approved by the U.S. Food and Drug Administration (FDA) for use in food contact films. Occupational exposure to caprolactam occurs primarily from the manufacture of nylon 6 fibers and resins. Highly soluble in water, caprolactam leaches from clothing made from polyamide fibers when the clothing is soaked in simulated perspiration (Statsek and Ivanova 1978). It has been found in groundwater, surface waters, and finished water (IARC 1986; EPA 1988). Water produced in the Shuttle from fuel cells is iodinated, collected in large containers called contingency water containers (CWCs), and transferred to the International Space Station (ISS) for use by the crew. These CWC bags are used to store drinking water containing silver used as a biocide, and for collection and storage of humidity condensate that will be processed to potable water. The bags are lined with a material called Combitherm. When the Crew and Thermal Systems Division of the National Aeronautics and Space Administration (NASA) was performing material compatibility testing to see if CWC-stored water undergoes quality degradation, it was found that the total organic carbon (TOC) concentration increased. It was determined that caprolactam was the only contributor to this increased TOC. It was also found that the Combitherm material leaches caprolactam during storage, and irrespective of the biocide used (iodine or silver), the leaching continued. A concentration of 16 milligrams per liter (mg/L) of caprolactam was found at the end of 24 weeks (wk). Thus, NASA was prompted to evaluate caprolactam for potential health hazards at this concentration and to recommend a spacecraft water exposure guideline (SWEG).
No human data are available on the absorption of caprolactam from an oral dose. However, from an animal study of disposition pharmacokinetics described below (Unger et al. 1981), it appears that caprolactam is almost completely absorbed from the gastrointestinal (GI) tract, because within 24 hours (h), more than 80% of the administered dose (14C-caprolactam) was recovered in urine, feces, and expired air.
Two sets of studies were carried out by Unger et al. (1981) on the disposition kinetics of caprolactam when dosed via the oral route. In the first set of experiments, a single oral bolus of 14C-caprolactam in water