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How Much Cobalt Is in Your Metal Alloy?

EU to set threshold for triggering design justification and carcinogen labeling.

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The European Union is moving forward on its proposal to set risk management and labeling requirements relevant to the amount of cobalt in medical devices. The rule would be triggered at a limit of 0.1% by weight. This action is predicated on elevating the carcinogenic risk level of cobalt into a category known as 1b-Substances presumed to have carcinogenic potential for humans. At a minimum, compliance with these regulations will require knowledge of the amount of cobalt present in the metal alloys from which devices are made. For alloys that intentionally contain cobalt, this information should be readily available from the medical supplier. But for alloys that do not require cobalt, the relevant ASTM standards are generally silent about the amount of cobalt that the alloy can contain.

For example, ASTM F138 Standard Specification for Wrought 18Chromium-14Nickel-2.5Molybdenum Stainless Steel Bar and Wire for Surgical Implants says nothing about the amount of cobalt that may be present. But this does not necessarily mean there is no cobalt. Notably with regard to the new EU requirement, the specification does not exclude cobalt. What F138 does specify is a permissible range for chromium, nickel, and molybdenum along with limits on seven other elements, along with a requirement on the combined amount of chromium and molybdenum. According to the specification, the amount of iron need not be measured but is instead determined by subtraction. As a result of this method, the amount of iron cited actually includes iron plus everything else not named. And also as a result of this method, cobalt could be present in amounts exceeding the EU threshold, but unless a full elemental analysis is obtained, the buyer of the alloy would not know the amount of cobalt in any shipment, and that amount could vary from one shipment to the next.

This presents two challenges. One is that the buyer will have to specify the permissible amount of cobalt outside of the confines of the standard. This would require an analysis by the vendor beyond that required to meet the ASTM specification. In fact, the specification currently states that “Analysis for elements not listed in Table 3 is not required to certify compliance with this specification.” Adding extra specifications has been controversial at times, and some ASTM standards have sought to limit the buyer’s ability to add additional requirements or reject shipments based on a full analysis. It is expected that ASTM will seek to modify specifications such as F138 to include a cobalt requirement.

The second challenge of meeting the forthcoming EU requirements is that the alloy supplier may have to make changes in its processes in order to produce materials with a specified and consistent limit on the amount of cobalt. At present it is not publicly known how much cobalt is typically present, or how much it varies. Lowering the amount of cobalt, if necessary, may require a higher degree of control of the ingredients going into the mix. This may not be easy or inexpensive.

For alloys that do contain cobalt, the amount is included in the specification, so it is not an unknown. This will trigger the new EU risk management and labeling considerations but not affect the production and purchase of the corresponding alloys. Whether or not carcinogen labeling will cause alarm among purchasers and users will be something to be determined. This may require some educational outreach to explain the new labeling and its significance. A related question is whether EU warning labeling should be different from U.S. labeling.

William A. Hyman

William A. Hyman is a professor emeritus in the department of biomedical engineering at Texas A&M University and adjunct professor of biomedical engineering at the Cooper Union. Reach him at [email protected].

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