Transcriptome sequencing (RNA-seq) analysis of the effects of metal nanoparticle exposure on the transcriptome of Chlamydomonas reinhardtii.

The widespread use of nanoparticles (NPs) raises concern over their potential toxicological effects in humans and ecosystems. Here we used transcriptome sequencing (RNA-seq) to evaluate the effects of exposure to four different metal-based NPs, nano-Ag (nAg), nano-TiO2 (nTiO2), nano-ZnO (nZnO), and CdTe/CdS quantum dots (QDs), in the eukaryotic green alga Chlamydomonas reinhardtii. The transcriptome was characterized before and after exposure to each NP type. Specific toxicological effects were inferred from the functions of genes whose transcripts either increased or decreased. Data analysis resulted in important differences and also similarities among the NPs. Elevated levels of transcripts of several marker genes for stress were observed, suggesting that only nZnO caused nonspecific global stress to the cells under environmentally relevant conditions. Genes with photosynthesis-related functions were decreased drastically during exposure to nTiO2 and slightly during exposures to the other NP types. This pattern suggests either toxicological effects in the chloroplast or effects that mimic a transition from low to high light. nAg exposure dramatically elevated the levels of transcripts encoding known or predicted components of the cell wall and the flagella, suggesting that it damages structures exposed to the external milieu. Exposures to nTiO2, nZnO, and QDs elevated the levels of transcripts encoding subunits of the proteasome, suggesting proteasome inhibition, a phenomenon believed to underlie the development and progression of several major diseases, including Alzheimer's disease, and used in chemotherapy against multiple myeloma.

Evaluation of a titanium dioxide-based DGT technique for measuring inorganic uranium species in fresh and marine waters.

A new diffusive gradients in a thin film (DGT) technique for measuring dissolved uranium (U) in freshwater is reported. The new method utilises a previously described binding phase, Metsorb (a titanium dioxide based adsorbent). This binding phase was evaluated and compared to the well-established Chelex-DGT method. Batch experiments showed quantitative uptake (100±3%) of dissolved U by Metsorb and an elution efficiency of 95% was obtained using a mixed eluent of 1 mol L(-1) NaOH/1 mol L(-1) H(2)O(2). The mass of U accumulated by Metsorb was linear (R(2)≥0.98) with time across the pH range 3.0-8.1, validating the DGT measurement. The measured effective diffusion coefficients were highly dependent on pH, ranging from 2.74-4.81×10(-6)cm(2)s(-1), which were in reasonable agreement with values from the literature. Ionic strength showed no effect on the uptake of U, and thereby on diffusion coefficients, at NaNO(3) concentrations ≤0.01 mol L(-1), but caused the U concentration to be underestimated by 18% and 24% at 0.1 mol L(-1) NaNO(3) and 0.7 mol L(-1) NaNO(3), respectively. Deployment of Metsorb-DGT in synthetic freshwater resulted in reliable measurement of the dissolved U concentration (C(DGT)/C(Sol)=1.05), whereas Chelex-DGT significantly underestimated the dissolved U concentration (C(DGT)/C(Sol)=0.76). Metsorb-DGT was found to give reliable results after 8h deployments in synthetic seawater but experienced competition effects with longer deployments. The Chelex-DGT was unable to measure U at all in synthetic seawater. A field deployment in a freshwater stream (Coomera River) confirmed the utility of the Metsorb-DGT method for measuring U in natural freshwaters, but performance of field deployments may require further evaluation due to the possibility of major changes in uranium speciation with pH and water composition. We recommend a filtered sample, of any water in which DGT measurements are to be made, be used to determine the appropriate diffusion coefficient under controlled laboratory conditions.

Influence of sediment metal spiking procedures on copper bioavailability and toxicity in the estuarine bivalve Indoaustriella lamprelli.

The effect of three methods for spiking sediments with Cu on the reburial behavior, mortality, and tissue Cu accumulation of a lucinid bivalve (Indoaustriella lamprelli) and the influence of the bivalve on the sediment geochemistry were investigated. Methods used to create Cu concentration gradients were direct spiking with and without pH adjustment to pH 7 and also dilution of sediment, previously spiked with Cu and adjusted to pH 7, using a low-Cu sediment (known to produce the lowest pore-water Cu concentrations). The presence of the bivalve within Cu-spiked sediment increased the flux of Cu and Mn to overlying waters at high Cu concentrations (550 microg/g). Bivalve behavioral response, metal accumulation, and mortality varied with the method by which Cu was spiked. In direct Cu-spiked sediment, the bivalves were inactive at concentrations of 550 and 1,100 microg/g, with mortality induced in sediment spiked with 1,100 microg/g (pH 6.5-7.1). Complete bivalve inactivity was observed only at 1,100 microg/g in direct Cu-spiked sediment with pH adjustment, whereas percentage reburial was reduced to 30% at 1,100 microg/g for sediment prepared by the dilution method. Relative reburial rates in the three spiked sediment types (direct << direct pH-7 < dilution) were proportional to dissolved Cu concentrations in the overlying water. Bivalve reburial, in addition to the method of Cu addition, affected tissue Cu accumulation. Inhibition of bivalve reburial decreased the amount of accumulated Cu, confounding relationships between tissue Cu and pore water, overlying water, or extractable metal fractions.

The influence of small-scale circum-neutral pH change on Cu-bioavailability and toxicity to an estuarine bivalve (Austriella cf plicifera) in whole-sediment toxicity tests.

In whole-sediment toxicity tests employing metal-spiked sediment, pH is a crucial determinant of sediment geochemistry, sediment-porewater metal partitioning and metal bioavailability to benthic organisms. Small pH changes in metal-spiked sediment may therefore have important implications for toxicity to organisms. The present study evaluated the effect of small-scale pH changes (pH 6.6, 7.2, 7.6) in Cu-spiked sediment on metal bioavailability and subsequent organism response. Variation of pH produced distinct changes in sediment geochemistry. Increasing pH from 6.6 to 7.6 resulted in lower redox potential, greater acid volatile sulfide (AVS) formation, and lower partitioning of Cu, Fe and Mn to the porewater. The minor pH changes and associated variation in sediment geochemistry modified reburial rates and copper accumulation by the bivalve, Austriella cf plicifera. Bivalve reburial was slowest for the 1400 microg g(-1) Cu-spiked pH 6.6 sediment, in which porewater copper concentrations exceeded 50 microg L(-1). Bivalve reburial was higher for pH 7.2 Cu-spiked sediments at all concentrations of copper investigated than in pH 6.6 and 7.6 sediments, where reburial rates were similar. Higher levels of bivalve activity suggest that A. cf plicifera may have an optimal pH range in the vicinity of pH 7.2. Tissue Cu concentrations varied with pH and appear dependent on spiked Cu concentration and organism activity. Strong linear correlations of tissue Cu concentration with all three Cu phases (overlying water, porewater and particulate phases), however, limited the ability to accurately determine the source of Cu uptake.

Cu and Zn concentration gradients created by dilution of pH neutral metal-spiked marine sediment: a comparison of sediment geochemistry with direct methods of metal addition.

The geochemistry of artificially metal contaminated sediments prepared using three methods of metal-spiking was compared in this study. Marine sediments with a gradient of Cu and Zn concentrations were prepared by direct-spiking without and with pH-adjustment to pH 7, and also by serial dilution of direct-spiked sediment (4000 microg g(-1), pH 7 adjusted) with uncontaminated sediment. Porewater concentrations of Cu, Zn, Fe, and Mn in direct-spiked sediments without pH adjustment were orders of magnitude higher than the equivalent sediments adjusted to pH 7 or those prepared by the serial dilution method. Despite pH-adjustment, porewater Cu and Zn concentrations of direct-spiked sediment remained higher than concentrations observed within metal-contaminated natural sediment. The serial dilution of metal-spiked, pH-adjusted sediment substantially decreased Cu and Zn partitioning to the dissolved phase, and minimized the variation of potential competitive ions (H+, Fe2+, Mn2+) over the entire gradient of spiked Cu and Zn concentrations. Metal concentration gradients created using serial dilution of Cu- and Zn-spiked, pH-adjusted sediments produced porewater Cu or Zn, Fe, and Mn concentrations that resemble sediment-porewater partitioning (Cu, Zn, Fe, Mn) typical of metal-contaminated natural sediments. This method is recommended for whole-sediment toxicology studies.

The effect of manipulating sediment pH on the porewater chemistry of copper- and zinc-spiked sediments.

Spiking of sediment with metal cations that readily hydrolyse causes the sediment pH to decrease. Displaced iron and manganese also oxidise and hydrolyse, further lowering sediment pH. The lower pH of metal-spiked sediments requires a subsequent sediment neutralisation. This research compared the pH adjustment of Cu- and Zn-spiked sediments using single and multiple additions of 1M NaOH. Sediment pH, redox potential, and porewater metal concentrations were monitored over 40 days. Depth profiles were also measured to investigate stratification. A single pH adjustment to pH 7 and 8 initially counteracted the pH change caused by metal additions, however, pH continued to decrease slowly thereafter. Multiple pH adjustments diminished porewater Cu, Zn and Fe concentrations to a greater extent than a single pH adjustment, but the ongoing oxidative precipitation of porewater metals continued to consume OH(-) ions and impede pH maintenance. Displacement of high iron(II) concentrations and the opposing rates of iron(II) oxidative precipitation and bacterially-mediated iron(II) production, affected the partitioning of the added metals between the sediment and pore water. Despite similar pH over the spiked-metal concentration gradient following pH adjustment, sediments spiked with higher metal concentrations produced lower porewater Fe concentrations, possibly due to toxicity to iron(III) oxyhydroxide reducing bacteria. Distinct stratification of redox potential and dissolved Fe and Cu developed over a depth of 6cm during the 40-day equilibration period. Recommendations are provided on methods for preparing metal-spiked sediments in which the partitioning of metals between dissolved and particulate phases better resembles that of in situ (field) metal-contaminated sediments.

Dopamine receptor genes and migraine with and without aura: an association study.

OBJECTIVE: To investigate the role of the dopamine receptor genes, DRD1, DRD3, and DRD5 in the pathogenesis of migraine. BACKGROUND: Migraine is a chronic debilitating disorder affecting approximately 12% of the white population. The disease shows strong familial aggregation and presumably has a genetic basis, but at present, the type and number of genes involved is unclear. The study of candidate genes can prove useful in the identification of genes involved in complex diseases such as migraine, especially if the contribution of the gene to phenotypic expression is minor. Genes coding for proteins involved in dopamine metabolism have been implicated in a number of neurologic conditions and may play a contributory role in migraine. Hence, genes that code for enzymes and receptors modulating dopaminergic activity are good candidates for investigation of the molecular genetic basis of migraine. METHODS: We tested 275 migraineurs and 275 age- and sex-matched individuals free of migraine. Genotypic results were determined by restriction endonuclease digestion of polymerase chain reaction products to detect DRD1 and DRD3 alleles and by Genescan analysis after polymerase chain reaction using fluorescently labelled oligonucleotide primers for the DRD5 marker. RESULTS: Results of chi-square statistical analyses indicated that the allele distribution for migraine cases compared to controls was not significantly different for any of the three tested gene markers (chi2 = 0.1, P =.74 for DRD1; chi2 = 1.8, P =.18 for DRD3; and chi2 = 20.3, P =.08 for DRD5). CONCLUSIONS: These findings offer no evidence for allelic association between the tested dopamine receptor gene polymorphisms and the more prevalent forms of migraine and, therefore, do not support a role for these genes in the pathogenesis of the disorder.