This scientific article describes how solar light and oxygen lead to damage of faecal coliforms in waste stabilization ponds. Humic substances absorb the energy of the sunlight and react with surrounding oxygen, leading to the formation of toxic reactive oxygen species (ROS).
CURTIS, T.P. ; MARA, D.D. ; SILVA, S.A. (1992): Influence of pH, Oxygen, and Humic Substances on Ability of Sunlight to Damage Faecal Coliforms in Waste Stabilization Pond Water. In: Applied and Environmental Microbiology : Volume 58 , 1335-1343. URL [Accessed: 02.04.2010]