Assessment of selected native plants growing along Nairobi river for uptake of copper, zinc and cadmium

Nairobi River has high quantities of heavy metals emanating mainly from industrial and domestic wastes. Phytoremediation is a promising alternative to conventional clean‐up methods; however, not enough information is available on plant species suitable for this application, especially in Kenya. Plant screening on contaminated sites is necessary and may lead to the identification of more species. A phytoremediation study was carried out along Nairobi River in six sites; Kikuyu, Kawangware, Chiromo, Gikomba, Njiru, and Fourteen falls. The objective of this study was to ascertain the extent of heavy metal pollution and the potential of Polygonum senegalensis (P. senegalensis), Amaranthus hybridus (A. hybridus) and Eichhornia crassipes (E. crassipes) as phytoremediants. The heavy metals studied were Copper (Cu), Cadmium (Cd) and Zinc (Zn) in the selected native plants (biotic indicators), water and soil (abiotic indicators). The metals were detected using the atomic absorption spectrophotometer (AAS). The observed values of heavy metals in water, soil and plants did not vary significantly (p>0.05) among the sampling sites. The mean concentration of these metals in soil (43.01 ± 0.03 mg/Kg) was higher than the values recorded in water (37.61 ± 0.65 mg/L). The ability of the plants to take up heavy metals (BCF) was evaluated from the ratio of metal concentration in the plants and water. The Bio‐concentration factor (BCF) obtained was P. senegalensis: 8.83 ± 0.62, A. hybridus; 8.44 ± 0.59 and E. crassipes: 7.56 ± 0.42. The BCF show that the selected plants accumulate Cu, Zn and Cd from water. The mean concentrations of heavy metals obtained in the plants are: Cu 6.73 ± 0.74 mg/Kg, Zn 16.53 ± 2.59 mg/Kg and Cd 2.57 ± 0.83 mg/Kg. Based on the results observed in the plants, Zn showed the largest accumulation and can be considered as one of the major pollutants of Nairobi River. The results showed differences in accumulation of metals ‐ Zn, Cu and Cd ‐ in different plant organs, roots > stems > leaves. This study showed that P. senegalensis and A. hybridus can accumulate Cu, Zn and Cd even when the concentrations of the metals in the abiotic components (soil and water) of the aquatic environment is low, suggesting that the plants are promising candidates for phytoremediation of aquatic ecosystems polluted with Cu, Zn and Cd.Key words: Native plants, Nairobi River, copper, zinc, cadmiu

Enhanced single-photon emission in the near infrared from a diamond color center

Individual color centers in diamond are promising for near-term quantum technologies including quantum key distribution and metrology. Here we show fabrication of an as-yet uncharacterized nickel-related complex in diamond which has photophysical properties surpassing the two main-stay centers for single-photon applications, namely, the nitrogen-vacancy and the nickel-nitrogen complex (NE8) center. This center was fabricated using focused ion-beam implantation of nickel into isolated chemical vapor-deposited diamond crystals. A possible correlation of the center to a Ni/Si complex is substantiated by a coimplantation of Ni and Si into a pure bulk diamond. Room-temperature photoluminescence studies reveal a narrow emission in the near infrared region centered at 768 nm with a lifetime as short as 2 n

Near coalescent submicron polycrystalline diamond films deposited on silicon: hydrogen bonding and thermal enhanced carbide formation

The influence of high temperature annealing up to 1200 °C in vacuum on ∼100 nm nearly continuous thick diamond films consisting of 30-50 nm crystallites, deposited onto silicon substrates is reported. The hydrogen bonding and phase composition of the films were studied with Raman spectroscopy, while the surface microstructure and composition were studied with high resolution scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS), respectively. Annealing to 800-900 °C of ∼100 nm thick films results in a decrease in the intensities of the peaks associated with hydrogen bonding (Raman), as well as changes to the morphological microstructure at the film surface. Heating the films to 1000 °C resulted in the complete disappearance of the Raman peaks associated with hydrogen bonding at grain boundaries, and an increase in the relative intensity of the diamond peak relative to the graphite-related D and G Raman peaks, concomitant with changes to the microstructure (SEM and TEM). Ex situ XP analysis of the films annealed to 800 and 1000 °C provides clear evidence for the formation of SiC on the films surface and near surface region. However a sharp SiC Raman peak at 796 cm-1 appears only after annealing to 1200 °C and it is concomitant with a decrease in the Raman peaks associated with sp2 bonded carbon. Our results suggest that formation of SiC phase preferentially consumes sp2/sp hybridized carbon matrix, produced by thermal desorption of hydrogen atoms at diamond grain boundary and at the diamond film-silicon substrate interface

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10-30 nm grain size prepared by chemical vapor deposition

The thermal stability of nanocrystalline diamond films with 10-30 nm grain size deposited by microwave enhanced chemical vapor deposition on silicon substrate was investigated as a function of annealing temperature up to 1200&deg;C. The thermal stability of the surface-upper atomic layers was studied with near edge x-ray absorption fine structure (NEXAFS) spectroscopy recorded in the partial electron yield mode. This technique indicated substantial thermally induced graphitization of the film within a close proximity to the surface. While in the bulk region of the film no graphitization was observed with either Raman spectroscopy or NEXAFS spectroscopy recorded in total electron yield mode, even after annealing to 1200&deg;C. Raman spectroscopy did detect the complete disappearance of transpolyacetylene (t-PA)-like 1 and 3 modes following annealing at 1000&deg;C. Secondary ion mass spectroscopy, applied to investigate this relative decrease in hydrogen atom concentration detected only a &sim;30% decrease in the bulk content of hydrogen atoms. This enhanced stability of sp3 hybridized atoms within the bulk region with respect to graphitization is discussed in terms of carbon bond rearrangement due to the thermal decomposition of t-PA-like fragments. <br /

In vivo hippocampal subfield volumes in bipolar disorder—A mega-analysis from The Enhancing Neuro Imaging Genetics through Meta-Analysis Bipolar Disorder Working Group

The hippocampus consists of anatomically and functionally distinct subfields that may be differentially involved in the pathophysiology of bipolar disorder (BD). Here we, the Enhancing NeuroImaging Genetics through Meta‐Analysis Bipolar Disorder workinggroup, study hippocampal subfield volumetry in BD. T1‐weighted magnetic resonance imaging scans from 4,698 individuals (BD = 1,472, healthy controls [HC] = 3,226) from 23 sites worldwide were processed with FreeSurfer. We used linear mixed‐effects models and mega‐analysis to investigate differences in hippocampal subfield volumes between BD and HC, followed by analyses of clinical characteristics and medication use. BD showed significantly smaller volumes of the whole hippocampus (Cohen's d = −0.20), cornu ammonis (CA)1 (d = −0.18), CA2/3 (d = −0.11), CA4 (d = −0.19), molecular layer (d = −0.21), granule cell layer of dentate gyrus (d = −0.21), hippocampal tail (d = −0.10), subiculum (d = −0.15), presubiculum (d = −0.18), and hippocampal amygdala transition area (d = −0.17) compared to HC. Lithium users did not show volume differences compared to HC, while non‐users did. Antipsychotics or antiepileptic use was associated with smaller volumes. In this largest study of hippocampal subfields in BD to date, we show widespread reductions in nine of 12 subfields studied. The associations were modulated by medication use and specifically the lack of differences between lithium users and HC supports a possible protective role of lithium in BD

Selective augmentation of striatal functional connectivity following NMDA receptor antagonism: implications for psychosis

The psychotomimetic effect of the N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine is thought to arise from a functional modulation of the brain's fronto-striato-thalamic (FST) circuits. Animal models suggest a pronounced effect on ventral ‘limbic' FST systems, although recent work in patients with psychosis and high-risk individuals suggests specific alterations of dorsal ‘associative' FST circuits. Here, we used functional magnetic resonance imaging to investigate the effects of a subanesthetic dose of ketamine on measures of functional connectivity as indexed by the temporal coherence of spontaneous neural activity in both dorsal and ventral FST circuits, as well as their symptom correlates. We adopted a placebo-controlled, double-blind, randomized, repeated-measures design in which 19 healthy participants received either an intravenous saline infusion or a racemic mixture of ketamine (100 ng/ml) separated by at least 1 week. Compared with placebo, ketamine increased functional connectivity between the dorsal caudate and both the thalamus and midbrain bilaterally. Ketamine additionally increased functional connectivity of the ventral striatum/nucleus accumbens and ventromedial prefrontal cortex. Both connectivity increases significantly correlated with the psychosis-like and dissociative symptoms under ketamine. Importantly, dorsal caudate connectivity with the ventrolateral thalamus and subthalamic nucleus showed inverse correlation with ketamine-induced symptomatology, pointing to a possible resilience role to disturbances in FST circuits. Although consistent with the role of FST in mediating psychosis, these findings contrast with previous research in clinical samples by suggesting that acute NMDAR antagonism may lead to psychosis-like experiences via a mechanism that is distinct from that implicated in frank psychotic illness

Editorial panel: Herbal medicine in Kenya: Evidence of safety and efficacy

(East African Medical Journal: 2002 79(7): 341-342