg protein(-1). No phase II metabolites of TBBA or TBMEHP were observed. More research is needed to understand the in vivo toxicokinetics and health effects of these compounds given their current ubiquitous presence in most US households and the resulting probability of chronic exposure, particularly to young children.

Separation of polybrominated diphenyl ethers in fish for compound-specific stable carbon isotope analysis

A separation and isotopic analysis method was developed to accurately measure the stable carbon isotope ratios of polybrominated diphenyl ethers (PBDEs) with three to six substituted bromine atoms in fish samples. Sample extracts were treated with concentrated sulfuric acid to remove lipids, purified using complex silica gel column chromatography, and finally processed using alumina/silica (Al/Si) gel column chromatography. The purities of extracts were verified by gas chromatography and mass spectrometry (GC-MS) in the full-scan mode. The average recoveries of all compounds across the purification method were between 60% and 110%, with the exception of BDE-154. The stable carbon isotopic compositions of PBDEs can be measured with a standard deviation of less than 0.5‰. No significant isotopic fraction was found during the purification of the main PBDE congeners. A significant change in the stable carbon isotope ratio of BDE-47 was observed in fish carcasses compared to the original isotopic signatures, implying that PBDE stable carbon isotopic compositions can be used to trace the biotransformation of PBDEs in biota.

Gastrointestinal absorption, metabolic debromination, and hydroxylation of three commercial polybrominated diphenyl ether mixtures by common carp

The gastrointestinal absorption, metabolic debromination, and hydroxylation of three commercial brominated diphenyl ether (BDE) mixtures were separately studied in juvenile common carp. The absorption rate of penta-BDE was higher than that of octa- and deca-BDE, likely because of the lower molecular volumes of its major congeners. However, no significantly positive relationships were found between the number of bromine atoms and the absorption rate, especially for congeners with a bromine atom number larger than six. The major congeners in fish carcass were, respectively, BDE-47 and BDE-100 in the penta-BDE exposure; BDE-154, -155, -149, and BDE-153 in the octa-BDE exposure; and BDE-154, -155, -149, -188, -179, and BDE-202 in the deca-BDE exposure. Congeners with at least one meta- or para- doubly flanked bromine atom easily undergo metabolic debromination in fish. None of the targeted MeO-polybrominated diphenyl ether (PBDE) congeners were detected in serum samples, implying that the methylation of OH-PBDE is not likely occurring in fish. Eleven OH-PBDEs and several unidentified OH-PBDE congeners were found in penta-BDE-exposed fish. The similar level among three mono-OH-BDE47 congeners suggested that the position of OH in the phenyl ring is not selective. The hydroxylation is not a significant metabolic pathway compared with debromination. No OH-PBDE congeners were found in the serum samples from deca-BDE-exposed fish, which may attributable to the low level of PBDE precursors in fish.

Bioaccumulation and metabolism of polybrominated diphenyl ethers in carp (Cyprinus carpio) in a water/sediment microcosm: important role of particulate matter exposure

Microcosms were built up to simulate a pond system with polybrominated diphenyl ether (PBDE) contaminated sediment and bioorganisms. The microcosms were divided into groups A and B. In group A, both benthic invertebrates (tubificid worms) and carp (Cyprinu carpio) were added, while in group B, only fish were added. After exposure for 20 d, the fish were sampled (exposure I). A net was fixed in the microcosms, and new fish were added (exposure II). These fish were prohibited from contacting the sediment by the net, and the accumulation and depuration of PBDEs in the fish were investigated. Among 11 monitored PBDE congeners (BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, BDE-183, BDE-206, BDE-207, BDE-208, and BDE-209), only 5 congeners (BDE-28, BDE-47, BDE-100, BDE-153, and BDE-154) were detected in the carp fillets and liver. BDE-99 and BDE-183 were not detected in the fish because of the efficient metabolic debromination in carp tissues. The uptake of PBDEs in exposure I was significantly higher/faster than that in exposure II, since the fish in exposure I had an opportunity to take in more of the highly contaminated particles. The uptake kinetics (k(s)) and elimination (k(e)) rate coefficients showed a general trend of decreasing with increasing log K(ow). No significant difference was observed in uptake/depuration kinetics between groups A and B, indicating that the tubificids' reworking does not affect the bioaccumulation of sediment-associated PBDEs in fish significantly. All the PBDE congeners, including nona- and deca-BDEs, were bioaccumulated in the tubificid worms. The PBDE concentrations in the worms were significantly higher than those in the fish, and the congener profile of the sevem major congeners (BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, and BDE-183) was distinctly different from that of fish tissues. The biota-sediment accumulation factors in the worms ranged from 0.01 to 5.89 and declined with increasing bromination and log K(ow.).

BDE 49 and developmental toxicity in zebrafish

The polybrominated diphenyl ethers (PBDEs) are a group of brominated flame retardants. Human health concerns of these agents have largely centered upon their potential to elicit reproductive and developmental effects. Of the various congeners, BDE 49 (2,2',4,5'-tetrabromodiphenyl ether) has been poorly studied, despite the fact that it is often detected in the tissues of fish and wildlife species. Furthermore, we have previously shown that BDE 49 is a metabolic debromination product of BDE 99 hepatic metabolism in salmon, carp and trout, underscoring the need for a better understanding of biological effects. In the current study, we investigated the developmental toxicity of BDE 49 using the zebrafish (Danio rerio) embryo larval model. Embryo and larval zebrafish were exposed to BDE 49 at either 5 hours post fertilization (hpf) or 24 hpf and monitored for developmental and neurotoxicity. Exposure to BDE 49 at concentrations of 4iμ-32 μM caused a dose-dependent loss in survivorship at 6 days post fertilization (dpf). Morphological impairments were observed prior to the onset of mortality, the most striking of which included severe dorsal curvatures of the tail. The incidence of dorsal tail curvatures was dose and time dependent. Exposure to BDE 49 caused cardiac toxicity as evidenced by a significant reduction in zebrafish heart rates at 6 dpf but not earlier, suggesting that cardiac toxicity was non-specific and associated with physiological stress. Neurobehavioral injury from BDE 49 was evidenced by an impairment of touch-escape responses observed at 5 dpf. Our results indicate that BDE 49 is a developmental toxicant in larval zebrafish that can cause morphological abnormalities and adversely affect neurobehavior. The observed toxicities from BDE 49 were similar in scope to those previously reported for the more common tetrabrominated congener, BDE 47, and also for other lower brominated PBDEs, suggest that these compounds may share similarities in risk to aquatic species.

Acute toxicity of polybrominated diphenyl ethers (PBDEs) for turbot (Psetta maxima) early life stages (ELS)

BACKGROUND, AIM AND SCOPE

The environmental presence of polybrominated diphenyl ethers (PBDEs), among which BDE-47 and BDE-99 are particularly abundant, makes toxicity data necessary to assess the hazard risk posed by PBDE to aquatic organisms. This study examines the effects of BDE-47 and BDE-99 on embryo-larval stages of the marine flatfish turbot.

MATERIALS AND METHODS

The turbot embryos were exposed at nominal concentrations of BDE-47 and BDE-99 for 6 days. Selected dose levels were relevant for investigating sublethal and lethal effects.

RESULTS

Both tested compounds caused lethal toxicity as well as non-lethal malformations during embryo development. We found a high toxic potency of BDE-47 compared to BDE-99 (LC₅₀ values for embryos and larvae, respectively, BDE-47: 27.35 and 14.13 μg L⁻¹; BDE-99: 38.28 and 29.64 μg L⁻¹).

DISCUSSION

The present study shows high sensitivity of fish early life stages (ELS) to PBDE compounds. Based on environmental concentrations of dissolved PBDEs from various aquatic ecosystems, waterborne BDE-47 and BDE-99 pose little risk of acute toxicity to marine fish at relevant environmental concentrations.

CONCLUSIONS

Turbot fish ELS proved to be an excellent model for the study of ecotoxicity of contaminants in seawater. The results demonstrate harmful effects of PBDE on turbot ELS at concentrations in the range of parts per billion units.

RECOMMENDATIONS AND PERSPECTIVES

In the perspective of risk assessment, ELS endpoints provide rapid, cost-effective and ecologically relevant information, and links should be sought between these short-term tests and effects of long-term exposures in more realistic scenarios.

Complete debromination of tetra- and penta-brominated diphenyl ethers by a coculture consisting of dehalococcoides and desulfovibrio species

Polybrominated diphenyl ethers (PBDEs) are widespread global contaminants due to their extensive usage as flame retardants. Among the 209 PBDE congeners, tetra-brominated diphenyl ether (tetra-BDE) (congener 47) and penta-BDEs (congeners 99 and 100) are the most abundant, toxic, and bioaccumulative congeners in the environment. However, little is known about microorganisms that carry out debromination of these congeners under anaerobic conditions. In this study, we describe a coculture GY2 consisting of Dehalococcoides and Desulfovibrio spp., which is capable of debrominating ∼1180 nM of congeners 47, 99, and 100 (88-100% removal) to the nonbrominated diphenyl ether at an average rate of 36.9, 19.8, and 21.9 nM day(-1), respectively. Ortho bromines are preferentially removed during the debromination process. The growth of Dehalococcoides links tightly with PBDE debromination, with an estimated growth yield of 1.99 × 10(14) cells per mole of bromide released, while the growth of Desulfovibrio could be independent of PBDEs. The growth-coupled debromination suggests that Dehalococcoides cells in the coculture GY2 are able to respire on PBDEs. Given the ubiquity and recalcitrance of the tetra- and penta-BDEs, complete debromination of these congeners to less toxic end products (e.g. diphenyl ether) is important for the restoration of PBDE-contaminated environments.

Accumulation and debromination of decabromodiphenyl ether (BDE-209) in juvenile fathead minnows (Pimephales promelas) induces thyroid disruption and liver alterations

Polybrominated diphenyl ether (PBDE) flame retardants are known to affect thyroid hormone (TH) regulation. The TH-regulating deiodinases have been implicated in these impacts; however, PBDE effects on the fish thyroid system are largely unknown. Moreover, the liver as a potential target of PBDE toxicity has not been explored in young fish. This study measured decabromodiphenyl ether (BDE-209) effects on TH regulation by measuring deiodinase activity in juvenile fathead minnows (Pimephales promelas). Dietary accumulations and debromination of BDE-209 were also measured, and the morphology of thyroid and liver tissues was examined. Juvenile fathead minnows (28 days old) received a 28-day dietary treatment of BDE-209 at 9.8 ± 0.16 μg/g of food at 5% of their body weight per day followed by a 14-day depuration period in which they were fed clean food. Chemical analysis revealed that BDE-209 accumulated in tissues and was metabolized to reductive products ranging from penta- to octaBDEs with 2,2',4,4',5,6'-hexabromodiphenyl ether (BDE-154) being the most accumulative metabolite. By day 28 of the exposure, rates of outer and inner ring deiodination (ORD and IRD, respectively) of thyroxine (T4) were each reduced by ∼74% among treatments. Effects on T4-ORD and T4-IRD remained significant even after the 14-day depuration period. Histological examination of treated fish showed significantly increased thyroid follicular epithelial cell heights and vacuolated hepatocyte nuclei. Enlarged biliary passageways may be the cause of the distinctive liver phenotype observed, although further testing is needed. Altogether, these results suggest that juvenile fish may be uniquely susceptible to thyroid disruptors like PBDEs.

Persistent organic pollutants in blood plasma of satellite-tracked adult male loggerhead sea turtles (Caretta caretta)

Risks from persistent organic pollutants (POPs) remain largely a mystery for threatened loggerhead sea turtles (Caretta caretta). The present study examines regional-scale POP differences in blood plasma from adult male C. caretta based on movement patterns. Turtles were captured near Port Canaveral, Florida, USA, in April of 2006 and 2007 and fitted with satellite transmitters as part of a National Marine Fisheries Service-funded project. Residents (n = 9) remained near the capture site, whereas transients (n = 10) migrated northward, becoming established in areas largely from south of Pamlico Sound, North Carolina, to north of Cape May, New Jersey, USA. Blood was sampled from the dorsocervical sinus of each turtle and analyzed using gas chromatography-mass spectrometry for organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and toxaphenes. Blood plasma concentrations of OCPs and total PBDEs were elevated in transients (p < 0.05) and in some cases were correlated with turtle size. Migratory adults showed an atypical PBDE congener profile relative to other published studies on wildlife, with PBDE 154 being the dominant congener. Additionally, PCB congener patterns differed between groups, with total PCBs slightly elevated in transients. This supports the idea that foraging location can influence exposure to, and patterns of, POPs in highly mobile species such as C. caretta. Understanding patterns of contamination informs wildlife managers about possible health risks to certain subpopulations. The present study is the first to examine POPs in the rarely studied adult male sea turtle and to couple contaminant measurements with satellite tracking.