Characterization of Freshwater Natural Dissolved Organic Matter (DOM): Mechanistic Explanations for Protective Effects Against Metaltoxicity and Direct Effects on Organisms

Dissolved organic matter (DOM) exerts direct and indirect influences on aquatic organisms. In order to better understand how DOM causes these effects, potentiometric titration was carried out for a wide range of autochthonous and terrigenous freshwater DOM isolates. The isolates were previously characterized by absorbance and fluorescence spectroscopy. Proton binding constants (pKa) were grouped into three classes:acidic (pKa ≤ 5), intermediate (5 \u3c pKa ≤ 8.5) and basic (pKa \u3e 8.5). Generally, the proton site densities (LT) showed maximum peaks at the acidic and basic ends around pKa values of 3.5 and 10, respectively. More variably positioned peaks occurred in the intermediate pKa range. The acid–base titrations revealed the dominance of carboxylic and phenolic ligands with a trend for more autochthonous sources to have higher total LT. A summary parameter, referred to as the Proton Binding Index (PBI), was introduced to summarize chemical reactivity of DOMs based on the data of pKa and LT. Then, the already published spectroscopic data were explored and the specific absorbance coefficient at 340 nm (i.e. SAC340), an index of DOM aromaticity,was found to exhibit a strong correlation with PBI. Thus, the tendencies observed in the literature that darker organic matter is more protective against metal toxicity and more effective in altering physiological processes in aquatic organisms can now be rationalized on a basis of chemical reactivity to protons

The Influence of Dissolved Organic Matter (DOM) on Sodium Regulation and Nitrogenous Waste Excretion in the Zebrafish (Danio rerio)

Dissolved organic matter (DOM) is both ubiquitous and diverse in composition in natural waters, but its effects on the branchial physiology of aquatic organisms have received little attention relative to other variables (e.g. pH, hardness, salinity, alkalinity). Here, we investigated the effects of four chemically distinct DOM isolates (three natural, one commercial, ranging from autochthonous to highly allochthonous, all at ∼6 mg C l−1) on the physiology of gill ionoregulation and nitrogenous waste excretion in zebrafish acclimated to either circumneutral (7.0–8.0) or acidic pH (5.0). Overall, lower pH tended to increase net branchial ammonia excretion, net K+ loss and [3H]PEG-4000 clearance rates (indicators of transcellular and paracellular permeability, respectively). However, unidirectional Na+ efflux, urea excretion and drinking rates were unaffected. DOM sources tended to stimulate unidirectional Na+ influx rate and exerted subtle effects on the concentration-dependent kinetics of Na+ uptake, increasing maximum transport capacity. All DOM sources reduced passive Na+ efflux rates regardless of pH, but exerted negligible effects on nitrogenous waste excretion, drinking rate, net K+ loss or [3H]PEG4000 clearance, so the mechanism of Na+ loss reduction remains unclear. Overall, these actions appear beneficial to ionoregulatory homeostasis in zebrafish, and some may be related to physicochemical properties of the DOM sources. They are very different from those seen in a recent parallel study on Daphnia magna using the same DOM isolates, indicating that DOM actions may be both species and DOM specific

Disease and psychological status in ankylosing spondylitis.

Objectives. Psychological factors may be important in the assessment and management of ankylosing spondylitis (AS). Our primary objective was to describe associations between disease and psychological status in AS, using AS-specific assessment tools and questionnaires. Our secondary objectives were to identify patient subgroups based on such associations and to determine the stability of the measures over time. Methods. A total of 110 patients were assessed at 6-monthly intervals up to four times using tools to measure disease [Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI) and the Bath Ankylosing Spondylitis Metrology Index (BASMI)], psychological [Hospital Anxiety and Depression Questionnaire (HADS), Health Locus of Control—Form C Questionnaire (HLC-C)] and generic health [Short form (SF)-36] status. Results. Eighty-nine participants completed all four assessments. Throughout the study, BASDAI, BASFI and BASMI scores correlated significantly with anxiety, depression, internality and health status, but not with levels of belief in chance or powerful others. Clinically anxious or depressed subgroups had significantly worse BASDAI and BASFI, but not BASMI, scores. BASMI scores were the least closely linked to psychological status. Mean scores for disease, psychological and health status were clinically stable over the 18 months period. Conclusions. Disease status scores in AS correlated significantly with anxiety, depression, internality and health status. Interpretation of AS disease scores should take an account of psychological status and the choice of measures used. These findings have important potential applications in AS management and monitoring, including the identification of patients for biological therapies

The nature of a primary jet within a circumbinary disc outflow in a young stellar system

Most stars form in binaries, and both stars may grow by accreting material from a circumbinary disc onto their own discs. We suspect that in many cases a wide molecular wind will envelope a collimated atomic jet emanating from close to an orbiting young star. This so-called Circumbinary Scenario is explored here in order to find common identifiable properties. The dynamical set up is studied with three dimensional simulations with chemistry and cooling included. We extract the properties on scales of order 100 AU and compare to the Co-Orbital Scenario in which the wind and jet sources are in orbit. We find that the rapid orbital motion generates a wide ionised sheath around the jet core with a large opening angle at the base. This is independent of the presence of the surrounding molecular outflow. However, the atomic jet is recollimated beyond ∼ 55 AU when the molecular outflow restricts the motion of the ambient medium which, in turn, confines the jet. These physical properties are related to the optical Hα imaging, providing a means of distinguishing between models. The high excitation sheath and recollimation region can be explored on these scales through the next generation of instruments. However, in general, the amount and location of the ionised material, whether in the knots or the sheath, will depend on several parameters including the orbital period, axis alignment and pulse amplitude

Comparison of Metabolic Variables during the 2-Minute Walk Test and 6-Minute Walk Test

Assessing for functional mobility and fitness in deconditioned populations is common practice in many clinics. Comparison of the 2-minute walk test (2MWT) as a predictor for 6-minute walk test (6MWT) metabolic variables will save clinicians time and effort when performing baseline testing. PURPOSE: To determine if the 2MWT can be used as a viable means of accessing baseline fitness versus the 6MWT. METHODS: Ten subjects (48.3±15.7 yrs, 168.5±8.6 cm, 75.5±13.6 kg) reported on two separate days to perform the tests. Once fitted with a heart rate (HR) monitor and portable O2 analyzer, they performed either the 2MWT or 6MWT and on the second day performed the other. Repeated measures ANOVA were used to determine significant differences with pairwise comparisons utilizing the Bonferroni technique. Alpha was set at .05 for all tests. RESULTS: While there was no significant difference in VO2 between the 2-min time point of the 2MWT (16.9±4.6 ml/kg/min) and the 2-min time point of the 6-min walk test (17.1±5.6 ml/kg/min), p=1.0, there was a significant difference between the 2-min time point of the 2MWT and the 6-min time point of the 6MWT (21.4±4.6 ml/kg/min), p=. 007. There was no significant difference in HR between any of the time points (p\u3e.05). CONCLUSION: Caution should be taken if using the 2MWT as a measure of fitness since it seems participants are not yet in steady state at the 2-minute mar