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Greater Respiratory Effects of Acute Biomass Smoke Inhalation in Mice Compared with Episodic Exposures
Citation:
Hargrove, M., Y. Kim, C. King, Ian Gilmour, AND S. Gavett. Greater Respiratory Effects of Acute Biomass Smoke Inhalation in Mice Compared with Episodic Exposures. Society of Toxicology, Baltimore, Maryland, March 10 - 14, 2019.
Impact/Purpose:
Despite the potential public health threat from an increased exposure to wildland fire emissions, little is known about the relative toxicity of aerosols separated under different combustion conditions. The relative toxicity of biomass smoke inhaled at high concentrations for short periods of time compared with lower concentrations inhaled over longer periods of time is a question which needs to be addressed to assess public health impact. This study assesses the relative toxicity of eucalyptus wood smoke inhaled over varying periods of time with the same overall concentration times time (CxT) product. This information will inform the risk assessment of inhaled woodsmoke emissions.
Description:
Biomass smoke emissions can produce acute and chronic health effects including alterations in physiological responses within animal models. Health effects from wildfire biomass smoke emissions are determined by concentration and duration of exposures, but the relationship of concentration times time (C×T) to biomass smoke toxicity is unclear. Respiratory effects of biomass smoke generated from eucalyptus under high temperature (640 °C) flaming conditions were examined with a constant C×T target of 15 mg-hr/m3 in female Balb/cJ mice. Mice were exposed to biomass smoke at this C×T target under the following conditions: 3 mg/m3 particulate matter (PM), 1 h/d for 5 consecutive days (5D) or 1 h/d, 1 d/week over 5 weeks (5W), or a single 3 h exposure of 5 mg/m3 PM (unfiltered (1D) or filtered to examine effects of gases only (1Df)). CO levels were within a range of ~80-180 ppm for the exposures, and matching air-exposed control groups were included with all smoke-exposed groups. Pulmonary responses were assessed using head-out plethysmography to measure thoracic flow and ventilatory parameters prior to (20 min) and during each exposure. The 1D exposure reduced breathing frequency (vs. 5D and 5W groups) and minute volume (vs. 5W group) 40-60%. In addition, a prolonged relaxation time was observed for the entire exposure compared to both 5D and 5W exposure groups. The 5W exposure significantly lowered inspiratory time compared to both 1D and 5D exposure groups. The 1D exposure prolonged inspiratory, expiratory and relaxation times significantly during the 3rd hr of exposure when compared to the 1Df group. Moreover, a decreased breathing frequency during the last 40 minutes of the 3 h exposure period was observed during the1D exposure. BALF cell types were not altered significantly following any of the exposures. No significant changes were observed in BALF biomarkers of lung injury (protein, albumin, NAG and GGT) or cytokines (TNF-α, MIP-2) following flaming eucalyptus exposures compared to air exposures. We conclude that exposure to flaming eucalyptus for 3 h alters ventilatory parameters to a greater extent than intermittent 1 h exposures in healthy mice. (This abstract does not represent U.S. EPA policy.)