Winter 2024

Recent Scientific Research to Support Development of Occupational Exposure Limits for Copper

By David G. Dodge, M.S., DABT, CIH, and Charlotte Marsh, M.S., CPPS

Copper is a metal element distributed widely in nature.  It has excellent thermal and electrical conductivity, strength, resistance to corrosion, and malleability.  Given these important properties, copper is mined, processed, and used in the manufacture of a variety products across a number of industries.  These products include industrial machinery (e.g., transformers), building wiring, plumbing parts, automobiles, electronic equipment, marine vessels, consumer products (e.g., cookware, locks and keys), and more.  In addition, copper does and will play a vital role in the transition to renewable energy sources, like solar, wind, geothermal, and fuel cells, because all of these sources are dependent on the excellent conductivity of copper.

Copper is also an essential element for many forms of life, including humans, who require copper to maintain normal body functions.  Thus, as an essential element, adverse health effects can occur with too little or too much copper intake.  While the general population is exposed to copper primarily through the diet, inhalation exposure to copper can occur in some occupational settings where operations involve airborne emissions of copper, such as mines, mills, smelters, and refineries.  To ensure the safety and sustainability of copper-related industries, it is important to understand the potential occupational health risks of copper and the exposure conditions associated with any potential health risks.

Unlike other metals, such as arsenic, beryllium, lead, and mercury, copper has not been generally associated with appreciable occupational health concerns and has not received significant research attention in this context.  Historically, health outcomes that have been associated with occupational copper exposures include respiratory irritation, nausea, and metal fume fever.  With regards to metal fume fever, however, a review of the medical literature found insufficient evidence to conclude exposure to copper as a cause (Borak et al., 2000).  Currently, established and proposed occupational exposure limits (OELs) for copper in the United States (US) and Europe, developed to protect worker health, range from 0.01 to 1 mg/m³, and encompass different copper forms (dust vs. fumes) and size fractions (respirable vs. inhalable vs. total) (see Table).  These values, however, have been based largely on sparse and dated human and animal studies of limited reliability.

Current Occupational Exposure Limits (OELs) for Copper

The development of updated copper OELs has generated interest in the US and Europe.  Key to this process is the availability of relevant, high-quality data.  In recent years, the copper industry, in collaboration with independent scientific experts, has conducted targeted, copper-related research in the areas of animal toxicology, occupational medical surveillance, and source and exposure characterization of workplace dust, which can help inform evidence-based OELs for copper.  Examples of this research include:

• In a recently published Organization for Economic Co-operation and Development (OECD) guideline study, rats were exposed to aerosols of dicopper oxide at concentrations of up to 2 mg/m³ for 28 days via inhalation, with a recovery period of 13 weeks, and evaluated for a number of toxicological parameters, including lung histopathology (Poland et al., 2022).
• Two recent occupational health studies investigated the potential chronic effects of inhalation exposure to copper-containing dusts at a European copper smelting plant.  The first study was a comprehensive review of medical surveillance and exposure data at the plant (Haase et al., 2021).  The second study relied on medical examinations and testing of current employees of the plant who had been chronically exposed to inhalable and respirable copper (Haase et al., 2022).
• The forms and size fractions of copper present in workplace air samples vary by operation, activity, and composition/purity of the materials handled.  Kelvin et al. (2023) characterized airborne and settled dust at a copper smelter in Europe, and identified influential factors in the types of copper present under varying activities.

Given the widespread use and commercial importance of copper and its compounds, it is imperative that scientifically based OELs are developed that protect workers without being unnecessarily restrictive.”

These recent scientific studies on copper exposure and toxicity provide a notable example of an industry-led, collaborative research program aimed to fill important data gaps.  When integrated appropriately with the body of scientific evidence, this research can help to ensure that OELs for copper are appropriately protective of all copper forms.  Given the widespread use and commercial importance of copper and its compounds, it is imperative that scientifically based OELs are developed that protect workers without being unnecessarily restrictive.  The availability and interpretation of these studies will likely play a key role in determining updated OELs for copper.