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Fullerene research in biological systems has been hindered by the compound's relative insolubility in water. However, C60 molecules can be made to aggregate, forming stable fullerene water suspensions (FWS) whose properties differ from those of bulk solid C60. There are many different protocols for making FWS. This paper explores four of these methods and establishes the antibacterial activity of each resulting suspension, including a suspension made without intermediary solvents. The aggregates in each polydisperse suspension were separated by size using differential centrifugation and tested for antibacterial activity using Bacillus subtilis as a test organism. All suspensions exhibited relatively strong antibacterial activity. Fractions containing smaller aggregates had greater antibacterial activity, although the increase in toxicity was disproportionately higher than the associated increase in putative surface area. This suggests the need for improved understanding of the behavior of FWS towards organisms and in the environment to determine how C60 can be safely used and disposed.

Previous work has shown that microbial communities in As-mobilizing sediments from West Bengal were dominated by Geobacter species. Thus, the potential of Geobacter sulfurreducens to mobilize arsenic via direct enzymatic reduction and indirect mechanisms linked to Fe(III) reduction was analyzed. G. sulfurreducens was unable to conserve energy for growth via the dissimilatory reduction of As(V), although it was able to grow in medium containing fumarate as the terminal electron acceptor in the presence of 500 M As(V). There was also no evidence of As(III) in culture supernatants, suggesting that resistance to 500 M As(V) was not mediated by a classical arsenic resistance operon, which would rely on the intracellular reduction of As(V) and the efflux of As(III). When the cells were grown using soluble Fe(III) as an electron acceptor in the presence of As(V), the Fe(II)-bearing mineral vivianite was formed. This was accompanied by the removal of As, predominantly as As(V), from solution. Biogenic siderite (ferrous carbonate) was also able to remove As from solution. When the organism was grown using insoluble ferrihydrite as an electron acceptor, Fe(III) reduction resulted in the formation of magnetite, again accompanied by the nearly quantitative sorption of As(V). These results demonstrate that G. sulfurreducens, a model Fe(III)-reducing bacterium, did not reduce As(V) enzymatically, despite the apparent genetic potential to mediate this transformation. However, the reduction of Fe(III) led to the formation of Fe(II)-bearing phases that are able to capture arsenic species and could act as sinks for arsenic in sediments.The mobilization of arsenic from sediments to drinking water constitutes a major toxic hazard to millions in Bangladesh and West Bengal. A number of mechanisms have been proposed for the release of arsenic into the groundwater in Bengal shallow alluvial sedimentary aquifers (1,3,8,11,12,18,21,(33)(34)(35)39), including the oxidation of arsenic-rich pyrite in aquifer sediments, driven by lowering of the water level by abstraction, and then penetration of the aquifer by oxygen (8,11,12), or the reductive dissolution of arsenic-rich iron-oxyhydroxides, driven by the microbial consumption of sedimentary organic matter in anoxic groundwater (33,34,39). The latter mechanism has received recent support as the dominant mechanism for groundwater arsenic contamination (3,20,21,39).In a recent microcosm-based study (21), we provided the first direct evidence of the role of indigenous metal-reducing bacteria in the formation of toxic, mobile As(III) in sediment from the Ganges Delta. The study showed that addition of acetate to anaerobic sediments, as a proxy for organic matter and a potential electron donor for metal reduction, resulted in stimulation of the microbial reduction of Fe(III), followed by As(V) reduction and release of As(III). Culture-dependent techniques confirmed a role for Fe(III)-reducing bacteria in As release, while PCR studies showed that the microbial communities in these sediments were ...

TiO2, SiO2 and ZnO are common additives with improved applications at the nanoscale. The antibacterial activity of TiO2, which has important ecosystem health implications, is well understood. However, less attention has been paid to the antibacterial activity of SiO2 and ZnO despite them also producing reactive oxygen species. This paper explores the relative toxicity of TiO2, SiO2 and ZnO water suspensions towards bacteria (B. subtilis, E. coli) and the eukaryotic Daphnia magna. These three photosensitive nanomaterials were hazardous to all test organisms, with toxicity increasing with particle concentration. Toxicity of the three compounds decreased from ZnO to TiO2 to SiO2 and Daphnia were most susceptible to their effects. Nominal particle size did not affect the toxicity of these compounds. Antibacterial activity was noted under both dark and light conditions indicating that mechanisms additional to ROS production were responsible for growth inhibition. These results highlight the need for caution during the use and disposal of such manufactured nanomaterials to prevent unintended environmental impacts, as well as the importance of further research on the mechanisms and factors that increase toxicity to enhance risk management.

The disappearance of selected tetracycline resistance genes was investigated in different simulated receiving waters to determine conditions that maximize resistance gene loss after release. Wastewater from an operating cattle feedlot lagoon was provided to four pairs of duplicate 3-L flasks, and tet(O), tet(W), tet(M), tet(Q), and 16S rRNA gene levels were monitored over 29 days using real-time PCR. Treatments included simulated sunlight with 0, 25, and 250 microg L(-1) nominal oxytetracycline (OTC) levels, respectively, and 'dark' conditions. Gene disappearance rates were always highest when light was present, regardless of OTC level. First-order loss coefficients (k(d)) for the sum of resistance genes were 0.84, 0.75, and 0.81 day(-1) for 0.0, 25, and 250 microg L(-1) OTC treatments over the first 7 days after release, respectively, whereas k(d) was 0.49 day(-1) under dark conditions, which is significantly lower (P<0.10). k(d) varied fourfold among the four individual genes, although disappearance patterns were similar among genes. Results suggest that light exposure should be maximized in receiving waters in order to maximize resistance gene loss rate after release.