Toxicity of elemental selenium and selenium substances after pulmonary exposure; and environmental and occupational air concentrations: a review

Selenium exposure via air can occur in the environment and workplace. To protect humans it is important to determine the concentrations at which different forms of selenium are toxic. We reviewed the literature on 1) selenium environmental and occupational air concentrations and 2) biokinetics and toxicity after pulmonary exposure. Environmental selenium ranged between 0.1 to 20 ng/m3, while occupational selenium was up to 2 mg/m3. Inhaled selenium distributes to blood and as demonstrated in animals to the internal organs. Excretion has been demonstrated to occur via urine, feces and breath. Toxicity data are scarce: two studies with occupational exposure to elemental selenium showed no effect at 0.11 and 0.32 mg Se/m3. In guinea pigs, inhalation of elemental selenium indicated a lowest-observed-adverse-effect concentration (LOAEC) of 33 mg Se/m3 on affected lung and spleen (no controls available). Inhalation of hydrogen selenide in the same species resulted in a LOAEC of 1 mg Se/m3 on lethality. Animal studies using intratracheal instillation resulted in lowest-observed-adverse-effect levels (LOAELs) set on lung function of 0.06 mg Se/kg bodyweight (bw) (selenite), and 0.6 mg Se/kg bw (selenium dioxide). For dimethyl selenide, a LOAEL on lethality was 0.1 mg Se/kg bw. In conclusion, environmental selenium ranges from 0.1 to 20 ng Se/m3, while occupational selenium levels can be magnitudes higher. Selenium distributes to blood and internal organs after pulmonary exposure. Animal inhalation studies indicate LOAECs of 1 and 33 mg Se/m3, while LOAELs of intratracheal instillation studies start at 0.06 mg Se/kg bw.