A combined QSAR and partial order ranking approach to risk assessment.

QSAR generated data appear as an attractive alternative to experimental data as foreseen in the proposed new chemicals legislation REACH. A preliminary risk assessment for the aquatic environment can be based on few factors, i.e. the octanol-water partition coefficient (Kow), the vapour pressure (VP) and the potential biodegradability of the compound in combination with the predicted no-effect concentration (PNEC) and the actual tonnage in which the substance is produced. Application of partial order ranking, allowing simultaneous inclusion of several parameters leads to a mutual prioritisation of the investigated substances, the prioritisation possibly being further analysed through the concept of linear extensions and average ranks. The ranking uses endpoint values (log Kow and log VP) derived from strictly linear 'noise-deficient' QSAR models as input parameters. Biodegradation estimates were adopted from the BioWin module of the EPI Suite. The population growth impairment of Tetrahymena pyriformis was used as a surrogate for fish lethality.

Global government applications of analogues, SARs and QSARs to predict aquatic toxicity, chemical or physical properties, environmental fate parameters and health effects of organic chemicals.

Faced with the need to predict physical and chemical properties, environmental fate, ecological effects and health effects of organic chemicals in the absence of experimental data, several Government organizations have been applying analogues, Structure Activity Relationships (SARs) and Quantitative Structure Activity Relationships (QSARs) to develop those predictions. To establish some benchmarks for monitoring future increases in applications of analogues, SARs and QSARs by global Government organizations, this paper describes the current applications of analogues, SARs and QSARs by Australian, Canadian, Danish, European, German, Japanese, Netherlands, and United States Government organizations to predict physical and chemical properties, environmental fate, ecological effects and health effects of organic chemicals.

Evaluation of empirical versus non-empirical descriptors.

In this case study, based on the notorious PCBs, the performance of selected empirical (EM) versus non-empirical and quantum chemical (NEM-QC) descriptors in multivariate QSARs have been evaluated. The informational content of the EM descriptors has been evaluated with respect to the physical understandable NEM-QC descriptors. Models for estimating key parameters for risk assessment have been developed, based on two-dimensional EM and three-dimensional NEM-QC descriptors, respectively. In spite of the simplicity of the two-dimensional descriptors, no evidence of lower predictive ability of the EM descriptors compared to the NEM-QC descriptors was observed. Homogeneity of variance within and between experimental methods, species and PCB congeners has been analysed, disclosing the importance for the need for handling uncertainty aspects of the results obtained by different laboratories and methods. The latter appears crucial for the model developments when using data from more than one source.

QSAR's based on partial order ranking.

The development of Quantitative Structure Activity Relationships (QSAR's) often relies heavily on the application of statistical methods such as multi-linear regression (MLR) or principal component analysis/partial least square (PCA/PLS). Partial order ranking (POR), which from a mathematical point of view is based on elementary methods of Discrete Mathematics, appears as an attractive and operationally simple and more general alternative since the method does not require specific functional relationships between the single descriptors or the end-points. The POR method allows ranking of a series of compounds, based on selected descriptors characterizing their structural and/or electronic nature (model diagram). The ranking of the compounds based on their end-points (experimental ranking) can then be compared to the model diagram. If the model diagram resembles the experimental ranking of the end-points under investigation, other compounds, not being experimentally investigated, can be assigned a rank in the model and hereby obtain an identity based on the known compounds. The present study elucidates the applicability of POR as a simple tool for QSAR modeling. Based on illustrative examples the POR approach to QSAR modeling will be presented with special focus on the precision and the uncertainties of the method, which will be discussed in terms of the number of descriptors and compounds involved. The advantageous interplay between POR and PCA, the latter being applied in order to reduce a possible large number of descriptors into a limited number of latent descriptors will be discussed.

QSARs for identifying and prioritizing substances with persistence and bioconcentration potential.

From the 8511 chemicals with 1998 production volumes reported to the U.S. Environmental Protection Agency (U.S. EPA), the TSCA Interagency Testing Committee's (ITC's) Degradation Effects Bioconcentration Information Testing Strategies (DEBITS) was used to identify 56 chemicals. The DEBITS Quantitative Structure-Activity Relationships (QSARs) and the U.S. EPA's PBT profiler QSARs were used to predict the persistence and bioconcentration factors of these 56 chemicals. Partial order ranking was used to prioritise the chemicals based on persistence and bioconcentration potential.

Humic complexes of diethyl phthalate: molecular modelling of the sorption process.

The sorption mechanisms and complex formation between humic acid (HA) and a successively increasing number of diethyl phthalate (DEP) molecules have been studied theoretically using molecular mechanics, the number (n) of DEP molecules being varied from 1 to 30. The energy components of the single HA x nDEP complexes have been used as explanatory variables in a principal component analysis for exploring the presence of similarities/dissimilarities in the energetic properties of the individual xenobiotic complexes. The sorption can be explained in terms of a two-step mechanism. Absorption takes place as long as the host humic acid structure offers (a) enough internal docking space and (b) favorable interactions (energy release) with the guest molecule. This takes place for up to 7 DEP molecules. Further increase in the number to 30 DEP molecules will, due to the lack of free available internal voids, lead to surface controlled adsorption. The two-step sorption process apparently results in (a) a linear increase in energy gain by DEP bonds, and similarly (b) a constant incremental rise in molecular properties of the complexes such as volume and surface area. Three outstanding observations emerge: (1) Structural features at the atomic level (nanochemistry), such as partial atomic charges and high aromaticity of the humic acid, are observed to be dominating the intermolecular interactions in the complexes at the specific sorption sites. (2) Torsional relief and favorable changes in bonding energy also prevail for the growing complex. The latter indicates both the structural flexibility of the HA host and the stabilizing effect of DEP on the complex, by filling of the voids within the HA molecule. (3) The intermolecular forces are described mainly by hydrogen bonds (electrostatic energy) and interactions between dipole-dipole, such as carboxylic functions and uncharged moieties such as aromatic rings (van der Waals energy).

Solubility of nonylphenol and nonylphenol ethoxylates. On the possible role of micelles.

The water solubility of nonylphenol (NP) has been estimated to be 4.9 +/- 0.4 mg/l corresponding to (2.22 +/- 0.18) x 10(-5) mol/l at 25 degrees C using shake flask and surface tension techniques. The low solubility in combination with an observed rather slow dissolution process will limit the leachability of NP in the terrestrial environment. Based on indirect evidence, it is suggested that NP, in contrast to nonylphenol ethoxylate (NPEO) with, e.g., 12 ethoxylate moieties, is not subject to micelle formation, and as such does not constitute a potential vehicle for the transport of hydrophobic pollutants in the environment. For NPEOs with a very high number of ethoxy moieties, e.g., 100, the compounds appear water soluble without micelle formation.

The use of Hasse diagrams as a potential approach for inverse QSAR.

Quantitative structure-activity relationships are often based on standard multidimensional statistical analyses and sophisticated local and global molecular descriptors. Here, the aim is to develop a tool helpful to define a molecule or a class of molecules which fulfills pre-described properties, i.e., an Inverse QSAR approach. If highly sophisticated descriptors are used in QSAR, the structure and then the synthesis recipe may be hard to derive. Thus, descriptors, from which the synthesis recipe can be easily derived, seem appropriate to be included within this study. However, if descriptors simple enough to be useful for defining syntheses recipes of chemicals were used, the accuracy of a numeric expression may fail. This paper suggests a method, based on very simple elements of the theory of partially ordered sets, to find a qualitative basis for the relationship between such fairly simple descriptors on the one side and a series of ecotoxicological properties, on the other side. The partial order ranking method assumes neither linearity nor certain statistical distribution properties. Therefore the method may be more general compared to many standard statistical techniques. A series of chlorinated aliphatic compounds has been used as an illustrative example and a comparison with more sophisticated descriptors derived from quantum chemistry and graph theory is given. Among the results, it was disclosed that only for algae lethal concentration, as one of the four ecotoxicological properties, the synthesis specific predictors seem to be good estimators. For all other ecotoxicological properties quantum chemical descriptors appear as the more suitable estimators.

Solubilities and surface activities of phthalates investigated by surface tension measurements.

Aqueous solutions of DEP (di-ethyl), DnBP (di-n-butyl), DnH(6)P (di-n-hexyl), and DEHP (di-[2-ethyl-hexyl]) phthalates have been investigated by use of surface tension measurements at temperatures between 10 and 35 degrees C. A tensiometric approach allows for the determination of unimeric solubilities and delta G degree, which is the standard Gibbs free energy change, for the dissolution of phthalates in water. The unimeric solubility of the phthalates increase with decreasing temperature. The delta G degree shows a linear increase with increasing phthalate alkyl chain length. The contribution of enthalpy (delta H degree) and entropy (delta S degree) to delta G degree were calculated from the temperature-dependent solubilities. The contributions of both delta H degree and delta S degree are negative and increase in magnitude with increasing alkyl chain length, suggesting hydrophobic interactions between phthalates and water. The ability of different phthalates to lower the surface tension decreases with increasing alkyl chain length, whereas the relative affinity for adsorption in the air-water interface increases drastically for long-chain phthalates. Despite the low surface activity of phthalates compared with that of common surfactants, they show significant affinity for adsorption in air-water interfaces of natural surface waters. This property, combined with their low solubilities, may affect the fate of these compounds within the natural environment, because they form emulsions above unimeric saturation in aqueous media.

Partial order ranking-based QSAr's: estimation of solubilities and octanol-water partitioning.

Partial order ranking appears as an attractive alternative to conventional Quantitative Structure Activity Relationships (QSAR) methods, the latter typically relying on the application of statistical methods. The method seems attractive as a priori knowledge of specific functional relationships is not required. In the present study, it is demonstrated that QSAR models based on a partial order ranking approach can be used satisfactorily to predict solubilities and octanol-water partitioning for a selection of organic compounds exhibiting different structural and electronic characteristics. The uncertainty is validated using well-established LSER descriptors. Two requirements to the model with regard to precision prevail, i.e., the model must be able to rank the single compounds in the basis set correctly compared to the experimental data, and the model should be based on a basis set of compounds large enough to secure a satisfactorily fine-meshed net, taking the number of descriptors into account. In the present study, the model was able to rank 318 out of 319 comparisons correctly in the case of solubilities. The corresponding figures for the octanol-water partitioning were 407 out of 408. The precision and the uncertainties of the method which, were found closely related to the mutual interplay between the number of compounds and the number of descriptors is discussed in terms of the number of descriptors and compounds involved. The limitations of the method are discussed.

Using a capsular flap to correct breast implant malposition.

Breast implant malposition may be corrected by designing a capsular flap to create a sling. This results in a vascularized, reinforced repair that places the suture line away from the maximum weight of the implants. The authors discuss the advantages of using a capsular flap for an impending extrusion of a breast implant or tissue expander, and present their technique. (Aesthetic Surg J 2001;21:441-444.).

The influence on partial order ranking from input parameter uncertainty. Definition of a robustness parameter.

The method of partial order ranking has been used within the environmental area for a variety of purposes as an attractive way of handling complex information. However, the environmental data are often associated with a significant degree of uncertainty. In this investigation the general nature of the influence from data uncertainty on the partial order ranking is analyzed. A Monte Carlo type analysis is performed in which a series of randomly formed data are used to test the influence of data uncertainty. The partial order ranking is interpreted, where the results are transferred to a one-dimensional ranking scale taking into account that not all elements are ranked with the same certainty. A simple general robustness parameter (E) in form of the expected number of comparisons for each ranking element is defined and correlated to the uncertainty analysis results. A simple equation relates E to the number of elements and the number of parameters, respectively. The magnitude of the ranking uncertainty is shown to increase rapidly when the E value decreases below 4-5 comparisons per element. When the E value exceeds 5 the ranking uncertainty becomes nearly constant and independent on the actual E value.

The effect of humic acids on the water solubility and water-organic carbon partitioning of fluorene and its NSO-heteroanalogues: carbazole, dibenzofuran, and dibenzothiophene.

The solubilizing effect of humic acids on fluorene and its NSO analogues carbazole, dibenzofuran and dibenzothiophene has been studied. The interaction between these substances and humic acids was found to depend significantly on the actual humic acid concentration. A pronounced decrease in the interaction constant, as well as in the water-organic matter partitioning coefficient was observed with increasing humic acid concentration. The effects are discussed in terms of concentration dependent macromolecular structural changes in the humic acids. A linear free energy relation for the interaction is suggested.

Review on persistent organic pollutants in the environment of Greenland and Faroe Islands.

The literature concerning persistent organic pollutants (POPs) in the environment of Greenland and the Faroe Islands covering the period up to 1995 has been revisited. It is difficult to compare data from earlier studies with those from more recent investigations. Thus as the former quantified the content of CBs by comparison to a technical mixture of CBs (e.g. Aroclor 1254), the latter analyses typically are quantified on a single congener level. Single CB congeners have in some cases been determined, but the results were subsequently expressed as total PCB related to an Aroclor standard. For studies based on single CB congener determinations, the highest levels are reported for porpoise blubber from Greenland (700-4500 micrograms/kg wet weight), the conclusion, however being based on two determinations only. In Greenlandic seal blubber and peregrine falcon plasma equal levels of CBs (130-750 micrograms/kg ww) and of DDTs (150-860 micrograms/kg ww) were found. Levels of CBs and DDTs in fish liver were found to be around 40-75 micrograms/kg ww. In sediment samples the CBs were almost all below the detection limit (< 0.02-0.1 microgram/kg dry weight), and thereby being the matrix with the lowest CBs concentration levels. Earlier data based on Aroclor standards showed DDT levels in Greenlandic whale blubber in the range of 2700-4100 micrograms/kg ww and PCB levels of 3700 micrograms/kg-5400 micrograms/kg ww. DDT levels for seal blubber were at the same level (2700-4500 micrograms/kg ww) whereas the PCB level was lower (900-3900 micrograms/kg ww). The PCB level corresponds to the level found in human adipose tissue determined with a similar quantification technique. The lowest levels reported for mammals correspond to walrus blubber, the sum of PCBs and DDTs being in the ranges of 180-360 micrograms/kg ww and 50-90 micrograms/kg ww, respectively. The content of PCBs in scallops was found to be 3 micrograms/kg ww near the Thule Air base.

[Patients' perception of symptoms in colorectal cancer. A cause of delay in diagnosis and treatment]. / Patientopfattelse af symptomer ved kolorektal cancer. En årsag til forsinkelse af diagnose og behandling.

A questionnaire was given to a series of 50 patients referred for colorectal cancer to the Department of Surgical Gastroenterology at Hvidovre Hospital, Copenhangen. The patients were asked about the length of the period from debut of symptoms to the first visit to their family doctor (patient's delay), detailed symptoms and their views and attitudes towards the significance of these symptoms. More than half of the patients first saw their own doctor more than three months after the first symptom: 17/33 (52%) with a change in bowel habits, 12/28 (43%) with rectal bleeding, 11/19 (58%) with abdominal pain and 4/6 (67%) with a palpable mass. Only 7/44 (15%) thought that cancer was the cause of their symptoms, and a similar minority was afraid of an operation or an ostomy. We conclude that the main cause of patient's delay is a lack of knowledge among the patients about the significance of bowel symptoms, rather than fear of cancer, operation or an ostomy. On this basis we recommend that an information campaign about cancer-related bowel symptoms (bleeding, change of bowel habits) should be carried out with the aim of reducing patient's delay and thereby possibly also improving the prognosis through an early diagnosis.

The Allergen Bank: a source of extra contact allergens for the dermatologist in practice.

The Allergen Bank was established to give dermatologists easy access to special test materials in order to make early diagnoses of special cases of allergic contact dermatitis. The Allergen Bank comprises a computer system to register several hundred contact allergens in appropriate patch test concentrations available at the allergy laboratory and the patch test results. At the request of dermatologists in practice for Allergen Bank may supply special contact allergens for aimed patch testing of contact dermatitis patients. The organization of the Allergen Bank and the procedure of its use are described. During its first 23 months 28 dermatologists asked for 2,209 allergen samples for testing of 386 patients, an average of 6 allergens per patient and 14 patients per dermatologist. A total number of 164 positive reactions have been registered, and 440 of the 540 allergens have been in use. One third of the positive reactions were caused by the 16 most frequently ordered allergens, which amounted to 340 allergen samples. The allergens included plant chemicals, acrylates, animal feed additives, fragrance chemicals and preservatives. Selected allergens were investigated for stability during handling and shipping under varying conditions relevant to the function of the Allergen Bank. The possible inhomogeneity of petrolatum based allergen preparations is discussed in relation to diagnostic patch testing.

Contact allergy to 2-hydroxy-5-tert-butyl benzylalcohol and 2,6-bis(hydroxymethyl)-4-tert-butylphenol, components of a phenolic resin used in marking pens.

2-hydroxy-5-tert-butyl benzylalcohol and 2,6-bis(hydroxymethyl)-4-tert-butylphenol were identified as contact allergens in a phenolic resin used as a tackifier in the ink of a marking pen, which, after being used directly on the skin, caused an acute contact dermatitis on the hand of a 13-year-old boy. The patient also reacted to 4-tert-butylphenol-formaldehyde resin (BPF resin) 1% pet. included in the European standard series.

Carvone: an overlooked contact allergen cross-reacting with sesquiterpene lactones?

The terpene l-carvone is one of the main constituents of spearmint oil. The sensitizing potential of l-carvone has been considered low, but it has occasionally caused contact allergy in users of spearmint toothpaste and chewing gum. l-Carvone is also an oxidation product of d-limonene that occurs in solvents used increasingly in industry. We included l-carvone 5% pet. in the standard patch test series. In the 1st year, 541 patients were tested and 15 (2.77%) had positive, and 12 doubtful positive (?+) reactions to l-carvone. The strongest reactions were observed in 9 patients with concomitant Compositae sensitivity. The key clinical features and other contact allergies of the patients are presented. When re-testing with l-carvone in the same or lower concentrations, only 2 out of 8 patients had positive reactions. Possible reasons for this discrepancy are discussed in terms of cross-reactions, concomitant sensitization, excited skin syndrome, irritancy and facilitated immunological response.

Evidence for endothelium-dependent and endothelium-independent vasodilation in human skin flaps.

Acetylcholine (ACh) and nitroglycerin (NTG) were used as probes to study endothelium-dependent and endothelium-independent vascular relaxation in isolated perfused transverse paraumbilical human skin flaps. It was observed that ACh (10(-6) M) significantly (p < 0.05) decreased the vascular resistance and increased dermal capillary perfusion (assessed by surface fluorometry) in norepinephrine (NE, 10(-6) M) preconstricted skin flaps, despite the presence of a cyclooxygenase inhibitor (indomethacin, 3 x 10(-5) M) and a beta-adrenergic receptor antagonist (propranolol, 10(-6) M). The ability of ACh to induce vascular relaxation in NE-preconstricted skin flaps was lost after damaging the vascular endothelial lining with saponin perfusion (100 mg.L-1, 5 min). In contrast, NTG (10(-6) M) induced vascular relaxation to a similar extent before and after saponin treatment. In a separate study, ACh was seen to induce vascular relaxation in a concentration-dependent manner in skin flaps preconstricted with NE (10(-6) M). This vascular relaxation effect of ACh over the dose range of 10(-9)-10(-5) M was significantly (p < 0.01) inhibited in the presence of N omega-nitro-L-arginine (10(-5) M), a nitric oxide (NO) synthesis inhibitor. These observations were taken to indicate the presence of endothelium-dependent and endothelium-independent vascular relaxation in human skin flaps and that the ACh-induced endothelium-dependent relaxation is probably mediated by NO. The importance of impairment of endothelium-dependent relaxation in the pathogenesis of skin flap ischemia, and the potential use of topical nitrovasodilators or NO donors for prevention and (or) treatment of skin flap ischemia were also discussed.