Photochemistry of copper complexes and their environmental aspects

Photochemical demethylation of methylmercury (MeHg) in aquatic systems: A review of MeHg species, mechanisms, and influencing factors

Photodemethylation is the major pathway of methylmercury (MeHg) demethylation in surface water before uptake by the food chain, whose mechanisms and influence factors are still not completely understood. Here, we review the current knowledge on photodemethylation of MeHg and divide MeHg photolysis into three pathways: (1) direct photodemethylation, (2) free radical attack, and (3) intramolecular electron or energy transfer. In aquatic environments, dissolved organic matter is involved into all above pathways, and due to its complex compositions, properties and concentrations, DOM poses multiple functions during the PD of MeHg. DOM-MeHg complex (mainly by sulfur-containing molecules) might weaken the C-Hg bond and enhance PD through both direct and indirect pathways. In special, synergistic effects of both strong binding sites and chromophoric moieties in DOM might lead to intramolecular electron or energy transfer. Moreover, DOM might play a role of radical scavenger; while triplet state DOM, which is generated by chromophoric DOM under light, might become a source of free radicals. Apart from DOMs, transition metals, halides, NO3-, NO2-, and carbonates also act as radical initialaters or scavengers, and significantly pose effects on radical demethylation, which is generally mediated by hydroxyl radicals and singlet oxygen. Environmental factors such as pH, light wavelength, light intensity, dissolved oxygen, salinity, and suspended particles also affect the PD of MeHg. This study assessed previously published works on three major mechanisms, with the goal of providing general estimates for photodemethylation under various environment factors according to know effects, and highlighting the current uncertainties for future research directions.

Differential interference of copper with endophytic bacterial inoculation: Atrazine decontamination in Acorus tatarinowii and culture solution

To clarify the interference effects of inorganic ions, Acorus tatarinowii and endophytic bacterium Herbaspirillum huttiense (Hh) were combined to decontaminate atrazine pollution under different copper levels. This study verified inoculation effects and revealed the complicated processes of atrazine transformation in solutions. 35.9% leaf biomass was promoted by Hh inoculation, and the value was lowered to 7.87% by high doses of copper. The changing trend of leaf N, K, and S contents, and tiller numbers were consistent with that of leaf biomass. Hh injection improved atrazine accumulation by 43.5% in roots, and under copper interference, this value lowered to 10.6%. Hh promoted atrazine deethylation in plants, which was copper-dose dependent in different plant organs. In solutions, atrazine was conjugated with small-molecule secretions at m/z 118, detoxicated into 2-hxydroatrazine and 2-hydroxy-4-acetamido-atrazine, then the triazine ring opened. Copper interference had a more significant impact on residual atrazine conversion products than Hh inoculation treatments. Hh treatment promoted the ring-opening degradation of atrazine in water. The addition of high doses of copper ions promoted the oxidative process of atrazine while inhibiting its ring-opening transformation process in water.

Relevance of photocatalytic redox transformations of selected pharmaceuticals in a copper- and iron-rich Mediterranean intermittent river

This work aimed at investigating specific attenuation pathways of pharmaceuticals in copper- and iron-rich Mediterranean intermittent and sunlit rivers by combining lab- and field-scale studies. Poorly photodegradable and biodegradable compounds such as fluconazole, oxazepam and venlafaxine attenuated in two river stretches with short hydraulic residence times (<3 h). This result was assumed to be related to their capacity to interact with photoreactive free Cu2+ and Fe3+ or their associated oxides. Lab-scale photodegradation experiments under simulated solar irradiation revealed the beneficial impact of a mixture Cu2+ and colloidal iron hydroxides at environmental concentrations and at neutral pH on the pharmaceuticals photodegradation kinetic rate constants. These latter were consistent with the in-stream attenuation rate constants of targeted contaminants which ranged from 0.104 to 0.154 h-1. Further identification of phototransformation products by LC-HRMS highlighted reductive transformation pathways including reductive dehalogenation and hydrogenation reactions. Several TPs were found to be stable under irradiation and were detected in field monitoring, accordingly. This was ascribed to the formation of a Cu/Fe composite material under solar irradiation with photocatalytic properties. The role of Cu was to trap the electron in the conduction band of the iron-based photocatalyst, which promoted separation efficiency of electron-hole pairs as well as enhanced photoreduction processes at the expense of oxidation ones. Even though, these mechanisms have been reported in water treatment field for organic micropollutants removal, their significance was demonstrated for the first time in natural settings.

Aquatic photochemistry of Cu(II) in the presence of As(III): Mechanistic insights from Cu(III) production and As(III) oxidation under neutral pH conditions

Surface complexation between arsenite (As(III)) and colloidal metal hydroxides plays an important role not only in the immobilization and oxidation of As(III) but also in the cycle of the metal and the fate of their ligands. However, the photochemical processes between Cu(II) and As(III) are not sufficiently understood. In this work, the photooxidation of As(III) in the presence of Cu(II) under neutral pH conditions was investigated in water containing 200 μM Cu(II) and 5 μM As(III) under simulated solar irradiation consisting of UVB light. The results confirmed the complexation between As(III) and Cu(II) hydroxides, and the photooxidation of As(III) is attributed to the ligand-to-metal charge transfer (LMCT) process and Cu(III) oxidation. The light-induced LMCT process results in simultaneous As(III) oxidation and Cu(II) reduction, then produced Cu(I) undergoes autooxidation with O₂ to produce O₂^•⁻ and H₂O₂, and further the Cu(I)-Fenton reaction produces Cu(III) that can oxidize As(III) efficiently (k_{Cu(III)+As(III)} = 1.02 × 10⁹ M^-1 s^-1). The contributions from each pathway (ρ_{rCu(II)-As(III)+hv} = 0.62, ρ_{rCu(III)+As(III)} = 0.38) were obtained using kinetic analysis and simulation. Sunlight experiments showed that the pH range of As(III) oxidation could be extended to weak acidic conditions in downstream water from acid mine drainage (AMD). This work helps to understand the environmental chemistry of Cu(II) and As(III) regarding their interaction and photo-induced redox reactions.

Nonpolar Side Chains Affect the Photochemical Redox Reactions of Copper(II)-Amino Acid Complexes in Aqueous Solutions

Photochemical redox reactions of Cu(II) complexes of eight amino acid ligands (L) with nonpolar side chains have been systematically investigated in deaerated aqueous solutions. Under irradiation at 313 nm, the intramolecular carboxylate-to-Cu(II) charge transfer within Cu(II)-amino acid complexes leads to Cu(I) formation and the concomitant decomposition of amino acids. All amino acid systems studied here can produce ammonia and aldehydes except proline. For the 1:1 Cu(II) complex species (CuL), the Cu(I) quantum yields at 313 nm (Φ_Cu(I),CuL) vary by fivefold and in the sequence (0.10 M ionic strength at 25 °C) alanine (0.094) > valine (0.059), leucine (0.059), isoleucine (0.056), phenylalanine (0.057) > glycine (0.052) > methionine (0.032) > proline (0.019). This trend can be rationalized by considering the stability of the carbon-centered radicals and the efficient depopulation of the photoexcited state, both of which are dependent on the side-chain structure. For the 1:2 Cu(II) complex species (CuL₂), the Cu(I) quantum yields exhibit a similar trend and are always less than those for CuL. The photoformation rates of ammonia, Cu(I), and aldehydes are in the ratio of 1:2.0 ± 0.2:0.7 ± 0.2, which supports the proposed mechanism. This study suggests that the direct phototransformation of Cu(II)-amino acid complexes may contribute to the bioavailable nitrogen for aquatic microorganisms and cause biological damage on cell surfaces in sunlit waters.

Photo Augmented Copper-based Fenton Disinfection under Visible LED Light and Natural Sunlight Irradiation

Copper-based Fenton disinfection system (Cu(II)/H₂O₂) is an emerging advanced oxidation process (AOP). Previous works have used reducing agents and organic ligands to improve the disinfection efficiency of Cu(II)/H₂O₂ system. Here, we report visible light/Cu(II)/H₂O₂ system showed enhanced disinfection compared to Cu(II)/H₂O₂ system, without the need of reducing chemical agent or organic ligand. Energy-efficient LED array was used as a visible light source in the visible light/Cu(II)/H₂O₂ system. Under the optimized condition, pseudo-first-order inactivation rate constant (k_obs) of E. coli by visible light/Cu(II)/H₂O₂ (0.613 ± 0.005 min^-1) was about ~8 times greater than Cu(II)/H₂O₂ (0.08 ± 0.011 min^-1). Scanning electron microscopy and Baclight Live/Dead assay proved enhanced cell membrane damage by visible light/Cu (II)/H₂O₂ in comparison with Cu(II)/H₂O₂. Based on the bovine serum albumin (BSA) degradation and OH˙ radical measurement by visible light/Cu(II)/H₂O₂, a ligand to metal charge transfer (LMCT) mechanism by Cu(II)-bacterial complex is proposed for enhanced disinfection. Electrical energy efficiency (E _E,1) for a log reduction of E. coli and the total treatment cost of visible light/Cu(II)/H₂O₂ was determined to be 32.64 KWh/m³ and 350 ₹/m³ (3.9 €/m³ or 4.74 $/m³), respectively, indicating its cost-effectiveness. Disinfection efficiency by sunlight/Cu(II)/H₂O₂ system (solar irradiance; 746 ± 138 W/m²) was almost comparable to LED-based visible light/Cu(II)/H₂O₂ system, with total treatment cost estimated to be 80 ₹/m³ (0.9 €/m³ or 1.1 $/m³).

Copper(i) halide cluster-based coordination polymers modulated by chiral ditopic dithiodianthranilide ligands: synthesis, crystal structure and photoluminescence

The influence of ligand chirality on the self-assembly and spectroscopic properties of copper(i) halide coordination polymers was investigated.

Recent advances in Cu-Fenton systems for the treatment of industrial wastewaters: Role of Cu complexes and Cu composites

Cu-based Fenton systems have been recognized as a promising suite of technologies for the treatment of industrial wastewaters due to their high catalytic oxidation capacity. Rapid progress regarding Cu Fenton systems has been made not only in fundamental mechanistic aspects of these systems but also with regard to applications over the past decade. Based on available literature, this review synthesizes the recent advances regarding both the understanding and applications of Cu-based Fenton processes for industrial wastewater treatment. Cu-based catalysts that are essential to the effectiveness of use of Cu Fenton reactions for oxidation of target species are mainly classified into two types: (i) Cu complexes with organic or inorganic ligands, and (ii) Cu composites with inorganic materials. Performance of the Cu-based catalysts for the removal of organic pollutants in industrial wastewaters are reviewed, with the key operating parameters illustrated. Furthermore, the roles of Cu complexes and composites in both homogeneous and heterogeneous Cu-Fenton systems are critically examined with particular focus on the mechanisms involved. Perspectives and future efforts needed for Cu-based Fenton systems using Cu complexes and composites for industrial wastewater treatment are presented.

Identification of avobenzone by-products formed by various disinfectants in different types of swimming pool waters

The increased use of sunscreens and other cosmetics containing UV filters causes human and environmental burden. Avobenzone is a widely used UV filter. In its pure form it is known to undergo several transformations including photo-isomerisation, photodegradation, and halogenation. Over 60 disinfection by-products were identified as transformation products of avobenzone in different disinfection reactions of chlorination and bromination in fresh and seawater. Two occasional samples of swimming pool water demonstrated the presence of some of these by-products at noticeable levels as judged by GC-MS peak areas. Although the toxicity of the majority of these products remain unknown, chlorinated phenols and acetophenones are known to be rather toxic. Aquatic bromination of avobenzone resulted in the identification of 33 disinfection by-products (DBPs). Many of them contain bromine in the molecular structure. Addition of copper salt slightly decreases conversion rate simultaneously increasing the levels of major brominated products. Photostability of 3 commercial sunscreen products (solar protection factor 30) containing avobenzone was studied under different experimental conditions including UVA/UVB, UVC photostimulation and chlorination. The commercial sunscreen products have completely different enhancing and inhibitory effect on avobenzone degradation under UVC light. The complex composition of commercial products caused also a protective shield in case of chlorinated solutions of commercial formulations exposed to chlorine and UVA/UVB light at the same time.

Vibrations tell the tale. A time-resolved mid-infrared perspective of the photochemistry of iron complexes

Time-resolved infrared spectroscopies are used to elucidate multiscalar photochemical processes of iron complexes.

Removal of Chloride Ions from Strongly Acidic Wastewater Using Cu(0)/Cu(II): Efficiency Enhancement by UV Irradiation and the Mechanism for Chloride Ions Removal

Strongly acidic wastewater, which is usually generated from nonferrous metal smelting industries, has the ability to be recycled as sulfuric acid. Before this wastewater is recycled, the removal of chloride ions is necessary to improve the quality of the recycled sulfuric acid. At present, the widely used method to remove chloride ions from acidic wastewater in the form of CuCl precipitate has several disadvantages, including low removal efficiency, high temperature, long treatment time, and high dosage of Cu(II). This study proposed an improved new method of removing Cl(-I) using Cu(0)/Cu(II) under UV irradiation, and the mechanism was investigated. The Cl(-I) concentration was lowered to below 50 mg/L at a Cu(II) dosage of 1200 mg/L. Under UV irradiation, ligand-to-metal charge transfer takes place, thereby resulting in the formation of Cl^•. Next, CuCl precipitates form through the reaction between Cu(0) and Cl^• and produce h⁺/^•OH under UV irradiation, which can oxidize Cl(-I) to Cl^•. Simultaneously, Cl₂ gas also forms directly from Cl^•. This study offered a theoretical foundation for the application of UV irradiation for the enhanced removal of chloride ions from strongly acidic wastewater.

Use of oxalic acid as inducer in photocatalytic oxidation of cresol red in aqueous solution under natural and artificial light

This work was carried out in the field of water treatment using advanced oxidation processes (AOPs), especially photolysis of carboxylic acid that leads to the formation in situ of hydroxyl radical (·OH). Cresol red (CR) degradation induced by organic acids/UV system was investigated in aqueous solution. The preliminary study of CR-organic acid mixture in the dark and at room temperature allowed confirming the absence of interaction under our experimental conditions. However, upon irradiation at 365 nm, the proportion of elimination of CR was 89% after 5 h of irradiation. Indeed, the CR degradation efficiency depends on the acid concentration and the pH of the medium. The concentration of acid is optimized to the 5 × 10^-3 M. pH 2.39 was the optimal one when C₂HO^- ₄ was the most important species at this pH. The use of i-PrOH as ^·OH confirmed the involvement of ^·OH in photodegradation of CR induced by Ox. The addition of metal ions including Zn²⁺ and Cu²⁺ to the CR-organic acid mixture slowed the CR degradation unlike Fe²⁺, hence an improvement of its disappearance was observed. The results showed a faster degradation of the pollutant under excitation by sunlight. This environmentally friendly method appears to be very effective in the treatment of wastewater.

Efficient removal of EDTA-complexed Cu(II) by a combined Fe(III)/UV/alkaline precipitation process: Performance and role of Fe(II)

Efficient removal of heavy metal-EDTA complexes from water remains a challenge because of their good solubility and chemical stability. Herein, we employed a proprietary process, i.e., the Fe(III) displacement/UV irradiation/alkaline precipitation (denoted as Fe(III)/UV/OH), to enable an efficient removal of Cu(II)-EDTA complex from 19.2 mg Cu(II)/L to <1 mg Cu(II)/L. The combined process includes Fe(III) replacement with the complexed Cu(II) to form Fe(III)-EDTA and release the free Cu(II), UV-mediated catalytic decarboxylation of EDTA to form amine ligands and reduction of Fe(III) to Fe(II), and the final removal of Cu(II) through precipitation. The in situ formed Fe(II) is crucial to the final Cu(II) removal because it tends to form stable complexes with amine ligands (EDTA and its decarboxylation products), thereby inhibiting their re-complexation with the released Cu(II) and facilitating the formation of copper precipitates. Consequently, the methods capable of prolonging the life of Fe(II), e.g., increasing the Fe(III) addition or direct addition of Fe(II) into the Cu(II)-EDTA solution and deoxygenating the solution, could dramatically enhance the final Cu(II) removal. We also optimized the operational conditions of the process at the initial Cu(II)-EDTA of 19.2 mg Cu(II)/L.

Chemical oxidation of a malodorous compound, indole, using iron entrapped in calcium alginate beads

Iron-alginate beads (Fe-ABs) were successfully prepared by the ion-gelation method, and applied as heterogeneous Fenton catalysts for the removal of a malodorous compound 'indole'. Similarly, copper-enriched alginate beads (Cu-ABs) were synthesized and tested as like-Fenton catalyst, however, their application proved not to be effective for this purpose. Fe-ABs catalysts were characterized by FTIR, SEM, EDS and AAS spectroscopy. Results pointed out that the parameters affecting Fenton catalysis must be carefully chosen to avoid excessive iron release. Under optimal conditions, complete indole removal and considerably high reduction of TOC, without significant leaching was achieved. Indole decay followed a pseudo-first-order kinetics. The absolute rate constant for indole hydroxylation was 3.59×10(9) M(-1) s(-1), as determined by the competition kinetics method. Four reaction intermediates (Isatin, Dioxindole, Oxindole and Anthralinic acid) were identified by ULC/MS/MS analysis. Short-chain aliphatic carboxylic acids like formic, acetic, oxalic, maleic, oxamic and pyruvic acids were identified by ion exclusion chromatography and as end-products. Based on the identified by-products, a plausible mineralization pathway was proposed. Moreover, the catalyst was recovered quantitatively by simple filtration and reused for several times without significant loss of activity.

A new combined process for efficient removal of Cu(II) organic complexes from wastewater: Fe(III) displacement/UV degradation/alkaline precipitation

Efficient removal of heavy metals complexed with organic ligands from water is still an important but challenging task now. Herein, a novel combined process, i.e., Fe(III)-displacement/UV degradation/alkaline precipitation (abbreviated as Fe(III)/UV/OH) was developed to remove copper-organic complexes from synthetic solution and real electroplating effluent, and other processes including alkaline precipitation, Fe(III)/OH, UV/OH were employed for comparison. By using the Fe(III)/UV/OH process, some typical Cu(II) complexes, such as Cu(II)-ethylenediaminetetraacetic acid (EDTA), Cu(II)-nitrilotriacetic acid (NTA), Cu(II)-citrate, Cu(II)-tartrate, and Cu(II)-sorbate, each at 19.2 mg Cu/L initially, were efficiently removed from synthetic solution with the residual Cu below 1 mg/L. Simultaneously, 30-48% of total organic carbon was eliminated with exception of Cu(II)-sorbate. Comparatively, the efficiency of other processes was much lower than the Fe(III)/UV/OH process. With Cu(II)-citrate as the model complex, the optimal conditions for the combined process were obtained as: initial pH for Fe(III) displacement, 1.8-5.4; molar ratio of [Fe]/[Cu], 4:1; UV irradiation, 10 min; precipitation pH, 6.6-13. The mechanism responsible for the process involved the liberation of Cu(II) ions from organic complexes as a result of Fe(III) displacement, decarboxylation of Fe(III)-ligand complexes subjected to UV irradiation, and final coprecipitation of Cu(II) and Fe(II)/Fe(III) ions. Up to 338.1 mg/L of Cu(II) in the electroplating effluent could be efficiently removed by the process with the residual Cu(II) below 1 mg/L and the removal efficiency of ∼99.8%, whereas direct precipitation by using NaOH could only result in total Cu(II) removal of ∼8.6%. In addition, sunlight could take the place of UV to achieve similar removal efficiency with longer irradiation time (90 min).

Photodegradation of α-cypermethrin in soil in the presence of trace metals (Cu2+, Cd2+, Fe2+ and Zn2+)

The influence of trace metals (Cu(2+), Zn(2+), Cd(2+) and Fe(2+)) on the photodegradation of α-cypermethrin (α-CYM) in agricultural soil was studied. The soil samples were spiked with α-cypermethrin with/without the presence of metal ions, irradiated under a UV irradiation chamber for a regular period of time and analyzed by using HPLC. The dark control sterile and unsterile soil samples spiked with α-cypermethrin and selected trace metals were incubated for the same interval of time at 25 °C. The results obtained indicated that α-cypermethrin photodegradation followed biphasic kinetics. α-cypermethrin photodegradation half-lives (t1/2) were increased to 0.71 and. 4.5 hours from 0.64 hours respectively in the presence of elevated Zn(2+) and Cu(2+) concentrations. Fe(2+) and Cd(2+) increased the photodegradation reaction kinetics from -1.078 h(-1) to -1.175 h(-1) and -1.397 h(-1) and varied the t1/2 from 0.64 ± 1.41 to 0.59 ± 2.07 and 0.49 ± 2.01 in the soil. Microbes also affected the degradation of α-cypermethrin in metal contaminated soil. The degradation rate was inhibited in unsterile soil and was found to be in the following order: Cd(2+)< Zn(2+)< Cu(2+)< Fe(2+). The degradation/persistence of α-cypermethrin was affected linearly with the increasing soil metal concentrations.

Visible light photodegradation of phenanthrene catalyzed by Fe(III)-smectite: role of soil organic matter

In the present study, phenanthrene is employed as a model to explore the roles played by three soil organic matter (SOM) fractions, i.e., dissolved organic matter (DOM), humic acid (HA), and fulvic acid (FA), in its photodegradation with assistance of Fe(III)-smectite under visible-light. Slight decrease in phenanthrene photodegradation rate was observed in the presence of DOM, which is explained in terms of oxidative-radical competition between DOM and target phenanthrene molecules due to the high electron-donor capacity of phenolic moieties in DOM. On the other hand, a critic content is observed with FA (0.70mg/g) and HA (0.65mg/g). Before reaching the critic content, the removal of phenanthrene is accelerated; while after that, the photodegradation rate is suppressed. The acceleration of phenanthrene degradation can be attributed to the photosensitization of FA and HA. Due to the strong interaction between phenanthrene and the phenyl rings, however, the retention of phenanthrene on SOM-Fe(III)-smectite in the presence of high content of HA or FA is enhanced, thus slowing down its photodegradation. Those observations provide valuable insights into the transformation and fate of PAHs in the natural soil environment and open a window for using clay-humic substances complexes for remediation of contaminated soil.

Photodegradation of propranolol by Fe(III)-citrate complexes: kinetics, mechanism and effect of environmental media

Photogeneration of HO was optimized in Fe(III)-citrate solution within the pH range of 3.0-9.0 to investigate its photoreactivity at neutral pH without the addition of H(2)O(2) under simulated sunlight. The generation of HO decreased with increasing pH within the range of 6.0-9.0 at the Fe(III)-to-citrate ratio of 10:50 (10(-6)M). However, when the concentration of citrate increased to 1.5 × 10(-4)M, the formation rate of HO increased in the order of pH 9.0<3.0<7.0<4.0<5.0. The pH-dependent HO production was governed by the stability of Fe(II)/Fe(II)-citrate and the amount of O(2)(-) in the solution. Propranolol can be efficiently photodegraded in Fe(III)-citrate system at pH 7.0 with pseudo-first-order constant 3.1 × 10(-4)s(-1). HO was verified to be the main reactive oxygen species (ROS) responsible for the photodegradation of propranolol. The presence of metal ions inhibited the Fe(III)-cit-induced photodegradation in the order of Mn(2+)>Cu(2+)>Ca(2+)>Mg(2+). Both humic acid (HA) and fulvic acid (FA) markedly suppressed the degradation of propranolol. Moreover, the iron in Fe(III)-citrate system was reused by a simple addition of citrate to the reaction solution. By GC-MS analysis, the photoproducts of the propranolol were identified and the degradation pathway was proposed. This work suggests that Fe(III)-citrate complexes are good alternative for the advanced treatment of organic pollutants at neutral pH in aqueous solution.

Effects of Cu(II) and humic acid on atrazine photodegradation

This work was designed to explore the characteristics of photodegradation of herbicides in the copper-polluted water body. The results showed that Cu(II) alone could induce a photo Fenton-like reaction to enhance the degradation of atrazine, in which hydroxyl radical (*OH) was a main active species. Humic acids restrained atrazine degradation, nevertheless, when introducing Cu(II), the photodegradation was accelerated, in which singlet oxygen (1O2) replaced *OH acting as the prevailing species. A feasible mechanism for the photochemical process was also proposed, which is helpful for better understanding the environmental photochemistry of atrazine in the copper-polluted water.

Effect of copper on the degradation of pesticides cypermethrin and cyhalothrin

The influence of coexisting copper (Cu) ion on the degradation of pesticides pyrethroid cypermethrin and cyhalothrin in soil and photodegradation in water system were studied. Serial concentrations of the pesticides with the addition of copper ion were spiked in the soil and incubated for a regular period of time, the analysis of the extracts from the soil was carried out using gas chromatography (GC). The photodegradation of pyrethroids in water system was conducted under UV irradiation. The effect of Cu2+ on the pesticides degradation was measured with half life (t0.5) of degradation. It was found that a negative correlation between the degradation of the pyrethroid pesticides in soil and Cu addition was observed. But Cu2+ could accelerate photodegradation of the pyrethroids in water. The t0.5 for cyhalothrin extended from 6.7 to 6.8 d while for cypermethrin extended from 8.1 to 10.9 d with the presence of copper ion in soil. As for photodegradation, t0.5 for cyhalothrin reduced from 173.3 to 115.5 min and for cypermethrin from 115.5 to 99.0 min. The results suggested that copper influenced the degradation of the pesticides in soil by affecting the activity of microorganisms. However, it had catalyst tendency for photodegradation in water system. The difference for the degradation efficiency of pyrethroid isomers in soil was also observed. Copper could obviously accelerate the degradation of some special isomers.

Photoformation of low-molecular-weight organic acids from brown water dissolved organic matter

This work describes the effects of simulated solar UV light on the bulk properties of dissolved organic matter (DOM) of bog lake water and on the formation of low-molecular-weight organic acids (LMWOAs). By means of size-exclusion chromatography it was shown that the more hydrophilic moieties of the DOM were preferentially photodegraded while the more hydrophobic ones remained relatively unaffected or were even formed. The combined photochemical-biological degradation proved to be more important than the pure photochemical mineralization. Formic, acetic, pyruvic, oxalic, malonic, and succinic acids were identified as important degradation products. Their contribution to the dissolved organic carbon increased from 0.31% before to 6.4% after 24 h irradiation. About 33% of the bioavailable photoproducts of DOM were comprised of these LMWOAs. The influence of nitrate on the formation of carboxylic acids could not be observed in the investigated system. Kinetic experiments indicated that degradation of LMWOAs occurred simultaneously during irradiation experiments, alpha-oxygen-substituted LMWOAs being more amenable to these processes. Dissolved iron acted as a catalyst of DOM photodegradation and LMWOA photoformation. Copper played an antagonistic role in the irradiation experiments, reducing the formation of formic, acetic, and malonic acids while increasing the formation of oxalic acid.