Effect of UVC pre-irradiation on the Suwannee river Natural Organic Matter (SRNOM) photooxidant properties.

The present study aimed to investigate the changes in the chemical composition, and in the optical and photooxidant properties of Suwannee River Natural Organic Matter (SRNOM) induced by UVC (254 nm) treatment. The extent of the photodegradation was first assessed by UV-visible/fluorescence spectroscopies and organic carbon analysis. An in-depth investigation of the chemical changes was also conducted using liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry after derivatizations. A series of mono, di and tricarbonyls and mono and dicarboxylic acids in C1C6 were identified in samples irradiated from 1 to 4 h. After 3 h of irradiation, carbonyls accounted for 46% of the organic carbon remaining in solution whereas carboxylic acids represented about 2%. Then, we investigated the modifications of the photooxidant properties of SRNOM induced by these chemical changes. At 254 nm, UVC pre-irradiated SRNOM photodegraded glyphosate 29 times faster than original SRNOM and the reaction was fully inhibited by 2-propanol (5 × 10-3 M). This enhanced photooxidant properties at 254 nm toward glyphosate was therefore reasonably due to •OH radicals formation, as confirmed by additional ESR measurements. A mechanism involving a chain reaction was proposed based on independent experiments conducted on carbonyl compounds, particularly pyruvic acid and acetone. The findings of this study show that UVC pre-treatment of NOM can enhance the removal of water pollutants and suggests a possible integration of a NOM pre-activation step in engineered water treatment sytems.

Photodegradation of Myrigalone A, an Allelochemical from Myrica gale: Photoproducts and Effect of Terpenes.

This study investigated the environmental fate of myrigalone A, a light absorbing natural herbicide found on leaves and fruits of Myrica gale. Myrigalone A was irradiated in water and as a dry solid deposit to simulate reactions on leaves, alone and in the presence of the terpenes generated by Myrica gale. The phototransformation was fast ( t1/2 = 35 min in water). Analyses by liquid chromatography coupled to high resolution orbitrap electrospray mass spectrometry (MS) and gas chromatography-MS revealed the formation of 11 photoproducts in water and solid and 9 in gaseous phase. Some were detected in the leaf glands and oil covering the fruits of Myrica gale, which suggested that photodegradation occurred in the field. Moreover, myrigalone A photoinduced the oxidation of terpenes that in turn protected it against photolysis. This highlights the need for additional research on the effect of terpenes on the photodegradation of pesticides on vegetation.

Photodegradation of brominated flame retardants in polystyrene: Quantum yields, products and influencing factors.

Brominated flame retardants (BFRs) are widely used as additives in plastics, textiles and electronics materials. Here, we investigated the photodegradation of four BFRs including decabromobiphenylether (BDE-209), tetrabromobipsphenol A (TBBPA), tetrabromobisphenol A-bis(2,3-dibromopropylether) (TBBPA-DBPE) and tetrabromobisphenol A bis (allyl) ether (TBBPA-BAE). Experiments were carried out in polystyrene (PS) films using monochromatic and polychromatic irradiations. For comparison, irradiations were also carried in a solvent (tetrahydrofuran: THF). Monitoring of BFR degradation was performed using bulk and surface infrared (IR) measurements, as well as by extraction and HPLC-UV. Photoproducts were characterized using HPLC-high resolution electrospray ionization mass spectrometry (HPLC-ESI-Orbitrap-MS). All four BFRs underwent photochemical transformation in THF at 290 nm with a quantum yield (Φ) ranging from 0.05 for TBBPA to 0.27 for BDE-209, indicating an increase of photoreactivity with the number of Br atoms in BFRs. On the other hand, no major difference in the Φ values was observed when BFRs were embedded in PS films (Φ: 0.82-0.89). The higher photoreactivity in PS appears to be associated with a fast oxidation of PS as revealed by infrared (IR) analysis and yellowing of the films. Interestingly, the faster the yellowing occurred, the faster the BFR degradation was inhibited due to light screening effect. Several major photoproducts were identified for TBBPA and TBBPA-DBPE. Additional photoproducts possibly arising from PS oxidation and bromination by Br● were observed for the first time. This work provides a better understanding of the reactivity and fate of BFRs in polymers allowing for a better assessment of their environmental impacts.

Phototransformation of Plastic Containing Brominated Flame Retardants: Enhanced Fragmentation and Release of Photoproducts to Water and Air.

Increasing attention is being paid to the environmental fate and impact of plastics and their additives under sunlight exposure. We evaluated the photodegradation of polystyrene (PS) films (∼100 µm) containing brominated flame retardants (BFRs): decabromodiphenylether (BDE-209), tetrabromobisphenol A (TBBPA), and tetrabromobisphenol A-bis (2.3-dibromopropylether) (TBBPA-DBPE). Irradiations were performed in a solar simulator and outdoors. Infrared (IR) analyses indicated an acceleration of the photooxidation rate of fire-retarded PS films compared to pure PS with an enhancement factor of 7 for TBBPA-DBPE and TBBPA, and 10 for BDE-209. The accelerating effect was found to be correlated with the quantum yield for BFR photodegradation and its absorbance in the PS films. The presence of BFRs also modified the PS photooxidation mechanism and resulted in the formation of 14 brominated photoproducts via bromination and oxidation of PS. Furthermore, a drastic increase in chain scissions and loss of molecular weight was revealed by size exclusion chromatography. This enhanced degradation of PS led to significant leaching (15%) of oxidation products from PS films after immersion in water, and to the gas-phase emission of several volatile brominated products. Our findings suggest that fire-retarded plastics may be a source of potentially hazardous contaminants when exposed to sunlight.

Characterization and Photodegradation of Polybrominated Diphenyl Ethers in Car Seat Fabrics from End-of-Life Vehicles.

In this study, we examined the photodegradation of decabromodiphenyl ether (BDE-209) on the surface of car seat covers from end-of-life vehicles (ELVs). Samples were collected at two car dismantling facilities in Sweden and cover car models from 1989 to 1998. The content of polybrominated diphenyl ethers (PBDEs) in nine real samples (fabric and polyurethane foam) was first characterized. Fabric samples that did not contain BDE-209 were then spiked with BDE-209 and irradiated in the laboratory and under sunlight. Photoproducts were identified using high performance liquid chromatography coupled to electrospray ionization mass spectrometer (HPLC-ESI-Orbitrap-MS), whereas volatile products were analyzed by gas chromatography-mass spectrometry (GC-MS). Similar photodegradation rates and oxidation products were observed in fabric samples irradiated in the laboratory and those collected from ELVs. Estimated half-life of BDE-209 on fabric inside vehicles ranged from 3 to 6 years. Thirteen major photoproducts were identified as lower brominated products, hydroxylated BDEs, brominated and hydroxylated dibenzofurans (PBDFs) and dioxins (PBDDs). Furthermore, several photoproducts were found to be transferable into water, particularly bromophenols and hydroxylated BDEs, and others into gas phase, such as bromomethanol and 1,2-dibromoethane. This should be taken into consideration for better estimating exposure to PBDEs and to develop strategies for ELV recycling.