Abstract This chapter deals with the crystal structure of regulated and unregulated mineral fibres. The aim is to provide readers, both specialists and researchers broadly interested in environmental problems, with up-to-date information on a topic that is expanding daily. The chapter describes specifically the structure of the fibrous modification whenever available and outlines possible differences from the corresponding prismatic variety. Details of the experimental techniques used for structure determination/refinement are reported also, if appropriate, to outline the experimental difficulties faced due to the small dimensions, sensitivity and chemical complexity of mineral fibres.

Abstract Many physicochemical properties of fibrous minerals concur – often simultaneously – in determining the fate of a particle within the human body. A complex chain of physicochemical transformations and biological reactions occur when a mineral fibre comes in contact with biological material and occasionally this results in inhaled material being held in an organism for a very long time. During that time, which might last for decades in the case of highly bio-persistent minerals such as amphibole asbestos, the fibre evolves and reacts with the human body, initially with body fluids and immune system cells, and dynamically interacts with its biological surroundings. To understand the molecular mechanisms of interaction, both bulk and surface properties of toxic – and potentially toxic – mineral fibres have to be considered. Far from being an exhaustive compendium of the enormous numbers of works dealing with the toxicological properties of minerals, this chapter is devoted to the discrimination of the bulk and surface – often interrelated – properties that impart toxic potential to fibrous minerals. To allow the establishment of a common background for a multidisciplinary audience, some general considerations of the factors influencing the health effect of mineral fibres aimed at clarifying some key toxicological concepts, including dose, exposure, clearance and molecular mechanisms, are provided in the initial paragraphs. Because asbestos accounts undoubtedly for the vast bulk of toxicological research on minerals, an essential introduction of the key toxicological properties of non-asbestos mineral fibres is also provided. The chapter is divided into two main sections dealing with bulk and surface properties of mineral fibres variously involved in toxicological response. Specifically, fibre morphology, biopersistence and fibre surface properties, including the generation mechanisms of particle-induced reactive oxygen species (ROS), the investigation of surface active sites and the surface modification induced by the biological environment, are reported and discussed with the support of more than 200 bibliographic references.

Abstract Dissolution rates of mineral fibres in several environments are obtained as proxies for their biodurability in body fluids. This chapter provides a description of the experimental methods, the parameters and characteristics to be fixed during the design of dissolution experiments in closed (batch reactors) and open systems (flow-through cells), as well as details of the dissolution media. The dissolution of mineral fibres in buffered inorganic solutions is the key to understanding their behaviour during weathering processes because it contributes not only to their chemical transformation, but also to the breakdown of the fibres that may be dispersed in the environment. On the other hand, preparation of fluids representing different interstitial conditions in the lung is described, with particular attention to artificial lysosomal fluid (ALF) employed to mimic the environment that inhaled particles would encounter after phagocytosis by alveolar and interstitial macrophages. Moreover, the use of a neutral fluid such as Gamble’s solution (GS) simulates the interstitial lung fluid and airway lining fluid. Finally, the results of studies of mineral-fibre dissolution in inorganic and body fluids, found in the literature, are discussed. Methodologies for assessing the biodurability of fibres are illustrated, starting from dissolution rate data, and focus on in vitro studies. Rate constants are used to assess fibre lifetimes utilizing a fibre-shrinking model equation. Finally, literature studies show differences in biopersistence between serpentine and amphibole asbestos, due to their different crystal structures and dissolution conditions of pH and solution composition.