Identification of hydrogen peroxide as a photoproduct toxic to human cells in tissue-culture medium irradiated with "daylight" fluorescent light.

Hydrogen peroxide, lethal for human cells, is produced in Dulbecco's modified Eagle's tissue culture medium when exposed to "daylight" fluorescent light. Addition of pure H2O2 and use of the enzyme catalase demonstrate that about 40% of the toxicity in irradiated medium is due to generated peroxide. Riboflavin and tryptophan, or riboflavin and tyrosine, are the components necessary for formation of lethal levels of H2O2 during light exposure.