Mercaptans
Environmental Sources
Mercaptans are colourless and odorous gases linked to animal facilities, wastewater
treatment plants, paper and pulp manufacturing and bio solids recycling
operations. Mercaptans are also used as a gas odorant, catalyst, intermediate
in manufacturing jet fuels, as well as, the manufacture of some pesticides
and fungicides. They are usually associated with garlic and rotten cabbage
like odours.
Human Health effects
The most frequently reported health complaints include eye, nose, and throat
irritation, headache, nausea, diarrhoea, hoarseness, sore throat, cough,
chest tightness, nasal congestion, palpitations, shortness of breath,
stress, drowsiness, and alterations in mood.
Typically, these symptoms occur at the time of exposure and remit after a short
period of time. However, for sensitive individuals such as asthmatic patients,
exposure to odours may induce health symptoms that persist for longer
periods of time as well as aggravate existing medical conditions.
Mercaptans are also irritating to the skin, eyes, mucous membranes and
respiratory tract and is considered to be slightly toxic if inhaled. High
concentrations may produce central nervous system (CNS) effects such as
headache, staggering gait, muscular weakness, tremors and, with severe
exposures, lung oedema (accumulation of fluid), convulsions, paralysis
of the respiratory centre and death.
Exposure limits
- The US EPA requires that discharges, spills, or accidental releases
of 100 pounds or more of methyl mercaptan must be reported to the EPA.
- The US Occupational Safety and Health Administration (OSHA) has set
a permissible exposure limit of 20 milligrams of methyl mercaptan per
cubic meter of air (20 mg/m3) for an 8-hour workday in a 40-hour
workweek.
- The American Conference of Governmental and Industrial Hygienists
(ACGIH) and the US National Institute for Occupational Safety and Health
(NIOSH) recommend an occupational exposure limit of 1mg/m3
for methyl mercaptan over 15 minutes and recommends a threshold limit
value (TLV), 8-hour time weighted average (TWA), of 0.5 ppm for methyl
mercaptan.
Sources and Links:
www.penweb.org/issues/sludge/health-odor.htm
www.e-organicchemicals.com/thio/msds/62.pdf
www.atsdr.cdc.gov/tfacts139.html
www.occuphealth.fi/ttl/projekti/htp/english/syn_eng.htm
www.modcon.co.il/exposure.htm
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