Ow Values Research Articles

Phloem Mobility of Xenobiotics

TWO BIOASSAYS WERE USED TO TEST PHLOEM MOBILITY OF SELECTED XENOBIOTIC COMPOUNDS: (a) excised bean leaf assay; (b) rooted bean leaf assay. Compounds assayed were N-alkylpyridiniums with systematic variation in octanol-water partition coefficients (log K(ow)), substituted benzoic acids with about the same log K(ow) value but variable acidities. Results of the assays strongly conform, quantitatively, to the predictions of the unified mathematical model. Results also indicate that the membrane permeability value of a compound, which depends directly on log K(ow) value, is the overriding factor in determining phloem mobility. When the weak acid functionality of a compound confers increased phloem mobility, it does so principally by making the log K(ow) value, and consequently the membrane permeability of the compound more optimal.

Advances in bioconcentration prediction

A reexamination of the log-log relationship between the bioconcentration factor in fish (BCF) and different types of P OW data for a set of 49 compounds of diverse chemical range reveals that the overall correlation between log BCF and log P OW is only moderate but gets significantly improved by restriction to the subset of CHCs and PAHs. Furthermore, a comparison of different theoretical descriptors shows that for the combined CHCs and PAHs the solvent accessible surface area (SASA) and the molar refraction (MR) are better predictors of log BCF than calculated log P OW values according to Leo's CLOGP-3.42 program.

Bioaccumulation of dyestuffs and organic pigments in fish. Relationships to hydrophobicity and steric factors

For 23 disperse dyestuffs, 2 organic pigments and a fluorescent whitening agent, for which experimental bioaccumulation factors in fish are known, log P OW values (partition coefficient octanol/ water) were calculated and determined, if possible. For comparison, 16 halogenated aromatic hydrocarbons are included. Two parameters were chosen to parameterise the size of the molecules: the molecular weight and, following a suggestion by Opperhuizen et al., the second largest v.d.Waals diameter of the molecules, measured on conformations optimised by force field calculations. None of the disperse dyestuffs, even the highly lipophilic ones with log P OW > 3.0, accumulate in fish to a significant degree. It is argued that their large molecular size effectively prevents their permeation through biological membranes and thus their uptake during the time of exposure. For screening organic colorants for their bioaccumulation potential a decision scheme is roposed using as parameters the solubility in water and in octanol, the partition coefficient octanol/water, and the molecular weight and size. This scheme suggests in its last step that there should be no need to perform a fish bioaccumulation test provided the organic colorants have a molecular weight of more than 450 Daltons and a second largest cross section of over 1.05 nanometers.

Estimation of octanol/water partition coefficients: Evaluation of six methods for highly hydrophobic aromatic hydrocarbons

Six methods for estimating log K ow were evaluated using a set of experimental values for 64 aromatic compounds. All log K ow values used in this evaluation were experimentally measured using a generator-column technique. This provided an accurate, self-consistent set of compounds having log K ow values ranging from 2.13 to 8.58. The estimation methods examined included two group contribution methods and four correlative methods utilizing molecular weight, HPLC retention time, molecular connectivity index, and total molecular surface area.

The limits of bioaccumulation of organic pigments in fish: Their relation to the partition coefficient and the solubility in water and octanol

A reliable experimental determination of the partition coefficient P ow of organic pigments is met with serious difficulties due to the extremely low water solubilities of these compounds. Therefore, the P ow values and the water solubilities were calculated for 11 typical organic pigments and some disperse dyes as well. The calculated P ow values of the pigments were very high predicting bioaccumulation factors (BF) several orders of magnitude above 100. Based on recent studies confirming that n-octanol simulates lipids in their solubilizing effect on organic chemicals, the solubilities of these organic pigments in n-octanol were measured in order to estimate their potential for lipid storage. The very low solubility values indicate that in spite of the very high predicted BF such pigments cannot build up concentrations in lipids (hence in fish) which could be of concern considering their generally low toxicity and the extremely small amounts entering the environment. Therefore, there should be no need to perform a fish bioaccumulation test for assessing the bioaccumulation potential of such compounds, provided they show comparable solubility characteristics as the pigments investigated in this study.

Kinetics of polychlorinated biphenyl (PCB) components in juvenile sole ( Solea solea) in relation to concentrations in water and to lipid metabolism under conditions of starvation

The kinetics of 19 PCB components in starving sole were related to PCBs in solution and to changes in lipid composition. Analyses were made of brain, liver, and ‘remainder’ of the fish. The pattern of PCBs in solution determined the pattern in fish. Lipid-based PCB concentrations in brain were 3–4 times lower than in liver and the remainder of the fish. No differences between the PCB patterns were observed. This allowed evaluation of PCB kinetics on the basis of total PCB concentrations (Σ-PCB as sum of the 19 components identified). The Σ-PCB concentrations on a lipid basis increased with starvation due to changing lipid contents and compositions of some organs and tissues or by an increase of PCB concentrations in solution with the pattern in solution remaining identical. Bioconcentration factors of PCB components were related to their K ow values. Despite the increase in concentrations, absolute amounts of PCBs in the remainder decreased with increasing starvation due to the decrease in lipid content of the tissues. In brain and liver the amounts per organ did not decrease. In field samples of organisms, PCB patterns remain essentially unchanged over a range of concentrations. This behaviour can be explained by the PCB kinetics observed in this laboratory study.

Relationship between log Pow, shake-flask values and capacity factors derived from reversed-phase high-performance liquid chromatography for n-alkylbenzenes and some oecd reference substances

The capacity factors ( k′) of eight n-alkylbenzenes and eleven reference substances used in the OECD Chemicals Testing Programme were determined using reversed-phase high-performance liquid chromatography (RP-18) at different compositions of the mobile phase (methanol—water). All substances except urea show a good linear relationship ( r ⩾ 0.995) between the 1n ḱ values and the volume fraction (ϕ CH 3OH ) of the organic modifier in the range 0.6–0.95. Correlation of n-octanol water partition coefficients (shake-flask values) given in the literature and from the OECD/EEC laboratory comparison tests with the experimental log k′ values results in a good linear relationship for the n-alkylbenzenes ( r, = 0.998) and a slightly poorer relationship for the OECD reference substances ( r = 0.967–0.986). If the log P OW values are related to extrapolated log k 0 values with pure water as the ecluent, the regression lines of both the homologues and the reference substances are nearly identical and can reciprocally be used to predict their log P OW values with reasonable accuracy.