Global modeling of lake-water indirect photochemistry based on the equivalent monochromatic wavelength approximation: The case of the triplet states of chromophoric dissolved organic matter

•The distribution of 3CDOM* concentration was assessed on a global scale.•Global databases of solar irradiation and lakes characteristics were used.•The Nordic latitudes show the highest values of [3CDOM*] during summer.•Photodegradation of clofibric acid was modelled in world's lakes.•Application of photochemical mapping to ecotoxicological risk assessment is shown. Chromophoric dissolved organic matter (CDOM) plays key role as photosensitizer in sunlit surface-water environments, and it is deeply involved in the photodegradation of contaminants. It has recently been shown that sunlight absorption by CDOM can be conveniently approximated based on its monochromatic absorption at 560 nm. Here we show that such an approximation allows for the assessment of CDOM photoreactions on a wide global scale and, particularly, in the latitude belt between 60°S and 60°N. Global lake databases are currently incomplete as far as water chemistry is concerned, but estimates of the content of organic matter are available. With such data it is possible to assess global steady-state concentrations of CDOM triplet states (3CDOM*), which are predicted to reach particularly high values at Nordic latitudes during summer, due to a combination of high sunlight irradiance and elevated content of organic matter. For the first time to our knowledge, we are able to model an indirect photochemistry process in inland waters around the globe. Implications are discussed for the phototransformation of a contaminant that is mainly degraded by reaction with 3CDOM* (clofibric acid, lipid regulator metabolite), and for the formation of known products on a wide geographic scale. [Display omitted]