Effect of humus on photodegradation of quinclorac under different fertilization modes.

Humus is a specific kind of organic matter widely distributed in soils. The characteristics of humus have significant impacts on the fate of pollutants in the environment. In this study, we examined the effects of fertilization modes from rice rotation systems on the contents, spectral properties, photochemical activity, and photosensitization of quinclorac (QNC) of humic (HA) and fulvic acids (FA). The results showed that under the rice-vegetable rotation system, organic fertilizer treatment decreased the humification degree and molecular weight of HA, but increased the number of oxygen-containing functional groups and the abilities of photoproducing hydroxyl radical (HO·), singlet oxygen (1O2) and photosensitizing QNC, compared with chemical fertilizer treatment. Under organic fertilization mode, the molecular weight of FA was increased, but the number of redox functional groups and the abilities of photoinducing HO· and 1O2 and photosensitizing QNC were decreased. Under rice-shrimp cultivation system, organic-inorganic fertilizer treatment increased the humification degree, molecular weight, number of redox functional groups and oxygen-containing functional groups, and 1O2 photogeneration of HA, but decreased the abilities of photoproducing HO· and photosensitizing QNC, as compared with chemical fertilizer treatment. The humification degree and molecular weight of FA under organic-inorganic fertilization mode were increased, while the abilities of photoproducing HO· and 1O2 and photosensitizing QNC were decreased. In conclusion, organic fertilization could enhance the photochemical activity and photosensitizing efficiency of humus, and further promote the photodegradation of QNC in the environment.

[Degradation of Triclosan by Heat Activated Persulfate Oxidation].

Sulfate radical (SO4·-)-based advanced oxidation technologies (SR-AOPs) are widely used for remediation of contaminated groundwater and soils. This study investigated the reaction kinetics, products, and transformation pathways of triclosan, a widely used antimicrobial agent, during its degradation by heat activated persulfate oxidation. Experimental results revealed that increasing temperature or initial persulfate concentration significantly enhanced the degradation of triclosan. The reaction could be fitted in the pseudo-first-order kinetic model and the activation energy (Ea) was determined to be 142 kJ·mol-1. The presence of humic acid markedly inhibited triclosan degradation, whereas chloride (Cl-) showed a more complicated effect. Triclosan degradation was slightly accelerated in the presence of 5 µmol·L-1 Cl-, however, a higher concentration of Cl- (e.g., 10 µmol·L-1) showed an inhibitory effect. Using liquid chromatography-mass spectrometry, a total of six transformation products, including 4-chlorocatechol, 2,4-dichlorophenol, and 2-chloro-5-(2,4-dichloro-6-hydroxyphenoxy)-1,4-benzoquinone, were identified. Accordingly, the cleavage of the ether bond and hydroxylation of the phenol ring were proposed as the principal pathways of triclosan degradation upon reaction with SO4·-. The findings of this study can be used to evaluate the feasibility of decontamination of triclosan by SR-AOPs.

[Formation of Halogenated By-products in Co²âº Activated Peroxymonosulfate Oxidation Process].

Sulfate radicals (SO4·â») generated by Co²âº catalyzed activation of peroxymonosulfate (PMS) are highly oxidative and can be applied to degrade various organic pollutants. It was revealed in this research that bromide could be transformed in this process to reactive bromine species which reacted with phenol subsequently, leading to the formation of bromophenols and brominated by-products such as bromoform and dibromoacetic acid. The formation of the brominated by-products first increased and then decreased. The maximum yields of bromoform (10.3 µmol · L⁻¹) and dibromoacetic acid (14.6 µmol · L⁻¹) occurred at approximately 8 h with initial phenol, PMS, Br⁻, Co²âº, concentrations of 0.05, 1.0, 0.2, and 5 µmol · L⁻¹, respectively. Formation of the brominated by-products decreased with increasing pH. With constant total halides, increasing Cl⁻/Br⁻ ratio decreased the total formation of halogenated by- products but generated more chlorinated byproducts. The findings of this research can provide valuable information in assessing the feasibility of SO4·â» based oxidation technologies in real practice.

[Photodegradation of atenolol in aqueous nitrate solution].

The aqueous photolysis of beta-blocker atenolol (ATL) using Xe lamp as simulated solar irradiation source was investigated in the presence of nitrate ions. The effects of nitrate ion concentration, solution pH value, and concentration of bicarbonate and humic substance on the photodegradation of ATL were studied. The results showed that photodegradation of ATL in nitrate solution followed pseudo-first-order kinetics. The increasing concentration of nitrate ion promoted the photodegradation rate of ATL. The first-order rate constant increased from 0.002 26 min(-1) to 0.009 4 min(-1) with nitrate concentration increasing from 0 to 5 mmol x L(-1). Acidic or alkaline condition of the solution favored the photodegradation of ATL. Different concentration of bicarbonate showed insignificant effect of the degradation while the increasing concentration of fulvic acid showed inhibiting effect. Hydroxyl radical was determined to be formed during the photolysis process of ATL using isopropanol as molecular probe. The main photoproducts of ATL were identified by using SPE-LC-MS techniques and possible photoinduced degradation pathways in nitrate solution were proposed.

[Photodegradation of UV filter PABA in nitrate solution].

The aqueous photolysis of a UV filter p-aminobenzoic acid (PABA) using Xe lamp as simulated solar irradiation source was investigated in the presence of nitrate ions. The effects of pH, concentration of nitrate ions and concentration of humic substance in natural water on the photodegradation of PABA were studied. The results showed that photodegradation of PABA in nitrate solution followed the first order kinetics. The increasing concentration of nitrate ion increased favored the photodegradaton of PABA, of which the first order constant increased from 0.002 2 min(-10 to 0.017 9 min(-1). The photodegradation of PABA promoted with the increase of pH while the increasing concentration of humic substance showed inhibiting effect. Hydroxyl radicals determined by the molecular probe method played a very importnant role in the photolysis process of PABA. Photoproducts upon irradiation of PABA in nitrate solution were isolated by means of solid-phase extraction (SPE) and identified by LC-MS techniques. The probable photoinduced degradation pathways in nitrate solution were proposed.