Ow Values Research Articles

Estimation of the oil water partition coefficient, experimental and theoretical approaches related to volatile behaviour in milk

Oil/water partition coefficients ( K ow) of 20 volatile compounds in model or milk-based emulsions were determined experimentally using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). The K ow values were estimated by comparing the headspace concentration of volatiles above solutions with different lipid content (2, 7, 12, 27, 62 and 102 g/L). This involved curve fitting of a series of the six experimental values to an equation describing the expected behaviour of volatiles in lipid containing systems. Alternatively, a simpler experimental method based on the comparison of only two samples was used. Overall, the K ow values determined in the milk-based emulsion were the same as those found in simple model emulsions, suggesting that the partitioning behaviour of volatiles between air and the two emulsion systems was the same. The Log P values of the 20 volatile compounds were calculated using four software programmes, the Log P values from EPI Suite™ were found to correlate best with experimental Log K ow values.

Does Metamorphosis Increase the Susceptibility of Frogs to Highly Hydrophobic Contaminants?

The purpose of this study was to determine whether the process of metamorphosis in amphibians increases the chemical activity of hydrophobic contaminants such as polychlorinated biphenyls (PCBs). We conducted an experiment in which green frog tadpoles were orally dosed with a PCB mixture; then placed into clean water to eliminate the chemicals as metamorphosis occurred. On several sampling dates before and during metamorphosis, organisms were sacrificed and analyzed to determine lipid contents and concentrations of individual PCB congeners. The majority of the PCBs studied in this experiment showed increases in chemical activity (fugacity) as a result of the physical changes that occurred during amphibian metamorphosis. A positive relationship was observed between PCB hydrophobicity and the magnitude of the fugacity increase. We determined that the fugacity of a persistent PCB congener will increase during green frog metamorphosis if its log K(ow) value is greater than 5.85. The fugacity of some of the more highly hydrophobic PCBs increased during metamorphosis by up to a factor of 4. Because of the rapid increases in chemical activity that were observed during metamorphosis, we conclude that toxicity tests involving hydrophobic organic contaminants should be conducted not only on tadpoles or adult frogs, but also on metamorphosing amphibians.

Residue levels of malathion and fenitrothion and their metabolites in postharvest treated barley during storage and malting

In order to investigate residue levels of malathion and fenitrothion and their metabolites (malaoxon, isomalathion and fenitrooxon) during storage and malting, pesticide-free barley was treated with these insecticides. Barley was placed in a sealed plastic container and treated with a dust of malathion (2%). Fenitrothion emulsion (41.6% wettable powder) was applied onto the walls of a small-scale storage vessel. Residues were determined in barley at about 1-month intervals during storage and in malt produced from the barley stored at various times. The analysis of the residues was carried out by GC equipped with a nitrogen-phosphorus detector (NPD). Although the approved doses of insecticides for stored grain were used, the residue levels exceeded the maximum residue limits (MRLs) at the beginning of storage. While the degradation of malathion and isomalathion in barley was observed to be about 65–72% during the storage period, the malaoxon was degraded extensively (85%). A significant percentage of fenitrothion residues (80%) were dissipated from grains for the short-term storage probably because of hot weather conditions. In malt, rates of degradation and volatilisation of the residues increased by the heat involved in malting. The carryover of the residues from barley into malt was also found to be dependent on the log P ow (partition coefficient between n-octanol and water) values of the insecticides.

Predicting the Toxicity of Substituted Phenols to Aquatic Species and Its Changes in the Stream and Effluent Waters

The changes in the acute toxicity of 16 phenols toward Selenastrum capricornutum and Daphnia magna were examined as a function of their physical/chemical properties. The results demonstrated that phenols with a higher octanol-water partition coefficient (K(ow)) had a higher toxicity toward aquatic organisms. The toxicity of phenols was closely related to the log K(ow) values, with correlation coefficients of 0.93 (except for the nitrophenols) and 0.89 for S. capricornutum and D. magna, respectively. The changes in the phenols toxicities in the site waters (i.e., stream and effluent waters) were investigated by calculating the water effect ratios (WER) from the results of the toxicity tests in the site waters using D. magna. The results showed that the degree of ionization for each phenolic compound was altered by the differences in the dissociation constant (pK(a)), and the change in the toxicity could be predicted. Therefore, the WER should be considered when the toxicity of phenolic compounds is estimated in site waters. The quantitative structure-activity relationships (QSAR) study showed that the toxicity of the phenols to D. magna could be predicted by the hydrophobicity (log K(ow)) alone and by combining the log K(ow) with pK(a), while the toxicity to S. capricornutum was predicted by a combination of hydrophobicity (log K(ow)) and E(LUMO) (or pK(a)).

Removal of neutral chloroacetamide herbicide degradates during simulated unit processes for drinking water treatment

Four chloroacetamide herbicides and 20 neutral chloroacetamide derivatives (known to occur as their environmental degradates) were subjected to simulated drinking water treatment (coagulation, oxidation and adsorption). Coagulation with alum and ferric chloride, at doses for optimum turbidity removal, provided little to no (<10%) removal of parent herbicides or neutral degradates. Chlorination with 6 mg/L applied free chlorine for 6 h was able to achieve 100% removal of those degradates lacking an acetanilide substituent; compounds possessing this functional group exhibited low (0–16%) removal efficiencies. Products were generally not identified, except in the case of dimethenamid and its deschloro degradate, both of which formed a single ring-chlorination product on their ready reaction (84% and 96% removal, respectively) with aqueous chlorine species. Treatment with ozone at an applied dose of 3 mg/L for 30 min proved effective (60–100%) at transforming all of the compounds under investigation to unidentified products. The parent herbicides and neutral degradates underwent adsorption by powdered activated carbon (PAC). Adsorption capacities (Freundlich K constants) correlated with K ow values.

Improved Prediction of Octanol−Water Partition Coefficients from Liquid−Solute Water Solubilities and Molar Volumes

A volume-fraction-based solvent-water partition model for dilute solutes, in which the partition coefficient shows a dependence on solute molar volume (V), is adapted to predict the octanol-water partition coefficient (K(ow)) from the liquid or supercooled-liquid solute water solubility (Sw), or vice versa. The established correlation is tested for a wide range of industrial compounds and pesticides (e.g., halogenated aliphatic hydrocarbons, alkylbenzenes, halogenated benzenes, ethers, esters, PAHs, PCBs, organochlorines, organophosphates, carbamates, and amides-ureas-triazines), which comprise a total of 215 test compounds spanning about 10 orders of magnitude in Sw and 8.5 orders of magnitude in K(ow). Except for phenols and alcohols, which require special considerations of the K(ow) data, the correlation predicts the K(ow) within 0.1 log units for most compounds, much independent of the compound type or the magnitude in K(ow). With reliable Sw and V data for compounds of interest, the correlation provides an effective means for either predicting the unavailable log K(ow) values or verifying the reliability of the reported log K(ow) data.

Assessment of the bioaccessibility of polycyclic aromatic hydrocarbons in soils from Beijing using an in vitro test

As an important human exposure pathway of contaminants, soil ingestion is of increasing concern for assessing health risk from polycyclic aromatic hydrocarbons (PAHs) in soils. A wide range of total PAH concentrations ranging from 0.112 μg g −1 to 27.8 μg g −1 in soils collected from different public sites, including gas stations, roadsides, bus stops, a kindergarten, primary and middle schools, a university and residential area, was detected. In general, total PAHs concentrations in soils from traffic areas were significantly higher than that from the other sites, indicating a dominant contribution from motor vehicles. Physiologically based in vitro tests were used to evaluate the oral bioaccessibility of PAHs in surface soil under different land uses in Beijing regarding both gastric and small intestinal conditions. It was found that the oral bioaccessibility of total PAHs in small intestinal condition, ranging from 9.2% to 60.5% of total PAHs in soil, was significantly higher than gastric condition, ranging from 3.9% to 54.9%. The bioaccessibility of individual PAHs in soils generally decreased with the increasing ring number of PAHs in both gastric and small intestinal conditions. However, the ratio of bioaccessibility of individual PAHs in gastric condition to that in small intestinal condition, generally increased with increasing ring number, indicating the relatively pronounced effect of bile extract on improving bioaccessibility of PAHs with relatively high ring numbers characterized by their high K ow values. The observation that bile extract at a level higher than critical micelle concentration could reduce the surface tension of digestive juice substantially, which may cause PAHs to be available for intestinal absorption, calls for more careful establishment of reliable soil criteria for PAHs, especially concerning the health of children who may ingest a considerable amount of PAH-contaminated soil via outdoor hand-mouth activities.

Efficiency of different clay minerals modified with a cationic surfactant in the adsorption of pesticides: Influence of clay type and pesticide hydrophobicity

In the present work we studied the efficiency of a series of clay minerals (montmorillonite, illite, muscovite, sepiolite and palygorskite) modified with the cationic surfactant octadecyltrimetylammonium bromide (ODTMA) in the adsorption of the pesticides penconazole, linuron, alachlor, atrazine and metalaxyl. A study was also carried out on the effect of the structure (expansible and non-expansible layered, and non-layered), the surface area and charge density of the clay minerals, and the hydrophobicity of the pesticides ( K ow) on the adsorption process. Adsorption–desorption isotherms of the pesticides by clay minerals were obtained and the constants of the Freundlich model ( K f and K fd) (natural clays) and of the linear model ( K and K des) (ODTMA-clays) were determined. Correlation coefficient values ( r 2) found between K and K des, and organic matter (OM) content of ODTMA-clays indicate a more effective partitioning of the pesticides in the organic phase of ODTMA after desorption. Furthermore the positive significant correlation found between the K des om values and the charge density of different ODTMA-clays indicates that a higher density of ODTMA in the clay gives rise to the formation of an organic phase more effective for the partition of the pesticides. This correlation explained that the highest K des om value obtained was for kaolinite and the lowest K des om value was for montmorillonite in the adsorption of all pesticides by the different organo clays. Simple correlations between adsorption constants and K ow values, and multiple correlations between these constants and clay OM contents and K ow values were also calculated. The results obtained indicate the interest of ODTMA-clays in the adsorption of hydrophobic pesticides. Non-expandible layered and fibrous clay minerals may also be of interest as adsorbents derived from their density charge, and these minerals, when modified with ODTMA, and used in appropriate amounts, higher than that of montmorillonite, or when present in soils with high clay contents, even in the absence of montmorillonite, may be good adsorbents for hydrophobic pesticides. According to the results of the study, ODTMA-clays and ODTMA-soils could be used as barriers to prevent the mobility of certain hydrophobic pesticides from a point source of pollution.

Retention behavior ofo-phthalic, 3-nitrophthalic, and 4-nitrophthalic acids in ion-suppression reversed-phase high performance liquid chromatography using acids instead of buffers as ion-suppressors

In reversed-phase high performance liquid chromatography, the logarithm of the retention factor, log k, is usually correlated with the logarithm of the octanol-water partition coefficient, log Kow. The k and Kow of an ionizable analyte are greatly influenced by the mobile phase pH. In this paper, log kw of diprotic o-phthalic, 3-nitrophthalic, and 4-nitrophthalic acids, are obtained by extrapolation to pure aqueous fraction of mobile phase in ion-suppression reversed-phase high performance liquid chromatography with acetic acid and perchloric acid as the ion-suppressors. The Kow values of the three analytes are calibrated according to the apparent octanol-water partition coefficient, Kow, under different pH conditions, and the log K"ow values show a much better correlation with log kw than do log Kow. The influences of two ion-suppressors, acetic and perchloric acids, on the retention behavior of these diprotic acids at different pH are contrasted. An abnormal trend is found in the k vs. pHw plot of the acetic acid system when the methanol content is low. A possible reason is that acetic acid is an even stronger organic modifier than methanol, besides being an ion-suppressor. The results make the selection of mobile phase for the separation of acidic compounds by ion-suppression reversed-phase high performance liquid chromatography direct, accurate, and practical.

Temperature dependencies of Henry’s law constants and octanol/water partition coefficients for key plant volatile monoterpenoids

To model the emission dynamics and changes in fractional composition of monoterpenoids from plant leaves, temperature dependencies of equilibrium coefficients must be known. Henry’s law constants ( H pc, Pa m 3 mol −1 and octanol/water partition coefficients ( K OW, mol mol −1) were determined for 10 important plant monoterpenes at physiological temperature ranges (25–50 °C for H pc and 20–50 °C for K OW). A standard EPICS procedure was established to determine H pc and a shake flask method was used for the measurements of K OW. The enthalpy of volatilization (Δ H vol) varied from 18.0 to 44.3 kJ mol −1 among the monoterpenes, corresponding to a range of temperature-dependent increase in H pc between 1.3- and 1.8-fold per 10 °C rise in temperature. The enthalpy of water–octanol phase change varied from −11.0 to −23.8 kJ mol −1, corresponding to a decrease of K OW between 1.15- and 1.32-fold per 10 °C increase in temperature. Correlations among physico-chemical characteristics of a wide range of monoterpenes were analyzed to seek the ways of derivation of H pc and K OW values from other monoterpene physico-chemical characteristics. H pc was strongly correlated with monoterpene saturated vapor pressure ( P v), and for lipophilic monoterpenes, Δ H vol scaled positively with the enthalpy of vaporization that characterizes the temperature dependence of P v Thus, P v versus temperature relations may be employed to derive the temperature relations of H pc for these monoterpenes. These data collectively indicate that monoterpene differences in H pc and K OW temperature relations can importantly modify monoterpene emissions from and deposition on plant leaves.

The partitioning of alkylphenolic surfactants and polybrominated diphenyl ether flame retardants in activated sludge batch tests

Polybrominated diphenyl ethers and nonylphenol polyethoxylates have been reported to be estrogenic and may enter the aquatic environment through the discharge of treated sewage effluent. Therefore, their fate during wastewater treatment processes is an important factor in determining their environmental impact. Batch tests with activated sludge from a Husmann apparatus were used to determine the effects of physico-chemical properties and sludge characteristics on the partitioning of polybrominated diphenyl ether flame retardants and nonylphenol polyethoxylate surfactants during biological wastewater treatment. Hydrophobic compounds, those with high log K ow values, were sorbed more rapidly and to a greater extent to the solid phase than more soluble compounds. For these hydrophobic compounds sorption may become an increasingly important removal mechanism as sludge age and therefore solids content increase. The initial rate of partitioning was greatest for the most hydrophobic compounds but all rates diminished with time as a result of progressive saturation of sorbent binding sites, a reduction of sorbate availability and as a consequence of the system reaching equilibrium. The sorption of polybrominated diphenyl ethers fit Freundlich adsorption isotherms demonstrating generally increasing adsorption capacity and efficiency with increasing hydrophobic nature. A correlation between increasing log K ow and increasing organic matter content was also observed for both polybrominated diphenyl ethers and nonylphenol polyethoxylates indicating the organic content of mixed liquor will also be influential in removing compounds during wastewater treatment.

Estimating octanol–air partition coefficients with octanol–water partition coefficients and Henry’s law constants

The octanol–air partition coefficient ( K OA) is useful for predicting the partitioning behavior of organic compounds between air and environmental matrices such as soil, vegetation, and aerosol particles. At present, experimentally determined K OA values are available for only several hundred compounds. Therefore, the ability to estimate K OA is necessary for screening level evaluation of most chemicals. Although it is possible to estimate K OA from the octanol–water partition coefficient ( K OW) and Henry’s law constant (HLC), various concerns have been raised in regard to the usability of this estimation methodology. This work examines the accuracy and usability of K OW and HLC in application to a comprehensive database set of K OA values for screening level environmental assessment. Results indicate that K OW and HLC can be used to accurately predict K OA even when estimated K OW and HLC values are used. For an experimental dataset of 310 log K OA values for different compounds, the K OW–HLC method was statistically accurate as follows: correlation coefficient ( r 2): 0.972, standard deviation: 0.526, absolute mean error: 0.358 using predominantly experimental K OW and HLC values. When K OW and HLC values were estimated (using the KOWWIN and HENRYWIN programs), the statistical accuracy was: correlation coefficient ( r 2): 0.957, standard deviation: 0.668, absolute mean error: 0.479.

Effects of activated carbon types and service life on removal of endocrine disrupting chemicals: amitrol, nonylphenol, and bisphenol-A

Removal performances of endocrine disrupting chemicals (EDC) such as amitrol, nonylphenol, and bisphenol-A were evaluated in this study using granular activated carbon (GAC) adsorption. This study found that GAC adsorption was effective in removal of EDCs with high K ow value. Nonylphenol and bisphenol-A were effectively adsorbed onto all carbons (including the used carbons) tested in this study. As indicated by K ow value, nonylphenol was more effectively adsorbed than bisphenol-A. The coal-based carbon was found more effective than other carbons in the adsorption of nonylphenol and bisphenol-A due to its larger pore volume. The adsorption capacity reduced with the operation year, and the extent of the reduction was different depending upon the carbon type and the operation year. Amitrol was effectively removed by biological degradation, but was poorly adsorbed. Since the microbes residing at the used carbons already accustomed to amitrol, the used carbons removed amitrol better than the virgin carbons. Although the coal-based carbon showed the best removal performance of amitrol, GAC adsorption could not be recommended for amitrol removal because considerable portion of incoming amitrol (9–87%) passed through GAC adsorption column. According to this study, pore volume mainly influenced the adsorption capacity, but the surface charge was also important due to electrical interaction. The adsorption parameters for nonylphenol and bisphenol-A provided by this study could be valuable when GAC adsorption was considered to handle an accidental spill of nonylphenol and bisphenol-A.

Estimation of log Pow values for neutral and basic compounds by microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (μMEEKC-IFD)

Microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (μMEEKC-IFD) was used to obtain log P octanol/water (log P ow) values for neutral and basic compounds. Six compounds, with log P ow values between 0.38 and 5.03, were used to create a calibration curve relating the log of retention factors (log k) obtained from μMEEKC-IFD with the known log P ow values. The log P ow values for six additional compounds were determined using the log k values obtained by μMEEKC-IFD and the linear relationship between log P ow and log k established for the standard compounds. The μMEEKC-IFD buffer was composed of 50 mM 3-[cyclohexylamino]-1-propane-sulfonic acid (CAPS) buffer (pH 10.4) containing 1.2% n-heptane (v/v), 2% sodium dodecylsulfate (w/v), 8% 1-butanol (v/v) and 4 μM 5-carboxytetramethyl-rhodamine (TAMRA) as the fluorophore probe for indirect detection. The μMEEKC-IFD provided an accurate method for estimating log P ow values and also a means for analyzing compounds that are non-fluorescent.

Comparative biodegradation studies of pre-emergence broadleaf and grass herbicides in aqueous medium

Abstract The biodegradation of the herbicides hexazinone, metribuzin, metobromuron and propachlor was evaluated in liquid cultures of an adapted and a non-adapted mixed microbial culture obtained from a wastewater treatment plant. All herbicides were poorly degraded after 50 days ( 50 % ) . The adaptation of microbial culture prior to the biodegradation test shortened only the lag-time in degradation of hexazinone. The level of biodegradation correlated with the log K ow values of the molecules tested ( R 2 = 0.970 ). Metobromuron at 100 mg L - 1 inhibited the metabolism of aniline by the mixed culture.

Excretion pattern of co-planar and non-planar tetra- and hexa-chlorobiphenyls in ovine milk and faeces

This study employed the gas chromatography with electron capture detection to determine residual levels and excretion patterns of two pairs of structurally diverse polychlorinated biphenyl (PCB) congeners (IUPAC Nos. 54, 80, 155, and 169) administered to lactating sheep by intramuscular injection. PCB levels and excretion patterns in blood, milk, and faeces were time-dependent and differed from the composition of PCB congeners administered. Lactational transfer substantially exceeded the faecal transfer. Between days 3 and 7, the amount of PCB congeners 54 and 169 excreted in milk was around 50- and 800-fold higher than the amount of these two congeners excreted via faeces. During the same period, the relative contribution of co-planar PCB congeners (80 and 169) in PCB pattern decreased in blood and increased in milk and faeces compared with non-planar PCBs (54 and 155). On day 3, the ratio PCB 169 to 54 was 7-fold higher in milk than in faeces. PCB congeners with log K ow values under 6.5 reached peaks of their excretion in milk within the first three days after administration, while the super-lipophilic PCB 169 congener with log K ow value of over 7 has not reached the plateau until day 10, but afterwards, its level remained relatively high throughout the observation period. During the 57-day follow-up period, the excretion of PCB 80, 155, and 169 in milk was 4.5-, 14-, and 46-fold greater compared with PCB 54. Differences in levels and patterns were explained with some physico-chemical properties of individual PCB congeners, such as lipophilicity, planarity, metabolic stability, sorption/diffusion properties.

Degradation of hydrophobic organic pollutants by titania pillared fluorine mica as a substrate specific photocatalyst

The photocatalytic degradation of a highly hydrophobic and stable organic pollutant, γ-hexachlorocyclohexane (γ-HCH), was performed in aqueous suspended mixture of TiO2-containing catalysts. Unlike most of the organic pollutants, γ-HCH was very stable under the conventional photocatalytic condition with TiO2 (P25). Among various catalysts, TiO2 pillared fluorine mica (Ti-mica) showed highest activity. The effect of preparation method of Ti-mica was also examined. The hydrothermal treatment increased the crystallinity of anatase pillar of Ti-mica, though the treatment at high temperature resulted in a decrease in the surface area and an increase in the pore size. Consequently, Ti-mica treated at lowest temperature (373K), Ti-mica-373, was the most effective photocatalyst. The catalytic activity of TiO2 and Ti-mica-373 was compared for 13 kinds of organic compounds with various hydrophobicity. Ti-mica-373 showed 5–66 times higher rate than TiO2 for the degradation of hydrophobic organic pollutants (α, β, γ and δ-HCH, trans- and cis-chlordane, DDE, DDD and DDT) of low concentration (10ppb). In contrast, TiO2 showed higher rate than Ti-mica-373 for the degradations of less hydrophobic compounds (benzonitrile, chlorobenzene, 4-chloroacetophenone and 4-chloronitrobenzene). Over TiO2-mica-373, organic compounds with higher logPOW value, i.e. more hydrophobic compounds, were decomposed with higher rate. A positive effect of the fluorine mica support is suggested to be caused by the interaction of hydrophobic reactant with the hydrophobic interlayer surface of pillared-clay.

Evaluation of mixture effects in a crude extract of compost using the CALUX bioassay and HPLC fractionation

Potential synergistic interactions between polycyclic aromatic hydrocarbons in a household sewage sludge compost extract were investigated using the Dioxin-Responsive Chemical-Activated Luciferase gene eXpression (DR-CALUX) assay and reverse-phase high-performance liquid chromatography (RP-HPLC) fractionation. The biological activity of the crude extract was measured in vitro using the CALUX assay. The CALUX activity of the extract was as potent as 360-pg CALUX-TEQ (2,3,7,8-TCDD equivalent value) per g sample, this was 70 times above the WHO-TEQ value which was derived from chemical analyses of dioxins/furans and dioxin-like PCBs of the mixture. The CALUX activity pattern of the crude extract and the retention times of 26 polycyclic aromatic compounds (PACs), as determined by RP-HPLC on an octadecylsilica column, suggested that the dioxin-like compounds with the log K OW ( n-octanol/water partition coefficient) values corresponding to 6.0–7.0 contributed highly to the whole activity. The CALUX activity of the crude extract was three times the sum of the CALUX activities of the RP-HPLC separated fractions. Mixture effects were assessed by co-exposure of each HPLC fraction and 2,3,7,8-TCDD to the cells. The four concentration levels of added 2,3,7,8-TCDD corresponded to the TEQ value in the original compost sample. The experimental CALUX activity was higher than the predicted CALUX activity for some fractions. It was demonstrated that some compounds in the compost sample interacted synergistically with 2,3,7,8-TCDD in terms of dioxin-like activity. This finding points out the necessity for detailed investigation of synergistic effects in environmental samples.

Biotransformation in double-phase systems: physiological responses of Pseudomonas putida DOT-T1E to a double phase made of aliphatic alcohols and biosynthesis of substituted catechols.

Pseudomonas putida strain DOT-T1E is highly tolerant to organic solvents, with a logP(ow) (the logarithm of the partition coefficient of a solvent in a two-phase water-octanol system of > or =2.5. Solvent tolerant microorganisms can be exploited to develop double-phase (organic solvent and water) biotransformation systems in which toxic substrates or products are kept in the organic phase. We tested P. putida DOT-T1E tolerance to different aliphatic alcohols with a logP(ow) value between 2 and 4, such as decanol, nonanol, and octanol, which are potentially useful in biotransformations in double-phase systems in which compounds with a logP(ow) around 1.5 are produced. P. putida DOT-T1E responds to aliphatic alcohols as the second phase through cis-to-trans isomerization of unsaturated cis fatty acids and through efflux of these aliphatic alcohols via a series of pumps that also extrude aromatic hydrocarbons. These defense mechanisms allow P. putida DOT-T1E to survive well in the presence of high concentrations of the aliphatic alcohols, and growth with nonanol or decanol occurred at a high rate, whereas in the presence of an octanol double-phase growth was compromised. Our results support that the logP(ow) of aliphatic alcohols correlates with their toxic effects, as octanol (logP(ow) = 2.9) has more negative effects in P. putida cells than 1-nonanol (logP(ow) = 3.4) or 1-decanol (logP(ow) = 4). A P. putida DOT-T1E derivative bearing plasmid pWW0-xylE::Km transforms m-xylene (logP(ow) = 3.2) into 3-methylcatechol (logP(ow) = 1.8). The amount of 3-methylcatechol produced in an aliphatic alcohol/water bioreactor was 10- to 20-fold higher than in an aqueous medium, demonstrating the usefulness of double-phase systems for this particular biotransformation.

Toxic effects of some major polyaromatic hydrocarbons found in crude oil and aquatic sediments on Scenedesmus subspicatus

The green alga, Scenedesmus subspicatus was exposed for 7 days to a series of PAHs (polyaromatic hydrocarbons) of increased molecular weight from two to five rings [naphthalene (Nap), anthracene (Ant), phenanthrene (Phe), pyrene (Pyr) and benzo(a)pyrene (BaP)]. The toxicity measured as population growth inhibition by individual PAH to the S. subspicatus followed the order: BaP>Pyr>Ant>Phe>Nap. These results confirmed that the toxicity potential of PAHs seems to be strongly influenced by their physico-chemical properties (aqueous solubility, K ow, coefficient of volatilization, etc.) and the conditions of algae culture (light, presence of nitrate ions, etc.). Consequently, Nap, Phe and Ant having low K ow values and low coefficient of volatilization values were less toxic than BaP with the highest k ow value, indicating for example why Nap with the lowest EC 50 value was nearly 2×10 5 times lower than that of BaP. Moreover, nitrate ions seemed to act directly on the degree of hydroxylated radical reactivity of PAHs, since BaP always remained the most toxic of the compounds tested. The results were also agreed with the QSAR model for toxicity prediction of PAHs to many aquatic organisms.