Vol. 12, no. 1, pp. 3-16, 1983 Photolysis of 2,4,6-trinitrotoluene (TNT) occurs rapidly in pure and natural waters irradiated with sunlight, with half-lives of less than a half-hour in some natural waters. Experiments to study the TNT photolysis products and to obtain evidence for complexation of TNT with natural substances are discussed. Vol 12, No 1, p 3-16, 1983. 2 Fig, 7 Tab, 13 Ref. The photolysis of 2,4,6-trinitrotoluene (TNT) was studied in aqueous solution to estimate the rates of transformation and transport of munitions chemicals in aquatic systems of interest to the US Army. In applying the findings to the environmental photolysis rate constants for TNT it is noted that although TNT photolyzes more rapidly in natural waters than in pure water it is useful to know the direct photolysis rate constants of TNT in sunlight in pure water as limiting (minimum) rate constants that can be expected in aquatic systems. For direct photolysis rate constants for TNT, it is the rate constant before rate acceleration by products that is relevant to environmental assessments, and thus the reaction quantum yield of .0027 is used for rate constant calculations. The products do accelerate the rate of photolysis, and thus rate constants measured in pure water would be expected to show a dependence on initial TNT concentration and the amount of TNT reacted if the TNT concentration is greater than 1 ppm. Even direct photolysis of TNT is a reasonably rapid process in aquatic systems. Photolysis of TNT in several natural waters is shown to be more rapid than in pure water, and thus TNT will photolyze very rapidly in aquatic systems of shallow depth and low absorbance. While the mechanism for photolysis of TNT is not known, evidence suggests that the photolysis may be occurring via a triplet-excited state. The products from TNT show an exceptional ability to promote TNT photolysis. (Baker-FRC)