Interactions of different arsenic species with thols: Chemical and biological implications

Arsenic has been classified as a group I carcinogen. It has been ranked number one in the CERCLA priority list of hazardous substances due to its frequency, toxicity and potential for human exposure. Paradoxically, arsenic has been employed as a successful chemotherapeutic agent for acute promyelocytic leukemia and has found some success in multiple myeloma. Since arsenic toxicity and efficacy is species dependent, a speciation method, based on the complementary use of reverse phase and cation exchange chromatography, was developed. Inductively coupled plasma mass spectrometer (ICP-MS), as an element specific detector, and electrospray ionization mass spectrometer (ESI-MS), as a molecule specific detector, were employed. Low detection limits in the µg. L−1 range on the ICP-MS and mg. L−1 range on the ESI-MS were obtained. The developed methods were validated against each other through the use of a Deming plot. With the developed speciation method, the effects of both pH on the stability of As species and reduced glutathione (GSH) concentration on the formation and stability of arsenic glutathione complexes were studied. To identify arsenicals in multiple myeloma (MM) cell lines post arsenic trioxide (ATO) and darinaparsin (DAR) incubation, an extraction method based on the use of ultrasonic probe was developed. Extraction tools and solvents were evaluated and the effect of GSH concentration on the quantitation of arsenic glutathione (As-GSH) complexes in MM cell extracts was studied. The developed method was employed for the identification of metabolites in DAR incubated cell lines where the effect of extraction pH, DAR incubation concentration and incubation time on the relative distribution of the As metabolites was assessed. A new arsenic species, dimethyarsinothioyl glutathione (DMMTA V-GS), a pentavalent thiolated arsenical, was identified in the cell extracts through the use of liquid chromatography tandem mass spectrometry. The formation of the new metabolite in the extracts was dependent on the decomposition of s-dimethylarsino glutathione (DMA(GS)). These results have major implications in both the medical and toxicological fields of As because they involve the metabolism of a chemotherapeutic agent and the role sulfur compounds play in this mechanism.

Interactions between nutrient availability and hydroperiod shape macroinvertebrate communities in Florida Everglades marshes

Hydroperiod and nutrient status are known to influence aquatic communities in wetlands, but their joint effects are not well explored. I sampled floating periphyton mat and flocculent detritus (floc) infaunal communities using 6-cm diameter cores at short- and long-hydroperiod and constantly inundated sites across a range of phosphorus (P) availability (total phosphorus in soil, floc and periphyton). Differences in community structure between periphyton and floc microhabitats were greater than any variation attributable to hydroperiod, P availability, or other spatial factors. Multivariate analyses indicated community structure of benthic-floc infauna was driven by hydroperiod, although crowding (no. g−1 AFDM) of individual taxa showed no consistent responses to hydroperiod or P availability. In contrast, community structure of periphyton mat infauna was driven by P availability, while densities of mat infauna (no. m−2) were most influenced by hydroperiod (+correlations). Crowding of mat infauna increased significantly with P availability in short-hydroperiod marshes, but was constant across the P gradient in long-hydroperiod marshes. Increased abundance of floating-periphyton mat infauna with P availability at short-hydroperiod sites may result from a release from predation by small fish. Community structure and density were not different between long-hydroperiod and constantly inundated sites. These results have implications for the use of macroinvertebrates as indicators of water quality in wetlands and suggest the substrate sampled can influence interpretation of ecological responses observed in these communities.

Indirect and direct controls of macroinvertebrates and small fish by abiotic factors and trophic interactions in the Florida Everglades

1. The roles of nutrients, disturbance and predation in regulating consumer densities have long been of interest, but their indirect effects have rarely been quantified in wetland ecosystems. The Florida Everglades contains gradients of hydrological disturbance (marsh drying) and nutrient enrichment (phosphorus), often correlated with densities of macroinvertebrate infauna (macroinvertebrates inhabiting periphyton), small fish and larger invertebrates, such as snails, grass shrimp, insects and crayfish. However, most causal relationships have yet to be quantified. 2.  We sampled periphyton (content and community structure) and consumer (small omnivores, carnivores and herbivores, and infaunal macroinvertebrates inhabiting periphyton) density at 28 sites spanning a range of hydrological and nutrient conditions and compared our data to seven a priori structural equation models. 3.  The best model included bottom-up and top-down effects among trophic groups and supported top-down control of infauna by omnivores and predators that cascaded to periphyton biomass. The next best model included bottom-up paths only and allowed direct effects of periphyton on omnivore density. Both models suggested a positive relationship between small herbivores and small omnivores, indicating that predation was unable to limit herbivore numbers. Total effects of time following flooding were negative for all three consumer groups even when both preferred models suggested positive direct effects for some groups. Total effects of nutrient levels (phosphorus) were positive for consumers and generally larger than those of hydrological disturbance and were mediated by changes in periphyton content. 4.  Our findings provide quantitative support for indirect effects of nutrient enrichment on consumers, and the importance of both algal community structure and periphyton biomass to Everglades food webs. Evidence for top-down control of infauna by omnivores was noted, though without substantially greater support than a competing bottom-up-only model.

Experimental deuteron momentum distributions with reduced final state interactions

This dissertation presents a study of the D( e, e′p)n reaction carried out at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) for a set of fixed values of four-momentum transfer Q 2 = 2.1 and 0.8 (GeV/c)2 and for missing momenta pm ranging from pm = 0.03 to pm = 0.65 GeV/c. The analysis resulted in the determination of absolute D(e,e′ p)n cross sections as a function of the recoiling neutron momentum and it's scattering angle with respect to the momentum transfer [vector] q. The angular distribution was compared to various modern theoretical predictions that also included final state interactions. The data confirmed the theoretical prediction of a strong anisotropy of final state interaction contributions at Q2 of 2.1 (GeV/c)2 while at the lower Q2 value, the anisotropy was much less pronounced. At Q2 of 0.8 (GeV/c)2, theories show a large disagreement with the experimental results. The experimental momentum distribution of the bound proton inside the deuteron has been determined for the first time at a set of fixed neutron recoil angles. The momentum distribution is directly related to the ground state wave function of the deuteron in momentum space. The high momentum part of this wave function plays a crucial role in understanding the short-range part of the nucleon-nucleon force. At Q2 = 2.1 (GeV/c)2, the momentum distribution determined at small neutron recoil angles is much less affected by FSI compared to a recoil angle of 75°. In contrast, at Q2 = 0.8 (GeV/c)2 there seems to be no region with reduced FSI for larger missing momenta. Besides the statistical errors, systematic errors of about 5–6 % were included in the final results in order to account for normalization uncertainties and uncertainties in the determi- nation of kinematic veriables. The measurements were carried out using an electron beam energy of 2.8 and 4.7 GeV with beam currents between 10 to 100 &mgr; A. The scattered electrons and the ejected protons originated from a 15cm long liquid deuterium target, and were detected in conicidence with the two high resolution spectrometers of Hall A at Jefferson Lab.^