Photochemical processes in surface water bodies and their potential impacts on the chemical composition of water: A review

The present study is a review of photochemical processes that occur in surface water bodies and which can affect the chemical composition of water. It is expected that water bodies with a slow rate of water exchange, including lakes, reservoirs, estuaries and ponds with significant areas of shallow water will be most vulnerable to the impacts of these processes. It involves natural organic compounds and xenobiotics of organic origin that enter water bodies from anthropogenic sources or are formed in water bodies because of the development of cyanobacteria and other algae species. Photodegradation of dissolved organic matter (DOM) occurs as a result of both direct photolysis and photosensitized cleavage involving inorganic and organic compounds, which are characterized by chromophore properties, such as humic substances. Photolysis is accompanied by the transformation of high molecular weight organic compounds into lower molecular weight compounds that can become bioavailable to, and promote the development of, microorganisms. Photodegradation results in bioavailable forms of nitrogen and phosphorus being released into the water column. Accordingly, the present study presents the results of analysis of the photochemical destruction of humic substances, such as the most widespread group of the surface water body DOM under the influence of artificial UV irradiation and solar radiation. The results provide data on the products of humic substances photolysis, as well as the influence of the latter on the destruction of a number of organic substances, including xenobiotics (herbicides, pesticides, etc.). Photolysis of algotoxins, which are mainly concentrated in the water of highly trophic reservoirs and lakes during the period of water “blooming,” is among the main concerns being addressed, noting photochemical destruction of these dangerous toxicants can be considered an important means of removing them from drinking water. Also emphasized is that photochemical processes in surface water will likely intensify in the future amid the recent climate changes, also affecting the chemical composition of water.