INHALATION OF THE PHOTOCHEMICAL SMOG COMPOUND PEROXYACETYL NITRATE

Inhalation of Simulated Smog Atmospheres Affects Cardiac Function in Mice

The health effects of individual criteria air pollutants have been well investigated. However, little is known about the health effects of air pollutant mixtures that more realistically represent environmental exposures. The present study was designed to evaluate the cardiac effects of inhaled simulated smog atmospheres (SA) generated from the photochemistry of either gasoline and isoprene (SA-G) or isoprene (SA-Is) in mice. Four-month-old female mice were exposed for 4 h to filtered air (FA), SA-G, or SA-Is. Immediately and 20 h after exposure, cardiac responses were assessed with a Langendorff preparation using a protocol consisting of 20 min of global ischemia followed by 2 h of reperfusion. Cardiac function was measured by index of left-ventricular developed pressure (LVDP) and cardiac contractility (dP/dt) before ischemia. Pre-ischemic LVDP was lower in mice immediately after SA-Is exposure (52.2 ± 5.7 cm H₂O compared to 83.9 ± 7.4 cm H₂O after FA exposure; p = 0.008) and 20 h after SA-G exposure (54.0 ± 12.7 cm H₂O compared to 79.3 ± 7.4 cm H₂O after FA exposure; p = 0.047). Pre-ischemic left ventricular contraction dP/dt_max was lower in mice immediately after SA-Is exposure (2025 ± 169 cm H₂O/sec compared to 3044 ± 219 cm H₂O/sec after FA exposure; p < 0.05) and 20 h after SA-G exposure (1864 ± 328 cm H₂O/sec compared to 2650 ± 258 cm H₂O/sec after FA exposure; p = 0.05). In addition, SA-G reduced the coronary artery flow rate 20 h after exposure compared to the FA control. This study demonstrates that acute SA-G and SA-Is exposures decrease LVDP and cardiac contractility in mice, indicating that photochemically-altered atmospheres affect the cardiovascular system.

Peroxyacetyl nitrate: review of toxicity

PAN is one of a class of common air pollutants formed by the action of sunlight on volatile organic compounds and nitrogen oxides. No toxicokinetic studies have been found in the available literature. The acute toxicity of PAN is less than that of ozone, similar to NO2 and higher than SO2. The LC30, in mice and rats were 718-743 mg/m3 (for 2 h) and 470 mg/m3 (for 4 h), respectively. Following acute exposure, severe lung lesions and, at the higher levels, damage to the epithelium of upper parts of the respiratory tract were found in animals. It seems that concentrations of 1.19-1.49 mg/m3 lie not far from the threshold required for pulmonary function effects in sensitive individuals. However, these PAN concentrations are well above the maximum ambient concentrations usually experienced within the USA and Canada (0.003-0.078 mg/m3). It appears unlikely that present ambient PAN concentrations would affect pulmonary functions responses to ambient ozone. In human, the lowest level causing eye irritations was 0.64 mg/m3 for 2 h. Concentrations of 0.99 and 4.95 mg/m3 were identified as no-observed-effect level (NOEL) and no-observed-adverse-effect level (NOAEL) for pathological and histological changes in the respiratory system (nasal passages) of rats during subchronic exposures to PAN, but were not considered to be relevant to derivation of a RfC for chronic inhalation exposure. PAN is a weak point mutagen or clastogen. The data are not sufficient to evaluate its carcinogenicity. No study was found which could be used for the derivation of a RfC for acute or chronic inhalation exposure to PAN.