Novel zeolites continue to be synthesized using organic structure directing agents in combination with unconventional choices of inorganic conditions. The latter include synthesis in concentrated ...fluoride media, synthesis in concentrated hydroxide media, synthesis in the presence of germanium, and synthesis with high concentrations of boron. Post-synthetic treatments of germanosilicates with the ADOR method have resulted in fully intact zeolites that cannot be obtained through direct synthesis. Unusual compositions of known frameworks have been obtained through topotactic condensation of layered precursors. Coupled with the appropriate choice of inorganic conditions, the use of new SDA molecules has also produced materials with known frameworks but with amazingly small crystal dimensions that are less than 10 nm. The preparations of once "exotic" materials are now being performed with commercially available or easily prepared organic structure directing agents. In some instances methods have been found to prepare high-silica zeolites from seeded preparations in the absence of an organocation. Methods to target zeolite catalysts for a particular reaction have been realized by identifying structure directing agent molecules that are a mimic of the transition state of the reaction.
The hypothesis that ‘microplastic will transfer hazardous hydrophobic organic chemicals (HOC) to marine animals’ has been central to the perceived hazard and risk of plastic in the marine ...environment. The hypothesis is often cited and has gained momentum, turning it into paradigm status. We provide a critical evaluation of the scientific literature regarding this hypothesis. Using new calculations based on published studies, we explain the sometimes contrasting views and unify them in one interpretive framework. One explanation for the contrasting views among studies is that they test different hypotheses. When reframed in the context of the above hypothesis, the available data become consistent. We show that HOC microplastic-water partitioning can be assumed to be at equilibrium for most microplastic residing in the oceans. We calculate the fraction of total HOC sorbed by plastics to be small compared to that sorbed by other media in the ocean. We further demonstrate consistency among (a) measured HOC transfer from microplastic to organisms in the laboratory, (b) measured HOC desorption rates for polymers in artificial gut fluids (c) simulations by plastic-inclusive bioaccumulation models and (d) HOC desorption rates for polymers inferred from first principles. We conclude that overall the flux of HOCs bioaccumulated from natural prey overwhelms the flux from ingested microplastic for most habitats, which implies that microplastic ingestion is not likely to increase the exposure to and thus risks of HOCs in the marine environment.
In Memorium: Calvin (Herb) Ward Wenning, Richard J.; Burton, G. Allen
Environmental toxicology and chemistry,
July 2024, Letnik:
43, Številka:
7
Journal Article
Animal and human studies indicate that electrical stimulation of dorsal root ganglion (DRG) neurons may modulate neuropathic pain signals. ACCURATE, a pivotal, prospective, multicenter, randomized ...comparative effectiveness trial, was conducted in 152 subjects diagnosed with complex regional pain syndrome or causalgia in the lower extremities. Subjects received neurostimulation of the DRG or dorsal column (spinal cord stimulation, SCS). The primary end point was a composite of safety and efficacy at 3 months, and subjects were assessed through 12 months for long-term outcomes and adverse events. The predefined primary composite end point of treatment success was met for subjects with a permanent implant who reported 50% or greater decrease in visual analog scale score from preimplant baseline and who did not report any stimulation-related neurological deficits. No subjects reported stimulation-related neurological deficits. The percentage of subjects receiving ≥50% pain relief and treatment success was greater in the DRG arm (81.2%) than in the SCS arm (55.7%, P < 0.001) at 3 months. Device-related and serious adverse events were not different between the 2 groups. Dorsal root ganglion stimulation also demonstrated greater improvements in quality of life and psychological disposition. Finally, subjects using DRG stimulation reported less postural variation in paresthesia (P < 0.001) and reduced extraneous stimulation in nonpainful areas (P = 0.014), indicating DRG stimulation provided more targeted therapy to painful parts of the lower extremities. As the largest prospective, randomized comparative effectiveness trial to date, the results show that DRG stimulation provided a higher rate of treatment success with less postural variation in paresthesia intensity compared to SCS.
Sediment quality guidelines vary wildly across nations. The approaches to derive these guidelines range from crude percentile rankings of total concentrations of single chemicals to theoretical ...approaches that are driven by biological available effect levels. This results in a range of orders of magnitude for “safe” or threshold levels by chemical. Even the more scientifically advanced approaches using theoretical approaches are problematic in that they do not consider chemical mixtures, alternate routes of exposure, and other ligands that limit bioavailability. In the end, all that matters is that desirable resident biota are protected and with no significant ecological impacts. Complicating this determination is the role of habitat, flow, sedimentation, and nutrients—all of which are common in human-dominated waterways. A possible effective way forward is to consider the common, relevant stressors that may influence biotic communities associated with sediments. This approach would consider relevant sensitive species in terms of their ecological context and dominant exposure pathway (considering habitat, overlying water, sediment, periphyton, and hyporheos). In addition, the sum of water column (and pore water) and sediment probable effect concentration vs probable no effect concentrations ratios would be summed and considered for mixtures. Since this non-scientific mixture effect assessment may be overly conservative, in situ caged toxicity tests with benthic and water column organisms exposed to sediments, pore waters, and overlying water would be conducted for field validations along with comparisons of indigenous biota to BioCriteria.
Communities of zooplankton, a critical portion of aquatic ecosystems, can be adversely affected by contamination resulting from human activities. Understanding the influence of environmental change ...on zooplankton communities under field-conditions is hindered by traditional labor-intensive approaches that are prone to taxonomic and enumeration mistakes. Here, metabarcoding of cytochrome c oxidase I (COI) region of mitochondrial DNA was used to characterize the genetic diversity of zooplankton. The species composition of zooplankton communities determined by metabarcoding was consistent with the results based on the traditional morphological approach. The spatial distribution of common species (frequency of occurrence >10 samples) by metabarcoding exhibited good agreement with morphological data. Furthermore, metabarcoding can clearly distinguish the composition of the zooplankton community between lake and river ecosystems. In general, rotifers were more abundant in riverine environments than lakes and reservoirs. Finally, the sequence read number of different taxonomic groups using metabarcoding was positively correlated with the zooplankton biomass inferred by density and body length of zooplankton. Overall, the utility of metabarcoding for taxonomic profiling of zooplankton communities was validated by the morphology-based method on a large ecological scale. Metabarcoding of COI could be a powerful and efficient biomonitoring tool to protect local aquatic ecosystems.
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