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Crude oil and refined petroleum products contain many polycyclic and heterocyclic aromatic hydrocarbons, in particular, alkylated PAHs. Although alkylated PAHs are found in significantly higher quantities than their corresponding unsubstituted PAHs, the most studies on the physico-chemical properties and toxicities of these compounds have been conducted on unsubstituted PAHs. In this study, we measured crucial physico-chemical properties (i.e., water solubility, partition coefficients between polydimethylsiloxane and water (KPDMSw), and partition coefficient between liposomes and water (Klipw)) of selected alkylated PAHs, and evaluated their toxicity using the luminescence inhibition of Aliivibrio fischeri and growth inhibition of Raphidocelis subcapitata. In general, the logarithms of these properties for alkylated PAHs showed good linear correlations with log Kow, as did those for unsubstituted PAHs. Changes in molecular symmetry on the introduction of alkyl groups on aromatic ring structure significantly altered water solubility. The inhibition of bacterial luminescence and algal growth by alkylated PAHs can be explained well by the baseline toxicity hypothesis, and good linear relationships between log Kow or log Klipw and log (1/EC50) were found.

Although the free concentration is more significant in the environmental chemistry and toxicology of receptor-mediated toxicants, few studies have been conducted to use it as a dose-metric. The relative binding affinity of three model endocrine disrupting compounds, diethylstilbestrol (DES), ethynylestradiol (EE2), and bisphenol A (BPA), were evaluated using a competitive ELISA with human estrogen receptor a. After measuring the available receptors and the dissociation constant for 17b-estradiol, binding inhibition curves using the free concentration as the dose-metric were obtained by assuming species equilibrium in the ELISA system and compared with apparent inhibition curves generated using the nominal concentration as the dose-metric. Because ligand binding to estrogen receptors may reduce its free concentration in the assay system, the differences between the two curves for free and nominal concentrations are more significant for more strongly binding ligands. The ratio of a compound’s nominal concentration causing 50% inhibition (IC50) to the IC50 of DES, the positive control, was strongly affected by specific assay conditions, while that estimated by modeling free concentration is independent of receptor concentration, indicating that the free concentration is a better dose-metric for a competitive binding assay. 2007 Elsevier Ltd. All rights reserved.

We study an (n+3)( real submanifold of a (4m+3)-unit sphere with Sasakian 3-structure induced from the canonical quaternionic structure of quaternionic (m+1)-number space , and especially determine contact three CR-submanifolds with (p-1) contact three CR-dimension under the equality conditions given in (4.1), where p

Interspecific difference in the developmental toxicity of crude oil to embryonic fish allows the prediction of injury extent to a number of resident fish species in oil spill sites. This study clarifies the comparative developmental effects of Iranian heavy crude oil (IHCO) on the differences of biouptake and toxic sensitivity between embryonic spotted sea bass (Lateolabrax maculates) and olive flounder (Paralichthys olivaceus). From 24 h after exposure to IHCO, several morphological defects were observed in both species of embryonic fish, including pericardial edema, dorsal curvature of the trunk, developmental delay, and reduced finfolds. The severity of defects was greater in flounder compared to that in sea bass. While flounder embryos accumulated higher embryo PAH concentrations than sea bass, the former showed significantly lower levels of CYP1A expression. Although bioconcentration ratios were similar between the two species for some PAHs, phenanthrenes and dibenzothiophenes showed selectively higher bioconcentration ratios in flounder, suggesting that this species has a reduced metabolic capacity for these compounds. While consistent with a conserved cardiotoxic mechanism for petrogenic PAHs across diverse marine and freshwater species, these findings indicate that species-specific differences in toxicokinetics can be an important factor underlying species' sensitivity to crude oil.

In this paper we introduce the concept of conformal curvature-like tensor on a semi-Riemannian manifold, which is weaker than the notion of conformal curvature tensor defined on a Riemannian manifold. By such kind of conformal curvature-like tensor we give a complete classification of conformally symmetric semi-Riemannian manifolds with generalized non-null stress energy tensor.

We study an (n+1)(n≥ 3)-dimensional contact CR-submanifold of (n−1) contact CR-dimension in a (2m+1)-unit sphere S2m+1, and especially determine such submanifolds under the equality conditions appearing in (3.12). We also provide a sufficient condition in order for such a compact submanifold to be the model space $$S^{2n_1+1}(1/\sqrt2) \times S^{2n_2+1}(1/\sqrt2)$$ given in the last Section 4.

In this paper we introduce new notions of Ricci-like tensor and many kind of curvature-like tensors such that concir- cular, projective, or conformal curvature-like tensors defined on semi-Riemannian manifolds. Moreover, we give some geometric conditions which are equivalent to the Codazzi tensor, the Weyl tensor, or the second Bianchi identity concerned with such kind of curvature-like tensors respectively and also give a generalization of Weyl's Theorem given in (18) and (19).

The accumulation of marine plastic debris is one of the main emerging environmental issues of the twenty first century. Numerous studies in recent decades have reported the level of plastic particles on the beaches and in oceans worldwide. However, it is still unclear how much plastic debris remains in the marine environment because the sampling methods for identifying and quantifying plastics from the environment have not been standardized; moreover, the methods are not guaranteed to find all of the plastics that do remain. The level of identified marine plastic debris may explain only the small portion of remaining plastics. To perform a quantitative estimation of remaining plastics, a mass balance analysis was performed for high- and low-density PE within the borders of South Korea during 1995-2012. Disposal methods such as incineration, land disposal, and recycling accounted for only approximately 40 % of PE use, whereas 60 % remained unaccounted for. The total unaccounted mass of high- and low-density PE to the marine environment during the evaluation period was 28 million tons. The corresponding contribution to marine plastic debris would be approximately 25,000 tons and 70 g km(-2) of the world oceans assuming that the fraction entering the marine environment is 0.001 and that the degradation half-life is 50 years in seawater. Because the observed concentrations of plastics worldwide were much lower than the range expected by extrapolation from this mass balance study, it is considered that there probably is still a huge mass of unidentified plastic debris. Further research is therefore needed to fill this gap between the mass balance approximation and the identified marine plastics including a better estimation of the mass flux to the marine environment.

In this paper. We Study (n + 1)-dimensional Contact CR-submanifolds of (n - 1) contact CR-dimension immersed in a Sasakian space form M2m+1/(c) (2m=n+p, p>0), and especially determine such submanifolds under additional condition concerning with shape operator.

The purpose of this paper is to study complete complex submanifolds of a locally symmetric Kaehler manifold with non-positive totally real normal bisectional curvature and k-pinched totally real tangent bisectional curvature.

Partition coefficients between plant cuticles and water (K cutw ) were measured for 10 selected polycyclic aromatic hydrocarbons (PAHs) to evaluate the sorption capacity of plant cuticular layers for hydrophobic organic chemicals. The partitioning properties of PAHs between cuticles and water were evaluated by using (1) isolated cuticular layers and (2) leaf homogenate. The abaxial and adaxial cuticular layers of Euonymus japonicus were isolated by enzymatic digestion. A third-phase partitioning method using poly(dimethylsiloxane) (PDMS) was used to obtain K cutw . The K cutw values for the selected PAHs showed no significant differences between the abaxial and adaxial cuticular layers and ranged between 10 4.1 and 10 7.6 . These values are close to or slightly higher than their 1-octanol/water partition coefficient (log K ow ), indicating high sorption capacity of plant cuticles. On the contrary, partition coefficients between the lipid tissues of homogenized leaves and water were lower than those obtained using isolated cuticular layers by factors of 3.7–190, which is likely due to the breakdown of lipid layers. This indicates that the sorption of hydrophobic organic chemicals by plant leaves is better evaluated using isolated cuticles and that the sorption potential of plant leaves may be underestimated when leaf homogenates are used.

C. However, these methods resulted in a poor yield of less than 45% due to the formation of 2,4-dimethoxy-6-chloroaniline as a byproduct. In addition, when we raised the reaction temperature to room temperature, we obtained 2,4-dimethoxy-6-chloroaniline as a major product. Since it is difficult to control the low-temperature reaction during the saturation of HCl gas in the dichlorination of

A prediction model for estimating the ecotoxicity of the water-accommodated fraction (WAF) and water-soluble fraction (WSF) of heavy crude oil is proposed. Iranian heavy crude oil (IHC), one of the major components of the Hebei Spirit oil spill in Korea in 2007, was used as a model crude oil for the preparation of the WAF and the WSF. Luminescence inhibition of Vibrio fischeri was chosen as the model ecotoxicity test for evaluating the baseline toxicity of aromatic hydrocarbons in the IHC. The measured concentration of each chemical species in WAF and WSF agreed well with the predicted soluble concentration calculated using Raoult's law from the measured amount in the IHC. This indicates that the toxic potential of an oil mixture can be evaluated from the dissolved concentration of each species, which in turn, may be predicted from the composition of the crude or weathered oils. In addition, the contribution of each species in the mixture to the apparent luminescence inhibition by the WAF and the WSF was assessed using a concentration-addition model. The relative contributions of benzene, toluene, ethylbenzene, xylenes (BTEX), polycyclic aromatic hydrocarbons (PAHs), and alkylated PAHs in luminescence inhibition were estimated to be 76%, 2%, and 21%, respectively. It was further identified that C3- and C4-naphthalenes were the most important aromatic hydrocarbons responsible for baseline toxicity. This indicates that alkylated PAHs would be the major components of oil-spill residue. Further research is needed to evaluate the fate and ecotoxicity of alkylated PAHs.

Effects of individual petroleum hydrocarbons on the luminescence inhibition of Vibrio fischeri were evaluated according to a standard protocol to develop a quantitative structureactivity relationship and identify the apparent toxicity cutoff. Eighteen aromatic hydrocarbons, including benzene and its derivatives and polycyclic aromatic hydrocarbons (PAHs), were chosen as model compounds with their log Kow values between 2.7 and 6.4. The obtained values of 50 percent luminescence inhibition (EC50) showed a good linear correlation with log Kow up to � 5. However, toxic effects were not observed for more hydrophobic chemicals with log Kow value 45. The calculated chemical activities that caused EC50 were mostly between 0.01 and 0.1. This agrees with an earlier hypothesis concerning a chemical activity resulting the critical membrane concentration of aromatic hydrocarbons. The highest chemical activities for aromatic hydrocarbons with log Kow value 45 or melting point 4100 1C are o0.01 when they are spiked at their water solubility level according to the standard test protocol; this occurs for two primary reasons: (1) partitioning between organism and the test solution and (2) decreasing fugacity ratio with increasing melting point. Accordingly, luminescence inhibition by petroleum hydrocarbons is well explained by the baseline toxicity model. However, the apparent toxicity cutoff observed for single chemicals is not necessarily valid in a complex mixture, because baseline toxicity is regarded concentration additive.

We investigated 33 pharmaceuticals and personal care products (PPCPs) with emphasis on anthelmintics and their metabolites in human sanitary waste treatment plants (HTPs), sewage treatment plants (STPs), hospital wastewater treatment plants (HWTPs), livestock wastewater treatment plants (LWTPs), river water and seawater. PPCPs showed the characteristic specific occurrence patterns according to wastewater sources. The LWTPs and HTPs showed higher levels (maximum 3000 times in influents) of anthelmintics than other wastewater treatment plants, indicating that livestock wastewater and human sanitary waste are one of principal sources of anthelmintics. Among anthelmintics, fenbendazole and its metabolites are relatively high in the LWTPs, while human anthelmintics such as albendazole and flubendazole are most dominant in the HTPs, STPs and HWTPs. The occurrence pattern of fenbendazole's metabolites in water was different from pharmacokinetics studies, showing the possibility of transformation mechanism other than the metabolism in animal bodies by some processes unknown to us. The river water and seawater are generally affected by the point sources, but the distribution patterns in some receiving water are slightly different from the effluent, indicating the influence of non-point sources.

In Korea, humidifier disinfectants have been putin the water tanks of humidifiers for the prevention of germs,mold, and/or algae. According to the authorities, as of August31, 2011, 28 adults, including 13 pregnant women, have beenhospitalized because of this unidentified lung disease similar toacute interstitial pneumonia. Among them, four patients passedaway because of the rapid development of pulmonary fibrosisafter long exposure to the disinfectants over several months.

Binding of hydrophobic chemicals to colloids such as proteins or lipids is difficult to measure using classical microdialysis methods due to low aqueous concentrations, adsorption to dialysis membranes and test vessels, and slow kinetics of equilibration. Here, we employed a three-phase partitioning system where silicone (polydimethylsiloxane, PDMS) serves as a third phase to determine partitioning between water and colloids and acts at the same time as a dosing device for hydrophobic chemicals. The applicability of this method was demonstrated with bovine serum albumin (BSA). Measured binding constants (K(BSAw)) for chlorpyrifos, methoxychlor, nonylphenol, and pyrene were in good agreement with an established quantitative structure-activity relationship (QSAR). A fifth compound, fluoxypyr-methyl-heptyl ester, was excluded from the analysis because of apparent abiotic degradation. The PDMS depletion method was then used to determine partition coefficients for test chemicals in rainbow trout (Oncorhynchus mykiss) liver S9 fractions (K(S9w)) and blood plasma (K(bloodw)). Measured K(S9w) and K(bloodw) values were consistent with predictions obtained using a mass-balance model that employs the octanol-water partition coefficient (K(ow)) as a surrogate for lipid partitioning and K(BSAw) to represent protein binding. For each compound, K(bloodw) was substantially greater than K(S9w), primarily because blood contains more lipid than liver S9 fractions (1.84% of wet weight vs 0.051%). Measured liver S9 and blood plasma binding parameters were subsequently implemented in an in vitro to in vivo extrapolation model to link the in vitro liver S9 metabolic degradation assay to in vivo metabolism in fish. Apparent volumes of distribution (V(d)) calculated from the experimental data were similar to literature estimates. However, the calculated binding ratios (f(u)) used to relate in vitro metabolic clearance to clearance by the intact liver were 10 to 100 times lower than values used in previous modeling efforts. Bioconcentration factors (BCF) predicted using the experimental binding data were substantially higher than the predicted values obtained in earlier studies and correlated poorly with measured BCF values in fish. One possible explanation for this finding is that chemicals bound to proteins can desorb rapidly and thus contribute to metabolic turnover of the chemicals. This hypothesis remains to be investigated in future studies, ideally with chemicals of higher hydrophobicity.

Despite the great success of time-weighted average passive sampling of hydrophobic contaminants, such as PCBs and PAHs, the sampling of polar organic compounds still presents a challenge because the equilibrium between water and most sampling phases is attained in a relatively short time. In this study, we proposed a new time-integrative sampler using in situ solvent extraction (TISIS) for polar organic chemicals. The sampler was composed of a 15 cm poly(dimethylsiloxane) (PDMS) tubing, with an internal diameter of 0.5 mm and wall thickness of 0.5 mm, through which an extraction solvent (acetonitrile) was passed. Four polar organic contaminants, caffeine, atrazine, diuron and 17α-ethynylestradiol, were chosen for the evaluation of the performance of the sampler. Without the use of in situ solvent extraction, the PDMS tubing when exposed to a constant aqueous concentration of the four model compounds was able to linearly accumulate those compounds for less than 12 h and equilibrium between the PDMS tubing and water was attained in 2 d under our laboratory conditions. However, TISIS when exposed to a constant aqueous concentration was able to linearly accumulate all the model compounds without any exposure time limitation. The measured sampling rates at three different extraction flow rates (0.2, 0.5, 1.5 mL min −1 ) were similar, regardless of the chemicals, indicating that the overall mass transfer from aqueous solution to the extraction solvent was most likely dominated by partitioning to the PDMS tubing and the internal diffusion within PDMS. In addition, a pulsed exposure experiment confirmed that TISIS operated in a time-integrative mode when the environmental concentration was highly fluctuated.

An improved synthesis is given for 4′-hydroxydiclofenac (VIII) which is needed for the investigation of the environmental and ecotoxicological effects of diclofenac.

Exact determination of the partition coefficient between 1-octanol and air (K(OA)) is very important because it is a key descriptor for describing the thermodynamic partitioning between the air and organic phases. In spite of its importance, the number and quality of experimental K(OA) values for hydrophobic organic chemicals are limited because of experimental difficulties. Thus, to measure K(OA) values, a high-throughput method was developed that used liquid-phase extraction with 1-octanol drop at the tip of a microsyringe needle. The concentration in the headspace surrounding the 1 muL octanol drop was equilibrated with liquid octanol containing polycyclic aromatic hydrocarbons (PAHs). The change in concentrations of PAHs in the octanol drop was measured to obtain mass transfer rate constants, and these rate constants were then converted into K(OA) values using a film diffusion model. Thirteen polycyclic aromatic hydrocarbons with log K(OA) between 5 and 12 were chosen for the proof of the principle. Experimental determination of log K(OA) was accomplished in 30 h for PAHs with their log K(OA) less than 11. The measured log K(OA) values were very close to those obtained by various experimental and estimation methods in the literature, suggesting that this new method can provide a fast and easy determination of log K(OA) values for many chemicals of environmental interests. In addition, the applicability of the method can be extended to determine Henry's law constant for compounds with low vapor pressure and to estimate gaseous transfer rate of semivolatile compounds for environmental fate modeling.

The sorption coefficients of four rarely studied zwitterionic pharmaceuticals (benzimidazoles: fenbendazole, albendazole, thiabendazole and flubendazole) and four metabolites of fenbendazole to various dissolved organic matter surrogates (humic acid, sodium dodecyl sulfate micelle, hydroxypropyl-beta-cyclodextrin and liposomes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and sewage sludge) were measured to extend the available sorption coefficients and eventually to evaluate their environmental fate in soil and water environment. For the entire range of dissolved organic matters, the more hydrophobic fenbendazole and albendazole had higher sorption coefficients than thiabendazole and flubendazole, indicating that the traditional hypothesis of hydrophobic interaction holds for zwitterionic benzimidazole anthelmintics. However, the sorption coefficients of a given benzimidazole to selected dissolved organic matters (DOMs) varied within an order of magnitude. The measured K(oc) values decreased in the order of fenbendazole, albendazole, thiabendazole and flubendazole for sewage sludge and hydroxypropyl-beta-cyclodextrin whereas the orders were different for the other DOM surrogates, implying the hydrophilic nature of sewage sludge. This was also supported by the (N+O)/C elemental ratio of the sewage sludge sample used in this study. The correlations between log K(oc) and log K(ow) were weak (r(2)=0.28-0.64) and the magnitude of the sorption coefficients to the hydrophilic organic matters (hydroxypropyl-beta-cyclodextrin and sewage sludge) were similar to or slightly smaller than those for the hydrophobic organic matters (humic acids and liposome). This suggests that specific hydrophilic interactions also play a significant role in the sorption of moderately hydrophobic benzimidazoles to organic matters.

There is an increasing need to monitor concentrations of polar organic contaminants in the aquatic environment. Integrative passive samplers can be used to assess time weighted average aqueous concentrations, provided calibration data are available and sampling rates are known. The sampling rate depends on environmental factors, such as temperature and water flow rate. Here we introduce an apparatus to investigate the sampling properties of passive samplers using river-like flow conditions and ambient environmental matrices: river water and treated sewage effluent. As a model sampler we selected Empore SDB-RPS disks in a Chemcatcher housing. The disks were exposed for 1 to 8 days at flow rates between 0.03 and 0.4 m s(-1). Samples were analysed using a bioassay for estrogenic activity and by LC-MS-MS target analysis of the pharmaceuticals sulfamethoxazole, carbamazepine and clarithromycin. In order to assess sampling rates of SDB disks, we also measured aqueous concentrations of the pharmaceuticals. Sampling rates increased with increasing flow rate and this relationship was not affected by the environmental matrix. However, SDB disks were only sampling in the integrative mode at low flow rates0.1 m s(-1) and/or for short sampling times. The duration of linear uptake was particularly short for sulfamethoxazole (1 day) and longer for clarithromycin (5 days). At 0.03 m s(-1) and 12-14 degrees C, the sampling rate of SDB disks was 0.09 L day(-1) for clarithromycin, 0.14 L day(-1) for sulfamethoxazole and 0.25 L day(-1) for carbamazepine. The results show that under controlled conditions, SDB disks can be effectively used as passive sampling devices.

Measurement of partition coefficients between poly(dimethylsiloxane) (PDMS) and water (KPDMSw) becomes more and more difficult as the hydrophobicity of the compound increases. Experimental challenges include long extraction times, sorption to various surfaces and materials, and incomplete dissolution of the compound in the aqueous phase. In order to avoid these artifacts and to shorten experimental time, a dynamic permeation method was developed. According to steady-state diffusion theory, KPDMSw is inversely proportional to the permeation rate through the aqueous boundary layer (ABL) from the donor PDMS to the acceptor PDMS. A simple ABL permeation reactor can thus be applied to determine KPDMSw values of hydrophobic chemicals within a few days. The obtained values were in good agreement with those obtained using a conventional shaking method and the partition controlled delivery system. A good linear correlation was obtained between the logarithm of the 1-octanol/water partition coefficient (log Kow) from the literature and log KPDMSw over 6 orders of magnitude.

The thermodynamics of partitioning of selected endocrine disruptors between water and synthetic membrane vesicles were investigated. For most of the chemicals investigated, partitioning is dominated by the enthalpy change for unsaturated lipid membrane vesicles and by the entropy contribution for saturated lipid membrane vesicles. The contribution of the entropy terms in determining the free-energy change becomes more important compared with the enthalpy terms with increased branching of p-substituted phenols. These results suggest that the thermal energy required for and the entropy gain associated with the creation of the cavity in the lipid bilayer is of critical importance in differentiating the process from 1-octanol/water partitioning. In addition, partitioning thermodynamics are significantly influenced by cholesterol content in the lipid membranes. Results of the present study and those in the literature suggest that partitioning processes significantly depend on the physical state of the lipid membranes and log K(ow)-based quantitative structure-activity relationships should be carefully applied for predicting bioconcentration by considering lipid compositions.

Environmental monitoring and assessment, 142 (1-3), ISSN:0167-6369, ISSN:1573-2959

The partition coefficient between water and lipid membrane vesicles (Klipw) has been used as an alternative to the 1-octanol-water partition coefficient (Kow) between water and organic solvent, because it more closely represents actual biological membranes. Despite theoretical differences, log Klipw correlates well with log Kow for conventional nonpolar organic pollutants. In the present study, Klipw values of 11 structurally diverse endocrine-disrupting chemicals (EDCs) were measured for three different types of lipid membrane vesicles from dipalmitoylphosphatidylcholine (DPPC), DPPC/cholesterol, and palmitoyloleoylphosphatidylcholine. Correlation analyses were conducted to evaluate the effects of hydrophobicity, molar liquid volume (MLV), and polar surface area (PSA) for 20 EDCs, including nine from a previous study. Correlations that include MLV and PSA reduce the predicted value of log Klipw, suggesting that lipid membranes are less favorable than 1-octanol for a hydrophobic solute because of the higher molar volume and higher hydrogen-bonding potential. These results suggested that Kow alone has limited potential for estimating Klipw and that additional descriptors are required. In addition, Klipw values vary by as much as two orders of magnitude because of the changes in membrane fluidity and the amount of cholesterol in the lipid bilayer. Therefore, lipid components should be chosen carefully to evaluate the bioconcentration of these compounds.

The purpose of this paper is to study several classes of an n-dimensional complete space-like complex sub-manifold of an (n + p)-dimensional indefinite complex space form M n + p 0 + t (c) of index 2t, and of an n-dimensional space-like complex hypersurface of a complex Minkowski space C n + 1 1 in terms of RS = 0.

Objectives: Potential environmental risks caused by chemicals that could be released from a recycled plastic product were assessed using a screening risk assessment procedure for chemicals in recycled products. Methods: Plastic slope protection blocks manufactured from recycled plastics were chosen as model recycled products. Ecological risks caused by four model chemicals ? di-(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), cadmium (Cd), and lead (Pb)?were assessed. Two exposure models were built for soil below the block and a hypothetic stream receiving runoff water. Based on the predicted no-effect concentrations for the selected chemicals and exposure scenarios, the allowable leaching rates from and the allowable contents in the recycled plastic blocks were also derived. Results: Environmental risks posed by slope protection blocks were much higher in the soil compartment than in the hypothetic stream. The allowable concentrations in leachate were 1.0×10 -4 , 1.2×10 -5 , 9.5×10 -3 , and 5.3×10 -3 ㎎/L for DEHP, DINP, Cd, and Pb, respectively. The allowable contents in the recycled products were 5.2×10 - 3, 6.0×10 -4 , 5.0×10 -1 , and 2.7×10 -1 ㎎/㎏ for DEHP, DINP, Cd, and Pb, respectively. Conclusions: A systematic ecological risk assessment approach for slope protection blocks would be useful for regulatory decisions for setting the allowable emission rates of chemical contaminants, although the method needs refinement.

Due to high usage of tetracycline antibiotics, concerns have been raised about their environmental fate. In this study, potential changes in the pseudo-first-order hydrolysis rate constants for three tetracyclines, tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC), were evaluated by measuring the rate constants in batch and column leaching experiments. The first-order hydrolysis rate constants were measured at pH 5, 7, and 9 using batch tests. The values were highest at pH 7 for all three tetracyclines (0.0030 ± 0.0004, 0.0042 ± 0.0001, and 0.0323 ± 0.0003 h(-1) for TC, OTC, and CTC, respectively), indicating relatively short environmental half-lives of tetracyclines. Interestingly, it was found that the rates of degradation of the parent tetracyclines were much faster when silica sand was present in a batch solution or when the solution was passed through a silica column. For example, the ratios of the first-order degradation rate constants obtained in the column experiments to those in batch experiments were 13.2, 2.1, and 2.0 for TC, OTC, and CTC at a volumetric flow rate of 0.08 mL h(-1), with an observed tendency for this ratio to increase with an increased flow rate. This indicates that the silica surface may serve as a catalyst for hydrolysis and that the actual environmental half-lives of tetracycline antibiotics could be shorter than those estimated from laboratory hydrolysis rate constants using the standard batch protocol. Furthermore, the toxicity of the column effluent containing hydrolysis metabolites was assessed using bioluminescence inhibition in Vibrio fischeri. It was estimated that the toxicity of the metabolites of CTC was lower than that of their parent compound, whereas the toxicity of metabolites of TC and OTC was as high as or higher than that of their parent compounds.

solvent. Methods: A custom cut polydimethylsiloxane (PDMS) tubing loaded with benzyl butyl phthalate (BBP) was placed in each well of a 24-well plate containing assay medium. The rate of the release of BBP from PDMS was evaluated by measuring the change in the concentration of BBP in the assay medium. The efficiency of maintaining constant exposure condition was also evaluated using a simple two-compartment mass transport model employing a film-diffusion theory. An acute mortality test using 10 C. elegans in each well was conducted for the evaluation of the validity of passive dosing and the comparative evaluation of the passive dosing method and the conventional spiking method. Results: Free concentration in the assay medium reached 95% steady state value within 2.2 hours without test organisms, indicating that this passive dosing method is useful for an acute toxicity test in 24 hours. The measured concentration after the mortality test agreed well with the estimated values from partitioning between PDMS and the assay medium. However, the difference between the nominal and the free concentration became larger as the spiked concentration approached water solubility, indicating the instability of the conventional spiking with a co-solvent. Conclusions: The results in this study support that passive dosing provides a stable exposure condition for an acute toxicity test. Thus, it is likely that more reliable toxicity assessment can be made for hydrophobic chemicals using passive dosing.

A parallel artificial lipid membrane system was developed to mimic passive mass transfer of hydrophobic organic chemicals in fish. In this physical model system, a membrane filter-supported lipid bilayer separates two aqueous phases that represent the external and internal aqueous environments of fish. To predict bioconcentration kinetics in small fish with this system, literature absorption and elimination rates were analyzed with an allometric diffusion model to quantify the mass transfer resistances in the aqueous and lipid phases of fish. The effect of the aqueous phase mass transfer resistance was controlled by adjusting stirring intensity to mimic bioconcentration rates in small fish. Twenty-three simple aromatic hydrocarbons were chosen as model compounds for purposes of evaluation. For most of the selected chemicals, literature absorption/elimination rates fall into the range predicted from measured membrane permeabilities and elimination rates of the selected chemicals determined by the diffusion model system.