No, NH3 is far more toxic. LC50 stands for the dosage or concentration of a particular chemical resulting in a 50% loss of tested animals within a specific time-frame. NO2 deprives tissue of receiving adequate oxygen into the bloodstream. The term "Brown Blood Disease" is associated with the 25%+ concentrated NO2 tinging the blood a tan-brown coloration and a tan gills. NO2 loses its toxicity to Chloride (Cl-) by inhibiting the gills to absorb NO2. NH3 at >1.00mg/l clinically shows death within days (weeks time) and sublethal standards heightens overall stress factors within the body, thus breaking down the internal structures that allows the animal to function...so to speak. This is often the case with "New Tank Syndrome" (NTS) when by the time NO2 has become active and beginning to spike, NH3 has already peaked in causing chronic NH3 poisoning and overall body/internal organ failure.