Effects of Inhalation Exposure to a Binary Mixture of Benzene and Toluene on Vitamin A Status and Humoral and Cell-Mediated Immunity in Wild and Captive American Kestrels

Abstract

Benzene and toluene are representative volatile organic compounds (VOC) released during production, storage, and transportation associated with the oil and gas industry and are chemicals of concern, as they are released in greater and possibly more biologically significant concentrations than other compounds. Most studies of air pollution in high oil and gas activity areas have neglected to consider risks to birds, including top-level predators. Birds can be used as highly sensitive monitors of air quality and since the avian respiratory tract is physiologically different from a rodent respiratory tract, effects of gases cannot be safely extrapolated from rodent studies. Wild and captive male American kestrels were exposed for approximately 1 h daily for 28 d to high (rodent lowest-observed-adverse-effect level [LOAEL] of 10 ppm and 80 ppm, respectively) or environmentally relevant (0.1 ppm and 0.8 ppm, respectively) levels of benzene and toluene. Altered immune responses characteristic of those seen in mammalian exposures were evident in kestrels. A decreased cell-mediated immunity, measured by delayed-type hypersensitivity testing, was evident in all exposed birds. There was no effect on humoral immunity. Plasma retinol levels as measured by high-performance liquid chromatography (HPLC) analysis were decreased in wild and captive kestrels exposed to the rodent LOAEL for combined benzene and toluene. This study indicates that American kestrels are sensitive to combined benzene and toluene. The study also illustrates the need for reference concentrations for airborne pollutants to be calculated, including sensitive endpoints specific to birds. Based on these findings, future studies need to include immune endpoints to determine the possible increased susceptibility of birds to inhaled toxicants.