As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SUSPECTED DE-ICE FLUID IN CABIN AIR SYSTEM. BURNING TYPE 1 SMELL OCCURRED ABOUT 10 SECONDS AFTER TAKEOFF WITH SMOKE TOILET CAUTION MESSAGE. CREW DECLARED EMERGENCY AND RETURNED TO DEPARTURE POINT. POST LANDING INVESTIGATION DID NOT REVEAL EVIDENCE OF FIRE. CREW SUSPECTS EXCESSIVE DE-ICE FLUID SPRAYED ON THE REAR OF THE AIRCRAFT. NO RELATED DISCREPANCIES INDICATED.