The Collaborative International Dictionary of English v.0.48:

decontaminate \de`con*tam"i*nate\
   (d[-e]`k[u^]n*t[a^]m"[i^]*n[=a]t), v. t.
   To remove contamination or contaminants from, by a cleansing
   process; -- usually used of radioactive, infectious, or toxic
   materials; as, to decontaminate clothing worn by persons with
   infective disease; decontaminate an area of PCB's after
   explosion of a transformer.
   [PJC]

WordNet (r) 3.0 (2006):

decontaminate
    v 1: rid of contamination; "The soil around the housing
         development had to be decontaminated by the city" [ant:
         contaminate]