Chromium and Noise in a Plating Shop: Which Exposure Drives the Medical Surveillance Plan?
A metal-finishing plant employs 40 workers in a hard-chrome plating line. Air sampling over three shifts shows hexavalent chromium (Cr VI) at 2.5 µg/m³ (8-h TWA) in two workers near the tanks, and 0.8 µg/m³ in the rest. Personal noise dosimetry shows 8-h TWA of 89 dBA for the two tank workers and 82 dBA for the rest, with occasional impact noise from parts dropping into bins. The plant physician is asked to design a surveillance program. Management proposes annual audiograms for everyone and 'a chromium blood test' for the two highest-exposed workers, and asks whether the plant must do anything else. There is no union, and workers are told the results are 'confidential.'
1. Evaluate management's proposal against the exposure data and identify the errors in the proposed surveillance plan.
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Two errors stand out. First, the chromium test proposed ('a chromium blood test') is not a valid biomarker of Cr VI exposure: chromium in blood/urine reflects recent total chromium and cannot distinguish trivalent from hexavalent species or reliably reflect low-level air exposure; the appropriate surveillance for Cr VI is not a blood test but exposure control, respiratory protection, and medical surveillance focused on respiratory and dermatologic effects (nasal septal ulceration/perforation, dermatitis, and respiratory symptoms), with attention to the fact that Cr VI is a recognized carcinogen and sensitizer. Second, the audiometric plan is mis-targeted: annual audiograms for all 40 workers is not wrong in principle, but the two tank workers at 89 dBA exceed the 85 dBA action level and require enrollment in a hearing conservation program (baseline + annual audiograms, training, hearing protection, noise monitoring), whereas the 82 dBA group is below the action level and does not require the full program. The impact noise from parts dropping is a distinct concern: a dosimeter 8-h TWA can underestimate impulsive exposure, and peak levels should be measured. The 'confidential' handling is also a problem: workers must be informed of their own results and the employer must maintain records; results are not secret from the worker.
2. Draft the surveillance and control recommendations, specifying who is enrolled and at what interval.
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Cr VI: enroll all workers with potential exposure (not only the two highest) in a medical surveillance program that includes a baseline history and physical with emphasis on respiratory symptoms, nasal examination, skin examination, and smoking history; repeat annually for those at or above the action level (the OSHA action level for Cr VI is 5 µg/m³ as an 8-h TWA, so the two at 2.5 µg/m³ are below it, but the program should still cover them because exposure is intermittent and engineering controls are incomplete). Controls: enclose/ventilate tanks, substitute trivalent or less hazardous processes where feasible, provide respirators (with fit testing and medical clearance) for tasks above the action level, and train on dermatitis and nasal irritation. Noise: enroll the two tank workers at 89 dBA in a hearing conservation program (baseline audiogram within 6 months of hire/exposure, annual thereafter, with standard threshold shift follow-up); measure peak impact noise and, if peaks exceed 140 dB, require impulse-rated hearing protection; the 82 dBA group gets information/training and optional audiometry. The judgment point is that surveillance follows the exposure assessment, not the org chart, and that a test must be valid for the hazard before it is ordered.