In “direct” phototransformation, photons are absorbed by the contaminant, while in “indirect” phototransformation, reactive species are formed through photon absorption by other substances. Pesticide electronic absorption spectra typically show little overlap with sunlight, such that only a few (e.g., trifluralin) are affected by direct phototransformation.[3] Various photochemically active light absorbers are present in surface waters, enhancing indirect phototransformation. The most prominent is dissolved organic matter (DOM), which is the precursor of excited triplet states, molecular oxygen, superoxide radical anions, and other radicals.