Multiphase photochemical reactions as sinks of nanoplastic photodissolution products in aqueous environments: a model study for benzene.

Carcinogenic benzene is the most concerning product of the irradiation of polystyrene nanoplastics in aqueous suspension. Interestingly, benzene formed in water from polystyrene can volatilise to the gas phase or react with aqueous-phase hydroxyl radicals (OH) to produce toxic phenol. The persistence of benzene in water would range from some weeks to some months, and the branching ratio between the OH reaction and volatilisation mainly depends on water depth and the DOC (dissolved organic carbon) concentration.

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

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.

Assessing the photochemical mineralisation of dissolved organic carbon in lakes.

Photochemical mineralisation is an abiotic process by which the organic matter in natural waters, which is mostly dissolved, is eventually transformed into CO by the action of sunlight. The process has important implications for global C cycling, the penetration of sunlight into the water column, photochemical reactions, and microbial processes. Here we applied an approximated photochemical model to assess the extent of CO photogeneration by mineralisation of dissolved organic matter in lakes located between 60°S and 60°N latitude.

Reaction kinetics and molecular characterization of the compounds formed by photosensitized degradation of the plastic additive bisphenol A in the atmospheric aqueous phase.

Bisphenol A (BPA, 4,4'-(propane-2,2-diyl)diphenol) is a common plasticizer that is very widespread in the environment and is also found at significant concentrations in the global oceans, due to contamination by plastics. Here we show that triplet sensitization is an important degradation pathway for BPA in natural surface waters, which could prevail if the water dissolved organic carbon is above 2-3 mg L. Bromide levels as per seawater conditions have the potential to slow down BPA photodegradation, a phenomenon that could not be offset by reaction of BPA with Br (second-order reaction rate constant of (2.

Two birds with one stone: Degradation of pharmaceuticals and elimination of bacteria upon treatment of urban wastewater with a Fenton-like process, based on zero-valent iron at pH 4.

ZVI-Fenton, which is the combination of zero-valent iron (metallic Fe) and HO is a relatively cheap advanced oxidation process for the elimination of contaminants from wastewater. Here we experimentally tested the ZVI-Fenton reaction at pH 4 towards two crucial goals in the treatment of secondary (partially treated) urban wastewater: (i) degradation of pharmaceuticals such as anti-inflammatory drugs (ibuprofen) and antibiotics (cefazolin, sulfamethoxazole), and (ii) elimination of a considerable fraction of bacteria through a combination of acidic pH and strongly oxidising conditions. In detail, ZVI-Fenton at pH 4 achieved degradation of both primary contaminants and potentially problematic transformation intermediates.

Photodegradation potential of selected non-steroidal anti-inflammatory drugs in a middle-order Alpine river downstream of a wastewater treatment plant, during a year of enduring water scarcity.

The year 2022 was characterised by significant water shortages and droughts in Italy, with the most pronounced impact observed in the North-Western regions, including Piemonte. In conditions of water scarcity, treated wastewater undergoes little dilution by natural flows and this can deeply affect the chemistry of water-poor rivers and streams. However, increased pollution by wastewater would be partially offset by fast photodegradation of pollutants in shallow water and by the longer time allowed to photochemical reactions if water flows more slowly.

Chemical characterization and speciation of the soluble fraction of Arctic PM.

The chemical composition of the soluble fraction of atmospheric particulate matter (PM) and how these components can combine with each other to form different species affect the chemistry of the aqueous phase dispersed in the atmosphere: raindrops, clouds, fog, and ice particles. The study was focused on the analysis of the soluble fraction of Arctic PM samples collected at Ny-Ålesund (Svalbard Islands, Norwegian Arctic) during the year 2012. The concentration values of Na, K, NH, Ca, Mg, Mn, Cu, Zn, Fe, Al, Cl, NO, NO, SO, PO, formate, acetate, malonate, and oxalate in the water-soluble fraction of PM were determined by atomic spectroscopy and ion chromatography.

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.

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.

Phototransformation of Vanillin in Artificial Snow by Direct Photolysis and Mediated by Nitrite.

The photodegradation of vanillin, as a proxy of methoxyphenols emitted by biomass burning, was investigated in artificial snow at 243 K and in liquid water at room temperature. Nitrite (NO) was used as a photosensitizer of reactive oxygen and nitrogen species under UVA light, because of its key photochemical role in snowpacks and atmospheric ice/waters. In snow and in the absence of NO, slow direct photolysis of vanillin was observed due to back-reactions taking place in the quasi-liquid layer at the ice-grain surface.

Assessing the photodegradation potential of compounds derived from the photoinduced weathering of polystyrene in water.

Benzoate (Bz) and acetophenone (AcPh) are aromatic compounds known to be produced by sunlight irradiation of polystyrene aqueous suspensions. Here we show that these molecules could react with OH (Bz) and OH + CO (AcPh) in sunlit natural waters, while other photochemical processes (direct photolysis and reaction with singlet oxygen, or with the excited triplet states of chromophoric dissolved organic matter) are unlikely to be important. Steady-state irradiation experiments were carried out using lamps, and the time evolution of the two substrates was monitored by liquid chromatography.

Photoinduced production of substances with humic-like fluorescence, upon irradiation of water samples from alpine lakes.

Evidence is here provided that irradiation of some lake water samples can trigger the formation of fluorophores with humic-like properties, at the same time increasing water absorbance. This phenomenon is the opposite of photobleaching, which is often observed when natural waters are irradiated. The photoproduced humic-like fluorophores observed here would be of autochthonous rather than allochthonous origin, which marks a difference with the fraction of humic substances that derives from terrestrial sources.

Evaluation of the Environmental Fate of a Semivolatile Transformation Product of Ibuprofen Based on a Simple Two-Media Fate Model.

Partitioning between surface waters and the atmosphere is an important process, influencing the fate and transport of semi-volatile contaminants. In this work, a simple methodology that combines experimental data and modeling was used to investigate the degradation of a semi-volatile pollutant in a two-phase system (surface water + atmosphere). 4-Isobutylacetophenone (IBAP) was chosen as a model contaminant; IBAP is a toxic transformation product of the non-steroidal, anti-inflammatory drug ibuprofen.

Direct photolysis of contaminants in surface freshwaters, within the equivalent monochromatic wavelength (EMW) approximation.

Abiotic photochemical reactions are usually very important degradation pathways for biorecalcitrant pollutants in surface freshwaters. Therefore, the assessment of photolytic lifetimes of contaminants helps estimate their impact on aquatic systems. This is commonly carried out by combining irradiation experiments and modelling, where the latter considers mathematical functions with polychromatic parameters, such as sunlight spectra, photolysis quantum yields (when Kasha's rule does not hold), and absorption coefficients.

Wavelength trends of photoproduction of reactive transient species by chromophoric dissolved organic matter (CDOM), under steady-state polychromatic irradiation.

The formation quantum yields of photochemically produced reactive intermediates (PPRIs) by irradiated CDOM (in this study, Suwannee River Natural Organic Matter and Upper Mississippi River Natural Organic Matter) decrease with increasing irradiation wavelength. In particular, the formation quantum yields of the excited triplet states of CDOM (CDOM*) and of singlet oxygen (O) have an exponentially decreasing trend with wavelength. The OH wavelength trend is different, because more effective OH production occurs under UVB irradiation than foreseen by a purely exponential function.

Phototransformation of the fungicide tebuconazole, and its predicted fate in sunlit surface freshwaters.

The fungicide tebuconazole (TBCZ) is expected to undergo negligible direct photolysis in surface freshwaters, but it can be degraded by indirect photochemistry. TBCZ mainly reacts with hydroxyl radicals and, to a lesser extent, with the triplet states of chromophoric dissolved organic matter (CDOM*). Indirect photochemistry is strongly affected by environmental conditions, and TBCZ lifetimes of about one week are expected in sunlit surface waters under favourable circumstances (shallow waters with low concentrations of dissolved organic carbon, DOC, during summer).

Inhibition by phenolic antioxidants of the degradation of aromatic amines and sulfadiazine by the carbonate radical (CO).

The carbonate radical CO and the excited triplet states of chromophoric dissolved organic matter play an important role in the photodegradation of some easily oxidized pollutants in surface waters, such as the aromatic amines. Anilines and sulfadiazine are known to undergo back-reduction processes when their degradation is mediated by the excited triplet states of photosensitizers (triplet sensitization). Back-reduction, which inhibits photodegradation, means that phenols or the antioxidant (mostly phenolic) moieties occurring in the natural dissolved organic matter of surface waters reduce, back to the parent compounds, the radical species derived from the mono-electronic oxidation of anilines and sulfadiazine.

Fluorophores in surface freshwaters: importance, likely structures, and possible impacts of climate change.

Fluorescence spectroscopy is one of the most useful techniques currently available for the characterisation of organic matter in natural water samples, because it combines easy availability of instrumentation, high sensitivity and limited requirements for sample treatment. The main fluorophores that can be found in natural waters are usually proteins (and/or free amino acids) and humic substances (humic and fulvic acids). The identification of these fluorescent compounds in water samples helps to obtain information about, among others, biological activity in the water body, possible transport of organic matter from soil, and the phenomenon of photobleaching that decreases both the absorbance and (usually) the fluorescence of natural organic matter.

A Review on the Degradation of Pollutants by Fenton-Like Systems Based on Zero-Valent Iron and Persulfate: Effects of Reduction Potentials, pH, and Anions Occurring in Waste Waters.

Among the advanced oxidation processes (AOPs), the Fenton reaction has attracted much attention in recent years for the treatment of water and wastewater. This review provides insight into a particular variant of the process, where soluble Fe(II) salts are replaced by zero-valent iron (ZVI), and hydrogen peroxide (HO) is replaced by persulfate (SO). Heterogeneous Fenton with ZVI has the advantage of minimizing a major problem found with homogeneous Fenton.

Geographical and temporal assessment of the photochemical decontamination potential of river waters from agrochemicals: A first application to the Piedmont region (NW Italy).

This work shows the potential of using photochemical modelling to assess the river-water ability to photodegrade agrochemicals on a geographic and temporal scale. The case of flowing water requires different data treatment compared to more stationary water bodies (e.g.

Tracking photodegradation products and bond-cleavage reaction pathways of triclosan using ultra-high resolution mass spectrometry and stable carbon isotope analysis.

Triclosan (TCS) is an antimicrobial compound ubiquitously found in surface waters throughout the world. Although several studies have focused on the photochemical degradation of TCS, there is still limited knowledge about its environmental fate. In this study, we got molecular-level insights into the photochemical degradation of TCS.

Superoxide-driven autocatalytic dark production of hydroxyl radicals in the presence of complexes of natural dissolved organic matter and iron.

We introduced superoxide as potassium superoxide (KO) to artificial lake water containing dissolved organic matter (DOM) without or with introduced ferric iron complexes (DOM-Fe(III)), and monitored the production rate of hydroxyl radicals as well as changes in the absorption and fluorescence properties of DOM. The introduction of KO decreased the absorption by DOM but increased the spectral slope coefficient of DOM more with complexed ferric Fe than without it. The introduction of KO increased the fluorescence of humic-like components in DOM without introduced ferric Fe but resulted in the loss of fluorescence in DOM with introduced ferric Fe.

Mapping the Photochemistry of European Mid-Latitudes Rivers: An Assessment of Their Ability to Photodegrade Contaminants.

The abiotic photochemical reactions that take place naturally in sunlit surface waters can degrade many contaminants that pose concern to water bodies for their potentially toxic and long-term effects. This works aims at assessing the ability of European rivers to photoproduce reactive transient intermediates, such as HO radicals and the excited triplet states of chromophoric dissolved organic matter (CDOM*), involved in pollutant degradation. A photochemical mapping of the steady-state concentrations of these transients was carried out by means of a suitable modeling tool, in the latitude belt between 40 and 50°N.

The role of direct photolysis in the photodegradation of the herbicide bentazone in natural surface waters.

The photochemical fate of the herbicide bentazone was assessed by lab experiments and modeling tools. Experimental and modeling results showed that bentazone is mainly photodegraded by direct photolysis in natural water samples, even in the presence of dissolved organic matter (DOM) that can act as light-screening agent, photosensitizer and scavenger of reactive species. Even when it was dissolved in natural water samples containing different DOM amounts, the phototransformation kinetics of bentazone was unchanged compared to irradiation runs in ultrapure water.