Iron dependent degradation of an isothiazolone biocide (5-chloro-2-methyl-4-isothiazolin-3-one)

Degradation of chloromethylisothiazolinone antimicrobial by Vacuum-Ultraviolet/Ultraviolet irradiation: Reactive species, degradation pathway and toxicity evaluation

Chloromethylisothiazolinone (CMIT) has been extensively used as antimicrobial in cosmetics, detergents, wall paints, and anti-fouling products. To prevent the potential ecological and health risks, the degradation mechanisms and toxicity changes of CMIT by Vacuum-Ultraviolet/Ultraviolet (VUV/UV) irradiation were investigated in this study. VUV/UV irradiation showed better performance on CMIT degradation compared to sole UV photolysis. The removal efficiency of CMIT with photon fluence of 0.6 μEinstein/cm² was 8% and 100% by UV or VUV/UV irradiation, respectively. Radical quenching experiments indicated that 254 nm photolysis, 185 nm photolysis, and •OH oxidation contributed to CMIT degradation during VUV/UV process, with fluence-based apparent rate constants of 0.16, 0.13, and 4.9 μEinstein^-1cm², respectively. The formation of H₂O₂ during VUV/UV process increased to 0.7 mg/L at 4.5 min, and the concentration of •OH ranged within 1.0-3.8 × 10^-12 M. The degradation of CMIT by VUV/UV irradiation in neutral condition was slightly higher than that in acidic and basic conditions. The removal efficiency of CMIT with reaction time of 2 min decreased from 92.2% to 34.3% when the concentration of HCO₃^-/CO₃^2- increased to 1 mM. The degradation of CMIT by VUV/UV irradiation in secondary effluents was lower than that in ultrapure water because of the •OH scavenging effects, but still 2.9 times higher than that by UV photolysis. Four main degradation mechanisms of CMIT were observed during VUV/UV process, including the oxidation of sulfur, addition of hydroxyl groups on the double-carbon-bond, demethylation on the nitrogen, and substitution of organochlorine atom by hydroxyl group. Based on the quantitative structure activity relationship analysis, most products of CMIT underwent complete detoxification to fish and daphnia. 40% of products still showed acute toxicity to algae, but most of them were less toxic than CMIT.

Study on synergistic effect of ozone and monochloramine on the degradation of chloromethylisothiazolinone biocide

In this study, it was found that monochloramine induced the formation of reactive species during ozonation of chloromethylisothiazolinone (CMIT). CMIT was found recalcitrant to chloramine. However, chloramine promoted the degradation of CMIT by ozonation significantly. Hydroxyl radicals contributed most to CMIT degradation (87%) during ozone/chloramine synergistic oxidation process (SOP). The hydroxyl radical exposure during ozone/chloramine SOP was around 7.9 times higher than that of ozonation process. The hydroxyl radical yield of ozone/chloramine SOP was estimated to be 32%. The reaction mechanisms between ozone and chloramine were postulated to include the oxygen transfer reaction to form singlet oxygen, and the formation of hydroxyl radical by the insertion pathway or electron transfer pathway. Chloramine dosage and pH are essential influencing factors. The degradation of CMIT increased from 41% to 74% with increasing chloramine dosage (0-20 μM), and then decreased to 65% when chloramine dosage continually increased to 40 μM. Ozone/chloramine SOP showed better performance at acidic or neutral conditions than basic condition. Based on the intermediates identified, the degradation pathway of CMIT during ozone/chloramine SOP included the oxidation of sulfur atom and the substitution of chlorine group by hydroxyl group. The oxidation of sulfur atom induced lower toxicities of transformation products. The toxicities of hydroxylation products were lower to fish and algae, but higher to daphnia. Based on the GC-ECD results, only trichloromethane (1.94 μg/L) was detected after ozone/chloramine SOP, accounting for 0.17% (μM/μM) of the CMIT removal.

Development of a highly efficient electrochemical flow-through anode based on inner in-site enhanced TiO2-nanotubes array

This paper reports on the development of macroporous flow-through anodes. The anodes comprised an enhanced TiO₂ nanotube array (ENTA) that was grown on three macroporous titanium substrates (MP-Ti) with nominal pore sizes of 10, 20, and 50 µm. The ENTA was then covered with SnO₂-Sb₂O₃. We refer to this anode as the MP-Ti-ENTA/SnO₂-Sb₂O₃ anode. The morphology, pore structure, and electrochemical properties of the anode were characterized. Compared with the traditional NTA layer, we found that the MP-Ti-ENTA/SnO₂-Sb₂O₃ anode has a service lifetime that was 1.56 times larger than that of MP-Ti-NTA/SnO₂-Sb₂O₃. We used 2-methyl-4-isothiazolin-3-one (MIT), a common biocide, as the target pollutant. We evaluated the impact of the operating parameters on energy efficiency and the oxidation rate of MIT. Furthermore, the apparent rate constants were 0.38, 1.63, and 1.24 min^-1 for the 10, 20, and 50 μm nominal pore sizes of the MP-Ti substrates, respectively, demonstrating the different coating-loading mechanisms for the porous substrate. We found that hydroxyl radicals were the dominant species in the MIT oxidation in the HO radical scavenging experiments. The radical and nonradical oxidation contributions to the MIT degradation for different current densities were quantitatively determined as 72.1%-74.8% and 25.2%-27.9%, respectively. Finally, we summarized the oxidation performance for MIT destruction for (1) the published literature on various advanced oxidation technologies, (2) the published literature on various anodes, and (3) our flow-by and -through anodes. Accordingly, we found that our flow-through anode has a much lower electrical efficiency per order value (0.58 kWh m^-3) than the flow-by anodes (6.85 kWh m^-3).

Isothiazolinone Biocides: Chemistry, Biological, and Toxicity Profiles

The importance of isothiazole and of compounds containing the isothiazole nucleus has been growing over the last few years. Isothiazolinones are used in cosmetic and as chemical additives for occupational and industrial usage due to their bacteriostatic and fungiostatic activity. Despite their effectiveness as biocides, isothiazolinones are strong sensitizers, producing skin irritations and allergies and may pose ecotoxicological hazards. Therefore, their use is restricted by EU legislation. Considering the relevance and importance of isothiazolinone biocides, the present review describes the state-of-the-art knowledge regarding their synthesis, antibacterial components, toxicity (including structure–activity–toxicity relationships) outlines, and (photo)chemical stability. Due to the increasing prevalence and impact of isothiazolinones in consumer’s health, analytical methods for the identification and determination of this type of biocides were also discussed.

Ultrafast photodegradation of isoxazole and isothiazolinones by UV254 and UV254/H2O2 photolysis in a microcapillary reactor

The photodegradation process of methylisothiazolinone (MIT), benzisothiazolinone (BIT), and isoxazole (ISOX) in ultrapure water and synthetic wastewater by means of UV₂₅₄ photolysis and by UV₂₅₄/H₂O₂ advanced oxidation process were investigated in a microcapillary photoreactor designed for ultrafast photochemical transformation of microcontaminants. For the first time, we estimated key photo-kinetic parameters, i.e. quantum yields (35.4 mmol·ein^-1 for MIT, and 13.5 and 55.8 mmol·ein^-1 for BIT at pH = 4-6 and 8, respectively) and rate constants of the reaction of photo-generated OH radicals with MIT and BIT (2.09·10⁹ and 5.9·10⁹ L mol^-1·s^-1 for MIT and BIT). The rate constants of the reaction of photo-generated OH radicals with ISOX in MilliQ water was also estimated (2.15·10⁹ L mol^-1·s^-1) and it was in good agreement with literature indications obtained in different aqueous matrices. The models were extended and validated to the case of simultaneous degradation of mixtures of these compounds and using synthetic wastewater as an aqueous matrix. High resolution-accurate mass spectrometry analysis enabled identification of the main intermediates (BIT200, B200, saccharin, BIT166) and enabled proposal of a novel degradation pathway for BIT under UV₂₅₄/H₂O₂ treatment. This study demonstrates an ultrafast method to determine key photo-kinetic parameters of contaminants of emerging concern in water and wastewater, which are needed for design and validation of photochemical water treatment processes of municipal and industrial wastewaters.

Effective degradation of methylisothiazolone biocide using ozone: Kinetics, mechanisms, and decreases in toxicity

Methylisothiazolone (MIT) is a common biocide that is widely used in water-desalination reverse-osmosis processes. The transformation of MIT during water treatment processes is poorly understood. The kinetics and mechanisms involved in the degradation of MIT during ozonation were investigated in this study. Ozonation was found to be a useful way of degrading MIT in water, and the degradation rate constant was 0.11 (±0.1) × 10³ L/(mol·s). The degradation rate constant did not change when the pH was increased from 3 to 9. The pre-exponential factor A and the activation energy E_a for the ozonation process were 7.564 × 10¹³ L/(mol·s) and 66.74 kJ/mol, respectively. The decrease in the MIT concentration and the amount of ozone consumed were measured, and the stoichiometric factor α for the ozone consumption to MIT removal ratio was found to be 1.8. Several ozonation products were detected using time-of-flight mass spectrometry. Almost 32% of the organic sulfur in the MIT was oxidized to release sulfate ions, which caused a decrease in pH. Sulfur atoms were oxidized to sulfone species and then hydrolyzed to give sulfate during ozonation. Addition reactions involving carbon-carbon double bonds and the oxidation of α-carbon atoms also occurred. MIT was found to be lethal to Daphnia magna Straus (D. magna) with a median lethal concentration of 18.2 μmol/L. Even though the primary ozonation products of MIT still showed some toxicity to D. magna, ozone could minimize the toxic effect after a long reaction time.