HEXAVALENT CHROMIUM

UPDATED OSHA ID 215 FOR HEXAVALENT CHROMIUM (VERSION 2) 9/2006

Hexavalent Chromium

Soluble or insoluble: that may be a question of the past. Depending on the operating process, monitoring hexavalent chromium (Cr(VI)) for workplace exposures can be a daunting task. Chromium is a naturally occurring element found in rocks, soil, plants and animals, and present in the environment in several different forms. Of particular interest are chromium trivalent and hexavalent states. Sources for hexavalent chromium include electroplating operations, battery makers, textiles, chemical manufacturing, wood preserving and stainless steel welding activities. Other processes that use hexavalent chrome products are corrosion inhibitors, drilling mud operations and even toner for printers.

Breathing hexavalent chromium levels greater than 2 micrograms per cubic metre (ug/m³) for extended periods of time can cause runny nose, sneezing, itching, nosebleeds, ulcers and holes in the nasal septum. The Department of Health and Human Services (DHHS) determined that because some hexavalent chromium compounds have been associated with lung cancer in workers, and caused cancer in animals, certain compounds such as calcium chromate, chromium trioxide, lead chromate, strontium chromate and zinc chromate are known human carcinogens. The Environmental Protection Agency (EPA) and the International Agency for Research on Cancer (IARC) concurs that there is sufficient evidence implicating hexavalent chromium in air as a human carcinogen.

In the Federal Register on February 28, 2006, the Occupational Safety and Health Administration (OSHA) published a final standard for occupational exposure to hexavalent chromium. The document reduces the permissible exposure limit (PEL) ceiling to an 8-hour time-weighted average (TWA) of 5 ug/m³, with an Action Level (AL) of 2.5 ug/m³ for hexavalent chromium compounds. The OSHA final standard also addresses ancillary provisions for employee protection with preferred methods for controlling exposure, respiratory protection, protective clothing and equipment, hygiene areas and practices, medical surveillance, hazard communication, and recordkeeping. The National Institute of Occupational Safety and Health (NIOSH) currently recommends an exposure limit of 1 ug/m³ for a 10-hour TWA for all hexavalent chromium compounds. NIOSH considers all hexavalent compounds (including chromic acid, tert-butyl chromate, zinc chromate, and chromyl chloride) to be potential occupational carcinogens. The American Conference of Governmental Industrial Hygienists (ACGIH) has adopted a time-weighted average of 50 ug/m³ for water soluble compounds and 10 ug/m³ for insoluble hexavalent compounds. Both soluble and insoluble forms carry the notation as a confirmed human carcinogen. According to ACGIH, the agent is carcinogenic to humans based on the weight of evidence from epidemiological studies.

SAMPLING METHODOLOGY

SGS Galson currently offers analysis for hexavalent chromium by NIOSH Method 7600 and OSHA Method ID 215. Both methods use similar collection media with slight variations in the sampling rates, different total sample volume and shipping preparation techniques. While NIOSH Method 7600 states a flow rate of 1-4 liters per minute (LPM), OSHA Method ID-215 states 2 LPM as a recommended sampling rate.

Both methods involve collection on a 5.0 um pore size, 37-mm diametre polyvinyl chloride (PVC) filter in a polystyrene cassette filter holder. A 25-mm PVC filter can be used with the OSHA method for placement within a welding face shield. Precaution should be taken to not exceed 1 mg total dust loading on the filter. Dusty conditions may warrant multiple samples to avoid filter overloading. When sampling in conditions that are dusty, switch out the sample cassettes to limit filter loading.

When sampling chrome plating operations the OSHA ID 215 allows the use of a 37-mm polystyrene cassette containing NaOH coated binderless quartz fibre filters. In studies, we have found the background levels of hexavalent chromium on these treated filters to be five times greater than our detection level. The background levels found on the treated filters raises the detection limit and we do not recommend them for sampling.

Final collection techniques and extraction procedures between the two methods differ greatly. The NIOSH 7600 sampling method stipulates filter removal from the cassette. Remove the filter from the cassette within one hour of completion of sampling and place it in a PTFE-lined screw capped vial to be shipped to the labouratory. Handle the filter with plastic or Teflon-coated forceps only. The backup pad may be discarded.

When using the OSHA ID 215 collection method, leave the filter media in the polystyrene cassette for shipment to the labouratory for analysis. The OSHA method requires special handling of the samples and holding time requirements for samples collected from welding and chromium plating operations. A summary of the special handling requirements follows:

1. Samples collected on PVC filters must be shipped overnight to the labouratory within 24 hours of sampling.
2. Samples collected on PVC filters from welding operations must be analyzed within 8 days of sampling.
3. Samples collected on PVC filters from chromium plating operations must be analyzed within 6 days of sampling or be stabilized at the labouratory upon receipt (can be stored up to 14 days after stabilization).

With the NIOSH 7600 method shipment to the labouratory is routine. No refrigeration or overnight delivery is required and analysis is within two weeks.

NIOSH method 7600 may be used for the determination of soluble (acidic extraction) or insoluble (alkaline extraction) compounds. The detection limit is 0.75 ug/m³ for a 400-liter air sample. Potential interference may occur from the presence of iron, copper, nickel and vanadium. A 10 ug mass of any of these metals may cause an absorbance up to 0.02 ug of hexavalent due to formation of colored complexes. The NIOSH 7600 method does not quite reach 1/10^th of the PEL when sampled at maximum volume (15% of the PEL is obtained). The detection limit is approximately 30% of the action level when sampled at 400-liters.

While the NIOSH method differentiates by extraction technique, OSHA ID 215 extracts total hexavalent chrome and cannot differentiate between soluble and insoluble compounds. OSHA ID 215 specifically uses an alkaline extraction solution, thereby improving sample recovery by preventing Cr(VI) losses which may occur in an acidic extraction media. Also, the OSHA method is specific for the hexavalent chrome in the presence of trivalent chromium. Most heavy metals, such as vanadium, copper, iron (III), and molybdenum, do not significantly interfere with detection. However, The Salt Lake Technical Centre has done studies that show sample loss/degradation on welding operation samples due to interaction of the Cr(VI) and Fe(II) after collection. They also found that chromium plating operations typically had significant amounts of sulfuric acid that reacts with the Cr(VI) after collection to form Cr(III). These interferences have caused OSHA to modify the method holding times and sample handling to reduce potential bias. If the samples are not treated according to these requirements – the results may be biased low. Their studies show up to approximately 25% negative bias after 14 days. OSHA ID 215 has a detection limit much lower than NIOSH 7600. A detection limit of 0.026 ug/m³ when sampling at the maximum air volume of 960-liters can be obtained with OSHA ID 215. This detection limit allows the sampler to obtain results at 1/50^th of the PEL and 1/100^th of the action level.

With the reduction of OSHA regulatory limits for hexavalent chromium, it is imperative a sampling method be available with analytical sensitivity and ease of use, for determining work place exposures. The OSHA ID 215 method was validated using soluble and insoluble chromate compounds. This method has adequate sensitivity for determining compliance with the OSHA TWA and Action Level PEL’s for hexavalent chromium exposure.

SGS Galson continues to meet the changing needs of our clients by developing new methodologies and striving to make additional services available. As in the past, SGS Galson remains a leader in analytical services laboratories with the best client service available. Call your SGS Galson client services representative today and see the difference SGS Galson can provide you.

References:

Federal Register, Vol. 69, No. 191, Docket No. H054A, 10/04/04, United States Department Of Labour

Federal Register, Vol. 71, No. 39, Docket No. H054A, 02/28/2006, United States Department of Labour, Hexavalent Chromium in Workplace Atmospheres, OSHA Method ID 215, Occupational Safety and Health Administration, Department of Labour. (Version 2, April 2006)

Chromium, Hexavalent, NIOSH Method 7600, National Institute of Occupational Safety and Health Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94.

NIOSH (1975) Criteria for a Recommended Standard: Occupational Exposure to Chromium (VI). Cincinnati, OH: Department of Health, Education, and Welfare, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 76-129.

Agency for Toxic Substances and Disease Registry (ATSDR). 2001, Toxicological Frequently Asked Questions for Chromium, 02/2001. Atlanta, GA: Department of Health and Human Services, Public Health Service.

Amdur et al, Casarett and Doull’s Toxicology, The Basic Science of Poisons, Fourth Edition, pp 638-639 New York : Pergamon Press, 1991.