New Look at BTEX: Are Ambient Levels a Problem?

Benzene, toluene, ethylbenzene, and xylene (BTEX) are retrieved during fossil fuel extraction and used as solvents in consumer and industrial products, as gasoline additives, and as intermediates in the synthesis of organic compounds for many consumer products. Emissions from the combustion of gasoline and diesel fuels are the largest contributors to atmospheric BTEX concentrations. However, levels indoors (where people spend greater than 83% of their time) can be many times greater than outdoors. In this review we identified epidemiological studies assessing the noncancer health impacts of ambient level BTEX exposure (i.e., nonoccupational) and discussed how the health conditions may be hormonally mediated. Health effects significantly associated with ambient level exposure included sperm abnormalities, reduced fetal growth, cardiovascular disease, respiratory dysfunction, asthma, sensitization to common antigens, and more. Several hormones including estrogens, androgens, glucocorticoids, insulin, and serotonin may be involved in these health outcomes. This analysis suggests that all four chemicals may have endocrine disrupting properties at exposure levels below reference concentrations (i.e., safe levels) issued by the U.S. Environmental Protection Agency. These data should be considered when evaluating the use of BTEX in consumer and industrial products and indicates a need to change how chemicals present at low concentrations are assessed and regulated. ■ INTRODUCTION As the demand for methane increased to meet the world’s growing energy needs, so grew the demand for aromatic compounds used as the feedstock for a vast number of materials and products upon which society has become dependent. Along with methane and crude oil, semivolatile gases also surface during fossil fuel extraction. Benzene, toluene, ethylbenzene, and xylene (BTEX; Figure 1) are of particular concern due to their widespread use in gasoline and other consumer products and exposures from vehicular traffic and fossil fuel extraction emissions which are occurring in closer proximity to populated areas. Sources and Uses. During the extraction of crude oil and raw natural gas, aromatic compounds, including BTEX are captured at the wellhead as liquids and delivered to refineries. BTEX are then isolated and/or synthesized by catalytic reforming, cracking of naphtha, and other chemical reactions including dealkylation, alkylation, and coal coking. Once isolated, they are used in a variety of products including adhesives, coatings, degreasers, detergents, dyes, explosives, fuels, ink, lacquers, paint, pesticides, polishes, resins, rubber cement, and solvents, which are then utilized in the manufacture of products found in businesses, homes, and schools. BTEX are also widely used as intermediates in the synthesis of thousands of other organic compounds by the chemical and pharmaceutical industries and product manufacturers. Another common use of BTEX is in fuel formulations. They are combined in specific proportions to make reformates, which are added to motor and aviation fuel to prevent autoignition of the fuels under high temperature and high pressure conditions. According to a 1998 report, BTEX collectively comprised as much as 27.5% of high octane gasoline at the pump. Received: February 27, 2014 Revised: February 6, 2015 Accepted: February 11, 2015 Published: April 15, 2015 Figure 1. Structures and Chemical Abstracts Service (CAS) Registry numbers of BTEX. Images reprinted from Toxnet, National Institutes of Health, U.S. National Library of Medicine. Critical Review