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By reducing immune function, trace metal deficiencies may substantially contribute to the global burden of diarrhea, pneumonia, and malaria. Human activities may be contributing to trace metal deficiency in soils and plants by exacerbating the preponderance of cereals and cash crops that reduce food diversity and micronutrient intake. Adaptive strategies are needed to reverse these trends. Anthropogenic activities have led to increased toxic metal exposure, and effects on human hosts need clarification. Metal toxicities can also impair the immune system and hence increase the susceptibility to infectious pathogens. Climate change affects metal speciation and the build-up of trace elements in the human food chain, with as yet unknown outcomes on infectious disease. Food processing and the use of metallic nanomaterials can alter human exposure to metals in ways that can influence the host–pathogen competition for metals. The effects of metals on human health may also be mediated through modification of the epigenome, conferring drug resistance on pathogenic bacteria and enhancing/ reducing human tolerance to infectious parasites. The emerging metals cerium, gadolinium, lanthanum, and yttrium constitute another driver of change in metal exposure and may potentially modulate the immune system with unknown consequences for human health.

Interest in processes at the nexus of host–microbe–metal interactions has risen as a result of advancements in the study of metallomics, proteomics, and genomics. These emerging fields have given rise to new developments in powerful analytical methods and technology for studying the identity, distribution, quantity, trafficking, fate, and effects of trace metals in biological systems. Applications of these advanced techniques to the study of metabolic cycles are yielding results and have placed scientists at the threshold of major paradigm shifts in our understanding of the relationships between homeostatic mechanisms of trace metals and pathogenesis of infectious diseases. Fields present at this Forum included chemistry, biology/biochemistry, toxicology, nutrition, immunology, microbiology, epidemiology, environmental and occupational health, as well as environmental and veterinary medicine. Participants were tasked with using their knowledge to discuss how the metabolic cycles of trace metals relate to the pathogenesis of disease during infection. The stimulating dialog that ensued covered a wide range of views, insights, and perspectives on current knowledge and raised important open questions that should be addressed by future research initiatives.

Trace metals are required in small quantities for a wide array of metabolic functions in the body. In terms of obesity, they can enhance insulin action through activating insulin receptor sites, serve as cofactors or components for enzyme systems involved in glucose metabolism, increase insulin sensitivity, and act as antioxidants to prevent tissue oxidation. Chronic hyperglycemia causes significant alterations in the status of many trace metals in the body and consequently increases the oxidative stress which can contribute to the pathogenesis of infectious diseases. Whether obese individuals with trace metal deficiency (or toxicity) are at increased risk for infection is a matter of concern in many developing countries, where a growing segment of the population (exposed to traditional health risks) has embraced Western dietary habits. A better understanding of the roles of different trace metals will undoubtedly facilitate the development of new treatment and prevention strategies that can more effectively reduce the silent burden of comorbid obesity and infectious diseases.

Like many other elements, natural background levels of trace elements exist in crustal rocks, such as shales, sandstones, and metamorphic and igneous rocks (Benjamin and Honeyman, 2000). In particular, the majority of trace metals are derived from igneous rocks, simply based on the relative fraction of igneous rocks in comparison with sedimentary and metamorphic rocks in the Earth’s crust. The release of trace metals from crustal sources is largely controlled by the natural forces of physical and chemical weathering of rocks, notwithstanding large-scale anthropogenic disturbances such as mining, construction, and coal burning (release of fly ash). As discussed later in the chapter, adjustments can be made for anthropogenic loading to different ecosystems based on an enrichment factor which compares metal concentrations in the ecosphere to average crustal composition. Biological effects of weathering, such as plant root growth and organic acid release associated with respiration also contribute to these weathering processes. As some trace metals are more volatile than others, release due to volcanic activity represents another source of metals with such properties (e.g., Pb, Cd, As, and Hg). Just as Goldschmidt (1954) grouped elements (e.g., siderophiles, chalcophiles, lithophiles, andatomophiles) based on similarities in geochemical properties, trace metals also represent a group of elements with similar chemical properties. One particularly important distinguishing feature of these elements is their ability to bond reversibly to a broad spectrum of compounds (Benjamin and Honeyman, 2000). Thus, the major inputs of trace metals to estuaries are derived from riverine, atmospheric, and anthropogenic sources. Although trace elements typically occur at concentrations of less than 1 ppb (part per billion) (or μg L−1, also reported in molar units), these elements are important in estuaries because of their toxic effects, as well as their importance as micronutrients for many organisms. The fate and transport of trace elements in estuaries are controlled by a variety of factors ranging from redox, ionic strength, abundance of adsorbing surfaces, and pH, just to name a few (Wen et al., 1999).

More than 80 percent of San Francisco Bay's historic tidal marshes have disappeared due to human activities, and the remaining marshes have been fragmented and contaminated. High levels of contaminants have contributed to the degradation of their habitat quality. After the implementation of management actions and the restriction on the use of toxic chemicals, a significant decrease in contaminant loading occurred, and marsh-habitat quality is being improved slowly. However, levels of contaminants in some tidal marshes are still high enough to threaten the well-being of aquatic life and wildlife. This review summarizes the geographical distribution and temporal trends of contaminants, especially mercury, polychlorinated biphenyls, and organochlorine pesticides, which are the most serious concerns for public health and environmental degradation in the San Francisco Bay.

A bioindicator species can be defined as “an organism that provides information on the environmental conditions of its habitat by its presence or absence, and its behavior.” In this sense, crustaceans present many biological and ecological characteristics that make them particularly useful as bioindicators (e.g., widespread distribution in different habitats and geographical areas, key role in community functioning, great diversity of life history strategies). Within Crustacea, the order Amphipoda has been considered an especially relevant and suitable group due to its direct development and its special sensibility to disturbances, among other reasons. Crustaceans can be used in biomonitoring studies in a wide variety of habitats (e.g., both soft- and hard-bottom substrata from intertidal to deep environments) and for different types of environmental stressors. An extensive amount of literature has reported the sensitivity of crustacean species to heavy metal contamination, sewage and desalination discharges, or engineering and aquaculture activities, among others. Special emphasis has been placed on the role of crustaceans in the most used indexes (e.g., AMBI, BENTIX, BOPA) developed to establish the environmental quality of European coastal and marine areas. Crustaceans are one of the groups with a higher contribution to those indexes, although their presence is not necessarily indicative of low environmental disturbances. Within amphipods, the importance of the family Caprellidae as a monitoring tool in environmental programs (e.g., trace metal or tributyltin pollution) is highlighted. Alien crustaceans can also play a pivotal role as bioindicators of anthropogenic pressures, and their likely influence on the accuracy of ecological assessment programs should be taken into account. Finally, there is an increasing need to improve our scarce taxonomic knowledge in many crustacean groups since that information is vital for the correct development of monitoring tools. Studies dealing with the species’ ecological and biological traits are also encouraged in order to understand the potential application of these species as bioindicators.

The chemical composition of seawater results from a combination of chemical and biological reactions and transport processes. The concentration of conservative elements is modified only by water mixing, whereas the concentration of minor or trace non-conservative elements is also sensitive to biological or chemical reactions. The distributions of nutrients such as nitrate, phosphate and silicate, as well as the oxygen concentration, are controlled by both ocean circulation and biological activity. Nutrients are consumed in surface water during photosynthesis and released in deep waters by remineralization of the sinking dead organic matter. Nutrients and oxygen are consumed and released in constant proportions called Redfield ratios. Most gases (including oxygen) are saturated with respect to the atmosphere in the surface water. The distinctive behavior of carbon dioxide comes from the carbonate system equilibria. The behavior of selected trace metals illustrates the respective roles of the redox reactions, complexation reactions and biological uptake.

Accurate determination of nucleic acid thermodynamics has become increasingly important in understanding biological function as well as applications in biotechnology and pharmaceuticals. Knowledge of the thermodynamics of DNA hybridization and secondary structure formation is necessary for understanding DNA replication fidelity (1), mismatch repair efficiency (2) and the mechanism of DNA triplet repeat diseases (3). In addition, RNA folding thermodynamics are an important aspect of understanding ribozyme catalysis, as well as understanding the regulation of protein expression, mRNA stability and the mechanism of protein synthesis by the ribosome (4). With the genome sequencing era upon us (5), it will increasingly become important to predict the folding and hybridization thermodynamics of DNA and RNA, so that accurate diagnostic tests for genetic and infectious diseases can be developed. Thus, there is a need to develop a database of accurate thermodynamic parameters for different nucleic acid folding motifs (4). This chapter describes practical aspects of the application of UV absorbance temperature profiles to determine the thermodynamics of nucleic acid structural transitions. Protocols and practical advice are presented for issues not normally addressed in the primary literature but that are crucial for the determination of reliable thermodynamics, such as sequence design, sample preparation, choice of buffer, protocols for determining strand concentrations and mixing strands, design of microvolume cuvettes and cell holder, instrumental requirements, data analysis methods, and sources of error. References to the primary literature and reviews are also provided where appropriate.