Researchers from the National Institute for Occupational Safety and Health (NIOSH), working in conjunction with management and employees at a label printing plant, discovered employees' exposure to two chemicals dimethylisopropanolamine (DMIPA) and dimethylaminoethanol (DMAE) both from a widely used category of chemicals called tertiary amines, caused blurred vision. Tertiary amines are widely found in solvents, chemical intermediates, catalysts, preservatives, drugs and herbicides.
The printing company requested help from NIOSH when several employees in the printing production area reported intermittent blurred vision. Although their vision typically improved within several hours of leaving work, the blurred vision caused a safety hazard while the employees were operating machinery on the job and while they were driving home. Employees could not predict when the condition would occur, but it was beginning to happen more frequently, they reported. One employee was examined by an ophthalmologist, who discovered "a film over his eyes."
"Employers and employees frequently turn to NIOSH for help in solving complex health and safety concerns," said NIOSH Director John Howard, M.D. "As in this case, finding the answer often involves a combination of technical expertise, practical experience on the shop floor, vigorous scientific sleuthing and close collaboration with our partners."
NIOSH's investigation determined the condition was related to exposure to DMIPA, a component of an additive used to thin ink, and DMAE, a component of water-based inks. The number of employees reporting blurred vision, the number with film or opacities on the cornea and the severity of the opacity increased with corresponding exposure to the compounds. Neither compound previously had been linked to vision disturbances in humans.
NIOSH investigators with participation from management and employees measured exposure levels, assessed the plant ventilation system, administered eye examinations and questionnaires and used vigorous statistical analysis to assess the likelihood that a given exposure was associated with symptoms of visual change. Although it was impossible in the statistical analysis to distinguish the role of one compound from that of the other, NIOSH reports that DMIPA was the more likely suspected cause, although both compounds would be expected to product the same effects.
As a result of the study:
- The company began diluting the DMIPA used in the printing process. Visual symptoms immediately ceased.
- Further recommendations were made to reduce exposures cost effectively by first controlling the specific sources of tertiary amines associated with the printing machines, and then repositioning the plant's outdoor air intakes and exhaust discharge locations.
- NIOSH generated new findings that may help employers and employees at other sites to anticipate, identify and solve previously unsuspected problems.
- NIOSH tested a new analytical method for detecting amines, and found it provided a more reliable tool for detecting amines than the existing method. NIOSH incorporated the new method in its widely used Manual of Analytical Methods, available at www.cdc.gov/niosh.
According to NIOSH, based on the last data collected in the 1980s, 35,000 employees were estimated to be exposed to DMAE and 20,000 were estimated to be exposed to DMIPA. The agency estimates those numbers have increased dramatically because solvent-based inks increasingly have been replaced with water-based inks containing amines.
NIOSH published its results in the January 2003 edition of the British journal Occupational and Environmental Medicine.