Toxicity report series
-
Toxicity report series · Aug 2006
NTP Toxicity Study Report on the atmospheric characterization, particle size, chemical composition, and workplace exposure assessment of cellulose insulation (CELLULOSEINS).
Cellulose insulation (CI) is a type of thermal insulation produced primarily from recycled newspapers. The newspapers are shredded, milled, and treated with fire-retardant chemicals. The blowing process for installing CI generates a significant quantity of airborne material that presents a potential inhalation hazard to workers. CI was selected for study based upon the high production volume, the potential for widespread human exposure, and a lack of toxicity data; insufficient information was available to determine whether inhalation studies in laboratory animals were technically feasible or necessary. Studies were conducted to characterize the chemical and physical properties of CI aerosols, to evaluate the potential acute pulmonary toxicity of CI, and to assess occupational exposure of CI installers. Workplace exposure assessments were conducted in collaboration with the National Institute for Occupational Safety and Health (NIOSH, 2001). ⋯ Chemical analyses of the four bulk CI samples revealed only minor differences in additives. The major elemental components detected were aluminum, boron, calcium, sodium, and sulfur, but they were attributed to the fire retardants aluminum sulfate, boric acid, and sodium sulfate. For all four CI samples, less than 0.1% by weight was collected as the small respirable particle fraction. The fractions consisted mainly of fire retardants and smaller quantities of clays and did not contain cellulose material. Intratracheal instillation of the respirable fraction in rats produced minimal to mild inflammatory responses in the lungs with no increase in severity by 28 days after dosage. Although a significant increase in lung collagen was detected at day 28 in treated rats, microscopic evaluation revealed only a minimal to mild increase in collagen fibrils associated with granulomatous nodules. The results of these studies indicated that few respirable particles or fibers are generated during the aerosolization of CI, and that even at very high doses of respirable CI particles, acute pulmonary toxicity is minimal. These results are supported by the NIOSH workplace exposure assessment conducted on CI workers. Based on the air sample data collected from the 10 contractor site visits, there is a potential for overexposure to CI; however, respirable dust concentrations were typically low. There was increased potential for 8-hour TWAs exceeding the OSHA PEL for total and respirable dust when employees were involved in CI application activities for longer periods of time. There was evidence of work-related eye and mucous membrane irritation among some workers, which were possibly caused by the additives present in CI, such as boric acid. There was little evidence of lower respiratory system health conditions associated with CI exposure. Based upon the results of the CI chemical characterization studies, the pulmonary toxicity study, and the worksite exposure assessment, the NTP concluded that additional studies of CI in laboratory animals are not warranted at this time. However, the animal pulmonary toxicity studies and worker health surveys focused on acute CI exposures and do not preclude the possibility of toxicity resulting from chronic exposure. Although exposure concentrations of respirable CI particulate matter were low, additional information is needed on the biodurability and reactivity of CI particles and fibers in the respiratory tract. CI should continue to be regarded as a nuisance dust, and workers should continue to wear protective masks to prevent inhalation exposure to CI dusts.