Geochemistry. Группа авторов

of toxic geogenic contaminants in serpentinite geological systems. Human exposure pathways in occupational and non-occupational settings are then summarized and their human health risks are also presented. Finally, mitigation measures to reduce human health risks are discussed and future research directions are proposed.

Chapter 2 reports detailed information on the application of essential minerals for the treatment of human diseases, including dental problems, cancer, hypertension, cardiovascular diseases, and goiters. Special attention is also paid to the application of essential elements for the management of animal and plant diseases.

      Chapter 3 highlights the benefits of the application of geochemistry in livestock, especially in the adequate maintenance of animal health and animal nutrition. The significance of numerous minerals that play several roles in the effective production of livestock is especially highlighted.

      Chapter 4 provides detailed information on the significance of geochemistry in the identification of useful mineral elements which could boost agricultural production and their significant role in the decontamination of heavily polluted soil and water, as well as their benefits especially in the area of sustainable agriculture.

      Chapter 5 details the cases of heavy metal contamination in soil using the ecological risk index. The major focus is the geochemistry and environmental impacts of arsenic, cadmium, chromium, copper, lead, nickel and zinc. The transfer of contaminants from sources to the higher trophic levels of the food chain is also summarized.

      Chapter 6 discusses the geochemical applications of both traditional and non-traditional stable isotopes. Beginning with basic definitions, the chapter goes on to discuss the variety of applications of traditional stable isotopes, geothermometers, tracers in hydrological and biological systems, ore deposits, hydrothermal systems, etc., and some applications of non-traditional stable isotopes.

      Chapter 7 is an overview of the research outcomes of the last decades and how geochemistry affects the sustainability of the environment and causes pollution at different levels. This chapter also explains the geochemical reactions of environmental pollutants and the physicochemical characteristics of various types of environmental samples.

      Chapter 8 focuses on the development of geochemistry and its distinct branches, as isotopic geochemistry reveals information about environmental health to avoid harmful chemicals that have antagonistic effects on health. Also discussed is the role of medical geochemistry in addressing many environmental health problems.

      Chapter 9 discusses the importance of inorganic geochemistry, the rock-forming minerals and their compositions. The characterization of minerals, elemental analysis and the determination of composition are elaborated. Clay minerals and their applications are also explained.

Chapter 10 discusses the periodic properties such as ionization energy, electronegativity, electron affinity and influence on the chemical bond formation among the elements. The distribution of elements in different layers present on the earth which depends on factors like temperature, pressure and altitude are discussed. Several subdisciplines and the scope of geochemistry are also presented.

      The Editors February 2021

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      Toxic Geogenic Contaminants in Serpentinitic Geological Systems: Occurrence, Behavior, Exposure Pathways, and Human Health Risks

       Willis Gwenzi

       Biosystems and Environmental Engineering Research Group, Department of Soil Science and Agricultural Engineering, University of Zimbabwe, Mt. Pleasant, Harare, Zimbabwe

       Abstract

Serpentinitic ultramafic geological systems contain toxic geogenic contaminants posing significant human health risks. The current chapter presents an overview of the nature, occurrence, behavior, and human health risks of toxic geogenic contaminants in serpentinitic geological systems. The geogenic contaminants include toxic metals (Co, Cr, Fe, Mn, Ni, and Zn), chrysotile asbestos, and rare earth elements. Occupational exposure occurs via inhalation in mining, milling, sculpturing, engraving, and carving industries. Non-occupational exposure include inhalation, and ingestion of toxic geogenic contaminants in contaminated geophagic earths, wild foods, herbal medicines, and water. Human exposure risk factors in Africa include weak and poorly enforced occupational and environmental regulations, consumption of contaminated foods and water, and lack of health surveillance systems. The prevalence of geophagy, high dietary intake of iron coupled with genetic disposition also increases iron overload and its health risks among native Africans. The human health risks of chrysotile (e.g., asbestosis, cancers) and toxic metals and rare earth elements (e.g., oxidative stress) are summarized. Human health risks may also occur via synergistic interactions among toxic geogenic contaminants (e.g., chrysotile and toxic metals), and with other health stressors (e.g., infectious diseases). Finally, mitigation measures to safeguard human health and future needs are highlighted.

      Keywords: Serpentines, ultramafics, medical geology, toxic metals, chrysotile asbestos, rare earth elements, asbestosis, human exposure pathways

1.1 Introduction

      Serpentinitic geological environments, consisting of serpentines and their ultramafic precursors or protoliths occur on all continents and cover about 1% of the earth surface [1]. To date, research on serpentinitic geological environments has been limited to their geology, geochemistry, and ecology [1, 2]. However, the medical geology of serpentinitic geological systems has received limited research attention. Medical geology seeks to understand how the interactions between humans and animals, and geological processes and activities influence human and animal health [3, 4]. The field of medical geology has attracted significant public and research attention, and an increasing body of literature exists on the subject [3, 5, 6]. The literature on medical geology, include (1) reviews presenting an overview of the discipline [3, 5, 6] and (2) empirical studies investigating the human health risks of specific geological processes and contaminants [7, 8].

      Serpentinitic geological systems contain anomalously high concentrations of toxic geogenic contaminants, which pose human health risks. These include, toxic elements such as rare earth elements and metals, and chrysotile asbestos [3, 4, 9]. Toxic metals occurring in serpentinitic geological environments include cobalt (Co), chromium (Cr), iron (Fe), manganese (Mn), nickel (Ni), and zinc (Zn). The 17 rare earth elements include the lanthanides, Yttrium, and Scandium [10]. Unlike toxic metals and rare earth elements, chrysotile asbestos is not a chemical element, but a compound. In view of this, the term “toxic geogenic contaminants” is broadly used in this chapter to refer to both chrysotile and toxic elements. Limited reviews exist on the occurrence, human exposure, and health risks of toxic geogenic contaminants in serpentinitic geological systems. An exception is a recent review investigating the nature, biogeochemical behavior, human exposure pathways, and health risks of toxic geogenic contaminants in serpentinitic ultramafic geological systems [4].

The current chapter seeks to present an overview of the nature, occurrence, environmental behavior, and human exposure pathways and health risks associated with toxic geogenic contaminants in serpentinitic geological systems. The specific objectives are to (1) discuss the occurrence and environmental behavior of toxic geogenic contaminants, (2) summarize the human