Concern regarding occupational exposures to hexavalent chromium has been growing in recent years. This is primarily a result of epidemiologic studies that have consistently shown a link between exposure to hexavalent chromium compounds and excess lung cancers. The World Health Organization (WHO), the Department of Health and Human Services (DHHS), the U.S. Environmental Protection Agency (EPA), and the International Agency on the Research of Cancer (IARC) have all determined that hexavalent chromium causes cancer in humans. In addition to lung cancer, hexavalent chromium compounds can also cause mucous membrane and skin ulcers and perforations of the nasal septum.
Who is at risk?
The Occupational Safety and Health Administration (OSHA) estimates that, across all industries, approximately one million workers are exposed to hexavalent chromium on a regular basis. Workers are potentially exposed to hexavalent chromium compounds when involved in the production and/or use of chromate pigments, chromium catalysts, chromate paints and coatings, printing inks, plastic colorants, electroplating chemicals, wood preserving chemicals, leather tanning chemicals, textile dyes, and industrial water treatment products. Workers that cut or weld stainless steel or handle refractory bricks may also be exposed to hexavalent chromium.
Current PEL and where it applies
The current OSHA Permissible Exposure Limit (PEL) listed for “chromic acids and chromates” is a ceiling value of 0.1 mg/m3. A ceiling value is a concentration that OSHA states shall not be exceeded at any time during a workday. This ceiling value applies to all forms of hexavalent chromium, which may include dusts (e.g., paints and coatings), fumes (e.g., welding stainless steel), and mists (e.g., electroplating baths). Hexavalent chromium compounds generally encountered in the occupational environment include: ammonium dichromate, barium chromate, calcium chromate, chromium trioxide (chromic acid), lead chromate, strontium chromate and zinc chromate
Proposed PELs
OSHA was recently issued a federal court order to develop a proposed rule for hexavalent chromium by October 2004 and a final rule by January 2006. The court order followed a long history of failed efforts by unions and public interest groups for establishment of an Emergency Temporary Standard (ETS) to reduce the PEL for hexavalent chromium. The groups that filed petitions requested that OSHA immediately reduce the PEL for hexavalent chromium to 0.0005 mg/m3, as an 8-hour time-weighted average. OSHA is considering 8-hour time-weighted average PELs ranging from 0.00025 mg/m3 to 0.01 mg/m3. It is expected that the proposed PEL will be in the lower end of this range.
The exposure limits that OSHA is considering are more in line with the current American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs). ACGIH has established specific 8-hour time-weighted average TLVs for calcium chromate (0.001 mg/m3), lead chromate (0.012 mg/m3), strontium chromate (0.0005 mg/m3), zinc chromates (0.01 mg/m3) and generic TLVs for water soluble (0.05 mg/m3) and insoluble (0.01 mg/m3) forms of hexavalent chromium, all measured as chromium.
OSHA’s sampling and analytical method for measuring hexavalent chromium (OSHA ID-215)
In anticipation of a lower PEL, OSHA has developed a sampling and analytical method (OSHA ID-215) that is capable of accurately measuring hexavalent chromium at very low concentrations. In addition to better sensitivity, the OSHA ID-215 method does not require special field sample preparation, and it does not have significant interference from other metals as the commonly used, older method (NIOSH 7600) does.
As with other substance specific standards (e.g., lead, arsenic, cadmium) it is expected that OSHA will have an initial monitoring requirement and periodic monitoring requirements, based on exposures. Biological monitoring requirements are not expected in the standard because current test methods cannot differentiate hexavalent chromium from other forms found in foods such as onions, broccoli, turkey legs, American cheese, potatoes, liver, brewer’s yeast, oysters and wheat germ, or in dietary supplements usually taken for weight loss.
Employers that use or process these compounds, or materials containing them, should review their status and ensure exposure controls are up to date. Exposure monitoring can be an important part of this assessment, by identifying areas or jobs where additional controls are needed. When feasible, use of less toxic materials should always be a consideration.