An Ammonia Abatement System for Whole-Body Small Animal Inhalation Exposures to Acid Aerosols

Abstract

Conducting whole-body acid aerosol inhalation exposures of laboratory animals is complicated by ammonia arising from the excrement of the test animals which is sufficient to completely neutralize much of the acid aerosol. The neutralization of acid by ammonia can only be controlled by the use of head-only exposure systems (Schlesinger et al., 1983), which are tedious for repetitive exposures for large numbers of rodents, or by complete elimination of ammonia as it is formed during the whole-body exposure. This latter approach appears to be most appropriate; therefore, the development of a small animal whole-body ammonia reduction system (SAWBARS) for inhalation exposures was desirable for long-term rodent exposure studies.

The removal of ammonia was accomplished by designing and fabricating stainless steel excreta pan manifolds to exhaust ammonia from the pans as it was generated. These manifolds were situated between neomycin-treated paper lining the excreta pans and a stainless steel screen that kept animal feces from entering the pans. Most ammonia is generated by the interaction of fecal urease bacteria with urinary urea and nitrogen products (Phalen, 1984). In addition, all chamber air influent was conditioned by a wet scrubber to remove ambient ammonia, minimizing background levels of the vapor. Total chamber air effluent was exhausted through the excreta pan manifolds.

The modification effectively removed up to 99% of the ammonia from the chamber atmosphere when incorporated with daily animal bedding changes during non-exposure periods. After incorporating the steps described, ammonia concentrations ranged from 13 to 25 ppb, with a mean of 20 ppb, for a chamber animal loading of twenty-nine guinea pigs (0.15% kg/I). Additionally, the ammonia levels in the chamber continued to decline over the 4-hour test period. This was believed to be associated with the continued desorption of ammonia from the animals' fur.