United States exposure limits

Production, Import/Export, Use, and Release and Disposal. Currently, heptachlor use in the United States is limited to fire ant control in power transformers (EPA 1990b). However, because of former widespread use of heptachlor and the persistence of heptachlor epoxide, these compounds and their degradation products can still be found at low levels in indoor air, water, soil, and food. Disposal methods are well documented in the literature however, more current information would be useful. Information on historical disposal practices would be helpful in evaluating the potential for environmental contamination. More information on the volume of heptachlor used in fire ant control would be useful in estimating potential occupational exposure. 

A. Lead poisoning. Availability in the United States is limited to an oral formulation (100-mg capsules) officially approved by the FDA for use in children with blood lead levels > 45 mcg/dL. However, DMSA can also lower lead concentrations in adults. Note Administration of DMSA should never be a substitute for removal from lead exposure. In adults, the federal OSHA lead standard requires removal from occupational lead exposure of any worker with a single blood lead concentration in excess of 60 mcg/dL or an average of three successive values in excess of 50 mcg/dL however, recent data suggest that removal at lower blood lead levels may be warranted. Prophylactic chelation, defined as the routine use of chelation to prevent elevated blood lead concentrations or to lower blood lead levels below the standard In asymptomatic workers, is not permitted. Consult the local or state health department or OSHA (see Table IV-3, p 525) for more detailed information. 

Permissible levels of methyl chloroform in the workplace have been established in several countries. In the United States, OSHA limits worker exposure to the chemical to a time-weighted average concentration of 350 parts per million (ppm) in the workplace air in any 8-hour work shift of a 40-hour week. This 350-ppm standard is well above the concentration at which presence of the chemical is noticeable (odor threshold = 100 ppm), and at or below EPA s estimated no-observed-effect level for short-term exposure of humans (350 to 500 ppm). OSHA also has established a short-term exposure limit, or STEL, of 450 ppm for any 15-minute period. No adverse health effects are likely to arise from the industrial use of methyl chloroform when it is handled in accordance with the manufacturer s instructions. 

Acetate and triacetate are essentially unaffected by dilute solutions of weak acids, but strong mineral acids cause serious degradation. The results of exposure of heat-treated and untreated triacetate taffeta fabrics to various chemical reagents have been reported (9). Acetate and triacetate fibers are not affected by the perchloroethylene dry-cleaning solutions normally used in the United States and Canada. Trichloroethylene, employed to a limited extent in the UK and Europe, softens triacetate. 

The nature of potential exposure ha2ards of low level microwave energy continues to be investigated (116—118). In the United States, leakage emission from microwave ovens is regulated to the stringent limit of 5 mW/cm at 5 cm (119). There is no federal limit on emission from industrial systems but the IMPI has set a voluntary standard which specifies 10 mW/cm at 5 cm (120). Emission values are equivalent to personnel exposures at several meters, well below limits that had previously prevailed in eastern Europe. This conclusion, derived for microwave ovens, should be vaUd for all microwave systems (121). 

It is good practice to keep concentrations of airborne nickel in any chemical form as low as possible and certainly below the relevant standard. Local exhaust ventilation is the preferred method, particularly for powders, but personal respirator protection may be employed where necessary. In the United States, the Occupational Safety and Health Administration (OSHA) personal exposure limit (PEL) for all forms of nickel except nickel carbonyl is 1 mg/m. The ACGIH TLVs are respectively 1 mg/m for Ni metal, insoluble compounds, and fume and dust from nickel sulfide roasting, and 0.1 mg/m for soluble nickel compounds. The ACGIH is considering whether to lower the TLVs for all forms of nickel to 0.05 mg/m, based on nonmalignant respiratory effects in experimental animals. 

Radiation dose limits at a disposal site boundary are specified by the NRC as 25 x 10 Sv/yr (25 mrem/yr), a small fraction of the average radiation exposure of a person in the United States of 360 x 10 /Sv/yr (360 mrem/yr). Protection against nuclear radiation is fully described elsewhere... 

Environmental Levels and Exposures. Barium constitutes about 0.04% of the earth s cmst (47). Agricultural soils contain Ba " in the range of several micrograms per gram. The Environmental Protection Agency, under the Safe Drinking Water Act, has set a limit for barium of 1 mg/L for municipal waters in the United States. 

In 1971 the OSHA standard for benzene (20 CFR, Part 1910.0000) adopted a permissible exposure limit (PEL) of 10 ppm benzene measured as an 8-h TWA. In October of 1976 NIOSH updated its earlier criteria document on benzene and recommended that OSHA lower the benzene exposure standard from 10 to 1 ppm. This proposed implementation was blocked by the United States Supreme Court iu 1980 on the basis of iusufficient evidence linking benzene to cancer deaths. By the mid-1980s convincing evidence of the carciuogenicity of benzene appeared through animal studies which justified reconsideration of the 1 ppm PEL (130). 

Thus, there is a clear need to establish the relationship between the health effects of hazardous chemical agents in the environment and the level of occupational exposure to the body by means of an occupational exposure limit, in which a reference figure for the concentration of a chemical agent is set. In fact, occupational exposure limits (OELs) have been a feature of the industrialized world since the early 1950s. They were introduced, primarily in the United States, at a time when measures to prevent occupational diseases were considered more beneficial than compensating victims, and in this sense OELs have played an important part in the control of occupational illnesses. 

PEL Pg pmol PHS PMR ppb ppm ppt REL RfD RTECS sec SCE SIC SIR SMR STEL STORET TLV TSCA TRI TRS TWA u.s. UF yr WHO wk permissible exposure limit picogram picomole Public Health Service proportionate mortality ratio parts per billion parts per million parts per trillion recommended exposure limit Reference Dose Registry of Toxic Effects of Chemical Substances second sister chromatid exchange Standard Industrial Classification Standardized incidence ratio standard mortality ratio short term exposure limit STORAGE and RETRIEVAL threshold limit value Toxic Substances Control Act Toxics Release Inventory total reduced sulfur time-weighted average United States uncertainty factor year World Health Organization week... 

United States, See also American entries Army Corps of Engineers Atomic Energy Commission (AEC) Environmental Protection Agency (EPA) Federal entries Food and Drug Administration (FDA) Government entries National entries OSHA ozone exposure limits U.S. entries acrylic fiber consumption in, ll 220t acrylic fiber production in, 11 189 advanced materials research, 1 696 air separation industry in, 17 754 aliphatic fluorocarbon production in,... 

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