Fundamental Studies of Humic Acid\u27s Influence on Pollutant Toxicity to Aquatic Organisms

The main purpose of the research presented in this dissertation was to further understand the intricate and convoluted interactions between natural organic material, biological entities, and pollutants. This was achieved by utilizing humic acids (HAs) from differing sources, chemically modified humic acid, two biological entities (model biomembranes and Artemia Franciscana), and three types of pollutants (cations, surfactants, and carbon nanotubes). Fluorescence spectroscopy and model biomembranes were used to measure the change in HA’s ability to interact with the biomembranes in the presence of cations. Three differently sourced HAs, chemical modified HAs, and a range of cations were studied to elucidate specific interactions that can occur in the environment. It was determined that the cations limited the ability of humic acids to interact with the biomembranes, which was attributed to humic acid conformation changes in the presence of cations, and the protection capacity increased as the softness of the cation increased. Artemia Franciscana (Artemia) was utilized as an analytic tool to determine the changes in toxicity of surfactants in the presence of humic acid. Artemia were exposed to three different surfactants, Triton X-100 (Tx-100), cetylpyridinium chloride (CPC), and sodium dodecyl sulfide (SDS), for both hatching studies and in vivo 31P NMR. It was determined by hatching assays that Tx-100 caused mortality after hatching while CPC and SDS inhibited hatching. 31P NMR corroborated these findings by showing an increase in phosphodiester bonds in saline water and in the Tx-100 exposure while there was no increase in the presence of the other two surfactants. HAs from three different sources were added to the surfactant exposures which showed that HAs played a mediation role in terms of toxicity and the extent of mediation was dependent on the type of HA and surfactant. Artemia was also utilized to measure the toxicity of carbon nanotubes under a variety of conditions. Both single-walled and multi-walled carbon nanotubes that were either in the presence of humic acid or had been sonicated were studied. Overall, there was no significant carbon nanotube toxicity to the Artemia

Risk of COVID-19 after natural infection or vaccinationResearch in context

Summary: Background: While vaccines have established utility against COVID-19, phase 3 efficacy studies have generally not comprehensively evaluated protection provided by previous infection or hybrid immunity (previous infection plus vaccination). Individual patient data from US government-supported harmonized vaccine trials provide an unprecedented sample population to address this issue. We characterized the protective efficacy of previous SARS-CoV-2 infection and hybrid immunity against COVID-19 early in the pandemic over three-to six-month follow-up and compared with vaccine-associated protection. Methods: In this post-hoc cross-protocol analysis of the Moderna, AstraZeneca, Janssen, and Novavax COVID-19 vaccine clinical trials, we allocated participants into four groups based on previous-infection status at enrolment and treatment: no previous infection/placebo; previous infection/placebo; no previous infection/vaccine; and previous infection/vaccine. The main outcome was RT-PCR-confirmed COVID-19 >7–15 days (per original protocols) after final study injection. We calculated crude and adjusted efficacy measures. Findings: Previous infection/placebo participants had a 92% decreased risk of future COVID-19 compared to no previous infection/placebo participants (overall hazard ratio [HR] ratio: 0.08; 95% CI: 0.05–0.13). Among single-dose Janssen participants, hybrid immunity conferred greater protection than vaccine alone (HR: 0.03; 95% CI: 0.01–0.10). Too few infections were observed to draw statistical inferences comparing hybrid immunity to vaccine alone for other trials. Vaccination, previous infection, and hybrid immunity all provided near-complete protection against severe disease. Interpretation: Previous infection, any hybrid immunity, and two-dose vaccination all provided substantial protection against symptomatic and severe COVID-19 through the early Delta period. Thus, as a surrogate for natural infection, vaccination remains the safest approach to protection. Funding: National Institutes of Health