EPA-Expo-Box (A Toolbox for Exposure Assessors)
Inorganics and Fibers
Inorganics are generally defined as substances that do not contain carbon or have structures that are not carbon-based. Examples include ammonia, hydrogen sulfide, all metals in their "free" state (e.g., silver, lead, aluminum, chromium, mercury, iron), and most elements, including nutrients (e.g., calcium, nitrogen, phosphorous). Some compounds that contain carbon are considered inorganic and referred to as carbon-containing inorganics because their behavior and characteristics are more similar to those of inorganic compounds (e.g., cyanides, carbonates, carbonic acid, and oxides of carbon such as carbon dioxide and carbon monoxide).
Inorganic substances might be naturally occurring, produced intentionally and incorporated in products, or produced unintentionally and released as byproducts. Inorganic is a highly general classification that refers to large and varied group of substances, and so generalizations regarding use and common routes of exposure are difficult to make for this broad class. Potential routes of exposure include ingestion via drinking water (e.g., nutrients, metals), dermal via contact with contaminated soil (e.g., carbon-containing inorganics and metals), and inhalation (e.g., carbon monoxide, fibers including asbestos).
Fibers, while not always inorganic, are often discussed with inorganic chemicals because exposure to inorganic fibers such as asbestos is often of more concern than exposure to organic fibers. Inorganic fibers like fiberglass, mineral wool, refractory ceramic fibers, and asbestos share a similar structure: they are elongated, thread-like strands of molecules of variable length that are often interwoven and entwined. The use of synthetic, inorganic fibers is widespread in consumer and industrial applications, such as textiles; plastics; construction and automotive materials (e.g., insulation materials, cements, steel fiber composites, sealants, rubbers); and electronics (e.g., cables). Inhalation of fibers, especially for workers, is often a concern because the size and shape of fibers lead to their tendency to penetrate deep into the lungs after inhaled.
It is not the intent of this tool set to provide information relevant to all inorganics and fibers. As mentioned above, this chemical class encompasses a large and varied group of substances. Instead, this tool set focuses on tools for assessing exposures to higher priority metals—lead and mercury—and metals identified as drinking water contaminants of concern; asbestos fibers; and general nutrient pollution.