Transfer kinetics of polar organic compounds over polyethersulfone membranes in the passive samplers POCIS and Chemcatcher

Passive samplers for polar organic compounds often use a polyethersulfone (PES) membrane to retain the particulate sorbent material (e.g., in a POCIS; polar organic chemical integrative sampler) or to reduce the sampling rate and thus extend the kinetic regime (e.g., in a Chemcatcher). The transport kinetics over the PES membrane are evaluated here in a short-term (6 days) and a long-term (32 days) experiment with POCIS and Chemcatchers. Passive samplers were placed in a channel with flowing river water that was spiked with 22 organic chemicals including pharmaceuticals, pesticides and biocides; with logK(ow) (logarithmic octanol-water partitioning coefficient) values between -2.6 and 3.8. Samplers were removed at intervals and membranes and sorbent material were extracted and analyzed with LC-MS/MS. Uptake kinetics of the compounds fell between two extremes: (1) charged chemicals and chemicals of low hydrophobicity did not accumulate in PES and rapidly transferred to the sorbent (e.g., diclofenac) and (2) more hydrophobic chemicals accumulated strongly in the PES and appeared in the sorbent after a lag-phase (e.g., diazinon and diuron). Sorption kinetics were modeled with a three-compartment first-order kinetic model to determine uptake and elimination rate constants and partitioning coefficients. Water PES partitioning coefficients fitted with the model correlated well with experimentally determined values and logK(ow). Sampling rates of Chemcatcher (0.02-0.10 L/d) and POCIS (0.02-0.30 L/d) showed similar patterns and correlated well. Thus the samplers are interchangeable in practical applications. Longer lag-phases may pose problems when calculating time-weighted average aqueous concentrations for short passive sampling windows and for a correct integrative sampling of fluctuating concentrations.     

仿星型拓扑几何结构聚氨酯/聚二甲基硅氧烷防水透湿膜制备与性能

为提高纳米纤维膜的防水性并探究膜表面微观结构对膜性能的影响机制,采用高可纺性的聚氨酯(PU)和无氟、低表面能的聚二甲基硅氧烷(PDMS)为原料,通过静电纺丝法制备了PU/PDMS纳米纤维膜,然后在该纤维膜基材上采用静电喷雾法沉积PU/PDMS微颗粒得到对环境友好的防水透湿膜,对其形貌、防水性能、透气透湿性能和力学性能进...     

Determination of xenobiotic intrinsic clearance in freshly isolated hepatocytes from rainbow trout (Oncorhynchus mykiss) and rat and its application in bioaccumulation assessment

Bioaccumulation in fish depends on the dynamics of various processes that involve fish uptake, storage, and elimination of xenobiotics. Elimination via fish biotransformation is a primary process that can be evaluated in an in vitro system to improve the performance of the prediction of xenobiotic bioaccumulation potentials. In this study, values of intrinsic clearance (CLint) of seven reference compounds (atrazine, molinate, 4,4-bis(dimethylamino)-benzophenone, 4-nonylphenol, 2,4-di-tert-butylphenol, trifluralin, benzo(a)pyrene) in hepatocytes freshly isolated from rainbow trout and rat were determined using a substrate depletion approach. Atrazine was metabolized in rat hepatocytes with a CLint value of 3.81 +/- 1.96 mL/h/ 10(6) cells, whereas in trout hepatocytes, the clearance was not significant until very high cell concentration was used and the rate was estimated to be approximately 0.002 mL/h/10(6) cells. Intrinsic clearance values for all other compounds were 5.5-78.5-fold lower in trout hepatocytes than those in rat hepatocytes. Trout hepatic clearance (CL(H)) values were extrapolated from the CLint values using a "well-stirred" liver model. Biotransformation rate constants (kMET) of the compounds in trout were subsequently estimated and used as inputs to a kinetic model for the prediction of bioconcentration factors (BCF) in fish. Compared to the BCF values predicted without consideration of fish biotransformation, the inclusion of estimated kMET values significantly improved fish BCF predictions for the reference compounds. This study demonstrates a framework for future bioaccumulation assessment of xenobiotics using combined information of the physical-chemical properties of the compounds and the biotransformation potentials of the compounds in fish.     

Calibration of an in situ membrane inlet mass spectrometer for measurements of dissolved gases and volatile organics in seawater

Use of membrane inlet mass spectrometers (MIMS) for quantitative measurements of dissolved gases and volatile organics over a wide range of ocean depths requires characterization of the influence of hydrostatic pressure on the permeability of MIMS inlet systems. To simulate measurement conditions in the field, a laboratory apparatus was constructed for control of sample flow rate, temperature, pressure, and the concentrations of a variety of dissolved gases and volatile organic compounds. MIMS data generated with this apparatus demonstrated thatthe permeability of polydimethylsiloxane (PDMS) membranes is strongly dependent on hydrostatic pressure. For the range of pressures encountered between the surface and 2000 m ocean depths, the pressure dependent behavior of PDMS membranes could not be satisfactorily described using previously published theoretical models of membrane behavior. The observed influence of hydrostatic pressure on signal intensity could, nonetheless, be quantitatively modeled using a relatively simple semiempirical relationship between permeability and hydrostatic pressure. The semiempirical MIMS calibration developed in this study was applied to in situ underwater mass spectrometer (UMS) data to generate high-resolution, vertical profiles of dissolved gases in the Gulf of Mexico. These measurements constitute the first quantitative observations of dissolved gas profiles in the oceans obtained by in situ membrane inlet mass spectrometry. Alternative techniques used to produce dissolved gas profiles were in good accord with UMS measurements.     

Application of multi-component Damage Assessment Model (MDAM) for the toxicity of metabolized PAH in Hyalella azteca

Biotransformation and time-dependent toxicity of pyrene and fluorene, in the presence and absence of the biotransformation inhibitor 6-propylpiperonyl butyl diethylene glycol ether known as piperonyl butoxide (PBO), were investigated in Hyalella azteca. Toxicokinetics and biotransformation were determined in both short- and longterm experiments. For pyrene, the uptake rate coefficient (ku = 99 +/- 9 L kg(-1) h(-1)), elimination rate constant for parent compound (kep = 0.050 +/- 0.008 h(-1)), biotransformation rate constant (km = 0.016 +/- 0.003 h(-1)), and elimination rate constant for metabolites (kem = 0.021 +/- 0.007 h(-1)) were determined from a short-term study. For fluorene, ku (130 +/- 30 L kg(-1) h(-1)) and kep (1.7 +/- 0.2 h(-1)) were estimated based on km (0.015 +/- 0.002 h(-1)) and kem (0.011 +/- 0.002 h(-1)) determined from a long-term study. At steady state, the percent metabolites for pyrene and fluorene were 43% and 58%, respectively, determined from km/(km +/- kem). Time-dependent toxicity was determined as both lethal water concentration and lethal body residue in the presence and absence of PBO. Co-exposure to PBO decreased the median lethal residue (LBR50) for parent pyrene and shortened the median lethal time (LT50). Pyrene toxicity was explained by the body residues of parent pyrene and PBO, where the metabolites' contribution was negligible. Forfluorene, co-exposure to PBO increased the LBR50 for parent fluorene and shortened the LT50. Thus, fluorene metabolites contributed significantly to the toxicity. Using a multicomponent damage assessment model, the toxicodynamic parameters, damage accrual rate coefficient, and damage recovery rate constant for parent pyrene and parent fluorene were very similar and estimated to be from 0.009 to 0.020 micromol(-1) g h(-1) and from 0.003 to 0.013 h(-1), respectively, and the incipient LBR50 at the infinite time (LBR50(t = infinity)) was from 0.24 to 0.46 micromol g(-1), respectively. These values are similar to the reported LBR50(t = infinity) for other nonpolar narcotics such as pentachlorobenzene (PCBz, 0.38 +/- 0.13 micromol g(-1)) and dichlorophenylchloroethylene (DDE, 0.41 +/- 0.19 micromol g(-1)). For fluorene metabolites, these values were 0.10 +/- 0.03 micromol(-1) g h(-1), 0.034 +/- 0.021 h(-1), and 0.33 +/- 0.23 micromol g(-1), respectively. However, for pyrene metabolites, since toxicity of pyrene metabolites was negligible, the parameters could not be estimated.     

Assessing the influence of meteorological parameters on the performance of polyurethane foam-based passive air samplers

Polyurethane foam (PUF) disk passive air samplers were evaluated under field conditionsto assessthe effect of temperature and wind speed on the sampling rate for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs). Passive samples integrated over 28-day periods were compared to high-volume air samples collected for 24 h, every 7 days. This provided a large data set of 42 passive sampling events and 168 high-volume samples over a 3-year period, starting in October 2003. Average PUF disk sampling rates for gas-phase chemicals was approximately 7 m3 d(-1) and comparable to previous reports. The high molecular weight PAHs, which are mainly particle-bound, experienced much lower sampling rates of approximately 0.7 m3 d(-1). This small rate was attributed to the ability of the sampling chamber to filter out coarse particles with only the fine/ultrafine fraction capable of penetration and collection on the PUF disk. Passive sampler-derived data were converted to equivalent air volumes (V(EQ), m3) using the high-volume air measurement results. Correlations of V(EQ) against meteorological data collected on-site yielded different behavior for gas- and particle-associated compounds. For gas-phase chemicals, sampling rates varied by about a factor of 2 with temperature and wind speed. The higher sampling rates at colder temperatures were explained bythe wind effecton sampling rates. Temperature and wind were strongly correlated with the greatest winds at coldertemperatures. Mainly particle-phase compounds (namely, the high molecular weight PAHs) had more variable sampling rates. Sampling rates increased greatly atwarmertemperatures as the high molecular weight PAH burden was shifted toward the gas phase and subject to higher gas-phase sampling rates. At colder temperatures, sampling rates were reduced as the partitioning of the high molecular weight PAHs was shifted toward the particle phase. The observed wind effect on sampling for the particle-phase compounds is believed to be tied to this strong temperature dependence on phase partitioning and hence sampling rate. For purposes of comparing passive sampler derived data for persistent organic pollutants, the factor of 2 variability observed for mainly gas-phase compounds is deemed to be acceptable in many instances for semiquantitative analysis. Depuration compounds may be used to improve accuracy and provide site-specific sampling rates, although this adds a level of complexity to the analysis. More research is needed to develop and test passive air samplers for particle-associated chemicals.     

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.     

Competitive sorption of pyrene on wood chars

Sorption isotherms of pyrene on original and heat-treated wood chars were examined to understand its sorption behavior. Pyrene in single-solute systems had nonlinear isotherms. Polanyi-based dual-domain model fit sorption data well, and the model results showed that the adsorption component dominated pyrene sorption by original char at all aqueous concentrations. In contrast, this adsorption component contributed a much lower fraction to the total sorption by the heat-treated char, and dominated only at low solute concentrations; with increasing concentration, partitioning became a predominant contributor to the total sorption. Competitive effect of four cosolutes, phenanthrene (Phen), benzo[a]anthracene (BaA), 2,2-methylene-bis (4-methyl-6-tert-butylphenol) (MMBP), and phenol on pyrene sorption by original and treated chars was examined to understand the underlying mechanism of competition. Hydrophobicity (adsorbability) and molecular size of competitors played an important role in competition with pyrene by both chars, suggesting the direct competition for sorption sites and pore blockage mechanism. Competitive sorption results indicated that the fate and transport of hydrophobic organic chemicals (e.g., pyrene) could be strongly affected in the presence of coexisting organic contaminants with high hydrophobicity and large molecularsize,thereby, enhancing the mobility and leachability of these chemicals.     

Diffusion of PAH in potato and carrot slices and application for a potato model

A method for quantifying the effect of medium composition on the diffusive mass transfer of hydrophobic organic chemicals through thin layers was applied to plant tissue. The method employs two silicone disks, one serving as source and one as sink for a series of PAHs diffusing through thin layers of water, potato tissue, and carrot tissue. Naphthalene, phenanthrene, anthracene, and fluoranthene served as model substances. Their transfer from source to sink disk was measured by HPLC to determine a velocity rate constant proportional to the diffusive conductivity. The diffusive flux through the plant tissue was modeled using Fick's first law of diffusion. Both the experimental results and the model suggest that mass transfer through plant tissue occurs predominantly through pore water and that, therefore, the mass transfer ratio between plant tissue and water is independent of the hydrophobicity of the chemical. The findings of this study provide a convenient method to estimate the diffusion of nonvolatile organic chemicals through various plant materials. The application to a radial diffusion model suggests that "growth dilution" rendersthe concentration of highly hydrophobic chemicals in potatoes below their equilibrium partitioning level. This is in agreement with field results for the bioconcentration of PAHs in potatoes.     

抗菌防沾污生物防护材料的制备及其性能

为保护医护人员生命健康安全,研制了一种兼具抗菌和阻隔功能的可重复使用生物防护材料。首先以纳米银(AgNPs)为抗菌剂,热塑性聚氨酯(TPU)为基体,通过静电纺丝技术制备载银TPU纳米纤维膜;然后以聚二甲基硅氧烷(PDMS)为疏水整理剂,涤纶织物为基材,通过等离子体刻蚀—浸轧PDMS—焙烘工艺制备防沾污织物;最后将制备的载银TPU纳米纤维膜与防沾污织物进行点胶复合制备生物防护材料。测试了生物防护材料的抗湿性能、透湿性能、防水性能及过滤性能等。结果表明：经过50次标准洗涤后,防沾污织物的水接触角达到143.1°;纳米银负载量为300 mg/kg的生物防护材料对大肠杆菌和金黄色葡萄球菌的抑菌率均达到99.99%,且沾湿等级达到5级,水蒸气透过量为2 654.8 g/(m²·24 h),断裂强力为450 N左右,静水压为53.6 kPa,过滤效率达到99%以上。     

ZnO-PDMS超双疏薄膜对腐败希瓦氏菌生物被膜的抑制机制

为提高食品贮藏加工材料表面对水产品腐败希瓦氏菌生物被膜的抗黏附性能,以聚二甲基硅氧烷(PDMS)为成膜剂,以水热合成法制备的不同微观形貌的ZnO微纳米粒子为改性剂,采用流延法制备了ZnO-PDMS薄膜,并研究了薄膜对腐败希瓦氏菌生物被膜的抑制性能及作用机理。结果表明：改性ZnO微纳米粒子的微观形貌影响PDMS薄膜的疏水疏油性能,以绒球状和花状ZnO微纳米粒子为改性剂,可获得ZnO-PDMS超双疏薄膜,对水和油的接触角均大于150°。薄膜的抗菌黏附性能与疏水疏油性能呈正相关,随着培养时间的延长,ZnO薄膜释放的Zn²⁺破坏了细菌细胞膜,并抑制胞内ATP酶和AKP酶活性,引起细菌代谢紊乱导致细菌死亡。相较于棒状和绒球状微纳米粒子改性的PDMS薄膜,花状ZnO-PDMS薄膜具有更强的抗黏附性能和抑菌效能。同时具有超双疏性能和抗菌性能的ZnO-PDMS薄膜可有效抑制腐败希瓦氏菌生物被膜的形成和生长,研究旨在为抗生物被膜材料的研制提供技术支持。     

Rainbow trout (Oncorhynchus mykiss) can eliminate chiral organochlorine compounds enantioselectively

Dietary accumulation of four chiral organochlorine compounds--alpha-hexachlorocyclohexane (alpha-HCH), trans-chlordane, and chlorobiphenyls (CBs) 95 and 136-by immature rainbow trout (Oncorhynchus mykiss) was studied to determine if fish can accumulate and eliminate these compounds enantioselectively. Fish rapidly accumulated all four compounds from food spiked at micrograms per gram concentrations during a 40-d feeding period. Depuration half-lives were from 13 d for (+/-)-alpha-HCH to 375 d for (+/-)-CB 136. Fish preferentially eliminated (-)-trans-chlordane and (+)-CB 136, with significant nonracemic residues observed after 20 d. These results are consistent with field measurements of these compounds in fish as well as known metabolic pathways. Enantiomeric fractions (EFs) for these two compounds changed significantly over the course of the experiment, suggesting that trout were enantioselectively biotransforming the compounds during the 238-d depuration phase. CB 95 and alpha-HCH residues were racemic throughout the experiment. High biomagnification factors for CB 95 suggest that it was not metabolized. Minimum values for metabolic elimination rates calculated from EF suggest that at least 58% of the trans-chlordane depuration rate can be attributed to metabolism, and all of the CB 136 depuration rate can be attributed to it. This study highlights the potential of chiral analysis as a tracer of in vivo biotransformation processes of xenobiotic compounds.     

Predicting concentrations of organic chemicals in fish by using toxicokinetic models

Quantification of chemical toxicity continues to be generally based on measured external concentrations. Yet, internal chemical concentrations have been suggested to be a more suitable parameter. To better understand the relationship between the external and internal concentrations of chemicals in fish, and to quantify internal concentrations, we compared three toxicokinetic (TK) models with each other and with literature data of measured concentrations of 39 chemicals. Two one-compartment models, together with the physiologically based toxicokinetic (PBTK) model, in which we improved the treatment of lipids, were used to predict concentrations of organic chemicals in two fish species: rainbow trout (Oncorhynchus mykiss) and fathead minnow (Pimephales promelas). All models predicted the measured internal concentrations in fish within 1 order of magnitude for at least 68% of the chemicals. Furthermore, the PBTK model outperformed the one-compartment models with respect to simulating chemical concentrations in the whole body (at least 88% of internal concentrations were predicted within 1 order of magnitude using the PBTK model). All the models can be used to predict concentrations in different fish species without additional experiments. However, further development of TK models is required for polar, ionizable, and easily biotransformed compounds.     

Prediction of time-dependent PAH toxicity in Hyalella azteca using a damage assessment model

A damage assessment model (DAM) was developed to describe and predict the toxicity time course for PAH in Hyalella azteca. The DAM assumes that death occurs when the cumulative damage reaches a critical point and was described by a combination of both first-order toxicokinetic and toxicodynamic models. In aqueous exposures, body residues increase in proportion to the water concentration. Damage is assumed to accumulate in proportion to the accumulated residue and damage recovery in proportion to the cumulative damage when damage is reversible. As a result, the toxicity time course, LC50(t), is determined by both a damage recovery rate and an elimination rate. The constant critical body residue (CBR) and the critical area under the curve (CAUC) models can be derived as two extreme cases from the DAM, and all three models were reanalyzed using a hazard modeling approach. As a result, the critical cumulative damage (D(L)) is the determinant of the concentration-time response relationship and not simply the CBR or the CAUC. Finally, from the DAM, two parameters, a damage recovery rate constant kr and the killing rate kt, were estimated and found to be relatively constant for selected PAH.     

Hydrolysis of environmental contaminants as an experimental tool for indication of their persistency

To predict the persistency of a chemical in the environment, the chemical's physical-chemical properties and its reactivity in the environment need to be known or at least estimated. The partitioning of a chemical can be described on the basis of its water solubility, its octanol/water partitioning coefficient, and its vapor pressure. The mechanisms by which a chemical can be transformed may be categorized as being hydrolysis, oxidation, reduction, and photolysis. This study establishes a method for estimating the relative susceptibility of some potential environmental pollutants to undergo hydrolysis reactions. The method used the second-order rate constant for the reaction with sodium methoxide in methanol/N,N-dimethylformamide (DMF) as an indicator of relative susceptibility toward hydrolysis. The decabromodiphenyl ether is rapidly hydrolyzed, that is, undergoes nucleophilic aromatic substitution, while the rate of reaction of less brominated diphenyl ethers decreased by roughly a factor of 10 for each decrease in the level of bromination. Hexachlorobenzene was found to have a similar rate to a nonabromodiphenyl ether. 2,2-Bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT) was transformed to 2,2-bis(4-chlorophenyl)-1,1-dichloroethene (DDE) immediately under these conditions, while DDE showed no apparent reaction. The results show that chemicals that can undergo elimination reactions are rapidly transformed, as are perhalogenated chemicals that can undergo substitution reactions. These chemicals are not likely to persist in the environment, while those that did not show any observable reactivity under similar hydrolytic conditions may persist for a very long time.     

Modeling effects of mixtures of endocrine disrupting chemicals at the river catchment scale

For endocrine disrupting chemicals in the environment, concerns arise primarily from the effects that may be induced in wildlife. A well studied example is estrogenic chemicals in the aquatic environment and their effects on fish. Directly measuring effects, in fieldwork studies, is an expensive and time-consuming approach that is fraught with many difficulties, ranging from study design right through to data analysis and interpretation. An alternative approach would be to predict the scale of effect(s) using suitable modeling techniques. We have attempted to do this using estrogenic chemicals as an example. We chose this group of aquatic pollutants because of the current considerable interest in them and the wealth of biological data available on them. Using the established GREAT-ER hydrological model,we have first predicted the concentrations and then the estrogenic effects on fish, of estrone, estradiol, ethinyl estradiol, and nonylphenol individually throughout an entire river catchment. We then show that knowledge of the biological responses of fish to mixtures of these chemicals can be used to predict the effect of environmentally realistic mixtures of them. To determine the degree of risk posed by this group of chemicals, it was necessary to take into account mixture effects: assessment on a chemical by chemical basis led to underestimations of the risk. Finally, we show that the approach can be used to predict how the risk will be affected by changes in the concentration of one chemical in the mixture. Although we have used only one endpoint (vitellogenin induction as an estrogenic response) and one group of similarly acting chemicals, we suggest that this general approach could prove extremely useful to regulatory authorities and other parties charged with protecting aquatic wildlife from adverse effects caused by chemicals in their environment.     

Toxicokinetic model describing bioconcentration and biotransformation of diazinon in Daphnia magna

A toxicokinetic model for Daphnia magna , which simulates the internal concentration of the insecticide diazinon, its detoxification product 2-isopropyl-6-methyl-4-pyrimidinol, and its active metabolite diazoxon, is presented. During in vivo exposure to diazinon with and without inhibition of cytochrome P450 by piperonyl butoxide, the parent compound as well as its metabolites were quantified with high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) in extracts of D. magna . Rate constants of all relevant toxicokinetic steps were obtained by modeling the time course of the internal concentrations with a multicomponent first-order kinetics model. When cytochrome P450 was inhibited, the kinetic bioconcentration factor (BCF) of diazinon increased from 17.8 to 51.0 mL·g(ww)(-1). This clearly indicates that diazinon is biotransformed to a high degree by cytochrome P450 in D. magna . The dominant elimination step of diazinon was shown to be its oxidative dearylation to pyrimidinol (62% of total elimination) with a corresponding rate constant of 0.16 h(-1). In contrast, oxidative activation to diazoxon with a rate constant of 0.02 h(-1) amounted to only 8% of the total elimination. During exposure to diazinon, the active metabolite diazoxon could be detected only in very low concentrations (approximately 0.5% of the parent compound), presumably due to a very fast reaction with the target site acetylcholinesterase. During the exposure experiments (no feeding of daphnids), an exponential decline of the lipid content in D. magna with a first-order rate constant of 0.013 h(-1) was observed. For short exposure times (≤ 24 h), this had only a minor influence on the determined TK parameters. Such a TK model containing detailed biotransformation processes is an important tool for estimation of the toxic potential of chemicals, particularly, when active metabolites are formed inside an organism.     

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.     

Dispersion state and humic acids concentration-dependent sorption of pyrene to carbon nanotubes

Sonication and humic acids (HA) are known to disperse carbon nanotube (CNT) suspensions, but potential effects on sorption of chemicals to CNTs remain poorly understood. We applied a passive sampling method to investigate the influence of dispersion/aggregation on sorption of pyrene to CNTs. Sonication broke down CNT aggregates and increased pyrene sorption affinity by up to 1.39 orders of magnitude. Sorption surfaces newly exposed by sonication remained available to pyrene even after reaggregation occurred, suggesting an irreversible effect of sonication. The presence of HA decreased sorption of pyrene to CNTs, but at the highest HA concentration investigated (200 mg/L), sorption affinity was still 1.90 orders of magnitude larger than sorption of pyrene to HA alone. Specific interactions between pyrene and CNTs were thus still taking place, in spite of the presence of a HA coating on the CNTs' surface. A greater suppression of sorption by CNTs occurred when the HA addition was combined with a sonication pretreatment. Sorption isotherm fitting indicated that the maximum sorption capacity, sorption affinity, and heterogeneity of the CNT surface were all affected by sonication and the presence of HA at a concentration as low as 1 mg/L. The present results contribute to an improved understanding of the sorption behavior of CNTs in both natural and wastewater systems.