Accumulation Of Transformation Products Research Articles

Chlorination of antiviral drug ribavirin: Kinetics, nontargeted identification, and concomitant toxicity evolution

Residual antiviral drugs in wastewater may increase the risk of generating transformation products (TPs) during wastewater treatment. Therefore, chlorination behavior and toxicity evolution are essential to understand the secondary ecological risk associated with their TPs. Herein, chlorination kinetics, transformation pathways, and secondary risks of ribavirin (RBV), one of the most commonly used broad-spectrum antivirals, were investigated. The pH-dependent second-order rate constants k increased from 0.18 M-1·s-1 (pH 5.8) to 1.53 M-1·s-1 (pH 8.0) due to neutral RBV and ClO- as dominant species. 12 TPs were identified using high-resolution mass spectrometry in a nontargeted approach, of which 6 TPs were reported for the first time, and their chlorination pathways were elucidated. The luminescence inhibition rate of Vibrio fischeri exposed to chlorinated RBV solution was positively correlated with initial free active chlorine, probably due to the accumulation of toxic TPs. Quantitative structure–activity relationship prediction identified 7 TPs with elevated toxicity, concentrating on developmental toxicity and bioconcentration factors, which explained the increased toxicity of chlorinated RBV. Overall, this study highlights the urgent need to minimize the discharge of toxic chlorinated TPs into aquatic environments and contributes to environmental risk control in future pandemics and regions with high consumption of antivirals.

Results of calculation of changing the pollution concentration and alkalinity of the gas engine oils

BACKGROUND: The issue of ensuring the reliability of internal combustion engines is a relevant composite task, solved in various directions. The important ones among them are the operation conditions, the type of fuel used, control of the motor oils condition, as well as justification of the service life of the latter. When ensuring the operational properties of engine oils of the dieselbased gas engines, the control of the main indicators of the operating oil is relevant.
 AIMS: Assessment of changes in the pollution load and alkalinity of the M10G2 oils of the dieselbased gas engines. Application of equations for the theoretical analysis of changes in the pollution concentration and decrease of alkalinity, as well as for building dependencies of oil indicators.
 METHODS: During the operation of internal combustion engines, thermochemical processes are actively developing in oils, leading to decrease in their quality due to the activation of additives and the accumulation of transformation products in oils. Mechanical impurities accumulate in the engine oil as a result of dust ingress with the sucked air or through leaks in the crankcase space, as well as due to the formation of insoluble oxidation products and wear of parts of the cylinder-piston group. The base number is a conditional measure of the oils ability to neutralize acids formed from the products of fuel combustion and oxidation of the oil base. The alkalinity specified by the presence of alkaline additives is consumed for the neutralization of acids at different rates.
 RESULTS: The process of oil aging in internal combustion engines and factors affecting the aging of engine oil are considered. Analytical equations are used to calculate changes in the pollution concentration and changes in the alkalinity of the diesel-based gas engine oil, graphical dependences of oil indicators on the service duration are given.
 CONCLUSIONS: The practical value of the study lies in the fact that, using the analytical equations, the value of changes in individual properties of diesel-based gas engine oils is analyzed. Operation of the engine with the oil which base number is below the limit leads to a decrease in engine reliability, accelerated wear of individual parts, lacquer formation and sludging on piston rings and cylinders. It is not allowed to use oils with the base number below 2 mg of KOH/g.

Degradation of metoprolol by UV/sulfite as an advanced oxidation or reduction process: The significant role of oxygen

The degradation of metoprolol (MTP) by the UV/sulfite with oxygen as an advanced reduction process (ARP) and that without oxygen as an advanced oxidation process (AOP) was comparatively studied herein. The degradation of MTP by both processes followed the first-order rate law with comparable reaction rate constants of 1.50×10−3sec−1 and 1.20×10−3sec−1, respectively. Scavenging experiments demonstrated that both eaq− and H• played a crucial role in MTP degradation by the UV/sulfite as an ARP, while SO4•− was the dominant oxidant in the UV/sulfite AOP. The degradation kinetics of MTP by the UV/sulfite as an ARP and AOP shared a similar pH dependence with a minimum rate obtained around pH 8. The results could be well explained by the pH impacts on the MTP speciation and sulfite species. Totally six transformation products (TPs) were identified from MTP degradation by the UV/sulfite ARP, and two additional ones were detected in the UV/sulfite AOP. The benzene ring and ether groups of MTP were proposed as the major reactive sites for both processes based on molecular orbital calculations by density functional theory (DFT). The similar degradation products of MTP by the UV/sulfite process as an ARP and AOP indicated that eaq−/H• and SO4•− might share similar reaction mechanisms, primarily including hydroxylation, dealkylation, and H abstraction. The toxicity of MTP solution treated by the UV/sulfite AOP was calculated to be higher than that in the ARP by the Ecological Structure Activity Relationships (ECOSAR) software, due to the accumulation of TPs with higher toxicity.

Synthesis of MnOx/SBA-15 for Norfloxacin degradation by catalytic ozonation

Abstract Norfloxacin, a kind of widely used fluoroquinolone antibiotics, was degraded by MnOx/SBA-15/O3 process. The prepared catalyst possessed a large surface area ranging from 405 to 671 m2 g−1, which was beneficial for surface reaction. The loaded MnOx on SBA-15 successfully increased its the adsorption ability and catalytic activity, and its surface property played an importance role in catalytic process. Under the adopted condition, both O3 and MnOx/SBA-15/O3 systems were effective for Nofloxacin removal. A high mineralization efficiency (54%) was achieved by MnOx/SBA-15/O3 process at 60 min, 1.36 times higher than that of single ozonation process. The protonated surface hydroxyl groups were the main reaction sites and more hydroxyl radicals generation were found after the presence of MnOx/SBA-15. Three kinds of common small molecule acid (oxalic acid, formic acid, acetic acid) were detected, and the concentration of oxalic acid in MnOx/SBA-15/O3 process was lower than that in sole ozonation process because more OH generated in catalytic ozonation. Toxicological tests were also conducted to evaluate their detoxification ability. As the accumulation of transformation products, the toxicity of solution increased at first and reached the highest after 15 min reaction time. And a high detoxification was achieved after 30 min.

Identification of transformation products during advanced oxidation of diatrizoate: Effect of water matrix and oxidation process

Removal of micropollutants from reverse osmosis (RO) brines of wastewater desalination by oxidation processes is influenced by the scavenging capacity of brines components, resulting in the accumulation of transformation products (TPs) rather than complete mineralization. In this work the iodinated contrast media diatrizoate (DTZ) was used as model compound due to its relative resistance to oxidation. Identification of TPs was performed in ultrapure water (UPW) and RO brines applying nonthermal plasma (NTP) and UVA-TiO2 as oxidation techniques. The influence of main RO brines components in the formation and accumulation of TPs, such as chloride, bicarbonate alkalinity and humic acid, was also studied during UVA-TiO2. DTZ oxidation pattern in UPW resulted similar in both UVA-TiO2 and NTP achieving 66 and 61% transformation, respectively. However, DTZ transformation in RO brines was markedly lower in UVA-TiO2 (9%) than in NTP (27%). These differences can be attributed to the synergic effect of RO brines components during NTP. Moreover, reactive species other than hydroxyl radical contributed to DTZ transformation, i.e., direct photolysis in UVA-TiO2 and direct photolysis + O3 in NTP accounted for 16 and 23%, respectively. DTZ transformation led to iodide formation in both oxidation techniques but it further oxidized to iodate by ozone in NTP. In total 14 transformation products were identified in UPW of which 3 were present only in UVA-TiO2 and 2 were present exclusively in NTP; 5 of the 14 TPs were absent in RO brines. Five of them were new and were denoted as TP-474A/B, TP-522, TP-586, TP-602, TP-628. TP-522 (mono-chlorinated) was elucidated only in presence of high chloride titer-synthetic water matrix in NTP, most probably formed by active chlorine species generated in situ. TPs accumulation in RO brines was markedly different in comparison to UPW. This denotes the influence of RO brines components in the formation of reactive species that could further attack DTZ/TPs and/or scavenging performed by these brine components that could limit further TPs degradation. Five plausible degradation pathways are proposed for DTZ transformation in UPW.

Flume Experiments To Investigate the Environmental Fate of Pharmaceuticals and Their Transformation Products in Streams

The hyporheic zone—the transition region beneath and alongside the stream bed—is a central compartment for attenuation of organic micropollutants in rivers. It provides abundant sorption sites and excellent conditions for biotransformation. We used a bench-scale flume to study the fate of 19 parent pharmaceuticals (PPs) and the formation of 11 characteristic transformation products (TPs) under boundary conditions similar to those in hyporheic zones. The persistence of PPs ranged from readily degradable with a dissipation half-life (DT50) as short as 1.8 days (acetaminophen, ibuprofen) to not degradable (chlorthalidone, fluconazole). The temporal and spatial patterns of PP and TP concentrations in pore water were heterogeneous, reflecting the complex hydraulic and biogeochemical conditions in hyporheic zones. Four TPs (carbamazepine-10,11-epoxide, metoprolol acid, 1-naphthol, and saluamine) were exclusively formed in the sediment compartment and released to surface water, highlighting their potential to be used as indicators for characterizing hyporheic transformation of micropollutants in streams. The accumulation of certain TPs over the experimental period illustrates that we might face a peak of secondary contamination by TPs far from the point of release of the original contaminants into a stream. Such TPs should be considered as priority candidates for a higher-tier environmental risk assessment.

Investigation of the reaction products of unsymmetrical dimethylhydrazine with potassium permanganate by gas chromatography-mass spectrometry

The gas chromatography-mass spectrometry technique was used to investigate the composition of the reaction products of unsymmetrical dimethylhydrazine with a potassium permanganate and potassium permanganate-hydrogen peroxide mixture. If the water contamination level is within 50 threshold limit values (TLV) (1 mg/ml), the proposed detoxication method utilizing potassium permanganate in combination with hydrogen peroxide allows for the reduction of the UDMH concentration to a safe level without the accumulation of transformation products. The detoxication of aqueous solutions with significant UDMH concentrations (up to 50000 TLV) (1 g/l) with potassium permanganate alone or in combination with hydrogen peroxide reduces the UDMH concentration to a safe level, but UDMH transformation products, including the extremely toxic nitrozodimethylamine, are accumulated in the solution.

Presence and partitioning properties of the flame retardants pentabromotoluene, pentabromoethylbenzene and hexabromobenzene near suspected source zones in Norway

The brominated flame retardants (BFRs), pentabromotoluene (PBT), pentabromoethylbenzene (PBEB) and hexabromobenzene (HBB), exhibit physical-chemical properties similar to other persistent organic pollutants, and have been in use as flame retardants for several decades. Data on these BFRs in diverse environmental samples can be found in studies from the 1970s and 1980s, as well as in recent years, though very little in the years in between. Due to a lack of data, the cause for the apparent re-emergence of these BFRs in recent studies is unclear, and could reflect changes in production volumes, accumulation of transformation products from BFR precursors, improved analytical techniques or simply a re-emergence in concern. Very little data are available on their environmentally relevant partitioning properties, which could help to explain the occurrence and fate of these BFRs. In this study we analysed for the presence of HBB, PBT, and PBEB in diverse environmental samples from potential Norwegian BFR source zones. Additionally, environmental partitioning properties of these BFRs as well as brominated benzenes were estimated and validated using experimental data for brominated benzenes. Of the three BFRs, HBB was identified in detectable quantities at most source zones, PBEB only near a metal recycling factory, and PBT only in a few additional locations from where PBEB was detected. Data from this study show that HBB is likely widely distributed, as verified both by chemical analysis and estimated properties. Measured HBB levels in wastewater treatment plants indicate that the treatment practices used in the study locations are not effective at lowering HBB levels, perhaps due to association with low density suspended solids (e.g. microplastics).

Heterogeneous photochemical reactions of decabromodiphenyl ether

Brominated diphenyl ethers are a major class of brominated flame retardants, with production of decabromodiphenyl ether (DBDPE) contributing significantly to this total. Although little is known about the mechanisms and rates of DBDPE decay in the natural environment, photochemical transformation is often suggested as a potentially important fate process. In this study, photochemical reactions of DBDPE precipitated onto hydrated surfaces (quartz glass, silica particles, and humic acid-coated silica particles) were measured. Decabromodiphenyl ether was irradiated within a Rayonet photochemical reactor equipped with lamps having maximum emissions (lambdamax) at 300 or 350 nm or with sunlight (West Lafayette, IN, USA at 40 degrees 26'N, 86 degrees 55'W). When DBDPE is plated onto quartz tubes and hydrated with reagent-grade water, phototransformation occurred over a period of days with each light source. With two lamps (lambdamax = 300 nm), about 31% of the initial mass of DBDPE remained after 60 h in the Rayonet reactor. Decabromodiphenyl ether transformed more slowly when irradiated by sunlight, with 30% of the initial compound recovered from tubes after 72 h. In the presence of humic acid (HA) solution, transformation of DBDPE by solar irradiation is slowed even further: approximately 70% remained after 72 h. Solar irradiation of DBDPE adsorbed to humic acid-coated sand particles resulted in the slowest irradiation rates; approximately 88% of the initial mass was recovered after 96 h of exposure. Although the parent compound exhibited slow transformation, analysis by high-performance liquid chromatography (HPLC) indicated some accumulation of transformation products.