Short-term rat inhalation study with aerosols of acrylic ester-based polymer dispersions containing a fraction of nanoparticles.

Aqueous polymer dispersions are important raw materials used in a variety of industrial processes. They may contain particles with diameters ranging from 10 to 1500 nm. Polymer exposure alone may cause pulmonary lesions after inhalation exposure. Polymer dispersions with increased proportions of nano-sized particles are being developed for improved material characteristics, and this may pose even increased pulmonary hazards upon potential inhalation exposure. In a 5-day screening study, male rats were nose-only exposed to aerosols generated from 2 dispersions of acrylic ester polymers with identical chemical composition but different nano-sized particle proportions at particle concentrations of 3 and 10 mg/m³. Immediately and 19 days after the end of inhalation, necropsies were conducted with major emphasis on respiratory tract histopathology. Three and 23 days after the end of inhalation, bronchoalveolar lavage was performed to screen for early pulmonary injury and inflammation. In contrast to the adverse effects known for other materials in short-term inhalation studies, none of the tested preparations of acrylic ester polymers elicited any adverse effect at the end of the inhalation or postinhalation periods. No shift in toxicity could be observed by the increased proportion of nano-sized polymer particles. Under the conditions of this study, the no observable adverse effect levels for both preparations were >10 mg/m³, that is 2- to 3-fold beyond current nuisance dust threshold limit values.