TISSUE DISTRIBUTION AND ELIMINATION OF INDIUM IN MALE FISCHER-344 RATS FOLLOWING ORAL AND INTRATRACHEAL ADMINISTRATION OF INDIUM-PHOSPHIDE

The use of indium phosphide (InP) in the semiconductor industry has ra ised concerns about potential occupational exposure. The tissue distri bution and elimination of indium were investigated in adult male Fisch er 344 rats following either a single or 14 consecutive daily oral dos es, or following an intratracheal instillation of InP (10 mg/kg). The concentrations of indium ions in blood, urine, feces, and tissues were quantified either using direct acid digestion followed by electrother mal atomic absorption spectrophotometry (ET-AAS) or using an extractio n method with methyltricapryl ammonium ions to remove indium from the matrix followed by ET-AAS. Indium was poorly absorbed from the gastroi ntestinal tract in both single and multiple oral dose studies. Upon it s absorption, indium was relatively evenly distributed among the major organs such as liver, kidney, lung, spleen, and testes. By 96 h after oral dose treatment, less than 0.11% of the dose of indium was recove red from tissues in the single- or multiple-dose experiment. At 96 h, retention of indium in the body was about 0.36% of the dose (except fo r lung) following intratracheal instillation of InP. Following oral do se administration, the majority of indium was recovered from the gastr ointestinal tract and its contents. The high recovery of indivm 73% of the dose) in the feces after intratracheal instillation presumably re flects mucociliary clearance and/or biliary excretion of indium. Urina ry indium accounted only for 0.08-0.23% of the dose during a 240-h col lection period in both single- and multiple-dose studies. It seems tha t fecal excretion serves as the major route for indium elimination, an d this results from poor absorption. Because of the poor absorption oi indium following multiple oral doses or intratracheal instillation of InP, it seems unlikely that indium will accumulate in the body follow ing InP exposure.