Chrome-6 research: The power of the combination

Chromium is a heavy metal and occurs as chromium-0, chromium-3 and chromium-6. Unlike chromium-6, the first two are harmless to human health. However, once you start working on objects with chromium-6-containing coating in them (sanding, grinding, cutting, burning, welding or sawing), dust or fumes containing chromium-6 can be released. It is therefore of great importance to know whether chromium-6 is present in the coating of the object to be machined, so that the appropriate precautions can be taken if necessary. Nebest Adviesgroep developed a method (now validated) to determine this with great certainty.

If the applicator shows a purple discoloration, it means that chromium-6 is present and no further investigation is necessary.

Chromium-6 is harmful when inhaled or ingested, it is common knowledge. "What many people don't know is that it can also enter your body through moisture, sweat or saliva," says Astrid Elzas of Nebest Adviesgroep in Vianen. "As soon as it gets on your body, you have a problem. So it's important to know if chromium-6 is present in the coating of the object you're going to work on. You will have to test that. There are several methods for testing a coating for the presence of chromium-6. Not one of those methods gives 100% certainty. To obtain as much certainty as possible, it is important to go through a clever combination of tests."

Nebest's methodology relies on multiple types of tests, with the smart combination providing assurance.

Chromium-6 is harmful when inhaled or ingested. What many people don't know is that it can also enter your body through moisture, sweat or saliva.

Purple discoloration

Nebest's chromium-6 investigation consists of a number of steps. Mark Lodema of Nebest Adviesgroep explains, "We always start with a visual inspection and a relatively simple on-site test, the in-situ rapid test. A notch is made in the paint at certain locations, a v-shaped cut, so that all layers of paint are exposed, down to the substrate. We then pass an applicator through the cut so that all layers of paint are touched. If the applicator shows a purple discoloration, this means that chromium-6 is present and no further investigation is necessary. Follow-up steps are, of course, in terms of precautions when maintaining the preservation or object. If the applicator does not discolor, this does not mean that chromium-6 is not present. There are several factors that can affect this in-situ rapid test. These include disruptive elements in the coating (not to be confused with the metal of the substrate) that can cause the conversion of chromium-6 to chromium-3 during the test. Therefore, follow-up testing is always required. For this, a paint sample of plusminus 5 by 5 centimeters is taken and presented for further investigation at our laboratory in Vianen."

The in-situ rapid test involves making a notch in the paint, a v-shaped cut, so that all layers of paint are exposed, down to the substrate.

Laboratory tests

In the laboratory, an XRF measurement is performed by Nebest on the powdered paint sample. "With this test, we measure the presence of elements that can cause a disturbing effect on the tests, as well as the presence of total chromium," explained Lodema. "To be sure, our laboratory also performs the indicator test, which is very similar to the in-situ test but performed under conditioned conditions. This makes it an optimized test. If chromium-6 is still not found, a wet-chemical analysis follows." Alsace adds: "The powdered paint sample is heated in an extraction solution. In the alkaline solution, extraction of chromium-6 from the sample takes place. After adding an indicator, discoloration occurs if chromium-6 is present. Using a UV/VIS spectrophotometer, the discoloration is quantified and the concentration of chromium-6 in the sample can be determined." Lodema: "The presence of interfering elements can affect the result. Therefore, in addition to the test on the paint sample, a second test is performed in which a known amount of chromium-6 is added. If we find most or all of this amount, the test is reliable. If not and chromium total is present and disturbing elements have been found with the XRF measurement, the statement:
suspected chromium-6 present."  

Using a UV/VIS spectrophotometer, the discoloration is quantified and the concentration of chromium-6 in the sample can be determined.

So Nebest's methodology relies on multiple types of tests, with the smart combination providing certainty. "The key is to assess the chromium-6 survey knowledgeably to interpret the result," says Alsace. "The turnaround time for our study is up to two weeks. With an urgent assignment, it can be done within a few days." Nebest conducts chromium-6 research for parties such as ProRail, Rijkswaterstaat and energy companies, as well as contractors in construction and industry. Incidentally, in many cases other heavy metals (including Pb, Zn, Al, Ni, Cu, Co) and PAHs (polycyclic aromatic hydrocarbons) are also measured in coating.