Concentrations and partitioning of polychlorinated biphenyls in the surface waters of the southern Baltic Sea-seasonal effects

In the marine environment, the partitioning of hydrophobic organic contaminants, such as polychlorinated biphenyls (PCBs), between the dissolved and suspended matter phases in the water column plays a fundamental role in determining contaminant fate (e.g., air-water exchange or food-chain uptake). Despite the pronounced seasonality in physical, chemical, and biological conditions in temperate marine ecosystems, little is known about the seasonality in organic contaminant partitioning behavior. Surface water from the western Baltic Sea was sampled regularly during an 18-month period between February 2003 and July 2004. The concentrations of seven PCB congeners were determined in the dissolved and particulate organic carbon (POC) phases. An inverse relationship was found between K(POC) (i.e., the ratio between the POC-normalized PCB concentration [pg/kg POC] and the dissolved concentration [pg/L]) and temperature. The decrease in the water temperature of 20 degrees C between summer and winter resulted in an increase in K(POC) by a factor of approximately five. The POC-normalized PCB concentrations were higher in winter than in summer by a factor of 9 to 20. This reflected the higher K(POC) and somewhat greater PCB concentrations in the dissolved phase, and it could have consequences for bioaccumulation of these chemicals in aquatic food webs. The results demonstrate a clear seasonality in contaminant partitioning in the temperate marine environment that should be accounted for when interpreting field data or modeling contaminant fate.     

A linear solvation energy relationship model of organic chemical partitioning to dissolved organic carbon

Predicting the association of contaminants with both particulate and dissolved organic matter is critical in determining the fate and bioavailability of chemicals in environmental risk assessment. To date, the association of a contaminant to particulate organic matter is considered in many multimedia transport models, but the effect of dissolved organic matter is typically ignored due to a lack of either reliable models or experimental data. The partition coefficient to dissolved organic carbon (K(DOC)) may be used to estimate the fraction of a contaminant that is associated with dissolved organic matter. Models relating K(DOC) to the octanol-water partition coefficient (K(OW)) have not been successful for many types of dissolved organic carbon in the environment. Instead, linear solvation energy relationships are proposed to model the association of chemicals with dissolved organic matter. However, more chemically diverse K(DOC) data are needed to produce a more robust model. For humic acid dissolved organic carbon, the linear solvation energy relationship predicts log K(DOC) with a root mean square error of 0.43.     

Bioconcentration of persistent organic pollutants in four species of marine phytoplankton

The uptake of polychlorinated biphenyls (PCBs) was studied in four species of marine algae. A novel experimental system to establish and maintain constant dissolved concentrations of PCBs was employed. Headspace sampling was used to verify that the freely dissolved concentrations remained constant with time. The headspace analysis also allowed sorption to dissolved organic carbon (DOC) to be quantified for all but the most lipophilic PCB congeners. Equilibration with the dissolved phase was rapid for three of the four algae species (<1 d for the majority of congeners). Organic carbon-normalized algae/water partition coefficients (KAlgW) were similar for three of the four species, but were lower by a factor of 10 to 20 for Phaeodactylum tricornutum. The KAlgW values of the first three species were similar to the octanol/water partition coefficient (Kow) for those PCB congeners for which DOC sorption could be quantified. These KAlgW values also agreed well with organic carbon-normalized bioconcentration factors for PCBs in suspended particulate matter (BCF(SPM)) sampled in Baltic Sea surface water during the summer.     

The Effects of Salinity, pH, and Dissolved Organic Matter on Acute Copper Toxicity to the Rotifer, Brachionus plicatilis (“L” Strain)

This paper presents data from original research for use in the development of a marine biotic ligand model and, ultimately, copper criteria for the protection of estuarine and marine organisms and their uses. Ten 48-h static acute (unfed) copper toxicity tests using the euryhaline rotifer Brachionus plicatilis (“L” strain) were performed to assess the effects of salinity, pH, and dissolved organic matter (measured as dissolved organic carbon; DOC) on median lethal dissolved copper concentrations (LC50). Reconstituted and natural saltwater samples were tested at seven salinities (6, 11, 13, 15, 20, 24, and 29 g/L), over a pH range of 6.8–8.6 and a range of dissolved organic carbon of <0.5–4.1 mg C/L. Water chemistry analyses (alkalinity, calcium, chloride, DOC, hardness, magnesium, potassium, sodium, salinity, and temperature) are presented for input parameters to the biotic ligand model. In stepwise multiple regression analysis of experimental results where salinity, pH, and DOC concentrations varied, copper toxicity was significantly related only to the dissolved organic matter content (pH and salinity not statistically retained; α = 0.05). The relationship of the 48-h dissolved copper LC50 values and dissolved organic carbon concentrations was LC50 (μg Cu/L) = 27.1 × DOC (mg C/L)^1.25; r ² = 0.94.     

Neutral and phenolic brominated organic compounds of natural and anthropogenic origin in northeast Atlantic Greenland shark (Somniosus microcephalus)

In the present study, muscle and liver tissue from 10 female Greenland sharks (Somniosus microcephalus) collected in Icelandic waters were analyzed for neutral and phenolic brominated organic compounds, including polybrominated diphenyl ethers (PBDEs) and the structurally related methoxylated (MeO) and hydroxylated (OH) PBDEs. Hydroxylated PBDEs exist both as natural products and as metabolites of the anthropogenic PBDEs, whereas MeO-PBDEs appear to exclusively be of natural origin. Other compounds examined were 2',6-dimethoxy-2,3',4,5'-tetrabromodiphenyl ether (2',6-diMeO-BDE68), 2,2'-dimethoxy-3,3',5,5'-tetrabromobiphenyl (2,2'-diMeO-BB80), 2,4,6-tribromoanisol (2,4,6-TBA) and 2,4,6-tribromophenol, all of natural origin, although 2,4,6-TBA and its phenolic counterpart may also be of anthropogenic origin. The major brominated organic compound was 6-MeO-BDE47, and ΣMeO-PBDE ranged from 49 to 210?ng/g fat in muscle and from 55 to 200?ng/g fat in liver tissue. Total concentrations of PBDEs were lower than ΣMeO-PBDE, in all but one sample, ranging between 7.3 to 190 and 9.9 to 200?ng/g fat in muscle and liver, respectively, and major congeners were BDE-47, BDE-99, and BDE-100. Polybrominated diphenyl ethers were analyzed using both high- and low-resolution mass spectrometry (MS) as a quality assurance, and the results from this comparison were acceptable. In accordance with previous work on Greenland sharks, no size/age-related accumulation was observed. Differences seen in concentrations were instead assumed to be a reflection of different feeding habits among the individuals. Phenolic compounds were only formed/retained in trace amounts in the Greenland shark. Among the phenolic compounds studied were 6-OH-BDE47, 2'-OH-BDE68, and 2,4,6-tribromophenol, all detected in liver and the latter two in muscle.     

Examining the role of temperature and sediment-chemical contact time on desorption and bioavailability of sediment-associated tetrabromo diphenyl ether and benzo(a)pyrene

The effects of temperature and sediment-chemical contact time on desorption and bioaccumulation of sediment-spiked (14)C-labelled 2,2',4,4'-tetrabromo diphenyl ether (BDE-47) and benzo(a)pyrene (BaP) were examined. Experiments were performed after 2 or 6 weeks and 23 or 24 months sediment-chemical contact time at 10 and 20 degrees C. Desorption was measured in a sediment-water suspension using Tenax extraction, and bioaccumulation was measured by exposing Lumbriculus variegatus (Oligochaeta) to BDE-47 and BaP-spiked sediments in a 10d kinetic study. Biota-sediment accumulation factors (BSAFs) ranged between 2.9 and 4.3 for BDE-47 and between 0.5 and 0.9 for BaP. Thus, temperature and aging had a minor effect on bioavailability estimates. On the other hand, the difference between the chemicals was clear and could not be interpreted solely by reference to the size of the desorbing fractions, although the rapidly desorbing fraction-revised estimate clearly reduced the difference. The remaining discrepancy may be related to methodological (Tenax extraction vs. worm exposure) and/or biological (digestive extraction) causes. However, the data support the role of diffusional forces in the bioavailability of sediment-associated organic contaminants. Therefore, desorption-revised bioavailability estimates would lead to more precise bioavailability estimates than the traditional sediment organic carbon-organisms' lipids-based equilibrium partitioning approach.     

Resuspension of polychlorinated biphenyl-contaminated field sediment: release to the water column and determination of site-specific K DOC

Sediments from the New Bedford Harbor (NBH) U.S. Environmental Protection Agency (U.S. EPA) Superfund site (Massachusetts, USA), contaminated with polychlorinated biphenyls (PCBs), were resuspended under different water column redox conditions: untreated, oxidative, and reductive. The partitioning of PCBs to the overlying water column was measured with polyethylene samplers and compared to partitioning without resuspension. Greater concentrations of total aqueous (freely dissolved + dissolved organic carbon (DOC)-associated) PCBs were found in all resuspended treatments for PCBs with mid-range K(OW)s, but no difference was observed in total aqueous concentrations among different redox conditions. The magnitude of increased concentrations depended on resuspension time and congener K(OW), but ranged from approximately one to eight times those found without resuspension. In a parallel study, DOC was flocculated and removed from smaller-scale NBH sediment resuspensions. In situ K(DOC)s were determined and used to calculate freely dissolved and DOC-associated fractions of the increase in total aqueous PCB concentrations due to resuspension. The importance of DOC-associated PCBs increased with increasing K(OW). In situ K(DOC)s were approximately one to two orders of magnitude greater than those calculated with a commonly used linear free energy relationship (LFER). The present study demonstrates that resuspension of contaminated sediments releases PCBs to the water column, of which a significant fraction are DOC-associated (e.g., 28, 65, and 90% for PCBs 28, 66, and 110, respectively). Results also imply that site-specific PCB K(DOC)s are superior to those calculated with generic LFERs.     

Mechanisms regulating bioavailability of phenanthrene sorbed on a peat soil-origin humic substance

The organic matter-mineral complex plays an important role in regulating the fate of hydrophobic organic compounds (HOCs) in the environment. In the present study, the authors investigated the microbial bioavailability of phenanthrene (PHE) sorbed on the original and demineralized humic acids (HAs) and humin (HM) that were sequentially extracted from a peat soil. Demineralization treatment dramatically decreased the 720-h mineralized percentage of HM-sorbed PHE from 42.5 ± 2.6% to 3.4 ± 1.3%, whereas the influence of this treatment on the biodegradability of HA-associated PHE was much lower. Degradation kinetics of HA- and HM-sorbed PHE showed that its initial degradation rate was negatively correlated with the aromatic carbon content of humic substances (p<0.05). This was attributed to the strong interactions between PHE and the aromatic components of humic substances, which hampered its release and subsequent biodegradation. The 720-h mineralized percentage of PHE was inversely correlated with the estimated thickness of the organic matter layer at the surfaces of HAs and HMs. Therefore, in a relatively long term, diffusion of PHE within the organic matter layer could be an important factor that may limit the bioavailability of PHE to bacteria. Results of the present study highlight the molecular-scaled mechanisms governing bioavailability of PHE sorbed on humic substances.     

Development of negligible depletion hollow fiber-protected liquid-phase microextraction for sensing freely dissolved triazines

A new sampling method, termed negligible depletion hollow fiber-protected liquid-phase microextraction, was developed for sensing the freely dissolved concentration (C(free)) and evaluating the availability of atrazine (ATR), desethyl atrazine (DEA), and simazine (SIM) in water. The sampling device was prepared by impregnating 1-octanol to both the pores and the lumen of a piece of polypropylene microporous hollow fiber membrane. After equilibrium and negligible depletion extraction, the 1-octanol in the lumen of the hollow fiber (10 microl) was collected for determination of triazines. Determination of C(free) and the distribution coefficient to 1-octanol (D(ow)) can be performed with this technique. A wide linear working range (1-200 microg/L) and low detection limits (0.1-1 microg/L) were obtained for triazines. Measured log D(ow) values of DEA (1.44 +/- 0.04), SIM (2.06 +/- 0.06), and ATR (2.33 +/- 0.05) agreed well with those reported in the literature. The measured D(ow) values were independent of the chemical concentration and sample pH (pH 3-10) and negligibly affected by the sample salinity (0-500 mM), suggesting that environmentally relevant pH and salinity have no significant effects on the availability of triazines. Although a slight (< or = 31%) increase of C(free) was observed, one-way analysis of variance indicated the C(free) of triazines were not significantly affected by the presence of Aldrich humic acid, Acros humic acid, and bovine albumin V (dissolved organic carbon [DOC], 0-100 mg/L). From 3 to 36% of the spiked triazines, however, were found to associate with the dissolved organic matter (DOM) in surface-water samples (DOC, 32.0-61.9 mg/L), suggesting the origin of the DOM is a key parameter in determining its association with and, thus, the availability of triazines.     

Copper toxicity in relation to surface water-dissolved organic matter: biological effects to Daphnia magna

Water quality standards for copper are usually stated in total element concentrations. It is known, however, that a major part of the copper can be bound in complexes that are biologically not available. Natural organic matter, such as humic and fulvic acids, are strong complexing agents that may affect the bioavailable copper (Cu2+) concentration. The aim of this study was to quantify the relation between the concentration of dissolved natural organic matter and free Cu2+ in surface waters, and the biological effect, as measured in a standardized ecotoxicological test (48 h-median effective concentration [EC50] Daphnia magna, mobility). Six typical Dutch surface waters and an artificial water, ranging from 0.1 to 22 mg/L dissolved organic carbon (DOC), were collected and analyzed quarterly. Chemical speciation modeling was used as supporting evidence to assess bioavailability. The results show clear evidence of a linear relation between the concentration of dissolved organic carbon (in milligrams DOC/L) and the ecotoxicological effect (as effect concentration, EC50, expressed as micrograms Cu/L): 48-h EC50 (Daphnia, mobility) = 17.2 x DOC + 30.2 (r2 = 0.80, n = 22). Except for a brook with atypical water quality characteristics, no differences were observed among water type or season. When ultraviolet (UV)-absorption (380 nm) was used to characterize the dissolved organic carbon, a linear correlation was found as well. The importance of the free copper concentration was demonstrated by speciation calculations: In humic-rich waters the free Cu2+ concentration was estimated at approximately 10(-11) M, whereas in medium to low dissolved organic carbon waters the [Cu2+] was approximately 10(-10) M. Speciation calculations performed for copper concentrations at the effective concentration level (where the biological effect is considered the same) resulted in very similar free copper concentrations (approximately 10(-8) M Cu) in these surface waters with different characteristics. These observations consistently show that the presence of organic matter decreases the bioavailability, uptake, and ecotoxicity of copper in the aquatic environment. It demonstrates that the DOC content must be included in site-specific environmental risk assessment for trace metals (at least for copper). It is the quantification of the effects described that allows policy makers to review the criteria for copper in surface waters.     

Binding interactions of 1-naphthol with dissolved organic matter of Lake Biwa and treated sewage wastewater: The role of microbial fulvic acid

The binding interactions of 1-naphthol with effluent and whole natural dissolved organic matter (DOM) samples were analyzed by using a fluorescence quenching technique. Nonfractionated DOM samples from Lake Biwa (Japan), creek water, treated sewage effluents, and an extracted Lake Biwa fulvic acid (LBFA) standard were used as quenchers and compared at the same 1-naphthol with DOM organic carbon ratios found for low natural dissolved organic carbon (DOC) levels (～4.5?mg/L). Natural and effluent DOM (eDOM) samples were characterized by the DOC level, relative hydrophobicity (RH%), ultraviolet (UV)-visible absorbance and fluorescence excitation emission spectroscopy. These parameters were compared with those of the reference LBFA standard. Concave-up Stern-Volmer plots accounted for both the partitioning and the adsorptive binding in the eDOM-polycyclic aromatic hydrocarbons (PAH) system as compared with the nonspecific partitioning in the natural DOM-PAH system. Strong linear regressions (r(2) >?0.80) between the log K(DOC) values, the RH%, the UV absorbances, and the Fl(340-435) -UV(340) indices for the structural composition and molecular weights of the DOM samples were obtained. These results suggest that low molecular weight microbial fulvic acid (<800 Da) is dominant in the eDOM-PAH binding interactions, as well as in the distinct molecular structure of the eDOM samples, which resulted in fivefold to sixfold higher binding magnitude for 1-naphthol than for the other samples. Environ. Toxicol. Chem. 2012; 31: 2201-2209. ? 2012 SETAC.     

Effects of using synthetic sea salts when measuring and modeling copper toxicity in saltwater toxicity tests

Synthetic sea salts are often used to adjust the salinity of effluent, ambient, and laboratory water samples to perform toxicity tests with marine and estuarine species. The U.S. Environmental Protection Agency (U.S. EPA) provides guidance on salinity adjustment in its saltwater test guidelines. The U.S. EPA suggests using commercial sea salt brands, such as Forty Fathoms (now named Crystal Sea Marinemix, Bioassay Grade), HW Marinemix, or equivalent salts to adjust sample salinity. Toxicity testing laboratories in Canada and the United States were surveyed to determine synthetic sea salt brand preference. The laboratories (n = 27) reported using four brands: Crystal Sea Marinemix (56%), HW Marinemix (22%), Instant Ocean (11%), and Tropic Marin (11%). Saline solutions (30 g/L) of seven synthetic sea salts were analyzed for dissolved copper and dissolved organic carbon (DOC) content. Brands included those listed above plus modified general-purpose salt (modified GP2), Kent Marine, and Red Sea Salt. The synthetic sea salts added from < 0.1 to 1.2 microg Cu/L to the solution. Solutions of Crystal Sea Marinemix had significantly elevated concentrations of DOC (range = 5.4-6.4 mg C/L, analysis of variance, Tukey, alpha = 0.05, p < 0.001) while other brands generally contained < 1.0 mg C/L. The elevated DOC in Crystal Sea Marinemix was expected to reduce copper toxicity. However, the measured dissolved copper effective concentration 50% (EC50) for Crystal Sea Marinemix was 9.7 microg Cu/L, similar to other tested sea salts. Analysis indicates that the organic matter in Crystal Sea Marinemix differs considerably from that of natural organic matter. On the basis of consistently adding little DOC and little dissolved copper, GP2 and Kent Marine are the best salts to use.     

Measuring the bioavailability of two hydrophobic organic compounds in the presence of dissolved organic matter

Bioavailability of benzo[a]pyrene (BaP) and 3,3',4,4'-tetrachlorobiphenyl (TCB) was studied in natural lake water containing dissolved organic matter (DOM). Lake water was diluted to give a dissolved organic carbon (DOC) range of 1 to 20 mg/L. Partition coefficients for the model compounds were assessed at different DOM concentrations and over time with three different methods, namely equilibrium dialysis and reverse-phase and liquid-liquid extraction. In addition, biological partition coefficients were estimated from the difference in the bioconcentration of the model compounds in Daphnia magna in the presence and absence of DOM. Results showed that bioavailability of the model compounds was reduced by the presence of DOM. The equilibrium dialysis method gave the best estimates for bioavailability of the model compounds when compared with biologically determined values. Both the reverse-phase and the liquid-liquid extraction overestimated the bioavailable fraction. The more pronounced overestimation of bioavailable fraction of TCB suggested that the sorption of TCB was not only lower but the interaction was also weaker than that of BaP. Increasing DOM concentration produced lower partition coefficients and the effect seemed to be more pronounced when measured by the reverse-phase and the extraction methods.     

Dissolved organic carbon reduces the toxicity of aluminum to three tropical freshwater organisms

The influence of dissolved organic carbon (DOC) on the toxicity of aluminum (Al) at pH 5 (relevant to acid mine drainage conditions), to the tropical green hydra (Hydra viridissima), green alga (Chlorella sp.), and cladoceran (Moinodaphnia macleayi) was assessed. Two DOC sources, a natural in situ DOC in soft billabong water (SBW) and Suwannee River fulvic acid (SRFA) standard, were compared. The order of sensitivity of the test organisms to dissolved Al (0.1 μm fraction) was Hydra viridissima > Moinodaphnia macleayi > Chlorella sp. with DOC reducing dissolved Al toxicity most for Hydra viridissima. However, colloidal or precipitated Al may contribute indirectly to the toxicity for M. macleayi and Chlorella sp. The toxicity of dissolved Al was up to six times lower in test waters containing 10 mg L(-1) DOC (in the form of SRFA), relative to toxicity observed at 1 mg L(-1) DOC. In contrast, the toxicity of Al was up to two times lower in SBW containing 10 mg L(-1) DOC, relative to water containing 1 mg L(-1) DOC. The increased ability of SRFA in reducing Al toxicity was linked to its greater affinity for complexing Al compared with the in situ DOC. This has important implications for studies that use commercial standards of humic substances to predict Al toxicity in local environments. Speciation modeling demonstrated that Al(3+) and AlOH(2+) provided a strong relationship with toxicity. An empirical relationship is provided for each organism that can be used to predict Al toxicity at a given Al and DOC concentration.     

Influence of flow-through and renewal exposures on the toxicity of copper to rainbow trout

We examined changes in water chemistry and copper (Cu) toxicity in three paired renewal and flow-through acute bioassays with rainbow trout (Oncorhynchus mykiss). Test exposure methodology influenced both exposure water chemistry and measured Cu toxicity. Ammonia and organic carbon concentrations were higher and the fraction of dissolved Cu lower in renewal tests than in paired flow-through tests. Cu toxicity was also lower in renewal tests; 96 h dissolved Cu LC(50) values were 7-60% higher than LC(50)s from matching flow-through tests. LC(50) values in both types of tests were related to dissolved organic carbon (DOC) concentrations in exposure tanks. Increases in organic carbon concentrations in renewal tests were associated with reduced Cu toxicity, likely as a result of the lower bioavailability of Cu-organic carbon complexes. The biotic ligand model of acute Cu toxicity tended to underpredict toxicity in the presence of DOC. Model fits between predicted and observed toxicity were improved by assuming that only 50% of the measured DOC was reactive, and that this reactive fraction was present as fulvic acid.     

Persistent organic pollutants (POPs) in the conventional activated sludge treatment process: fate and mass balance

The fate and the mass balance of persistent organic pollutants (POPs) during the conventional activated sludge treatment process were investigated in the wastewater treatment plant of the city of Thessaloniki, northern Greece. The POPs of interest were 7 polychlorinated biphenyls and 19 organochlorine pesticides. Target compounds were determined at six different points across the treatment system: the influent, the effluent of the primary sedimentation tank, the effluent of the secondary sedimentation tank, the primary sludge, the activated sludge from the recirculation stream, and the digested/dewatered sludge. The distribution of POPs between the dissolved and the adsorbed phases of wastewater and sludge was investigated. A good linear relationship between the distribution coefficients, Kd, and the octanol-water partition coefficients, Kow, of the solutes was observed only in raw wastewater, suggesting that other factors affect the phase distribution of organic compounds in treated wastewater. For all POPs, a significant increase in partitioning with a decreasing solids concentration was observed, revealing an effect from non-settling microparticles remaining in the "dissolved" phase during the separation procedure. A good linear relationship was also revealed between logKd and the dissolved organic carbon (DOC) content of wastewater, suggesting that DOC favors the advective transport of POPs in the dissolved phase. Almost all POPs showed good mass balance agreements at both the primary and the secondary treatment. The losses observed for some species could be attributed to biodegradation/biotransformation rather than volatilization. The relative distribution between the treated effluent and the waste sludge streams varied largely among different compounds, with p-p'-DDE being highly accumulated in the waste sludge (98%) but almost 60% of alpha-HCH remaining in the treated effluent.     

Measurement of polybrominated diphenyl ethers and metabolites in mouse plasma after exposure to a commercial pentabromodiphenyl ether mixture

BACKGROUND: Previous studies have shown that polybrominated diphenyl ethers (PBDEs) behave as weak estrogens in animal and cell culture bioassays. In vivo metabolites of PBDEs are suspected to cause these effects. OBJECTIVES: To identify candidate metabolites, mouse plasma samples were collected after continuous oral and subcutaneous exposure to DE-71, a widely used commercial pentabromodiphenyl ether product, for 34 days. METHODS: Samples were extracted, separated into neutral and phenolic fractions, and analyzed by gas chromatographic mass spectrometry. RESULTS: In the plasma samples of orally treated animals, 2,2',4,4',5,5'-hexabromodiphenyl ether (BDE-153) represented 52% of total measurable PBDEs, whereas it represented only 4.3% in the DE-71 mixture. This suggested that BDE-153 was more persistent than other congeners in mice. Several metabolites were detected and quantitated: 2,4-dibromophenol, 2,4,5-tribromophenol, and six hydroxylated PBDEs. The presence of the two phenols suggested cleavage of the ether bond of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and 2,2',4,4',5-pentabromodiphenyl ether (BDE-99), respectively. The hydroxylated (HO)-PBDEs might come from hydroxylation or debromination/hydroxylation. Among the quantitated hydroxylated metabolites, the most abundant was 4-HO-2,2',3,4'-tetra-BDE, which suggested that there was a bromine shift during the hydroxylation process. para-HO-PBDEs have been proposed to behave as endocrine disruptors. CONCLUSIONS: THERE SEEM TO BE THREE METABOLIC PATHWAYS: cleavage of the diphenyl ether bond, hydroxylation, and debromination/hydroxylation. The cleavage of the diphenyl ether bond formed bromophenols, and the other two pathways formed hydroxylated PBDEs, of which para-HO-PBDEs are most likely formed from BDE-47. These metabolites may be the most thyroxine-like and/or estrogen-like congeners among the HO-PBDEs.     

Effect of humic acids on toxicity of DDT and chlorpyrifos to freshwater and estuarine invertebrates

The effects of dissolved humic acids (HAs) on the acute toxicities of the organophosphate pesticide chlorpyrifos and the organochlorine pesticide 4,4'-dichlorodiphenyltrichloroethane (DDT) were assessed by using freshwater crustaceans (Ceriodaphnia dubia) and saltwater crustaceans (Americamysis bahia). The effects of filtered Aldrich HAs (10-100 mg/L) on organism mortality were determined. Humic acids had no effect on mortality of A. bahia for either pesticide at a salinity of 20 parts per thousand, but greatly reduced the mortality of C. dubia for both pesticides in freshwater (0 parts per thousand). In the latter case, the effect was proportional to the HA concentration. The difference in toxicity mitigation as a function of salinity is believed to be due to conformational changes in the HA molecules, which impact pesticide-HA binding, rather than to organismal effects.     

Kinetics of biodegradation of nitrilotriacetic acid (NTA) in an estuarine environment

The effects of salinity and dissolved organic carbon (DOC) on the kinetics of biodegradation of nitrilotriacetic acid (NTA) were studied in a Canadian estuary with a prior history of NTA exposure. Kinetic parameters for degradation of 14C-labeled NTA, maximum velocity (Vmax) and first-order rate constant (k1), were estimated by nonlinear regression models from velocity and time-course plots, respectively. The distribution of bacteria with NTA-degrading capability was also determined at various salinities and DOC levels by the 14C-most-probable-number (14C-MPN) technique. In general, NTA degradation was rapid in estuarine water over the range of salinities and DOC levels tested. Mean Vmax and k1 values (+/- standard deviation) across several sampling periods averaged 4753 +/- 2849 ng liter-1 hr-1 and 0.32 +/- 0.19 day-1, respectively. The estimated half-life for NTA degradation in estuarine water, based on the mean k1 value, was approximately 2 days. Degradation rates for NTA were relatively insensitive to changes in salinity or DOC values, and neither of these two parameters had significant effects on NTA degradation at the microbial community or individual cell levels. Based on 14C-MPN results, the distribution of estuarine bacteria capable of degrading NTA was broad and not related to salinity or DOC levels. The NTA degraders appeared to be indigenous members of the estuarine microbial community and not wastewater-associated microorganisms.     

Evaluation of brominated diphenyl ether-99 toxicity with Raphidocelis subcapitata and Daphnia magna

Brominated flame retardants belong to a new class of environmental contaminants. To obtain new information regarding the effects of 2,2',4,4',5-brominated diphenyl ether (BDE-99), one of the most frequently reported congeners in freshwater biota, the inhibition of algal growth of Raphidocelis subcapitara (also known as Selenastrum capricornutum) and acute toxicity to Daphnia magna were examined. The experimental design also involved a comparison with the polychlorinated biphenyl (PCB) Aroclor 1254. The uptake of BDE-99 by R. subcapitata and the transfer to D. magna (i.e., a higher level of aquatic biota in the food chain) was also assessed to verify the bioaccumulation phenomenon. After 24 h, BDE-99 appeared to be less toxic than Aroclor 1254 to D. magna, but the two compounds showed a similar toxicity at 48 h. In contrast to Aroclor 1254, BDE-99 was nontoxic to R. subcapitata at up to 100 microM, the highest tested concentration. However, the dose-dependent decrease in survival and impairment of reproduction of D. magna fed with BDE-99-treated algal culture demonstrate uptake by R. subcapitata. Because of the high persistence and bioconcentration, polybrominated diphenyl ethers as well as PCBs might be of environmental concern for years.