An assessment of the environmental toxicity of hexavalent chromium in fish

At present chromium is a common contaminant in surface waters in many countries. In water the metal may be present in the trivalent form (CrIII) or in the hexavalent form (CrVI), the latter of which is more toxic to aquatic organisms.The investigations presented in this thesis were aimed at a thorough understanding of the mechanism of action of hexavalent chromium in fish. The process of uptake and elimination was studied in detail, while special attention was paid to physiological and histological alterations underlying the toxic effects. Water pH was taken into consideration as a varying environmental factor, because of its known influence on the oxidizing action of Cr(VI) and on the distribution of the ionic species of Cr(VI) in water. Rainbow trout (Salmo gairdneri) was used as the test-species.Chapter 1 describes the effect of pH on uptake, tissue distribution and retention of Cr(VI) in trout. In trout exposed to Cr(VI) at pH 7.8 for 2-4 days the highest contents of chromium were found in gill, liver, kidney and digestive tract. Upon transfer of exposed fish to tap-water, chromium disappeared rapidly from blood, gill and digestive tract, whereas chromium contents in liver tended to remain high and in kidney even tended to increase. When the pH was decreased from 7.8 to 6.5, a different pattern of accumulation and elimination of chromium was observed. The major differences were found in the gills which concentrated significantly more chromium at pH 6.5 than at pH 7.8, irrespective of the exposure time and concentration. As the intensity of the electron -spin - resonance signal characteristic for trivalent or pentavalent chromium in the gills was somewhat higher at pH 6.5 than at pH 7.8, the differences must have been at least partly due to the higher oxidizing action of Cr(VI) at the lower pH.Chapter 2 deals with the effect of pH on the acute toxicity of Cr(VI) to trout. The lethal action of the metal increased with decreasing pH in the range from 7.8 to 6.5. Morphological changes that could be associated with acute Cr(VI) poisoning at pH 7.8 were found in gills, kidney and stomach, whereas those at pH 6.5 appeared to be restricted to the gills. These findings are in accordance with the results obtained in the Cr- uptake experiments. Consequently, the general assumption that Cr(VI) elicits its toxic effect in some internal organ and that the gill is not the target organ in acute Cr(VI) toxicity, is only appropriate at relatively high pH levels. At pH 6.5 the gills seems to be the primary target organ.To explain the acute toxic effects, hydrochromate (HCrO 4- and chromate (CrO 42- ) were considered as the toxic species of Cr(VI) The relative toxicities of these ionic species were calculated from empirical toxicity relationships for weak acids in fish, as described in the literature. By this calculation it was found that the relative toxicity of HCrO 4- to trout was from 3.6 to 11.9 times greater than that of CrO 42- ) depending on exposure time and fish weight.Chapter 3 reports on an in vitro study on transfer of oxygen and chromium in gills of trout. Gills were perfused according to the isolated head perfusion technique and externally exposed to Na 2 CrO 4 solutions containing 51 CrO 42- . The results show that the transfer of chromium is directly coupled with the transfer of oxygen from the external solution to the internal perfusion medium. Under similar conditions of oxygen transfer, however, chromium transfer was significantly more effective at pH 6.5 than at pH 8.1.The data suggest that chromium is taken up by the blood by passive diffusion from the external solution across the epithelium of the secondary lamellae. In addition it is indicated that the availability of the metal to the fish increases with decreasing pH.Gill preparations of trout that were structurally damaged by pre-exposure in vivo to Cr(VI) exhibited an impaired oxygen transfer.Chapter 4 describes the effect of Cr(VI) on respiration and osmoregulation in trout. Recordings were made of the ventilation frequency, coughing rate and rate of oxygen uptake in trout subjected to sublethal concentrations of Cr(VI) for 4 days at pH 7.8 and 6.5.During exposure no significant effect of chromium on oxygen uptake rate was detected. The ventilation frequency and coughing rate increased proportionally to an increase in metal concentration, with fish being more susceptible at the lower pH.Alterations in blood and plasma variables determined after exposure indicated a significant dose-dependent decrease in plasma osmolality and electrolyte concentrations, and an increase in hemoglobin, hematocrit, plasma glucose and lactate levels. The pattern of these changes was dependent on pH and exposure concentration, and seemed to be related with chromiuminduced histological alterations. The results indicate, that at pH 7.8 as well as at pH 6.5 both an osmoregulatory and respiratory dysfunction are part of the physiological mechanism of hexavalent chromium toxicity.In chapter 5 toxic effects of Cr(VI) are described in trout after prolonged exposure at different pH values for periods of up to 32 weeks. Different developmental stages were studied.In all stages tested, fish were more susceptible to Cr(VI) at pH 6.5 than at pH 7.8. Fish in the embryo-through-juvenile stage were the most susceptible to Cr(VI) For this developmental stage it can be estimated that concentrations affecting survival lie between 0.2 and 2.0 mg/I Cr(VI) at pH 7.8 and between 0.02 and 0.2 mg/l Cr(VI) at pH 6.5.Finally, the observed effects of a prolonged exposure are discussed in relation with the results of the short-term toxicity tests described in the preceeding chapters.The toxicological evaluation of chromium in surface waters in the Netherlands is hampered by a lack of information on the proportion of trivalent and hexavalent forms of chromium in the total chromium content. Until now only total chromium contents have been determined at various sampling locations. If one compares the total chromium levels in Dutch surface water with the lowest toxic concentrations of Cr(VI) in trout, it can not be excluded that chromium concentrations may locally exceed toxic levels for fish. However, a final conclusion can only be drawn when additional information on the chemical status of the metal in the aquatic environment in the Netherlands has been made available.<p/

Manifold-Topology from K-Causal Order

To a significant extent, the metrical and topological properties of spacetime can be described purely order-theoretically. The $K^+$ relation has proven to be useful for this purpose, and one could wonder whether it could serve as the primary causal order from which everything else would follow. In that direction, we prove, by defining a suitable order-theoretic boundary of $K^+(p)$, that in a $K$-causal spacetime, the manifold-topology can be recovered from $K^+$. We also state a conjecture on how the chronological relation $I^+$ could be defined directly in terms of $K^+$.Comment: v2: 9 pages, 2 figures. Minor change

The Vestibular Drive for Balance Control Is Dependent on Multiple Sensory Cues of Gravity

Vestibular signals, which encode head movement in space as well as orientation relative to gravity, contribute to the ongoing muscle activity required to stand. The strength of this vestibular contribution changes with the presence and quality of sensory cues of balance. Here we investigate whether the vestibular drive for standing balance also depends on different sensory cues of gravity by examining vestibular-evoked muscle responses when independently varying load and gravity conditions. Standing subjects were braced by a backboard structure that limited whole-body sway to the sagittal plane while load and vestibular cues of gravity were manipulated by: (a) loading the body downward at 1.5 and 2 times body weight (i.e., load cues), and/or (b) exposing subjects to brief periods (20 s) of micro- (&lt;0.05 g) and hyper-gravity (∼1.8 g) during parabolic flights (i.e., vestibular cues). A stochastic electrical vestibular stimulus (0–25 Hz) delivered during these tasks evoked a vestibular-error signal and corrective muscles responses that were used to assess the vestibular drive to standing balance. With additional load, the magnitude of the vestibular-evoked muscle responses progressively increased, however, when these responses were normalized by the ongoing muscle activity, they decreased and plateaued at 1.5 times body weight. This demonstrates that the increased muscle activity necessary to stand with additional load is accompanied a proportionally smaller increase in vestibular input. This reduction in the relative vestibular contribution to balance was also observed when we varied the vestibular cues of gravity, but only during an absence (&lt;0.05 g) and not an excess (∼1.8 g) of gravity when compared to conditions with normal 1 g gravity signals and equivalent load signals. Despite these changes, vestibular-evoked responses were observed in all conditions, indicating that vestibular cues of balance contribute to upright standing even in the near absence of a vestibular signal of gravity (i.e., micro-gravity). Overall, these experiments provide evidence that both load and vestibular cues of gravity influence the vestibular signal processing for the control of standing balance

Activation of TRPC6 channels is essential for lung ischaemia–reperfusion induced oedema in mice

Lung ischaemia–reperfusion-induced oedema (LIRE) is a life-threatening condition that causes pulmonary oedema induced by endothelial dysfunction. Here we show that lungs from mice lacking nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox2y/−) or the classical transient receptor potential channel 6 (TRPC6−/−) are protected from LIR-induced oedema (LIRE). Generation of chimeric mice by bone marrow cell transplantation and endothelial-specific Nox2 deletion showed that endothelial Nox2, but not leukocytic Nox2 or TRPC6, are responsible for LIRE. Lung endothelial cells from Nox2- or TRPC6-deficient mice showed attenuated ischaemia-induced Ca2+ influx, cellular shape changes and impaired barrier function. Production of reactive oxygen species was completely abolished in Nox2y/− cells. A novel mechanistic model comprising endothelial Nox2-derived production of superoxide, activation of phospholipase C-γ, inhibition of diacylglycerol (DAG) kinase, DAG-mediated activation of TRPC6 and ensuing LIRE is supported by pharmacological and molecular evidence. This mechanism highlights novel pharmacological targets for the treatment of LIRE

Congenital anomalies of the male urethra

The spectrum of congenital anomalies of the male urethra is presented. The embryologic basis of each anomaly, when known, is discussed. Clinical and imaging features of each entity are presented

Bmp7 Functions via a Polarity Mechanism to Promote Cloacal Septation

During normal development in human and other placental mammals, the embryonic cloacal cavity separates along the axial longitudinal plane to give rise to the urethral system, ventrally, and the rectum, dorsally. Defects in cloacal development are very common and present clinically as a rectourethral fistula in about 1 in 5,000 live human births. Yet, the cellular mechanisms of cloacal septation remain poorly understood.We previously detected Bone morphogenetic protein 7 (Bmp7) expression in the urorectal mesenchyme (URM), and have shown that loss of Bmp7 function results in the arrest of cloacal septation. Here, we present evidence that cloacal partitioning is driven by Bmp7 signaling in the cloacal endoderm. We performed TUNEL and immunofluorescent analysis on cloacal sections from Bmp7 null and control littermate embryos. We found that loss of Bmp7 results in a dramatic decrease in the endoderm survival and a delay in differentiation. We used immunological methods to show that Bmp7 functions by activating the c-Jun N-terminal kinase (JNK) pathway. We carried out confocal and 3D imaging analysis of mitotic chromosome bundles to show that during normal septation cells in the cloacal endoderm divide predominantly in the apical-basal direction. Loss of Bmp7/JNK signaling results in randomization of mitotic angles in the cloacal endoderm. We also conducted immunohistochemical analysis of human fetal sections to show that BMP/phospho-SMAD and JNK pathways function in the human cloacal region similar as in the mouse.Our results strongly indicate that Bmp7/JNK signaling regulates remodeling of the cloacal endoderm resulting in a topological separation of the urinary and digestive systems. Our study points to the importance of Bmp and JNK signaling in cloacal development and rectourethral malformations

Individual identification via electrocardiogram analysis

Background: During last decade the use of ECG recordings in biometric recognition studies has increased. ECG characteristics made it suitable for subject identification: it is unique, present in all living individuals, and hard to forge. However, in spite of the great number of approaches found in literature, no agreement exists on the most appropriate methodology. This study aimed at providing a survey of the techniques used so far in ECG-based human identification. Specifically, a pattern recognition perspective is here proposed providing a unifying framework to appreciate previous studies and, hopefully, guide future research. Methods: We searched for papers on the subject from the earliest available date using relevant electronic databases (Medline, IEEEXplore, Scopus, and Web of Knowledge). The following terms were used in different combinations: electrocardiogram, ECG, human identification, biometric, authentication and individual variability. The electronic sources were last searched on 1st March 2015. In our selection we included published research on peer-reviewed journals, books chapters and conferences proceedings. The search was performed for English language documents. Results: 100 pertinent papers were found. Number of subjects involved in the journal studies ranges from 10 to 502, age from 16 to 86, male and female subjects are generally present. Number of analysed leads varies as well as the recording conditions. Identification performance differs widely as well as verification rate. Many studies refer to publicly available databases (Physionet ECG databases repository) while others rely on proprietary recordings making difficult them to compare. As a measure of overall accuracy we computed a weighted average of the identification rate and equal error rate in authentication scenarios. Identification rate resulted equal to 94.95 % while the equal error rate equal to 0.92 %. Conclusions: Biometric recognition is a mature field of research. Nevertheless, the use of physiological signals features, such as the ECG traits, needs further improvements. ECG features have the potential to be used in daily activities such as access control and patient handling as well as in wearable electronics applications. However, some barriers still limit its growth. Further analysis should be addressed on the use of single lead recordings and the study of features which are not dependent on the recording sites (e.g. fingers, hand palms). Moreover, it is expected that new techniques will be developed using fiducials and non-fiducial based features in order to catch the best of both approaches. ECG recognition in pathological subjects is also worth of additional investigations