Repeated dose inhalation developmental toxicity study in rats exposed to cellulose insulation with boric acid additive.

Cellulose insulation (CI), a common building material, is a mixture of cellulose fibers and borates. Borates are approximately 20% of the product weight and act as a flame retardant. Given possible exposure to workers and consumers, an inhalation toxicity study was conducted following Organization for Economic Co-operation and Development (OECD) 414 for Prenatal Development Toxicity to evaluate if CI is a developmental toxicant. Pregnant female rats were exposed by nose-only inhalation to CI aerosols containing 20% boric acid for six h/day, from gestational day (GD) 6-19, and fetuses were evaluated for developmental parameters. Respirable CI was produced by grinding to produce respirable particles (MMAD 2.7-2.9 µm, geometric standard deviations (GSD) 1.9-2.6), which were then aerosolized. Target air concentrations were 15, 90, and 270 mg CI/m3 . Controls were exposed to air only. Slight body weight reductions (average decrease <7% vs. control) were observed in male and female GD 20 fetuses in the mid and high dose groups. No embryo/fetal developmental toxicity or alterations in any other measured variable were reported at any dose. The no observed adverse effect level (NOAEL) for developmental outcomes was 270 mg/m3 .