The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the U.S. Government.
The in-life phase of the study was conducted at Battelle Toxicology Northwest (Battelle), Richland, WA, under Battelle Protocol No. 20213-02 as a part of National Toxicology Program Contract No. N01-ES-55534. At the request of the NTP, an immunotoxicological evaluation was conducted at Virginia Commonwealth University, Richmond, Virginia, under NTP Contract No. N01-ES-55538. The Study Director/Principal Investigator for the immunotoxicology studies was Kimber L. White, Jr., Ph.D., while Tai L. Guo, Ph.D., DABT, served as the Assistant Study Director.
The objective of the studies described in this report was to determine the potential effects of Blasting Sand (Chemical Abstracts Service #BLASTINGSAND) on the immune system of Harlan Sprague Dawley rats. Female HSD rats were exposed to blasting sand by inhalation at four concentrations (0, 15, 30, and 60 mg/m3) for up to 27 weeks. Male HSD rats were exposed to blasting sand by inhalation at four concentrations (0, 15, 30, and 60 mg/m3) for up to 39 weeks. The evaluation of immune parameters was conducted on samples collected from two groups: an Immunotoxicology Group (female HSD rats) and a Core Group (male HSD rats). The animals from the Immunotoxicology group were further divided into two subgroups. One subgroup was immunized with sheep erythrocytes (sRBC) and was used to evaluate the T-dependent antibody-forming cell response to sRBC and serum anti-sRBC IgM antibody levels, while the second subgroup remained unimmunized and was evaluated for immune cell subpopulations in the spleen, anti-CD3 mediated spleen cell proliferation, natural killer cell activity, bronchoalveolar lavage fluid cytokine levels, and autoantibody formation (i.e. anti-nuclear antibodies. The Core Group was evaluated for BAL fluid cytokine levels and autoantibody formation only. Samples from the Immunotoxicology Group were received from Battelle at pre-determined time points over the duration of the study (4 and 26 weeks for unimmunized animals; 5 and 27 weeks for immunized animals). Samples from the Core Group were received from Battelle at four pre-determined time points during the course of the study (4, 16, 26, and 39 weeks after study initiation).
On the day of study termination, spleens were placed in tubes containing media, placed on crushed ice, and shipped to VCU in Richmond, VA, for immunotoxicological evaluation the following day. The collected BAL fluid and the serum for autoimmunity evaluation were frozen and shipped separately on dry ice to VCU, where they were maintained at -70° C until evaluated. Mediastinal and tracheobronchial lymph nodes from unimmunized animals in the Immunotoxicology Group received in RNAlater® from Battelle were stored at -70°C until requested for transfer to an NTP-designated facility for RNA evaluation.
No significant standard operating procedure deviations occurred during the studies conducted at VCU that affected the quality of the data and the ability to interpret the data with respect to the immunotoxicity of blasting sand. Table ES-1 and ES-2 summarize the results for samples taken from the Immunotoxicology Group (female HSD rats) after 4 and 26 weeks of exposure to blasting sand.
No significant effects were observed the on the AFC response, serum anti-sRBC IgM antibody levels, or NK cell activity. Spleen cell numbers and absolute numbers of splenic NK cells and macrophages were decreased in rats exposed to 60 mg/m3 blasting sand for 26 weeks. Absolute numbers of splenic B cells were decreased at all treatment levels following 26 weeks of exposure. The percentage of splenic T helper (TH) cells was increased at doses ≥ 30 mg/m3 after both 4 and 26 weeks of exposure, while the percentage of B cells was decreased at these same doses at the 26-week time point. Anti-CD3 mediated spleen cell proliferation was unaffected at 4 weeks but was increased at 26 weeks in rats exposed to 60 mg/m3 blasting sand. The predominant effect on BAL fluid cytokine levels was a dose-related increase in MCP-1 after 26 weeks of exposure. Autoantibody levels were unaffected.
For samples taken from the Core Group (male HSD rats) following exposure to blasting sand for 4, 16, 26, and 39 weeks, MCP-1 levels in BAL fluid were significantly increased at the 60 mg/m3 exposure level after 4 weeks and at all exposure levels at all subsequent time points. No exposure-related effects were observed on autoantibody levels.
In conclusion, blasting sand exposure by inhalation for up to 26 weeks in female HSD rats produced minimal immunotoxic effects. The functional responses of humoral and innate immunity were unaffected. Spleen cell numbers were decreased, while anti-CD3-mediated proliferation was increased in female rats exposed to 60 mg/m3 blasting sand. Levels of MCP-1 were increased in a dose-dependent manner in both male and female HSD rats, beginning at week 4 in males and at week 26 in females. Autoantibody levels in serum from male and female HSD rats were not affected by exposure to blasting sand.