December 4, 2009
Commander David L. McMillan, MD, MPH
Occupational and Environmental Medicine Programs and Policy
U.S. Department of the Navy
Bureau of Medicine and Surgery
2300 E Street, NW
Washington, DC 20372
Dear Dr. McMillan:
Thank you for your letter, July 20, 2009, to the Occupational Safety and Health Administration's (OSHA's) Office of Occupational Medicine, within the Directorate of Science, Technology and Emergency Management. Your letter has been referred to the Directorate of Enforcement Program's Office of Health Enforcement for an answer to your specific questions regarding medical exams and blood testing for zinc protoporphyrin (ZPP) under OSHA's Lead Standards. This reply letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any question not detailed within your original correspondence. Your paraphrased question and our reply are below.
Question: Your request on behalf of the U.S. Navy referred to recently published medical studies supporting the discontinuation of ZPP use in the surveillance of workers without lead overexposure and low blood lead levels. You asked, "Could OSHA provide an exemption letter from the requirements of 29 CFR 1910.1025, such that the ZPP is no longer required for medical surveillance of employees with a low prevalence of elevated blood lead levels?"
Reply: No. As you are aware, OSHA's Lead Standard requires medical surveillance, including ZPP sampling and analysis, of workers who are or may be exposed above the action level for more than 30 days per year, as per 29 CFR 1910.1025(j)(1)(i). Employers are required under 29 CFR 1910.1025(d) to conduct exposure assessments to determine whether employees are so exposed. With respect to the workers described in your letter as "clearly" not overexposed to lead, a new exposure assessment may help determine whether these workers are or may be exposed above the action level for more than 30 days. If exposure monitoring demonstrates that employees are not so exposed and you are determining blood lead levels to ascertain whether there is an effect from lower lead exposures, you would not need to obtain ZPP levels on these workers. If monitoring demonstrates that they are so exposed, however, this would trigger the requirements of 29 CFR 1910.1025(j)(1)(i).
As you also know, ZPP and blood lead concentrations are widely-used biomarkers for lead toxicity. ZPP levels greater that 35 micrograms per deciliter (µg/dL) indicate lead-induced heme inhibition and serve as a means of determining the internal toxic effect of lead absorption. The lag in ZPP elevation and decline compared to blood lead levels makes ZPP measurements useful for distinguishing between acute and chronic lead intoxication and may help to determine whether a mid-range blood lead level is likely to reflect prior higher-level exposure. At the blood lead levels currently permitted under the OSHA Lead standard, the ZPP test is a useful adjunct.
Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA requirements are set by statute, standards, and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at http://www.osha.gov. If you have any further questions, please feel free to contact the Office of Health Enforcement at (202) 693-2190.
Richard E. Fairfax, Director
Directorate of Enforcement Programs