Degradation Of Sulfachloropyridazine Research Articles

Iron anchored carbon–nitrogen catalyst for enhanced activation performance of peroxymonosulfate: Synergy of 1O2 and high-valent iron

Herein, Iron anchored in carbon–nitrogen nanosheets (Fe-CNx) catalysts were synthesized successfully through one-step in situ pyrolysis for activating peroxymonosulfate (PMS) to degrade sulfachloropyridazine (SCP). Fe-CN800/PMS could realized the complete removal SCP in 20 min (kobs = 0.644 min−1). Its reaction rates were 214.7 times higher than that in PMS system. Additionally, Fe-CN800 could effectively activate PMS in a wide range of pH (3–10.6). The relationship between the content of Fe-CNx functional groups and the catalytic performance indicated that C = O and Fe-N4 were the main active sites. The structural–functional association between active sites and reactive oxygen species (ROS) was revealed by regression analysis and Density Functional Theory calculations, indicating that C = O stimulated 1O2 production, while HV-Fe was derived from C = O and Fe-N4. Moreover, the PMS activation was enhanced via electron transfer between Fe(II) and Fe(III). Based on LC-MS and Fukui index, the action of ROS during SCP decomposition was analyzed, and proposed three probable pathways for SCP degradation. The transformation pattern of the structure and toxicity of the intermediates was revealed via T.E.S.T. analysis, and plant growth experiments showed that the effect of the treated SCP solution on Brassica napus significantly decreased. Finally, Fe-CN800 exhibited excellent stability, with SCP removal remaining above 95 % in five cycles and Fe leaching concentrations lower than ones which have been reported catalysts. This work provided new insights for the precise design of more efficient PMS catalysts. It will provide a fundamental basis for the practical application in wastewater treatment based on PMS-AOPs.

Development of a heterogenous catalyst FeWO4/Cu2S as peroxymonosulfate activator for effective sulfachloropyridazine elimination

This work successfully synthesized magnetic FeWO4/Cu2S through a facile method with efficient peroxymonosulfate (PMS) activation to eliminate sulfachloropyridazine (SCP) in water, in which 97.56% of SCP was removed in 30 min with activating only 0.2 mM PMS. Factors such as calcination temperature, the addition amount of WS2 in FeWO4/Cu2S, molar ratio of Cu/Fe in FeWO4/Cu2S, catalyst dosage, solution pH, inorganic anions and natural organic matters（NOM）were investigated. It was found that in FeWO4/Cu2S at 1:2 possessed the best catalytic performance for PMS. FeWO4/Cu2S performed well in a wide pH range (3–9) and the effect was better under acidic conditions. A high catalyst dosage could supply more catalytic active sites for PMS activation and encourage the production of reactive oxygen species. Anions (HCO3−and HPO42−) and NOM significantly inhibited SCP degradation, whereas Cl− had only a tiny inhibitory impact. In addition, H2PO4− and NO3− demonstrated duality in the degradation of SCP. The oxidation process was dominated by non free radical oxidation by 1O2 rather than free radicals oxidation by HO⋅ and SO4•−. Three SCP degradation pathways—SO2 extrusion, S-N bond cleavage and hydroxylation were proposed according to intermediate products analysis. The mechanism was found that the introduction of W improved the dual metals cycles of Fe3+/Fe2+ and Cu+/Cu2+ which could efficiently promote PMS activation. In addition, the magnetic FeWO4/Cu2S was easy to separate after reaction, which had great application potential in the water treatment.

Sulfachloropyridazine (SCP) effects on anaerobic microorganisms and its degradation pathways

Sulfachloropyridazine (SCP) is frequently detected in animal excreta, as SCP commonly used in livestock and poultry for disease prevention. Anaerobic digestion (AD) has attracted much attention due to its ability to degrade antibiotics in animal excreta and convert animal excreta into renewable energy (biogas). But the degradation pathways of SCP in AD microorganism growth and SCP effect on the growth of AD microorganism are still unclear. In this study, the impact of SCP at 100 mg/L on the growth of representative AD microorganisms and the degradation pathways of SCP during single microorganism growth process were investigated using a pure culture method. Results showed that SCP has no effect on the growth of Clostridium tyrobutyricum and Methanosarcina barkeri, a positive effect on Peptoniphilus stercorisuis, but an inhibitory effect on Terrisporobacter glycolicus, Bacteroides caccae, and Proteiniphilum saccharofermentans, based on changes of cell growth (OD600), cumulative gas production, and gas components of strains. Meanwhile, SCP was degraded in varying degrees during the whole growth cycles of P. saccharofermentans, T. glycolicus, C. tyrobutyricum, B. caccae, P. stercorisuis, and M. barkeri, with degradation rates of 80.9%, 43.5%, 56.7%, 70.8%, 51.0%, and 21.4%, respectively. The SCP degradation pathway is different for these different strains, but the common degradation pathways were hydroxylation, C–N bond cleavage, release SO2, and nitration. These results revealed that anaerobic microorganisms have the high capability of degrading antibiotics and revealing degradation pathway is important for improving antibiotic degradation in AD process.

WS2 significantly enhances the degradation of sulfachloropyridazine by Fe(III)/persulfate

The use of antibiotics has become an indispensable part of the production and life of human society. Among them, sulfonamide antibiotics widely used in humans and animals are considered to be one of the most crucial antibiotics. However, antibiotics are difficult to degrade naturally, leading to an accumulation in the environment and a potential hazard to human health. In this paper, WS2 as a co-catalyst could reduce trace Fe(III) to Fe(II) which exhibited a great activating ability to PS through the exposed W(IV) active sites, and formed the Fe(III)/Fe(II) cycle to degrade sulfachloropyridazine (SCP) continuously. This paper systematically discussed the degradation of SCP under different conditions in the PS/WS2/Fe(III) system, including the amount of WS2, Fe(III) concentration, PS concentration, initial pH, natural organic matter (NOM) and common anions (NO3−, Cl−, HCO3−, HPO42− and H2PO4−). The experimental results showed that PS/WS2/Fe(III) system possessed a strong degradation ability for SCP in a wide pH range. NO3− and Cl− could promote the degradation of SCP a little. HCO3−, HPO42− and H2PO4− could significantly inhibit the degradation of SCP. The main types of free radicals that degraded SCP were explored. In addition, the stability and reusability of WS2 were examined, and two possible degradation pathways of SCP were proposed.

Location and size regulation of manganese oxides within mesoporous silica for enhanced antibiotic degradation

Refractory antibiotics in domestic wastewater are hard to be completely eliminated by conventional methods, and then lead to severe environmental contamination and adverse effects on public health. In present work, advanced oxidation processes (AOPs) are adopted to remove the antibiotic of sulfachloropyridazine (SCP). Nanosized Mn 2 O 3 was fabricated on the SBA-15 material to catalytically activate potassium peroxydisulfate (PDS) to generate reactive oxygen radicals of ∙OH and SO 4 − · for SCP degradation. The effects of location and size of Mn 2 O 3 were explored through choosing either the as-made or template-free SBA-15 as the precursor of substrate. Great influences from the site and size of Mn 2 O 3 on the oxidation activity were discovered. It was found that Mn 2 O 3 with a large size at the exterior of SBA-15 (Mn- tf SBA) was slightly easier to degrade SCP at a low manganese loading of 1.0–2.0 mmol∙g −1 ; however, complete SCP removal could only be achieved on the catalyst of Mn 2 O 3 with a refined size at the interior of SBA-15 (Mn- as SBA). Moreover, the SO 4 − · species were revealed to be the decisive radicals in the SCP degradation processes. Exploring the as-made mesoporous silica as a support provides a new idea for the further development of environmentally friendly catalysts.

Magnetic Nitrogen–Doped biochar for adsorptive and oxidative removal of antibiotics in aqueous solutions

Pollution by antibiotics has received attention worldwide because they are difficult to remove in wastewater. Extensive researches on antibiotics removal using adsorption and advanced oxidation processes has not resulted in ideal and effective methods for widespread implementation. Herein, nickel–containing and nitrogen–doped biochars (Ni@NBCs) are synthesized via polymer–assisted metal deposition and pyrolysis processes. These Ni@NBCs exhibit good adsorption capacities and act as catalysts to activate potassium persulfate (PPS) for producing reactive oxygen species, which react with the broad–spectrum antibiotic sulfachloropyridazine (SCP) in an oxidative degradation process. Experimental results of SCP adsorption confirm that the adsorption process follows pseudo–second–order kinetics and Langmuir isotherm models. Oxidative degradation results show that the constructed heterogeneous Ni@NBC/PPS system has excellent SCP degradation ability with degradation rates exceeding 90% within 40 min under certain conditions. The Ni@NBC also exhibits excellent reusability and durability (>75% degradation rate after 20 cycles). The catalytic mechanism and possible degradation pathways for SCP removal are proposed. Considering the adsorption and catalytic properties of Ni@NBCs, such materials show great application prospects for antibiotics removal in water environments.

Efficient degradation of sulfachloropyridazine by sulfite activation with CuO-Al2O3 composites under neutral pH conditions: Radical and non-radical

In this work, CuO-Al2O3 composites were synthesized at higher temperatures to control the leaching of metal ions, which can activate sulfite (S(IV)) to degrade organic contaminants by generating reactive oxygen species (ROSs). The synthesized catalysts were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller, Raman spectroscopy, and Fourier transform infrared spectrophotometry. Sulfachloropyridazine (SCP) was almost completely removed (＞99%) at pH 6.8, and the leaching amount of Cu accounted for 0.027% of the total amount of Cu after the reaction. Notably, singlet oxygen (1O2) was found for the first time in the activated sulfite system, which removed organic pollutants together with sulfate (SO4•-) and hydroxyl (∙OH) radicals. And Al2O3 plays an important role in the catalyst, including anti-sintering, reducing the leaching of copper ions, and promoting the generation of oxygen vacancies. Based on the types of ROSs and X-ray photoelectron spectroscopy results, a possible ROSs generation mechanism was proposed. In addition, the stability of the catalyst and the effect of different factors on the degradation of SCP, including operating parameters and water quality, were further investigated. The intermediates were detected by using gas chromatography-mass spectrometry and a developmental toxicity assessment of the intermediates was defined based on the Toxicity Estimation Software Tool (TEST). Overall, this paper not only provides a new strategy for sulfite activation but also promotes more attention to non-radical processes in activated sulfite systems.

Activation of peracetic acid by metal-organic frameworks (ZIF-67) for efficient degradation of sulfachloropyridazine

Peracetic acid (PAA)-based system is becoming an emerging advanced oxidation process (AOP) for effective removal of organic contaminants from water. Various approaches have been tested to activate PAA, while no previous researches reported the application of metal-organic frameworks (MOFs) materials for PAA activation. In this study, zeolitic imidazole framework (ZIF)-67, a representative MOFs, was facile synthesized via direct-mixing method at room temperature, and tested for PAA activation and sulfachloropyridazine (SCP) degradation. The as-synthesized ZIF-67 exhibited excellent performance for PAA activation and SCP degradation with 100% of SCP degraded within 3 min, owing to the specific MOFs structure and abundant Co2+ sites. The pseudo-first-order kinetic model was applied to fit the kinetic data, with rate constant k1 of ZIF-67 activated PAA system 34.2 and 156.5 times higher than those of conventional Co3O4 activated PAA and direct oxidation by PAA. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis indicated that CH3C(O)OO• played a major role in this PAA activation system. Then, the Fukui index based on density functional theory (DFT) calculation was used to predict the possible reaction sites of SCP for electrophilic attack by CH3C(O)OO•. In addition, the degradation pathway of SCP was proposed based on Fukui index values and intermediates detection, which mainly included the S-N bond cleavage and SO2 extrusion and followed by further oxidation, dechlorination, and hydroxylation. Therefore, ZIF-67 activated PAA is a novel strategy and holds strong potential for the removal of emerging organic contaminants (EOCs) from water.

Catalytic oxidation of sulfachloropyridazine by MnO2: Effects of crystalline phase and peroxide oxidants

Catalytic activation of different oxidants including peroxymonosulfate (PMS), peroxydisulfate (PDS), hydrogen peroxide (H2O2) and ozone (O3) by MnO2 for degradation of sulfachloropyridazine (SCP) was investigated and the effects of different crystalline phases of MnO2 including nanowire α-MnO2, nanorod β-MnO2, nanofiber γ-MnO2, and nanosphere δ-MnO2 on catalytic ozonation of SCP were also studied. The SCP degradation and total organic carbon removal indicated that the oxidation efficiency of the peroxide oxidants followed an order of O3/MnO2 > PMS/MnO2 > PDS/MnO2 > H2O2/MnO2. In catalytic ozonation, SCP degradation rate constants of different MnO2 phases followed an order of δ-MnO2 > α-MnO2 > γ-MnO2> β-MnO2. Electron paramagnetic resonance (EPR) suggested that hydroxyl radicals (·OH) and singlet oxygen (1O2) might be more significant for SCP degradation than sulfate (SO4·−) and superoxide (·O2−) radicals. Radical competition experiments demonstrated that 1O2 and ·OH contributed to 63.16% and 28.07%, respectively, for the catalytic ozonation of SCP. It was also found that more oxygen vacancies, specific surface area and exposure of MnO6 edges could facilitate the activation of O3 for 1O2 and ·OH productions and SCP degradation. The degradation pathways of SCP could mainly follow the cleavage of S–C or S–N bond and dechlorination, accompanied by hydroxylation and oxidation.

In-situ construction of Co(OH)2 nanoparticles decorated urchin-like WO3 for highly efficient degradation of sulfachloropyridazine via peroxymonosulfate activation: Intermediates and DFT calculation

Sulfachloropyridazine (SCP) was commonly used as a broad-spectrum sulfonamide antibiotic and hard to be removed through traditional sewage treatment process. In this study, we developed a simple and controllable strategy to realize in-situ construction of Co(OH)2 nanoparticles decorated urchin-like WO3 (Co(OH)2/WO3), which could efficiently remove SCP through peroxymonosulfate (PMS) activation. Some tiny nanoparticles of Co(OH)2 decorated on the spines/nanorods or surfaces of urchin-like WO3 by transmission electron microscopy (TEM) analysis. The obtained 10 wt% Co(OH)2/WO3 realized completely removal of SCP (degradation efficiency 100%) with a high reaction rate constant (k1) of 0.88 min−1 within 3 min at optimal pH 7. That was because the urchin-like WO3 with numerous adsorption functional groups on its surface (e.g., W = O and –OH bonds) could adsorb the Co2+ easily to form CoOH+, which was perceived the rate-limiting step for PMS activation and generating radicals. Radical quenching experiments indicated that SO4•− played a more significant role than HO• radicals. Density functional theory (DFT) calculation revealed that the atoms of SCP with high Fukui index (f−) were active sites, which preferred to be attacked by the electrophilic SO4•− and HO• radicals. The toxicity of the intermediates by SCP degradation was evaluated by quantitative structure–activity relationship (QSAR) prediction through Toxicity Estimation Software Tool (T.E.S.T.). The possible degradation pathway and catalytic mechanism for SCP removal were proposed. Considering the good catalytic properties of Co(OH)2/WO3-PMS, the material will show great application potential in the removal of emerging contaminants in water.

Surface chemistry-dependent activity and comparative investigation on the enhanced photocatalytic performance of graphitic carbon nitride modified with various nanocarbons

Organic contaminants, dyes and antibiotics, discharged in wastewater systems, have posed great threats to the sustainability of the ecosystem. This study was performed to prepare graphitic carbon nitride (GCN) nanocomposites modified by nanocarbons, including carbon quantum dots (CQD), carbon nanotube (CNT), reduced graphene oxide (rGO), and carbon nanospheres (CNS), by a straightforward one-pot method. The characterization results suggest that after the modification with nanocarbons, GCN demonstrated slight red shift and stronger light absorption. The resultant photocatalysts revealed prominent performances for total photodegradation of organic contaminants. The degradation processes were investigated by in situ electron paramagnetic resonance (EPR). The mechanistic studies on the enhanced photoelectrochemical and photocatalytic performances were also conducted. Results indicate that GCN modified by the nanocarbon spheres displayed a substantial improvement in the degradation of sulfachloropyridazine (SCP) and dyes, compared favourably with other GCN samples modified by carbon nanotubes, quantum dots and layered graphene oxide. The photocatalytic degradation difference is mainly stemmed from the higher contents of COOH and CO functional groups. The intimate contact or interaction between the two phases of GCN and nanocarbon in the nanocomposites may further improve the activity. This work provides insight in the design of highly efficient metal-free photocatalysts to better utilise the clean and free solar energy for environmental remediation.

Nitrogen-doped Carbon Nanospheres-Modified Graphitic Carbon Nitride with Outstanding Photocatalytic Activity

HighlightsMonodisperse nitrogen-doped carbon nanospheres were synthesized and loaded onto graphitic carbon nitride and the composites show outstanding photocatalytic activity.Improved sulfachloropyridazine degradation is consistent with density functional theory calculation..

Degradation of sulfachloropyridazine by UV-C/persulfate: kinetics, key factors, degradation pathway

Antibiotics are frequently detected in water, which can pose a great threat to human health.

Nickel in hierarchically structured nitrogen-doped graphene for robust and promoted degradation of antibiotics

Nickel nanoparticles encapsulated in nitrogen-doped porous graphene (Ni@NPG) were synthesized through a one-pot method as a novel material for catalytic activation of persulfate (PS). The Ni@NPG catalysts were evaluated for adsorptive and catalytic removals of antibiotic sulfachloropyridazine (SCP) as an emerging pollutant and were found to exhibit excellent adsorption and catalysis with 100% SCP removal from water in only 30 min. Meanwhile, great stability and reusability can be achieved with satisfactory organic degradation after 4 successive runs. In addition, metal leaching was prohibited from the metal@carbon catalysts due to the protection of carbon walls. The influences of humid acid and inorganic anions (HCO3−, Cl−, Br− and H2PO4−) on SCP degradation at various concentrations were further investigated and the present study shows that all these species promoted the SCP degradation at a low concentration whereas an inhibition effect occurred at higher concentrations due to radical quenching. Electron paramagnetic resonance (EPR) and quenching experiments reveal the PS activation mechanism involving generation of SO4•−, •OH and •O2− without singlet oxygen. The synergistic effect of radical and nonradical pathways played crucial roles during the SCP oxidation process.

MXene as a non-metal charge mediator in 2D layered CdS@Ti3C2@TiO2 composites with superior Z-scheme visible light-driven photocatalytic activity

Z-Scheme CdS@Ti3C2@TiO2 nanohybrids using MXene Ti3C2 as a non-metal charge carrier mediator exhibited superior performance in sulfachloropyridazine degradation.

Activation of peroxymonosulfate by Al2O3-based CoFe2O4 for the degradation of sulfachloropyridazine sodium: Kinetics and mechanism

Abstract Al2O3-based CoFe2O4 (CoFe2O4/Al2O3) as a catalyst was prepared to activate peroxymonosulfate (PMS) for degradation of sulfachloropyridazine (SCP). In general, the catalytic performance of CoFe2O4/Al2O3 in activation PMS was demonstrated more effective than CoFe2O4. Several influence factors were inspected, including scavengers, PMS concentration, pH, anions, nature organic matter (NOM) and temperature. The oxidation of SCP fitted a pseudo-first-order kinetics model and was efficient with the pH from 5.00 to 8.00. The influence of scavengers demonstrated that SO 4 - · played a more significant role than HO · in the oxidation process. The removal was strongly inhibited by adding NOM or HCO 3 - , and almost unaffected by adding NO 3 - , while chloride could enhance the degradation in the system. The increasing temperature greatly promoted the degradation of SCP. After four recycles, CoFe2O4/Al2O3 still showed preferable catalytic performance with 97.6% removal rate of SCP. Furthermore, the degradation mechanism was explored based on the XPS results. In the composit of CoFe2O4/Al2O3, Al2O3 had no additional catalytic performance but just as a matrix base.

Carbocatalytic activation of persulfate for removal of antibiotics in water solutions

Emerging pharmaceutical contaminants have raised severe challenges to remediation technologies for water treatment. In this paper, we report a facile method for preparation of nitrogen doped reduced graphene oxide (N-rGO) using urea as a nitrogen precursor. The prepared metal-free N-rGO is able to efficiently activate persulfate (PS) to produce reactive radicals for degradation of an antibiotic of sulfachloropyridazine (SCP). The effects of reaction parameters on SCP degradation were investigated. The activation processes were studied by in situ electron paramagnetic resonance (EPR), which discovered the newly observed hydroxyl radicals from PS activation. This study suggests a green remediation for removal of antibiotics in wastewater without producing any heavy metal leaching as the secondary contamination.

Quantum chemical study of the photolysis mechanisms of sulfachloropyridazine and the influence of selected divalent metal ions

Sulfonamides have been found in aquatic environments. Degradation of sulfachloropyridazine (SCP) mainly proceeds through direct and indirect photolysis in the aquatic environment. However, the mechanisms underlying the triplet photolysis of SCP and the influence of metal ions on the photolysis mechanism have not yet been fully explained. In this study, we elucidated the triplet photolysis mechanisms of SCP and the effects of three selected metal ions (Zn2+, Ca2+, and Cu2+) on the SCP photolysis mechanisms using quantum chemical calculation. Optimization of molecular structures and reaction pathways analysis of SCP were carried out at the B3LYP/6-31+G(d,p) level of theory. Two minimum energy pathways were investigated in the triplet photolysis of SCP. In Step 2 of Path-I, the photolysis product of SCP is a sulfur dioxide extrusion product, (4-(3-chloro-6-iminopyridazine-1(6H)-yl)aniline). The estimated activation energies of Step 2 and Step 3 of Path-I were much higher than in Path-II. Therefore, Path-II was found as the lowest energy pathway to obtain the SCP photoproducts, and Step 2 of Path-II was confirmed as the rate-determining step (RDS) in the photolysis mechanism of SCP. For the RDS of Path-II, computations with the three metal ions complexes (IM1–Cu2+, IM1–Ca2+, and IM1–Zn2+) show that the metal ions Cu2+ and Ca2+ promote triplet-sensitized photolysis of SCP by reducing the activation energy of RDS of Path-II, whereas Zn2+ showed an inhibitory effect in photolysis of SCP by increasing the activation energy.

Electrochemical degradation of the antibiotic sulfachloropyridazine by hydroxyl radicals generated at a BDD anode

The treatment of aqueous solutions of the antibiotic sulfachloropyridazine (SCP) was carried out at the natural pH of the solution (pH 4.5) with hydroxyl radicals (OH) generated at a BDD anode surface by electro-oxidation using an undivided electrochemical cell equipped with a three-dimensional carbon-felt cathode. Hydroxyl radicals are powerful oxidants and react with the antibiotic leading to its overall mineralization. The kinetic study showed that oxidative degradation of SCP follows pseudo first-order reaction kinetics, with a relatively short degradation time. The degree of mineralization of SCP solutions increased with the applied current, being higher than 95% after 8h of electrolysis at 350mA or higher current. To determine the degradation pathway upon the action of hydroxyl radicals, the cyclic and aliphatic by-products, as well as the released inorganic ions, were identified and quantified over electrolysis time. The values of the rate constants of reactions between OH and the SCP and its intermediates were determined by the competition kinetics method using p-hydroxybenzoic acid. The absolute rate constant for the OH-mediated degradation of SCP was found to be 1.92×109M−1s−1. Toxicity assessment by the Microtox® method during the electro-oxidation of SCP solutions revealed the formation of compounds that can be more toxic than the parent molecule, but the overall results confirm the effectiveness of this electrochemical process for the removal of the antibiotic SCP and its by-products from aqueous media.

Electrochemical Treatment of the Antibiotic Sulfachloropyridazine: Kinetics, Reaction Pathways, and Toxicity Evolution

The electro-Fenton treatment of sulfachloropyridazine (SCP), a model for sulfonamide antibiotics that are widespread in waters, was performed using cells with a carbon-felt cathode and Pt or boron-doped diamond (BDD) anode, aiming to present an integral assessment of the kinetics, electrodegradation byproducts, and toxicity evolution. H(2)O(2) electrogeneration in the presence of Fe(2+) yielded (•)OH in the solution bulk, which acted concomitantly with (•)OH adsorbed at the anode (BDD((•)OH)) to promote the oxidative degradation of SCP (k(abs,SCP) = (1.58 ± 0.02) × 10(9) M(-1) s(-1)) and its byproducts. A detailed scheme for the complete mineralization was elucidated. On the basis of the action of (•)OH onto four different SCP sites, the pathways leading to total decontamination includes fifteen cyclic byproducts identified by HPLC and GC-MS, five aliphatic carboxylic acids, and a mixture of Cl(-), SO(4)(2-), NH(4)(+), and NO(3)(-) that accounted for 90-100% of initial Cl, S, and N. The time course of byproducts was satisfactorily correlated with the toxicity profiles determined from inhibition of Vibrio fischeri luminescence. 3-Amino-6-chloropyridazine and p-benzoquinone were responsible for the increased toxicity during the first stages. Independent electrolyses revealed that their toxicity trends were close to those of SCP. The formation of the carboxylic acids involved a sharp toxicity decrease, thus ensuring overall detoxification.