Studies of phenol photocatalyzed oxidation and of organic dye photolyzed or photocatalyzed destruction which explored variable initial concentrations, C-o, often assumed pseudo first order behavior, and fitted data to a semilog plot of concentration, C(t) vs time, and found that the apparent first order rate constant decreases with increasing C-o. We show from multiple literature examples that this behavior often disguises a true zero order initial rate of reaction. We recommend a re-analysis of existing literature reporting first order rate constants which vary with initial reactant concentration, C-o.