EFFECTS OF NITROUS-ACID EXPOSURE ON HUMAN MUCOUS-MEMBRANES

Nitrous acid (HONO) is formed both indirectly from the reaction of nit rogen dioxide (NO2) with water on indoor surfaces, and directly during combustion. This gaseous pollutant may be a previously unrecognized c ausal factor in assessments of nitrogen oxide exposure effects. The pr esent study is the first attempt to evaluate exposure effects of HONO on the human airways and the mucous membranes of the eyes and nose. Fi fteen healthy adult nonsmokers were exposed for 3.5 h in a double-blin d, balanced protocol to clean air, 77, and 395 ppb HONO. Each exposure was preceded by a 1-h baseline measurement period, and exposures were separated by 1 wk. There was a 10-min exercise period during exposure . Effects measurements included assessment of bronchial reactivity, me asurement of specific airway conductance, spirometry, acoustic rhinome try, nasal lavage, tear-fluid cytology, a CO2 eye-provocation test, ev aluation of eye redness, and subjective sensations. Effects of HONO ex posure on the eyes were found as exposure-related changes in tear-flui d cytology. In particular, the number of squamous cells increased by 2 0, 67, and 80% following exposure to clean air, 77, and 395 ppb HONO, respectively (p = 0.004). Possible indications of exposure effects on sensitivity to CO2 eye provocation and on specific airway conductance were also measured. For specific airway conductance there was an appro ximate 10% decrease in conductance following exercise in association w ith HONO exposure, compared with a 2% decrease with clean air (p = 0.0 38).