ata collected during the National Occupational Hazard Survey (NOHS) conducted by NIOSH during 1972-1974.15
In the United States, methyl chloride is produced primarily by the hydrochlorination of methanol.2,4,16 Although the primary use of methyl chloride is in the manufacture of silicones, this process is a closed system operation with minimal worker exposure. The manufacture of tetramethyl lead and triptane (2,2,3-trimethyl butane), both antiknock fuel additives,2 is the next largest use of methyl chloride. Other uses of methyl chloride include the production of butyl rubber; di-, tri-, and tetra-halogenated methanes; methyl cellulose; quaternary ammonium compounds; methyl mercaptan; methionine; and fungicides and pesticides (primarily methyl arsenate herbicides).16 A former high volume use of methyl chloride as a refrigerant and propellant has declined significantly in recent years with the substitution of chlorofluorinated alkane derivatives (chlorinated fluorocarbons). In 1981, approximately 362 million pounds of methyl chloride were produced in the United States, and domestic consumption is projected to expand by approximately 6.5% per year through the mid-1980's.16 Approximately 41,000 U.S. workers (Table 2) are potentially exposed to methyl chloride.15
Methyl bromide is produced by direct bromination of methane and by the hydrobromination of methanol.2 In the United States, methyl bromide is used primarily as a soil and spore fumigant.17 Methyl bromide is also used as a disinfectant, rodenticide, methylating agent, and wool degreaser and in ionization chambers.2,18,19
Table 2 Number of Workers Potentially Exposed to the Monohalomethanes by Industry15
|Sic* Code||Description||Number of Workers Potentially Exposed|
|Methyl Chloride||Methyl Bromide||Methyl Iodide|
|07||Agriculture Services and Hunting||647||5,922||-|
|13||Oil and Gas Extraction||24||129||-|
|15||General Building Contractors||1,301||934||-|
|16||Heavy Construction Contractors||405||-||-|
|17||Special Trade Contractors||1,143||1,936||-|
|20||Food and Kindred Products||2,720||4,356||-|
|22||Textile Mill Products||8||237||-|
|23||Apparel and Other Textile Products||-||52||-|
|24||Lumber and Wood Products||112||471||-|
|26||Paper and Allied Products||-||1,270||-|
|27||Printing and Publishing||212||80||-|
|28||Chemicals and Allied Products||980||4,859||394|
|29||Petroleum and Coal Products||16||11||-|
|30||Rubber and Plastics Products, NEC||-||89||-|
|31||Leather and Leather Products||85||38||-|
|33||Primary Metal Industries||1,223||44||-|
|34||Fabricated Metal Products||238||65||-|
|35||Machinery, Except Electrical||1,292||357||-|
|36||Electrical Equipment and Supplies||451||345||-|
|38||Instruments and Related Products||453||174||-|
|39||Miscellaneous Manufacturing Industries||418||34||-|
|41||Local and Interurban Passenger Transit||73||27||-|
|45||Transportation by Air||1,115||11,496||-|
|49||Electric, Gas, and Sanitary Service||-||10,069||-|
|53||Retail General Merchandise||402||1,356||-|
|55||Automotive Dealers & Service Stations||14,734||-||-|
|58||Eating and Drinking Places||-||17,958||-|
|73||Miscellaneous Business Services||8,960||l2,600||20|
|79||Amusement and Recreation Services||342||4,l47||-|
|80||Medical and Other Health Services||431||12,015||-|
*Standard Industrial Classification Code [return to table]
Most of the exposure data available on methyl bromide come as a result of the uses of methyl bromide as an agricultural fumigant. These include use as a nematocide, fungicide, herbicide, and insecticide.17 Methyl bromide is applied into the soil under plastic sheets or used in space fumigation under tarpaulins. It is also applied to a variety of agricultural commodities in specially designed fumigation chambers. Worker exposure may result from leaks in the plastic sheets or the tarpaulin or from failure to allow adequate time for the methyl bromide to dissipate following fumigation.
In 1979, the latest year for which any production quantities are available, between 60 and 80 million pounds of methyl bromide were domestically produced for use 