NIOSH – Criteria for a Recommended Standard Occupational Exposure to Inorganic Mercury


The Occupational Safety and Health Act of 1970 created The National Institute for Occupational Safety and Health (NIOSH). NIOSH is part of the Centers for Disease Control and Prevention (CDC) in the Department of Health and Human Services (HHS). NIOSH is an agency established to help assure safe and healthful working conditions for working men and women by providing research, information, education, and training in the field of occupational safety and health.

NIOSH recommends that employee exposure to inorganic mercury in the workplace be controlled by adherence to the following sections. The standard is designed to protect the health and safety of workers for an 8-hour day, 40-hour week over a working lifetime. Compliance with the standard should prevent adverse effects of inorganic mercury on the health and safety of workers. The standard is measurable by techniques that are valid, reproducible, and available to industry and governmental agencies and is attainable with existing technology. The criteria and the standard recommended in this document will be reviewed and revised as necessary.

“Inorganic mercury” in this document includes elemental mercury, and all inorganic mercury compounds and organic mercury compounds other than ethyl and methyl mercury compounds. “Exposure to inorganic mercury” is defined as exposure to a concentration of inorganic mercury greater than 40% of the recommended level in the workplace. 


NIOSH – Criteria for a Recommended Standard Occupational Exposure to Inorganic Mercury

The onset of symptoms of mercury toxicity from chronic exposure is insidious, and with the exception of tremor, may be ignored by the individual or attributed to other causes. This is particularly  true with erethism, which is characterized by irritability, outbursts of temper, excitability, shyness, resentment of criticism, headache, fatigue, and indecision. Erethism is the most difficult manifestation of chronic mercury toxicity to evaluate, particularly when tremor is absent and these symptoms may be attributed to anxiety or neurasthenia. 

A group of nonspecific signs and symptoms have been associated with intoxication by inorganic mercury. [16,26,28] These include weakness, unusual fatigue, loss of weight, loss of appetite, insomnia, and gastrointestinal disturbances. Their association with mercury poisoning is difficult to assess. However, they may be considered a prelude to the appearance of more specific or severe symptoms of mercury toxicity when they are manifested in individuals having known exposure to mercury. [28] 

In tabulating the signs and symptoms in 87 cases of organic mercury poisoning reported in the literature since 1940, these authors found considerable overlap between signs and symptoms of mercury toxicity from organic mercury compounds and those usually associated with toxicity from inorganic mercury compounds. 

The kidney, in almost all situations, accumulates the highest concentrations of mercury as compared to other organs. [23] Kidney damage may result from excessive exposure to mercury as manifested by the nephrotic syndrome of edema, proteinuria, and the presence of casts or cells in the urine. Such damage may or may not be accompanied by an elevated mercury level in the urine. [16] The nephrotic syndrome may be the only manifestation of mercury intoxication and recovery from the nephrotic syndrome usually follows removal from exposure. In more severe cases of kidney damage, renal failure and oliguria may develop, leading to complete anuria.

Because of the wide variability in the exposure individuals may receive, a “normal” level of mercury in the body is difficult to establish with certainty. To complicate factors further, many of the investigations reporting on “normal” levels of mercury in “nonexposed” individuals fail to give adequate consideration to the population sampled, to all  possible sources of exposure, to the sampling and analytical methods employed; thus, the data do not permit definite evaluation and comparison. [13]

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