Test for Hexavalent Chromium

Hexavalent chromium, Cr(VI), is a toxic chemical that is used in many manufacturing processes. Workers exposed to this substance can have serious health consequences and it is important to know how to test for contamination. The simplest method of checking for Cr(VI) is by making a surface "wipe test" and sending the sample to a laboratory for analysis.

Significance

• Cr(VI) is an industrial compound used in paints, dyes and rust prevention. It is sometimes appears as a contaminant in Portland cement, which can be particularly threatening to workers because it hovers over a work site in dust. The most common industrial form is chromic trioxide, a deep purple crystal. Workers in a variety of occupations from welding, metallurgy, construction, painting and manufacturing can be exposed. Contamination can occur through aerosols, fumes, dust or contact with solid materials or liquids containing Cr(VI). It is therefore necessary to test for Cr(VI) in areas that are susceptible to contamination.

Effects

• Cr(VI) comes in numerous chemical forms that cause burns to exposed skin, and irritation and tissue damage can also occur in the eyes and in the respiratory tract. The compounds not only can cause burns, they also make the affected areas more susceptible to continued absorption of these and other potentially toxic substances. Cr(VI) is a suspected carcinogen. Repeated skin exposure can cause ulceration or contact dermatitis--swelling and rash that worsens with repeated exposure (reference 1).

Expert Insight

• The method developed by the United States Department of Labor to test for hexavalent chromium is fairly simple. The procedure requires a "wipe test" with a small piece of filter paper. The filter paper is used to collect potential contamination from a surface by "using firm hand pressure to move a 37-mm diameter polyvinyl chloride (PVC) filter, 5-micron pore size, across the surface of interest. An alternate medium for rough surfaces is a 37-mm binderless quartz fiber filter" (reference 2).

  OSHA further notes: "In chrome-plating environments, wipe samples taken on a PVC filter or an uncoated binderless quartz fiber filter, should be placed in a vial containing 5ml of an aqueous solution containing 10 percent Na2CO3 with 2 percent NaHCO3 immediately after sampling to eliminate the interference from the acid used in the chrome-plating process. An alternate medium that does not require extraction in the field is a binderless quartz fiber filter coated with 1 percent NaOH."

  Place the filter paper in a clean, dry vial for shipment and analysis at a laboratory. The OSHA method of analysis: "Samples are digested with multiple buffered solutions. After dilution, an aliquot of this solution is analyzed for hexavalent chromium by ion chromatography with poscolumn derivatization of the Cr(VI) with 1,5-diphenyl carbazide and detected by a UV-vis detector at 540nm" (reference 2).

Function

• OSHA guidelines for the filter paper are specific: Don't use any other type of paper for the test. Use protective gloves.

  1. Make the wipe test as illustrated above.

  2. Fold the paper with the sample on the inside until it will fit in the vial.

  3. Seal the vial and label it with a letter or number and the date so you know where it came from (A-11/09/2009, for example).

  4. Note in your notebook the sample name and date, describe where it came from, and make an approximate measurement of the area that was wiped. This will allow you to estimate the concentration of Cr(VI) over the given area.

  If you are testing multiple areas, try to use the same procedure for each. This means if you wipe one area twice over, do the same for the next area. Write this information in your lab book. Testing for airborne levels of Cr(VI) is more complicated and beyond the present scope, but it is critical as well.

Warning

• Hexavalent chromium is extremely toxic. Exercise care and judgment when taking a sample. Always use protective gloves and eyewear, and if appropriate a respirator. Anything that is handled while you have gloves on should be considered "contaminated," so use one hand to take the sample and place it in the vial (held with the "clean" hand). Take the contaminated glove off, inside out, and dispose of safely.