Chapter 29: Metals

INTRODUCTION

The diverse physical properties of metals have resulted in their extensive use in industry. These naturally occurring materials have long been recognized for their ability to impart a variety of valuable characteristics to finished goods. Metals are used in the construction, automotive, aerospace, electronics, glass, and numerous other manufacturing industries. Metals are major sources of pigments and stabilizers for paints and plastics. Metals are also used as catalysts and intermediates in the chemical and pharmaceutical industries. Occupational and environmental exposure to metals may occur during the manufacture or fabrication of finished products, as well as later in the product life cycle during modification, physical disturbance, or disposal. For some metals, such as arsenic in drinking water, significant exposure may occur primarily as the consequence of geologic rather than anthropogenic activity.

Metals are used rarely in their pure form, usually being present in alloys. They also may be bound to organic materials, altering their physical characteristics and potential toxicity. Some compounds, such as hydrides and carbonyls, are highly toxic and may be formed accidentally when the parent metal reacts with acids. Metals may be altered by burning and smelting or after uptake by biologic systems. The chemical structure of the metal or organometallic compound alters absorption, distribution, and toxicity.

Metals exert biologic effects through numerous modes of action. These may include chemical interactions, such as binding to sulfhydryl groups, that alter the structure and function of many proteins and enzyme systems. Metals may react with cellular structures and macromolecules in ways that may induce oxidative stress, alter gene expression, disturb the function of essential cations, and trigger immune responses. Certain metals, such as zinc, copper, chromium, cobalt, molybdenum, and manganese, are essential for normal metabolism. Others, such as lead, mercury, arsenic, and cadmium, serve no recognized biologic purpose, raising public health concerns owing to their ubiquitous presence in living organisms.

General population exposure to most metals arises primarily from ingestion in food and water, with lesser degrees of exposure from inhalation of contaminated air. Hazardous levels of exposure from inhalation is more commonly encountered in occupational settings. Familiarity with the potential health effects of metals in different settings is helpful not only for the occupational health and safety professional but also for primary and specialty care medical providers.

Because metals may perturb biochemical and physiochemical functions in cells throughout the body, overexposure to metals should often be considered in the differential diagnosis of patients presenting with multisystemic signs or symptoms. Health care providers should also be aware that low levels of metal exposure not associated with overt manifestations or symptoms may nonetheless contribute to deleterious effects such as cancer, adverse reproductive and developmental outcomes, immune dysfunction, and latent neurodegeneration.

ARSENIC