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The fish intestine is an important barrier for environmental toxicants, including metals and metal nanoparticles. Tracking chemical transformation at the interface between the intestinal epithelium and the intestinal lumen can inform us about chemicals' bio-reactivity and toxicity but is challenging due to the lack of appropriate models. To allow for such investigations, a model of the fish intestine derived from rainbow trout ( Oncorhynchus mykiss ), the RTgutGC cell line, was used. Cells were exposed to silver nitrate (AgNO 3 ) or citrate coated silver nanoparticles (cit-AgNPs) in Leibovitz's L-15 medium without amino acids and vitamins (L-15/ex), which allowed the determination of the extracellular silver species using a chemical equilibrium model. X-ray absorption spectroscopy (XAS) was used to track intracellular silver speciation. Cellular toxicity, silver accumulation, and metallothionein (MT) mRNA levels were also measured. Cells accumulated the same concentrations of silver when exposed to equimolar amounts ( i.e. 1, 5 and 10 μM) of AgNO 3 or cit-AgNPs. However, AgNO 3 was shown to be more toxic than cit-AgNPs. Intracellular silver speciation changed over time in both exposure series. After 1 hour, intracellular silver speciation was dominated by chloride complexation in both exposures. After 24 and 72 hours of exposure to cit-AgNPs, ∼7% of silver was complexed to cysteine, whereas the remaining silver was AgNPs. In cells exposed to AgNO 3 for 72 hours, 97% of Ag was complexed to cysteine. A significant increase, compared to controls, in metallothionein mRNA levels at 24 and 72 hours of exposure to AgNO 3 and cit-AgNPs can explain the formation of Ag–cysteine complexes. In summary, these data show that silver chloride species are bioavailable and that complexation to cysteine scavenges intracellular dissolved silver ions, thus preventing toxicity. Silver nanoparticles present a similar but attenuated toxic response to AgNO 3 . Thus, at least in acute exposures, existing risk assessment for dissolved silver species could be protective for nanosilver. 

Abstract Here we present a study on the quenchability of hydrous mafic melts. We show via hydrothermal experiments that the ability to quench a mafic hydrous melt to a homogeneous glass at cooling rates relevant to natural samples has a limit of no more than 9 ± 1 wt% of dissolved H2O in the melt. We performed supra-liquidus experiments on a mafic starting composition at 1–1.5 GPa spanning H2O-undersaturated to H2O-saturated conditions (from ~1 to ~21 wt%). After dissolving H2O and equilibrating, the hydrous mafic melt experiments were quenched. Quenching rates of 20 to 90 K/s at the glass transition temperature were achieved, and some experiments were allowed to decompress from thermal contraction while others were held at an isobaric condition during quench. We found that quenching of a hydrous melt to a homogeneous glass at quench rates comparable to natural conditions is possible at water contents up to 6 wt%. Melts containing 6–9 wt% of H2O are partially quenched to a glass, and always contain significant fractions of quench crystals and glass alteration/devitrification products. Experiments with water contents greater than 9 wt% have no optically clear glass after quench and result in fine-grained mixtures of alteration/devitrification products (minerals and amorphous materials). Our limit of 9 ± 1 wt% agrees well with the maximum of dissolved H2O contents found in natural glassy melt inclusions (8.5 wt% H2O). Other techniques for estimating pre-eruptive dissolved H2O content using petrologic and geochemical modeling have been used to argue that some arc magmas are as hydrous as 16 wt% H2O. Thus, our results raise the question of whether the observed record of glassy melt inclusions has an upper limit that is partially controlled by the quenching process. This potentially leads to underestimating the maximum amount of H2O recycled at arcs when results from glassy melt inclusions are predominantly used to estimate water fluxes from the mantle. 

Adsorption processes at mineral–water interfaces control the fate and transport of arsenic in soils and aquatic systems. Mechanistic and thermodynamic models to describe this phenomenon only consider inner-sphere complexes but recent observation of the simultaneous adsorption of inner- and outer-sphere arsenate on single crystal surfaces complicates this picture. In this study, we investigate the ionic strength-dependence of the macroscopic adsorption behavior and molecular-scale surface speciation of arsenate bound to gibbsite and bayerite. Arsenate adsorption decreases with increasing ionic strength on both minerals, with a larger effect at pH 4 than pH 7. The observed pH-dependence corresponds with a substantial decrease in surface charge at pH 7, as indicated by zeta-potential measurements. Extended X-ray absorption fine structure (EXAFS) spectroscopy finds that the number of second shell Al neighbors around arsenate is lower than that required for arsenate to occur solely as an inner-sphere surface complex. Together, these observations demonstrate that arsenate displays macroscopic and molecular-scale behavior consistent with the co-occurrence of inner- and outer-sphere surface complexes. This demonstrated that outer-sphere species can be responsible for strong adsorption of ions and suggests that environments experiencing an increase in salt content may induce arsenic release to water, especially under weakly acidic conditions.