Effect of Agglomeration on the Toxicity of Nano-sized Carbon Black in Sprague-Dawley Rats

OBJECTIVES: Recent studies have shown that nano-sized carbon black is more toxic than large respirable carbon black because of its higher surface area. However, it is not clear if carbon black made larger by agglomeration demonstrates decreased toxicity. The purpose of this study was to verify if agglomeration affects the toxicity of carbon black using three differently prepared nano-sized carbon black aerosols in nose-only inhalation chambers for 13 weeks. METHODS: Printex 90 was selected as a representative nano-sized carbon black. To generate aerosols of three different types of agglomerates, Printex 90 was dispersed in distilled water by three different methods: vortex, vortex+sonication, and vortex+sonication with dispersion in a stabilizer. Then, the three differently prepared solutions were aerosolized through venturi nozzles. Male Sprague-Dawley rats were exposed to Printex 90 aerosols in a nose-only exposure chamber for 6 h/d, 5 d/wk for 13 weeks at a concentration of approximately 9 mg/m(3). RESULTS: Numbers of total cells in the bronchoalveolar lavage (BAL) fluid, macrophages, and polymorphonuclear leukocytes were increased and carbon black masses were clearly seen in BAL cells and lung tissues of rats exposed to Printex 90. However, few differences were found between the three differently agglomerated aerosols. In addition, there were no significant differences in other parameters, such as body weight, lung function or cytokine levels in BAL fluid following carbon black exposure. CONCLUSIONS: Only mild to moderate respiratory effects were found in rats exposed to nano-sized carbon black at 9 mg/m(3) for 13 weeks. Agglomeration did not affect the toxicity of nano-sized carbon particles.