Aging of TiO2 Nanoparticles Transiently Increases Their Toxicity to the Pelagic Microcrustacean Daphnia magna

During their aquatic life cycle, nanoparticles are subject to environmentally driven surface modifications (e.g. agglomeration or coating) associated with aging. Although the ecotoxicological potential of nanoparticles might be affected by these processes, only limited information about the potential impact of aging is available. In this context, the present study investigated acute (96 h) and chronic (21 d) implications of systematically aged titanium dioxide nanoparticles (nTiO₂; ~90 nm) on the standard test species Daphnia magna by following the respective test guidelines. The nTiO₂ were aged for 0, 1, 3 and 6 d in media with varying ionic strengths (Milli-Q water: approx. 0.00 mmol/L and ASTM: 9.25 mmol/L) in the presence or absence of natural organic matter (NOM). Irrespective of the other parameters, aging in Milli-Q did not change the acute toxicity relative to an unaged control. In contrast, 6 d aged nTiO₂ in ASTM without NOM caused a fourfold decreased acute toxicity. Relative to the 0 d aged particles, nTiO₂ aged for 1 and 3 d in ASTM with NOM, which is the most environmentally-relevant setup used here, significantly increased acute toxicity (by approximately 30%), while a toxicity reduction (60%) was observed for 6 d aged nTiO₂. Comparable patterns were observed during the chronic experiments. A likely explanation for this phenomenon is that the aging of nTiO₂ increases the particle size at the start of the experiment or the time of the water exchange from <100 nm to approximately 500 nm, which is the optimal size range to be taken up by filter feeding D. magna. If subjected to further agglomeration, larger nTiO₂ particles, however, cannot be retained by the daphnids’ filter apparatus ultimately reducing their ecotoxicological potential. This non-linear pattern of increasing and decreasing nTiO₂ related toxicity over the aging duration, highlights the knowledge gap regarding the underlying mechanisms and processes. This understanding seems, however, fundamental to predict the risks of nanoparticles in the field.     

Molecular Characterization of Cryptosporidium spp. among Children in Rural Ghana

BackgroundThe relevance of Cryptosporidium infections for the burden of childhood diarrhoea in endemic settings has been shown in recent years. This study describes Cryptosporidium subtypes among symptomatic and asymptomatic children in rural Ghana to analyse subtype-specific demographic, geographical, seasonal and clinical differences in order to inform appropriate control measures in endemic areas.Conclusions/SignificanceCryptosporidiosis is characterized by seasonal anthroponotic transmission of strains typically found in Sub-Saharan Africa. The infection mainly affects young infants, with vomiting and diarrhoea being one of the leading symptoms in C. parvum infection. Combining molecular typing and clinical data provides valuable information for physicians and is able to track sources of infections.     

Release of molybdenum co-factor from nitrate reductase and xanthine oxidase by heat treatment

Heat treatment (90 sec at 70°) is shown to convert the bound molybdenum co-factor of tobacco cell-free extracts and bovine milk xanthine oxidase into a form capable of complementing the Neurospora crassa mutant nit-1.In the presence of 1 mM ascorbic acid, 25 mM molybdate and, for plant extracts, sulphydryl group protecting agents, the molybdenum co-factor can survive incubations up to 100° whilst maintaining its biological activity. Especially with plant extracts, the efficiency of heat treatment is considerably higher than that of the acidification procedure which is often utilized for releasing molybdenum co-factor.     

A quick method for the determination of dissolved and precipitated sulfides in cultures of sulfate-reducing bacteria

Dissolved sulfide was determined spectrophotometrically as a colloidal solution of copper sulfide. Calibration curves were linear. Maximal deviation error was below 5%. Sulfide precipitated as FeS was determined after acidification of the medium.