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Case Study 4: Benzene Toxicity
Pages 189-207

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From page 189...
... Or Benzene in the workplace has been associated with aplasfic anemia and leukemia and may also cause nonhematologic cancers. This monograph is one in a series of self-instructionalpublications designed to increase the primary care pro videos knowledge of hazardous substances in the environment and to aid in the evaluation of potentially exposed patients.
From page 190...
... The patient occasionally drinks beer; he quit smoking cigarettes 4 years ago. He does not have allergies and is taking no medications at this time.
From page 191...
... Sources of benzene in air are usually associated with chemical manufacturing or gasoline, including gasoline bulkloading and discharging facilities and combustion engines (such as in automobiles, lawn mowers, and snow blowers)
From page 192...
... in drinking water would correspond to, at most, 1 additional cancer case in 10,000 people exposed. (The current EPA maximum contaminant level [MCL]
From page 193...
... estimates that approximately two to three million workers in the United States may be exposed to benzene during refining operations; gasoline storage, shipment, and retail operations; chemical manufacturing; plastics and rubber manufacturing; shoe manufacturing; printing; and activities in chemical laboratories. A review of benzene exposure in the U.S.
From page 194...
... Bone marrow is the main target organ of benzene toxicity. It contains the MFO enzymes necessary to metabolize benzene, and although benzene metabolism in bone marrow is not clearly understood, one or more benzene metabolites are suspected as responsible for the hematotoxicity.
From page 195...
... Pathologic findings in fatal cases have included respiratory tract inflammation, lung hemorrhages, kidney congestion, and cerebral edema. Central Nervous System Effects Acute benzene exposure results in classic symptoms of CNS depression such as dizziness, ataxia, and confusion.
From page 196...
... However, a person exposed to benzene may develop leukemia without having aplastic anemia. Studies addressing the risk of leukemia associated with low-level benzene exposures have been inconclusive.
From page 197...
... History and Physical Examination In addition to a thorough medical history and physical examination, important factors in evaluating a patient potentially exposed to benzene include a detailed family history of blood dyscrasias including hematologic neoplasms, genetic hemoglobin abnormalities, bleeding abnormalities, and abnormal function of formed blood elements; an environmental history focusing on activities and possible sources of benzene exposure at home; and an occupational history, including past exposures to hematologic toxicants such as solvents, insecticides, and arsenic. A history of ionizing radiation exposure, medications, and smoking should also be explored.
From page 198...
... However, these methods are not clinically useful for patients exposed to the low levels of benzene typically found In ambient air. Urinary phenol concentrations generally correlate well with benzene exposure at concentrations above to ppm.
From page 199...
... If aplastic anemia is suspected, a bone marrow aspiration and biopsy should be performed. Aspiration of the marrow space often produces no sample (dry tap)
From page 200...
... Chronic Exposure In treating persons chronically exposed to benzene, the most important actions are to remove the patient from the source of benzene exposure and to prevent further exposure. Benzeneinduced depression of blood elements generally reverses after exposure is terminated.
From page 201...
... In 1 987, the Occupational Safety and Health Administration (OSHA) instituted a permissible exposure limit for benzene of 1 ppm, measured as an 8-hour time-weighted average (TWA)
From page 202...
... EPA has not promulgated a specific ambient air standard for benzene but has imposed restrictions designed to lower industrial emissions of benzene by 90% over the next 20 years. In addition, regulations have been proposed that would control benzene emissions from industrial solvent use, waste operations, transferoperations, and gasoline marketing.
From page 203...
... The maximum contaminant level goal (MCLG) , a nonenforceable health goal that would allow an adequate margin of safety for the prevention of adverse effects, is zero benzene concentration in drinking water.
From page 204...
... Benzene exposure in the United States, 1978-1983: an overview.
From page 205...
... . The registries will facilitate the identification and subsequent tracking of persons exposed to a defined substance at selected sites and will coordinate the clinical and research activities involving the registrants.
From page 206...
... The patient only occasionally drinks beer and did not take medications before his illness, and so he avoids the risk factors of alcohol and medications. However, if the patient is suffering from a hematologic abnormality, as his symptoms and laboratory evaluation suggest, he will have increased risk if benzene exposure continues.
From page 207...
... Finally, assuming the patient's condition is due to benzene exposure, you would need to weigh the significance of benzene sources other than the drinking water. For example, the patient is a diesel mechanic and most likely has inhalation and dermal exposure to gasoline (which contains benzene)


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