Hexavalent Chromium Exposure From Metal Fumes

Hexavalent Chromium, referred to as chromium(VI), Cr(VI) or chromium 6, is a toxic valence state of the elemental metal chromium. Workers in the welding, metal plating and automotive manufacturing industries are more prone to occupational exposure when working with steel alloys that can contain up to 20% chromium metal.

Metal fumes are often released during a fabrication process where materials are joined or welded together under extreme temperatures to form a strong joint. The high heat applied to this welding process produces visible smoke that contains vaporized metals, which quickly condenses into fumes. Chromium exposed to this high heat can be converted to its hexavalent state and can exist in the fumes that may cause damage to the workers’ eyes, skin, nose, throat, and lungs. When inhaled, it can induce upper respiratory issues such as nosebleeds, bronchitis, damage to the nasal septum, and a demonstration of asthmatic symptoms.

The International Agency for Research on Cancer (IARC) has found that hexavalent chromium poses such a risk to human health that they have classified it as a group 1 carcinogen. Prolonged or repeated exposure is known to lead to nasal, sinus, and lung cancer.

Several companies also use hexavalent chromium in their manufacturing processes, which can inadvertently expose their factory workers to the toxin. Dyes, paints, and inks are often pigmented with Cr(VI), and it is also frequently used as an anticorrosive agent in primers and coatings.

Regulatory Standard for Hexavalent Chromium

Hexavalent chromium is regulated according to the following criteria as soluble/insoluble compounds:

• OSHA TWA --- 0.005 mg/m³
• NIOSH RELs --- 0.0002 mg/m³
• ACGIH TLV-TWA --- 0.0002 mg/m³ as inhalable
• ACGIH TLV-STEL ---0.0005 mg/m³ as inhalable

Collecting Hexavalent Chromium Samples

Bureau Veritas uses OSHA ID 215 (version 2) for the collection and analysis of Cr(VI). This is an active sampling method that requires a pump capable of pulling 2 L/min of air during an 8-hour period.

Air samples must be collected in polystyrene cassettes using a 37 mm 5-micron PVC filter with a binderless quartz backup pad. Additionally, samples should also be collected using an IOM sampler with a PVC filter when ACGIH Threshold Limit Values (TLVs) are used for comparison.

Surface wipe samples must be collected with a dry PVC filter or a dry binderless quartz filter. A wetting agent should not be used as it could reduce the presence of Cr(VI) to the chromium III (Cr(III)) valence state, which is not recovered in this method.

Deciding on which dry filter to use for your environment is fairly straightforward. PVC filters have the advantage of a lower hexavalent chromium background, but they are more fragile. This background may originate from the filter’s manufacturing process or from the raw materials used to make the filter. A quartz filter is better for rough surfaces, but has a higher hexavalent chromium background and therefore, a higher reporting limit.

Wiping procedures for Cr(VI) can be found in OSHA W4001. Other methods, such as NIOSH 7600 and OSHA ID 103 are not used as they are no longer sensitive enough to meet the current exposure limit standards.

Hexavalent Chromium Sample Analysis

After collecting a sample, it is recommended that filters be sent to the laboratory for analysis as soon as possible. OSHA recommends analyzing samples within a specific timeframe as chemicals present in those environments can create a reduction in the valence state of Cr(VI) over time (see table 1). Samples collected from a paint process require an additional extraction step in order to break down the paint coating and must be noted upon receipt at the laboratory. If this extra extraction step is not performed, results may have a significantly low bias.

This analysis is specific to Cr(VI), so the sample cannot be analyzed for other metals.

Table 1: Recommended Hold Times For Samples

Cr(VI) samples are analyzed using an Ion Chromatography instrument equipped with post column derivatization and UV-Vis detection at 540 nm. Samples are extracted as prescribed in the OSHA 215 (version 2) procedure using a series of buffers in order to precipitate any other metals and break down the compound. If not precipitated out, these additional metals can interfere with the analysis.

Selecting the Right Laboratory for Hexavalent Chromium Analysis

When selecting a laboratory to perform hex chrome analysis, it is highly advised that the laboratory should be accredited to ISO 17025 by AIHA LAP to ensure that the quality system of the laboratory meets the high standards required for IH analysis. Secondly, the reporting level (RL) of the analysis should be low enough to support the ACGIH standard TLV for the operation. In their TLV handbook, ACGIH states that standards are based on toxicology, not technical feasibility. These low levels require a quality laboratory that can consistently meet the high sensitivity needed for analysis.

Working with Bureau Veritas

The Bureau Veritas Industrial Hygiene laboratory in Novi, MI has been analyzing Cr(IV) for more than 40 years and was one of the first labs to become accredited by the American Industrial Hygiene Association (AIHA LAP). We offer some of the lowest detection limits for Cr(VI) in the industry (see table 2), and we can meet the current published ACGIH guidelines, with the exception of STEL paint sampling.

Table 2: Reporting and Detection Limits