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Methemoglobinemia due to Occupational Exposure to Dinitrobenzene -- Ohio, 1986

On April 23, 1986, five steam-press operators at an Ohio rubber plant became ill with symptoms including yellow discoloration of the hands, blue discoloration of the lips and nail beds, headache, nausea, chest pain, dizziness, confusion, and difficulty in concentrating. One worker suffered a seizure. Medical examinations showed that blood methemoglobin (MetHb) levels in the workers ranged from 3.8% to 41.2% (normal level less than or equal to1%).

The workers had been using an adhesive to bond metal studs into rubber strips to be attached to automotive bumpers. When the outbreak occurred, officials of the company voluntarily stopped steam-press operations and asked that representatives from the Occupational Safety and Health Administration (OSHA) and the Ohio Industrial Commission investigate. Five days later, a plant supervisor operated the steam-press for about 2 hours so that an industrial hygienist with the Ohio Industrial Commission could take air samples. After the 2-hour simulation, the supervisor's blood MetHb level was 12.5%. Since the cause of the incident remained unknown 1 week later, plant management requested technical assistance from the National Institute for Occupational Safety and Health (NIOSH) (1).

The product being used is a solvent-borne adhesive that is composed of carbon black (less than 5% by weight), a proprietary curative system (less than 5% by weight), and xylene as a solvent (approximately 78% by weight). NIOSH personnel collected bulk samples from the lot ("old" lot) of adhesive used at the time of the outbreak and from a new lot that arrived after the outbreak. Samples were extracted with carbon disulfide and methanol, and the extracts were analyzed by using a gas chromatograph equipped with a flame ionization detector. Para-dinitrobenzene (p-DNB) was identified as a contaminant in the old lot of adhesive. So that concentrations of p-DNB in both the old and new lots could be determined, portions of the samples were extracted and p-DNB standards were dissolved in acetone and analyzed by gas chromatography. The concentration of p-DNB in the old lot (1% by weight) was approximately 30 times that in the new lot (0.03% by weight).

The NIOSH investigation, in conjunction with that of the adhesive manufacturer, revealed that p-DNB had been inadvertently formed during the manufacture of one of the proprietary substances used as a base chemical in the adhesive. This p-DNB- contaminated chemical was then introduced into the adhesive during its formulation. When notified of these findings, the manufacturer of the adhesive recalled all lots thought to be contaminated with significant quantities of p-DNB. The manufacturer also revised the material safety data sheet for this adhesive to indicate that trace amounts of dinitrobenzene, which can cause cyanosis, may be present.

NIOSH recommended that workers in the plant use butyl rubber gloves to avoid skin contact with the dried adhesive and that plant management institute periodic medical monitoring of all workers exposed to the adhesive. After plant officials replaced the p-DNB-contaminated adhesive with another product and implemented the recommendations, the steam-press operations were resumed.

NIOSH personnel monitored workers throughout the first day of operation for any signs of p-DNB exposure. No workers complained of any symptoms during or after the work shift, and none showed evidence of cyanosis during physical examination. To monitor workers for MetHb, NIOSH also collected preshift and postshift blood samples from nine steam-press workers using the new adhesive and from six office workers (controls) with no chemical exposure. MetHb levels in all blood samples were within normal limits and remained essentially unchanged over the workday. Reported by: Hazard Evaluations and Technical Assistance Br; Div of Surveillance, Hazard Evaluations, and Field Studies; National Institute for Occupational Safety and Health, CDC. Editorial Note: Aromatic nitro compounds, such as p-DNB, are used in many industries, including the manufacture of dyes, explosives, pigments, insecticides, textiles, plastics, resins, elastomers, photographic developers, pharmaceuticals, plant-growth regulators, fuel additives, rubber accelerators, and antioxidants (2,3). Because of this wide variety of uses, the potential for occupational exposure to these compounds is great.

The present incident illustrates that excessive exposure to aromatic nitro compounds may cause adverse health effects. p-DNB is readily absorbed by the skin and exerts its adverse health effects via the formation of MetHb from hemoglobin (Hb). Accumulations of MetHb greater than 1% of the total Hb substantially reduce the blood's capacity to carry oxygen to tissues of the body. Symptoms of illness are generally related to the percentage of MetHb in the blood: cyanosis and headache occur first (in persons with greater than 15% MetHb); dizziness and fatigue appear next (with greater than 40% MetHb); and ataxia, shortness of breath, tachycardia, nausea, vomiting, and drowsiness follow and can progress to stupor, coma, and possibly death (when levels exceed 70% MetHb).

The overall effect of substances that form MetHb is known as the "cyanosis- anemia syndrome" (4,5). p-DNB ranks second among cyanosis-producing chemicals and is also potent in causing anemia (Table 1).

The current OSHA permissible exposure limit and the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value for p-DNB is 1 mg/m3 based on an 8-hour time-weighted average, and the ACGIH notes that p-DNB can be absorbed cutaneously, which can contribute to overall exposure (6). Indeed, the skin is the main route by which several fat-soluble aromatic nitro compounds, including p-DNB, enter the body. For this reason and also because many nitrobenzene derivatives have low vapor pressures and do not reach high levels in the air, measures of airborne concentrations alone may not be the best indicator of total exposure.

The incident at this plant demonstrates the adverse health effects of a common class of industrial chemicals--aromatic nitro compounds--and emphasizes that employers and employees should know the potential dangers of exposure to these substances as well as to toxic substances in general. Further, since the incident was caused by a contaminated base chemical, the prevention of future episodes also depends on careful quality control in manufacturing that chemical. The actions of company officials in stopping the steam-press operations and cooperating with NIOSH technical personnel led to the rapid and successful resolution of this problem. References

  1. Stephenson RL, Gupta S, Rondinelli R. Health hazard evaluation report no. HETA 86-350-1815. Cincinnati, Ohio: US Department of Health and Human Services, Public Health Service, 1987.

  2. Centers for Disease Control, Occupational Safety and Health Administration. NIOSH/OSHA occupational health guidelines for chemical hazards. Cincinnati, Ohio: US Department of Health and Human Services, Public Health Service; US Department of Labor, Occupational Safety and Health Administration, 1981; DHHS publication no. (NIOSH)81-123.

  3. International Labour Office. Encyclopaedia of occupational health and safety. Vol 2. 3rd ed. Geneva: International Labour Organization, 1983:1355-6,1451-4.

  4. Linch AL, Wuertz RL, Charsha RC. Chemical cyanosis and anemia control. In: Steere NV, ed. CRC handbook of laboratory safety. 2nd ed. West Palm Beach, Florida: CRC Press, 1978:342-78.

  5. Linch AL. Biological monitoring for industrial exposure to cyanogenic aromatic nitro and amino compounds. Am Ind Hyg Assoc J 1974;35:426-32.

  6. American Conference of Governmental Industrial Hygienists. Threshold limit values and biological exposure indices for 1987-1988. Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists, 1987:20.

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