Global modeling of photochemical reactions in lake water: A comparison between triplet sensitization and direct photolysis

Abstract

The equivalent monochromatic wavelength (EMW) approximation allowed us to predict the photochemical lifetimes of the lipid regulator metabolite clofibric acid (CLO, triplet sensitization) and of the non-steroidal anti-inflammatory drug diclofenac (DIC, direct photolysis + triplet sensitization) in lakes worldwide. To do so, we used large lake databases that collect photochemically significant parameters such as water depth and dissolved organic carbon, which allow for a preliminary assessment of some photoreactions. Extension to other photoreactions is currently prevented by the lack of important parameters such as water absorption spectrum, suspended solids, nitrate, nitrite, pH, and inorganic carbon on a global scale. It appears that triplet-sensitized CLO photodegradation would be strongly affected by the dissolved organic carbon values of the lake water and, for this reason, it would be fastest in Nordic environments. By contrast, direct photolysis (DIC) would be highly affected by sunlight irradiance and would proceed at the highest rates in the tropical belt. Interestingly, the predicted lifetimes of CLO and DIC are shorter than the residence time of water in the majority of global lake basins, which suggests a high potential for photoreactions to attenuate the two contaminants on a global scale. Photodegradation of DIC and CLO would also be important in waste stabilization ponds, except for elevated latitudes during winter, which makes these basins potentially cost-effective systems for the partial removal of these emerging contaminants from wastewater.