Occurrence and transformation of phenoxy acids in aquatic environment and photochemical methods of their removal: a review

Abstract

The article presents the behavior of phenoxy acids in water, the levels in aquatic ecosystems, and their transformations in the water environment. Phenoxy acids are highly soluble in water and weakly absorbed in soil. These highly mobile compounds are readily transported to surface and groundwater. Monitoring studies conducted in Europe and in other parts of the world indicate that the predominant phenoxy acids in the aquatic environment are mecoprop, 4-chloro-2-methylphenoxyacetic acid (MCPA), dichlorprop, 2,4-dichlorophenoxyacetic acid (2,4-D), and their metabolites which are chlorophenol derivatives. In water, the concentrations of phenoxy acids are effectively lowered by hydrolysis, biodegradation, and photodegradation, and a key role is played by microbial decomposition. This process is determined by the qualitative and quantitative composition of microorganisms, oxygen levels in water, and the properties and concentrations of phenoxy acids. In shallow and highly insolated waters, phenoxy acids can be decomposed mainly by photodegradation whose efficiency is determined by the form of the degraded compound. Numerous studies are underway on the use of advanced oxidation processes (AOPs) to remove phenoxy acids. The efficiency of phenoxy acid degradation using AOPs varies depending on the choice of oxidizing system and the conditions optimizing the oxidation process. Most often, methods combining UV radiation with other reagents are used to oxidize phenoxy acids. It has been found that this solution is more effective compared with the oxidation process carried out using only UV.

Secondary Formation of Aromatic Nitroderivatives of Environmental Concern: Photonitration Processes Triggered by the Photolysis of Nitrate and Nitrite Ions in Aqueous Solution

“…Evidence of the possible occurrence of photonitration processes in the natural environment has been obtained in the case of natural surface waters, although biological nitration pathways cannot be ruled out. In particular, it appears that the environmental conditions of the Rhône delta lagoons (shallow and sunlit waters, elevated concentrations of nitrate and nitrite) are particularly favourable to the transformation of phenolic compounds, arising from the environmental dissipation of phenoxyacid herbicides, into the corresponding nitroderivatives [31,[65][66][67][68][69] It should be remarked that natural waters are indeed much more complex compared to simplified laboratory systems, thus interaction between different components is highly likely. For instance, nitrate and nitrite occur together in the Rhône-delta lagoon water, and the processes they may trigger differ from the mere sum of the separate photoreactions.…”

“…Molecules 2021,26, x FOR PEERREVIEW 13 tration pathways cannot be ruled out. In particular, it appears that the environme conditions of the Rhône delta lagoons (shallow and sunlit waters, elevated concentrat of nitrate and nitrite) are particularly favourable to the transformation of phenolic c pounds, arising from the environmental dissipation of phenoxyacid herbicides, into corresponding nitroderivatives[31,[65][66][67][68][69]:…”

Development and validation of a stability-indicating HPLC assay method for determination of ethacrynic acid in solution formulation. HPLC-MS identification of hydrolytic and oxidative degradation products

“…The exact mass of the component corresponding to the HPLC peak with RRT = 1.35 (t R = 6.80 min) is 244.01 (50.54%). Based on the negative ion mode mass spectrum ( Figure 14) and the previously published path of oxidation of phenoxyacetic acids with hydrogen peroxide [38] , the structure of the new compound can be considered to be 8 (C 11 H 10 O 2 Cl 2 ; [M 8 − H + ] − = 242.97) ( Figure 15). The other proposed structure corresponding to the HPLC peak with RRT = 0.46 (t R = 2.30 min) can be considered to the 9 epoxide ( Figure 15).…”

Microwave-Assisted Synthesis of Chalcopyrite/Silver Phosphate Composites with Enhanced Degradation of Rhodamine B under Photo-Fenton Process

“…Among the many sources of water pollution, wastewater from the printing and dyeing industry is a major concern. The decolorization and degradation of most chromophores in dyes are difficult because of their stable aromatic structures, leading to prolonged toxic effects and environmental hazards [ 4 , 5 , 6 ]. Furthermore, dyes can absorb sunlight and reduce water clarity, preventing photosynthesis in aquatic plants, decreasing dissolved oxygen in water, affecting microbial diversity, and disrupting the self-purification capacity of water [ 7 ].…”