title: Acceptable levels for ingestion of dimethylsilanediol in water on the International Space Station.
abstract: BACKGROUND
  Water is recovered aboard the International Space Station (ISS) from humidity condensate and treated urine. The product water is monitored for total organic carbon (TOC). In 2010 the TOC readings indicated that a new contaminant had entered the potable water and was steadily increasing toward the TOC screening limit of 3 mg x L(-1). In a ground-based laboratory, chemists discovered that dimethylsilanediol (DMSD) was the principal new contaminant. As no standard existed for safe levels of DMSD in water, the Toxicology Office at Johnson Space Center was asked to set such a standard.
  
  
  METHODS
  The Toxicology Office used methods developed over the past decade, in collaboration with the National Research Council Committee on Toxicology, for setting Spacecraft Water Exposure Guidelines (SWEGs). These methods require a thorough literature search and development of an acceptable concentration (AC) for each potential toxic effect, keeping in mind that the adverse effects that accompany spaceflight could increase toxicity for certain end points. Benchmark dose modeling was encouraged if sufficient data were available. The most sensitive AC becomes the driver for the SWEG.
  
  
  RESULTS
  Hematotoxicity, hepatotoxicity, and possibly neurotoxicity were the most sensitive toxicological endpoints for DMSD.
  
  
  CONCLUSIONS
  The SWEG for DMSD for 100 d of ingestion was set at 35 mg x L(-1), which is equivalent to 9 mg x L(-1) as TOC. This is well above the TOC SWEG of 3 mg x L(-1) and the peak DMSD level of processed water observed on orbit, which was 2.2 mg x L(-1) asTOC (8.5 mg x L(-10 of DMSD).
authors: Habitability & Environmental Factors Branch, NASA Johnson Space Center, 2101 NASA Parkway, Mail Stop SF2, Houston TX 77058, USA.
authors: Raghupathy
authors: R
authors: Ramanathan
authors: John T
authors: JT
authors: James
authors: Torin
authors: T
authors: McCoy
mesh_terms: D000328:Adult; D000818:Animals; D019985:Benchmarking; D060766:Drinking Water / Q000032:analysis* / Q000592:standards; D018504:Ecological Systems, Closed; D005260:Female; D006801:Humans; D008297:Male; D008452:Maximum Allowable Concentration; D017646:Organosilicon Compounds / Q000032:analysis / Q000592:standards / Q000633:toxicity*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013026:Space Flight; D014873:Water Pollutants / Q000032:analysis / Q000592:standards / Q000633:toxicity*
chemical_list: D060766:Drinking Water; D017646:Organosilicon Compounds; D014873:Water Pollutants; C412583:dimethylsilanediol