Benzene documenting exposure

The Benzene Subregistry Baseline Technical Report of the National Exposure Registry contains information on 1,143 persons who had documented exposure to benzene in their drinking water and were exposed for at least 30 days (ATSDR 1995). Although no causal relationship has been proposed for health conditions identified in the subregistry, continued follow-up of the population is planned to provide information on health effects of environmental exposure to benzene. 

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). 

However, there are some potential effects of spilled oil on fish. The impacfs on fish are primarily to fhe eggs and larvae, wifh limited effecfs on fhe adulls. The sensitivity varies by species pink salmon fry are affected by exposure to water-soluble fractions of crnde oil, and pink salmon eggs are very tolerant to benzene and water-soluble petroleum. The general effects are difficnlt to assess and document quantitatively, dne to the seasonal and natural variability of the species. Fish rapidly metabolize aromatic hydrocarbons, due to their enzyme system. 

The exact mechanism of action of most volatile substances remains unknown. Altered function of ionotropic receptors and ion channels throughout the central nervous system has been demonstrated for a few. Nitrous oxide, for example, binds to NMDA receptors and fuel additives enhance GABAa receptor function. Most inhalants produce euphoria increased excitability of the VTA has been documented for toluene and may underlie its addiction risk. Other substances, such as amyl nitrite ("poppers"), primarily produce smooth muscle relaxation and enhance erection, but are not addictive. With chronic exposure to the aromatic hydrocarbons (eg, benzene, toluene), toxic effects can be observed in many organs, including white matter lesions in the central nervous system. Management of overdose remains supportive. 

OSHA requires employers of workers who are occupationally exposed to benzene to institute engineering controls and work practices to reduce and maintain employee exposure at or below permissible exposure limits (PEL). If the employer can document that benzene is used in the workplace less than 30 days per year, the employer can use any combination of engineering controls, work practice controls, or respirators to reduce employee exposure to or below the (PEL) of 1 ppm. However, the employer must use... 

The oral toxicity in animals was found to be low to very low. An LD50 value of 3500 mg/kg for rats has been documented (NIOSH 1986). No adverse effects were noted in animals subjected to chronic inhalation exposure at below 400 ppm. At higher dosages only the liver was affected (ACGIH 1986). Ethyl benzene is eliminated from the body by metabolic excretion. The urinary metabolites in humans are mainly mandelic acid, C6HsCH(OH)COOH, and benzoyl-formic acid, CeHsCOCOOH. 

Benzene has the ability to damage the bone marrow and to cause anemia and leukemia. This hematopoietic toxicity shown by benzene is unique as the myelotoxic effect disappears when one or more alkyl groups are attached to the benzene structure. Toluene and xylene are examples of the aromatic solvents which do not show the hematopoietic toxicity. The OS HA regulation 29 CFR 1910.1028 allows a Permissible Exposure Limit (PEL) of 1.0 ppm benzene in the work area for an 8 hr day and 40 hr work week. The current documents of both the OSHA and ACGIH organizations consider benzene as a suspected human carcinogen. 

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