Ow Values Research Articles

Development and evaluation of a ceramic diffusive layer based DGT technique for measuring organic micropollutants in seawaters.

Diffusive gradients in thin-films (DGT) technique has been well demonstrated as a robust tool for measuring organic micropollutants (OMPs) in the aquatic environment. However, potential adsorption of the OMPs on organic polymer filters and flow rate of waters can affect the measuring results of the DGT method, hence tedious work should be conducted to reduce these interferences. In the present study, a novel DGT technique coupled with a ceramic diffusive layer was developed to measure the OMPs in seawaters. The ceramic diffusive layer exhibited adsorption inertness to the OMPs with various logKow values. Moreover, the ceramic diffusive layer based DGT technique was proved to be less affected by the flow rate than the traditional DGT with agarose diffusive layer. The developed DGT device exhibited kinetic accumulation for the targets during a 6-d deployment, and measurement of the OMPs by the DGT method was independent with pH and ionic strength. Finally, the developed DGT sampler was applied in coastal waters of Dalian, and eight OMPs were detected with levels ranging from 1.58 to 13.1ng/L. The development of the ceramic diffusive membrane can lead to simplification of the DGT applications, promoting the progress of the OMPs monitoring technology.

Determining binding of polycyclic aromatic hydrocarbons to micelles formed by SDS and SOL using semi-equilibrium dialysis

Micellar enhanced ultra-filtration (MEUF) is a modified ultrafiltration (UF) method that can remove small molecules that are not effectively removed by UF alone. In this work we used a similar semi-equilibrium dialysis (SED) method to characterize two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium laurate (SOL), as MEUF candidates to remove several polycyclic aromatic hydrocarbon (PAH) compounds. These anionic surfactants have low toxicity and are more biodegradable compared to the fairly toxic and persistent cetyltrimethylammonium bromide (CTABr) and similar cationic surfactants, which is important as MEUF surfactants may be present in the treated effluent. The log binding constants (Log KB) of the PAHs naphthalene, phenanthrene, pyrene and fluorene to SDS ranged from 3.07 to 4.48, which compared well with the previous results for CTABr and indicated that SDS is an excellent candidate for MEUF. The log binding constants for the same PAHs with SOL micelles ranged from 2.11 to 3.53, which suggested that SOL might be adequate for stronger-binding PAH like pyrene and fluorene but less suitable for naphthalene and phenanthrene. The results demonstrated a strong correlation between the Log KB with one micelle type and the Log KB with the other, suggesting a common set of properties and interactions are responsible for the binding. Similar to the previous results for CTABr, a significant correlation between Log KB and Log KOW values indicates that hydrophobic character is the main driving force for PAH binding with these anionic micelles. This may also be useful for predicting MEUF performance for various compound/surfactant combinations where Log KB is not known.

Learned Discourses: Timely Scientific Opinions.

The fate of a chemical in the environment is primarily controlled by the physico-chemical properties of the substance, prevailing environmental conditions, and patterns of use (Mackay et al. 1997). Thus, accurate determination of physico-chemical properties is critical to the formulation of valid environmental models and assessments (Bennett et al. 2001). As litigation becomes an increasingly common aspect of environmental science, such studies may be challenged and even refuted. Recent legislation in the United States mandates that federal agencies must ensure the quality of data upon which regulatory action and policy decisions are founded (Reichhardt 2002). Some observers have suggested that because this legislation provides for unprecedented scrutiny of agency data quality, regulatory agencies might face a marked increase in the number of legal challenges. Two of the most important physico-chemical properties relating to the environmental behavior of hydrophobic organic compounds are aqueous solubility (S w ) and the octanol-water partition coefficient (K ow ). Much of the interest in these properties comes from the fact that they can be used to estimate or predict other properties of more immediate environmental and ecotoxicological interest. For this reason, a primary focus of research in the last 20 years has been development of linear regression models in which S w and K ow (or more accurately, their logarithms) are correlated with parameters such as the organic carbon-normalized partition coefficient, bioconcentration and bioaccumulation factors, and indices of biodegradability or toxicity. These, in turn, can be incorporated into models that attempt to characterize the equilibrium distribution and transport rates of organic contaminants among environmental media or to predict impacts on biota. The predictions of such multimedia models have taken on greater immediacy with the recognition that certain persistent organic pollutants, such as DDT and DDE, are globally distributed and may be exerting adverse biological effects far from their original source areas (Wania and Mackay 1996). Our interest in the K ow and S w values of DDT and DDE arose in the context of research we were conducting on the geochemical fate of these compounds in sediments of the Palos Verdes Shelf, California. We expected that studies reporting S w and K ow values for DDT and DDE would be well documented because DDT has a very long history, and its widespread application and biological effects are well known. Results of our initial literature survey, however, were unsatisfactory due to a large spread in data values. We decided to undertake an exhaustive review to identify all measured and estimated values of S w and K ow for these compounds. It soon became apparent that a number of serious problems severely limited use of the database and that our initial expectations had been naive. A complete description of the study discussed here can be found in a USGS report (Pontolillo and Eganhouse 2001) available in PDF format on the web (http://pubs.water.usgs.gov/ wri01-4201/). We examined more than 700 publications including databases, handbooks, review articles, and bibliographies for data, methodological details, and pertinent literature citations. The initial survey was augmented by computerized searches of the scientific literature using the Chemical Abstracts Search Service Index (CASSI) database and the World Wide Web using a variety of Internet searchengines. Several hundred potential articles were generated in this fashion. Each article was retrieved and scrutinized, and additional relevant leads were identified from the reference lists. The search progressed until no further leads could be identified (approximately 2 years). Two problems are evident with the available database: egregious errors in reporting data and references, and poor data quality and/or inadequately documented procedures. The published literature is characterized by a preponderance of unnecessary data duplication. Numerous data and citation errors are also present. The percentage of original S w and K ow data for DDT

Approach to Designing Systems for Delivering Value

AbstractHow value emerges from the interactions between different classes of stakeholders (like customers, service providers, suppliers, acquirers and so on) and the ways and means to enhance the interactions is a phenomenon that is increasingly becoming a significant game changer in any human endeavor. Increasingly, stakeholders expect something of interest to emanate for them whenever they participate in an endeavor. This thing that the stakeholders wish to create or experience is subjective and every stakeholder has their own perception of what this thing is. It is often the case that the thing that enthuses a stakeholder is the perceived value that they feel they can obtain; and the thing that they experience or create when participating in the endeavor is the actual value. In this situation, stakeholders often try to minimize the gap between their perceptions and actuals. This is often difficult to achieve as the notion of what is of value is time and stakeholder dependent. In order to address these issues, in this paper, a systematic approach to facilitate stakeholder value creation is presented and the underlying rationale for the approach discussed. This approach is based on the premise that in all human endeavors, goal or purpose of the endeavor, human centric processes, quality of these human‐centric processes, outcomes and the quality of the outcomes determine the value that different stakeholders create or experience. It is essential to understand, establish and articulate the right value influencing factors and criteria so that value is created for all stakeholders. This is further substantiated by the system value cycle wherein value created by the stakeholder by utilizing one or more systems. A set of eight different processes to institutionalize the stakeholder value creation dynamics is also presented to aid in the value co‐creation, sustenance and transformation.

Is pesticide sorption by constructed wetland sediments governed by water level and water dynamics?

Constructed wetlands (CWs) are used to reduce the pesticide inputs from tile drainage or run-off to surface water. Their effectiveness appears variable and remains to be better characterized and understood. The aim of this study was to assess the influences of two hydraulic parameters (i.e., dynamics and water level) on the sorption process occurring in CWs. Then, two solid/liquid ratios were studied (1/1 and 1/5) to mimic the water level variation in the field, and two agitation speeds were used (none and gentle agitation) to simulate different water dynamics (stagnation and flow pass, respectively). Sorption kinetics and isotherms were obtained for four pesticides with contrasting properties. The pesticide adsorption coefficients were classified as follows: boscalid (BSC) > cyproconazole (CYP) > isoproturon (IPU) ∼ dimethachlor (DMT) at any ratio or agitation, in agreement with their water solubilities and K ow values. The effect of the solid/liquid ratio was evidenced for all conditions. Indeed, the adsorption equilibrium time was reached more quickly for the 1/1 ratio (24-72h) than for the 1/5 ratio (96-120h). In addition, the adsorption coefficients (K fads) were larger for the 1/1 ratio (1.8-11.2Lkg-1) than for the 1/5 ratio (1.0-5.9Lkg-1). The agitation effect was more evidenced for the 1/5 ratio and for the more hydrophobic molecules, such as BSC and CYP, for which adsorption equilibrium time was never reached with agitation (>120h), while it was reached at 96h without agitation. Moreover, the K fads values were larger with agitation than without agitation for BSC and CYP, whereas they were similar for the two agitations for IPU and DMT. Our results demonstrated that the hydrodynamic function of CWs could influence pesticide sorption with variable effects according to the molecular properties and consequently influence the mitigation effect of CWs throughout the year.

Oxygen isotope fractionation between bird eggshell calcite and body water: application to fossil eggs from Lanzarote (Canary Islands).

Oxygen and carbon isotope compositions of fossil bird eggshell calcite (δ(18)Ocalc and δ(13)Ccalc) are regularly used to reconstruct paleoenvironmental conditions. However, the interpretation of δ(18)Ocalc values of fossil eggshells has been limited to qualitative variations in local climatic conditions as oxygen isotope fractionations between calcite, body fluids, and drinking water have not been determined yet. For this purpose, eggshell, albumen water, and drinking water of extant birds have been analyzed for their oxygen and carbon isotope compositions. Relative enrichments in (18)O relative to (16)O between body fluids and drinking water of +1.6±0.9‰ for semi-aquatic birds and of +4.4±1.9‰ for terrestrial birds are observed. Surprisingly, no significant dependence to body temperature on the oxygen isotope fractionation between eggshell calcite and body fluids is observed, suggesting that bird eggshells precipitate out of equilibrium. Two empirical equations relating the δ(18)Ocalc value of eggshell calcite to the δ(18)Ow value of ingested water have been established for terrestrial and semi-aquatic birds. These equations have been applied to fossil eggshells from Lanzarote in order to infer the ecologies of the Pleistocene marine bird Puffinus sp. and of the enigmatic giant birds from the Pliocene. Both δ(13)Ccalc and δ(18)Ocalc values of Puffinus eggshells point to a semi-aquatic marine bird ingesting mostly seawater, whereas low δ(13)Ccalc and high δ(18)Ocalc values of eggshells from the Pliocene giant bird suggest a terrestrial lifestyle. This set of equations can help to quantitatively estimate the origin of waters ingested by extinct birds as well as to infer either local environmental or climatic conditions.

UV photolysis of diclofenac in water; kinetics, degradation pathway and environmental aspects.

In this study, the photolysis behavior of commonly used anti-inflammatory drug diclofenac (DCF) was investigated using UV-C and UV-A irradiation. In that purpose, DCF conversion kinetics, mineralization of organic content, biodegradability, and toxicity were monitored and compared. The results showed different kinetics of DCF conversion regarding the type of UV source applied. However, in both cases, the mineralization extent reached upon complete DCF conversion is rather low (≤10%), suggesting that the majority of DCF was transformed into by-products. Formation/degradation of main degradation by-products was monitored using high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS), whereas different profiles were obtained by UV-C and UV-A photolysis. The results of bioassays revealed that biodegradability of DCF solutions remained low through the applied treatments. The toxicity of irradiated DCF solutions was evaluated using Vibrio fischeri. A significant reduction of toxicity, especially in the case of UV-A radiation, was observed upon complete degradation of DCF. In addition to toxicity reduction, calculated Log K OW values of DCF degradation by-products indicate their low potential for bioaccumulation (Log K OW ≤ 3) in comparison to the parent substance.

Stable isotope study on ancient populations of central sudan: Insights on their diet and environment.

A contribution to the knowledge of the economy and the environmental surroundings of the populations living along the Nile valley in three different periods. This study reports stable isotope analyses on apatite bone samples of 139 humans, 48 mammals, and 43 fish from the Al Khiday archaeological sites in Sudan. The bones belong to four archaeological periods: pre-Mesolithic, Mesolithic, Neolithic, and Meroitic. Data were processed statistically. A significant difference exists between the pre-Mesolithic and Mesolithic mean δ(18) Ow value and the mean of the modern Nile. The mean δ(18) Ow values for the Neolithic humans and bovids are very similar (+1.5‰ ±4‰, and -2‰, respectively) and more positive than the mean values of Mesolithic mammals and Pre-Mesolithic humans. The water ingested by Meroitic humans (+7‰ ± 2.5‰) is enriched in (18) O in respect to the water ingested by the Neolithic population. There is a separation in the δ(13) Cdiet values between the pre-Mesolithic humans (-14‰ ± 1‰) and Mesolithic mammals (-12‰ ± 2‰) group and the Neolithic humans (-18‰ ± 1‰), Meroitic humans (-19‰ ±1‰), Neolithic mammals (-21‰), and the modern (mean δ(13) Cdiet = -19‰ ±2‰) mammal group. The climate became warmer and more arid from the pre-Mesolithic/Mesolithic to the Meroitic period. The environmental conditions influenced the strategies of subsistence and, in particular, the changes occurring from the pre-Mesolithic to the Neolithic can be considered contemporaneous to the transition from hunting-gathering-fishing to cultivation-herding. Am J Phys Anthropol 160:498-518, 2016. © 2016 Wiley Periodicals, Inc.

A soil-column gas chromatography (SCGC) approach to explore the thermal desorption behavior of hydrocarbons from soils.

A soil-column gas chromatography approach was developed to simulate the mass transfer process of hydrocarbons between gas and soil during thermally enhanced soil vapor extraction (T-SVE). Four kinds of hydrocarbons-methylbenzene, n-hexane, n-decane, and n-tetradecane-were flowed by nitrogen gas. The retention factor k' and the tailing factor T f were calculated to reflect the desorption velocities of fast and slow desorption fractions, respectively. The results clearly indicated two different mechanisms on the thermal desorption behaviors of fast and slow desorption fractions. The desorption velocity of fast desorption fraction was an exponential function of the reciprocal of soil absolute temperature and inversely correlated with hydrocarbon's boiling point, whereas the desorption velocity of slow desorption fraction was an inverse proportional function of soil absolute temperature, and inversely proportional to the log K OW value of the hydrocarbons. The higher activation energy of adsorption was found on loamy soil with higher organic content. The increase of carrier gas flow rate led to a reduction in the apparent activation energy of adsorption of slow desorption fraction, and thus desorption efficiency was significantly enhanced. The obtained results are of practical interest for the design of high-efficiency T-SVE system and may be used to predict the remediation time.

Adaptation Mechanisms to Toxic Solvents in Shewanella Putrefaciens

Shewanella putrefaciens is a Gram-negative bacterium which is widespread in various environments, including in sites polluted with petroleum and petroleum products. S. putrefaciens IBB Po6 used organic solvents with log P OW (logarithm of the partition coefficient of the solvent in an octanol-water mixture) values above 4 (i.e., n -decane) and below 4 (i.e., cyclohexane, n -hexane, toluene, o -xylene, ethylbenzene) as growth substrates. More-robust biofilms were developed when S. putrefaciens IBB Po6 cells were grown in the presence of cyclohexane, n -hexane, toluene, o -xylene or ethylbenzene, as compared with those formed in the presence of n -decane. Four biosurfactants were detected in the cell-free culture broths of S. putrefaciens IBB Po6 cells grown in the presence of tested organic solvents. There were observed differences between the PCR pattern of S. putrefaciens IBB Po6 cells grown in the presence of n -decane, and those of cells grown in the presence other tested organic solvents (i.e., cyclohexane, n -hexane, toluene, o -xylene, ethylbenzene).

Evaluation of different QuEChERS procedures for the recovery of selected drugs and herbicides from soil using LC coupled with UV and pulsed amperometry for their detection.

Seven quick, easy, cheap, effective, rugged and safe (QuEChERS)-based procedures, differing in both the extraction and clean-up steps, were investigated for the recovery of bentazone (BTZ), atrazine (ATZ), carbamazepine (CBZ), phenytoin (PNT) and its metabolite 5-(p-hydroxyphenyl-),5-phenylhydantoin (HPPH) from soil. Target analytes were chosen for their extensive use and/or occurrence in soil, as well as for their medium-high polarity characteristics (log K OW values in the range 0.88-2.80), which have been reported as a critical parameter for the recovery from soil with QuEChERS approaches. Liquid chromatography coupled with UV and pulsed amperometric (PA) detection at a glassy carbon electrode was used as instrumental technique. The recovery data obtained within each tested procedure were discussed for each compound investigated, highlighting different behaviour depending on the specific physicochemical characteristics of the analytes. The optimized QuEChERS conditions consisted of the extraction of analytes with CH3CN:H2O 70:30, 5% CH3COOH, followed by a dispersive solid-phase extraction (d-SPE) clean-up step with C18 sorbent. This method, in which water is directly added to the soil together with acetonitrile and salts, allowed the rehydration step to be avoided, which can be as long as 30min. Matrix effects were evaluated for both the detection techniques at different concentration levels, and they were below 24% for both the detection technique used. The recoveries were evaluated at three concentration levels by a matrix-matched calibration and were in the ranges of 83-113% (relative standard deviations (RSD) ≤ 14%) and 88-109% (RSD ≤ 11%) for UV and PA detection, respectively, highlighting very good performances of the method, even for the more polar analytes. Method detection limits ranged from 4μg/kg (BTZ) to 493μg/kg (PNT) and from 4μg/kg (HPPH) to 11μg/kg (BTZ) for UV and PA detection, respectively. The method was finally compared with a microwave-assisted extraction procedure which provided less satisfactory extraction performances than the optimized QuEChERS procedure.

Bioconcentration of TNT and RDX in coastal marine biota.

The bioconcentration factor (BCF) was measured for 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in seven different marine species of varying trophic levels. Time series and concentration gradient treatments were used for water column and tissue concentrations of TNT, RDX, and their environmentally important derivatives 2-amino-4,6-dintrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT). BCF values ranged from 0.0031 to 484.5 mL g(-1) for TNT and 0.023 to 54.83 mL g(-1) for RDX. The use of log K ow value as an indicator was evaluated by adding marine data from this study to previously published data. For the munitions in this study, log K ow value was a good indicator in the marine environment. The initial uptake and elimination rates of TNT and RDX for Fucus vesiculosus were 1.79 and 0.24 h(-1) for TNT and 0.50 and 0.0035 h(-1) for RDX respectively. Biotransformation was observed in all biota for both TNT and RDX. Biotransformation of TNT favored 4-ADNT over 2-ADNT at ratios of 2:1 for F. vesiculosus and 3:1 for Mytilus edulis. Although RDX derivatives were measureable, the ratios of RDX derivatives were variable with no detectable trend. Previous approaches for measuring BCF in freshwater systems compare favorably with these experiments with marine biota, yet significant gaps on the ultimate fate of munitions within the biota exist that may be overcome with the use stable isotope-labeled munitions substrates.

Multi-Taxa Isotopic Investigation of Paleohydrology In the Lower Cretaceous Cedar Mountain Formation, Eastern Utah, U.S.A.: Deciphering Effects Of the Nevadaplano Plateau On Regional Climate

We investigate the regional climatic effects of the formation of the ''Nevadaplano'' plateau during the Sevier Orogeny in an overall warming world. Paleohydrology was reconstructed from 590 individual measurements of phosphate O isotopes in continental faunas of the Lower Cretaceous Cedar Mountain Formation, Utah, U.S.A. Semi-aquatic (turtles, crocodiles) and terrestrial (dinosaurs) taxa are compared to coeval pedogenic carbonates to interpret changing water sources over time. Samples were grouped into four stratigraphic faunas (lower Yellow Cat, upper Yellow Cat, Ruby Ranch, and Mussentuchit members). Resulting isotopic values were converted to d18 Ow values using established d 18 Op-d 18 Ow and d 18 Oc-d 18 Ow relationships. At a formation scale, turtles (d 18 Op = 14.1 to 15.7% V-SMOW) and crocodiles (d 18 Op = 15.0 to 19.2%) document water compositions of 28.1 to 26.1% and 27.7 to 24.2%, respectively, within the zonal range for formation-scale meteoric water at 34u N paleolatitude (27.1 to 24.8%) established by pedogenic carbonates (d18 Oc = 22.0 to 23.5% V-SMOW). These data suggest that, like soil carbonates, turtle and crocodile phosphate isotopes can be used as proxies for meteoric water isotopic composition.Dinosaurd18 Op(sauropods: 19.7 to 21.9%, ornithischians: 16.6to 21.7%, small theropods: 16.9to 18.2%, andlarge allosauroids: 19.1 to 20.3%) values generally exceed those of semi-aquatic taxa. Using mass-balance equations for modern terrestrial animals adjusted for size and inferred dinosaur physiology, ingested water is calculated for the above dinosaur groups. On a member scale, when meteoric-water values are compared with calculated dinosaur drinking water, values are equal to or lighter than meteoric water for most herbivorous groups (as low as 215.5% for ornithischians) and equal to or heavier than meteoric water for most carnivorous groups (as high as 22.0% for allosauroids). Changes in d18 Ometeoric water, d 18 Odinosaur ingested water, faunal assemblages, and sedimentology, from member to member, correlate to thrusting events of the Sevier Orogeny. High elevations in the orogeny attenuated the influences of Pacific moisture, causing rainshadow-induced aridity on the leeward foreland basin during upper Yellow Cat time, and hosted seasonal snow accumulation by the end of Ruby Ranch time, as suggested by 18 O-enriched water (e.g., up to an average of 22.0% from an allosauroid tooth) and extremely 18 O-depleted water (e.g., 215.5% for ornithischians) in the Ruby Ranch Member. By Mussentuchit-time, delivery of the Western Interior Seaway-dominated moisture to the region, despite continued rise of the Sevier Mountains.

Occurrence and fate of selected endocrine-disrupting chemicals in water and sediment from an urban lake.

Occurrence of five endocrine-disrupting chemicals (EDCs)-bisphenol-A (BPA), triclosan (TCS), 17α-ethinyl estradiol (EE2), benzophenone-3, and 4-methylbenzylidene camphor-were monitored in East Lake, the largest urban lake in China. Other than EE2, all selected EDCs were detected at least once in the lake water with concentrations ≤89.1 ng/L. EDCs were detected with greater occurrence in spring than in other seasons. In lake sediment, TCS was detected at the greatest concentration (30.9 ng g(-1)), whereas BPA and EE2 were not detected. Spatial distribution of the EDCs in the lake water and the lake sediment showed similar patterns, and greater EDC residuals were found from those sites with known wastewater input. The linear adsorption coefficients (K d) varied from 17.9 to 1,017 L kg(-1) and were related to the octanol-water partition coefficient (K ow) values of the compounds. Photodegradation was a major process removing the EDCs from the lake water, and the presence of dissolved organic material and NO3 (-) in the lake water can accelerate the photodegradation process. Degradation of the EDCs in the lake sediment was relatively slow and occurred mainly due to the microbial processes. All compounds were found more persistent under anoxic conditions than under oxic conditions.

Prediction of n-octanol/water partitioning coefficients for selected metabolites of polybrominated diphenyl ethers by DFT method

A quantum chemical method has been developed to estimate the n -octanol/water partitioning coefficient (log K ow ) of metabolites of polybrominated diphenyl ethers (PBDEs). The data set covers 19 hydroxylated-PBDEs (HO-PBDEs) and 15 methoxylated PBDEs (MeO-PBDEs), with log K ow values varying from 4.63 to 7.67. The optimized ground-state geometries were calculated using density functional theory to quantify six quantum chemical descriptors. The resultant regression model through multiple linear regression had a correlation coefficient r 2 = 0.941 and a root-mean-square error rmse = 0.198. The polarizability and the most negative atomic partial Mulliken charge on a hydrogen atom were the most important parameters affecting the partitioning of the PDBEs between n -octanol and water. Simulated external validation and leave-10%-out cross-validation demonstrate the statistical robustness and prediction power of the derived model, which could be applied to predict log K ow values of HO-PBDE and MeO-PBDE congeners.

Direct QSPR: the most efficient way of predicting organic carbon/water partition coefficient (log K OC) for polyhalogenated POPs

The organic carbon/water partition coefficient (K OC) is one of the most important parameters describing partitioning of chemicals in soil/water system and measuring their relative potential mobility in soils. Because of a large number of possible compounds entering the environment, the experimental measurements of the soil sorption coefficient for all of them are virtually impossible. The alternative methods, such as quantitative structure–property relationship (QSPR techniques) have been applied to predict this important physical/chemical parameter. Most available QSPR models have been based on correlations with the n-octanol/water partition coefficient (K OW), which enforces the requirement to conduct experiments for obtaining the K OW values. In our study, we have developed a QSPR model that allows predicting logarithmic values of the organic carbon/water partition coefficient (log K OC) for 1,436 chlorinated and brominated congeners of persistent organic pollutants based on the computationally calculated descriptors. Appling such approach not only reduces time, cost, and the amount of waste but also allows obtaining more realistic results.

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.

Determination of Tissue to Blood Partition Coefficients for Nonvolatile Herbicides, Insecticides, and Fungicides Using Negligible Depletion Solid-Phase Microextraction (nd-SPME) and Ultrafiltration

Partition coefficients (PCs) are used in physiologically based pharmacokinetic (PBPK) models to estimate the free concentration of a chemical in specific blood or organs. Biological PCtissue:blood (tissue to blood) values were determined for a series of nonvolatile herbicides, insecticides, and fungicides in liver, brain, skin, fat, kidneys, and muscle of male Sprague-Dawley rats using two different analytical methods. The free phase concentration (in phosphate-buffered saline) of a given chemical was measured in the presence and absence of tissue (including blood) and used to calculate the PC, defined as the ratio of the concentration of the chemical in saline to the concentration in the tissue. PCs were determined for 13 compounds with aqueous solubility ranging from 20 to 4100 mg/L, molecular weights from 187.3 to 342.2 g/mol, and log K ow values from –0.18 to 3.9. An ultrafiltration high-performance liquid chromatography (HPLC) method was implemented for compounds with log K ow near 0.1 or less and a negligible depletion solid-phase microextraction (nd-SPME) method for compounds with higher log K ow. PCtissue:saline coefficients of variation were 0.13 (n = 3 compounds) on average for the HPLC method and 0.29 (n = 10 compounds) for the nd-SPME method. Presented here is one of the most comprehensive data sets of biological partition coefficients for herbicides, insecticides, and fungicides.

Effect-Directed Assessment of the Bioaccumulation Potential and Chemical Nature of AhReceptor Agonists in Crude and Refined Oils.

Recent studies have indicated that in addition to narcosis certain chemicals in crude oils and refined petroleum products may induce specific modes of action, such as aryl hydrocarbon receptor (AhR) agonism. The risks these toxic compounds pose to organisms depend on internal exposure levels, as driven by the chemicals' bioaccumulation potential. Information on this potential however is lacking, as the chemicals' identity mostly is unknown. This study showed that AhR agonists bioaccumulate from oil-spiked sediments into aquatic worms and persist in the worms for at least several weeks. Chemical fractionations of eight pure oils into saturates, aromatics, resins, and asphaltenes (SARA), followed by effect-directed analyses using in vitro reporter gene assays revealed that the agonists predominantly are aromatic and resin-like chemicals. Some of the compounds were easily metabolized in vitro, while others were resistant to biotransformation. HPLC-assisted hydrophobicity profiling subsequently indicated that the AhR-active chemicals had a high to extremely high bioaccumulation potential, considering their estimated logK(ow) values of 4 to >10. Most of the AhR agonism, however, was assigned to compounds with logK(ow) of 5-8. These compounds were present mainly in the mid to high boiling point fractions of the oils (C(14)-C(32) alkane range), which are usually not being considered (the most) toxic in current risk assessment. The fractionations further revealed considerable oil and fraction-dependent antagonism in pure oils and SARA fractions. The results of this study clearly demonstrate that crude oils and refined petroleum products contain numerous compounds that can activate the AhR and which because of their likely persistence and extremely high bioaccumulation potential could be potential PBT (persistent, bioaccumulative and toxic) or vPvB (very persistent and very bioaccumulative) substance candidates. Many chemicals were identified by GC-MS, but the responsible individual compounds could not be exactly identified in the complex mixtures of thousands of compounds. Because this obstructs a classical PBT risk assessment, our results advocate an adapted risk assessment approach for complex mixtures in which low concentrations of very potent compounds are responsible for mixture effects.

RP TLC-based lipophilicity assessment of some natural and synthetic coumarins

The lipophilic character of twelve coumarins was investigated by reversed-phase thin-layer chromatography (RP TLC) on RP-18 silica. The three different binary solvent systems composed of water and organic modifier (methanol, tetrahydrofuran or acetonitrile) were used in order to determine retention parameter (R M0) and octanol-water partition coefficient (log P OW) as a measure of the lipophilicity of the tested compounds. Lipophilicity parameter (log P OW) was experimentally determined using eight standard solutes with known log P OW values which were analyzed under the same chromatographic conditions as the target substances. Lipophilicity parameters together with 2D molecular descriptors were subjected to the multivariate statistical analysis (principal component analysis (PCA) and partial least square (PLS) regression) in order to reveal the most influential factors governing the retention, i.e., lipophilicity of the investigated compounds. The quantitative structure-retention relationship models reveal the importance of descriptors which describe the size and the shape of the molecule as well as their polar properties.