od 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 as a pesticide; however, approximately 50% of this amount was exported to other nations.20 Approximately 105,000 U.S. workers (Table 2) are potentially exposed to methyl bromide.15
Methyl iodide is produced on a limited commercial scale by any of the following methods: 1) the reaction of methanol and iodine in the presence of phosphorous; 2) the reduction of an aqueous solution of iodine with bisulfate ion to yield hydriodic acid, which reacts with dimethyl sulfate to form methyl iodide; or 3) the reaction of hydrogen gas, elemental iodine, and aqueous methanol,2 which is similar to the production method of methyl chloride and methyl bromide. Methyl iodide is used primarily as a methylating agent2 with approximately 400 U.S. workers (Table 2) potentially exposed.15
Exposure Standards and Guides
The current Occupational Safety and Health Administration (OSHA) permissible exposure limits (PEL's) (29 CFR 1910.1000) for occupational exposure to these monohalomethanes are as follows:21
|Methyl Chloride||100 ppm, 8-hr time-weighted average (TWA) concentration|
|200 ppm, acceptable ceiling concentration|
|300 ppm, acceptable maximum peak for 5 minutes in any 3-hr period above the acceptable ceiling for an 8-hr shift|
|Methyl Bromide||20 ppm (80 mg/m3), ceiling concentration; Skin|
|Methyl Iodide||5 ppm (28 mg/m3), 8-hr TWA; Skin|
The OSHA PEL's for occupational exposure to methyl chloride and methyl iodide are intended to protect against the neurotoxic effects of these compounds. For methyl bromide, the OSHA PEL is intended to protect against the development of pulmonary edema as well as neurotoxic effects. The PEL for methyl chloride is based upon ANSI Z37.18-1969 as developed by the American National Standards Institute (ANSI),22 while the PEL's for methyl bromide and methyl iodide are based upon the 1968 Threshold Limit Values (TLV®s) of the American Conference of Governmental Industrial Hygienists (ACGIH).23 At the present time, NIOSH has no recommended exposure limit for the monohalomethanes.
ACGIH in its 1984-85 e