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Phototransformation of the “emerging” BFR 1,3,5-Tris-(2,3-dibromopropyl)-1,3,5-triazine-2,4,6-trione
(2017)
The occurrence and fate of brominated flame retardants (BFRs) in the environment are topics of increasing concern. In recent years, numerous studies about their global transport, UV degradation, bioaccumulation and toxicity were performed to assess their environmental fate. As a result, most of the first generation BFRs are banned or restricted, and replaced by new ones. However, based on similar properties these new compounds may also pose a serious risk by causing adverse effects to human health and the environment. According to the European Food Safety Authority (EFSA) the class of the “emerging” BFRs are defined as compounds that have been identified in any environmental compartments, but the potential for degradation or bioaccumulation of these emerging BFRs is partially unknown.
A representative of this class of compounds is the heterocyclic TDBP-TAZTO which was first detected in mollusks from Chinese bohai sea and in environmental matrices near a manufacturing plant in southern china. Furthermore, Wang et al. describe that the growth of the alga Nannochloropsis sp. is inhibited by TDBP-TAZTO in a concentration dependent manner but the photo-chemical behavior as well as the formation of possible photo-transformation products (PTPs) are still unknown. In order to clarify this complex issue photo-degradation experiments were by determining the rate constants and degradation half-life times of TDBP-TAZTO in different solvent compositions. In this study, the photodegradation of TDBP-TAZTO was performed for the first time to identify its photolysis products and to get a first understanding about the main degradation pathway in environmental matrices.
Outdoor exposure tests are a common tool to evaluate the weathering resistance of a polymeric material or component. However, they have only a limited validity, mainly due to the limited reproducibility of the weather as well as of the bad adaptability to other exposure sites. Typically, an outdoor exposure is characterized by the measured radiant exposure; sometimes averaged temperature data are added. These can be – separately – related to long-term annual means, to get an idea on the severity of the exposure.
However, as for polymeric ageing, irradiance and temperature act simultaneously, such severity of an outdoor exposure could be better described by a computed property change of a similar material, which is calculated from the hourly irradiance and temperature values on the base of established exposure response functions.
In this way, various outdoor exposures are evaluated. For several exposure sites, annual deviations of the ageing amount are related to annual mean values, to evaluate the weathering reproducibility at the exposure site. Additionally, correlations to relevant weather parameters are illuminated. Also some specific exposure conditions, such as tilt angle, are tested. Compared to the use of weathering reference materials, this procedure unfavourably depends on the availability of a suited control as well as on the quality of the established exposure response function. In contrast, it enables a later exposure evaluation, on the base of documented weather data, if for instance no reference material was exposed.
Biocides are commonly applied to building materials such as renders and paints in order to protect them from microbial spoilage. Since the building materials are commonly exposed to weathering conditions, biocides incorporated within the material matrices tend to leach out during the rain events. Moreover, photodegradation processes play an important role in the fate of biocides, due to the exposure to natural sunlight. Leaching of biocides and their moderate persistence, indicate that photodegradation products of biocides can also be found as environmental contaminants in runoff waters. In this study we investigated the photodegradation of four commonly used biocides (carbendazim, diuron, octylisothiazolinone and terbutryn) in four different paint formulations with selected pigments (red, white, black and one artificial, not commercial pigment-free formulation for comparison). As pigments interact with the spectrum of the incoming light, the effect of pigments on photodegradation rates was assumed to be relevant.
Samples were prepared by painting 2 layers of selected paints on glass plates. The dry paint samples were exposed to UV light for designated time periods ranging from 0 h to 1056 h of total exposure time in a commercial UV-Test® Fluorescent / UV Instrument (Atlas Material Testing Technology, Illinois, USA). The applied energy was 1.2 W/m2. The black panel temperature was established at 40 ºC. The radiant energy from the UV fluorescent lamps was concentrated in the wavelength region at 351 nm and below. All samples were prepared in triplicates. After irradiation, paint samples were removed from glass carriers and extracted with methanol. The remaining biocide concentrations as well as the amounts of photodegradation products were analysed with the use of liquid chromatography coupled to mass spectrometry.
The transparent, pigment-free formulation was the most vulnerable to light exposure, a visible colour change from white to yellow was observed after 1056 h of irradiation. Diuron, octylisothiazolinone and terbutryn degraded from pigment-free formulation following first-order degradation kinetics. A decrease of carbendazim was also observed. The remaining formulations showed similar degradation patterns for all analysed biocides. All paints showed degradation for octylisothiazolinone with 3-octyl-2(3H)-thiazolone being the main product for red, white and black pigment paint. N-octylacetamide and N-octyloxamic acid were dominant in the pigment-free formulation. Terbutryn sulfoxide was the main degradation product of terbutryn in case of the white paint, while other pigments showed higher concentrations of desbuthyl-2-hydroxy-terbutryn and desethyl-2-hydroxy-terbutryn.
A determination of photodegradation in terms of pigment type, measured light spectra and intensity as outlined in this study, could provide a basis for establishing a quantitative description of the fate of biocides in paints, which has significance not only in terms of environmental science, but also could provide a guideline for developing new and effective products.
Nowadays, electrochemistry coupled online to mass spectrometry (EC-MS) or to liquid chromatography-mass spectrometry (EC-LC-MS) is a technique of interest to investigate metabolic transformation of xenobiotics in living organisms. It enables the production of redox products in an electrochemical cell, the separation by an analytical column and the detection by mass spectrometry online. Furthermore, EC-LC-MS enables to determine short lived transformation products (TPs) and their bioconjugates in a fully automated way. Although the EC-MS selectivity is incomparable to enzymatic reactions, it is advantageous by reducing analysis time and matrix complexity compared to cytochrome based metabolism. However, in the development of EC-MS, most efforts are devoted for prediction of drug metabolism in the human body and there is very limited work on agrochemicals in general.
The main objective of this work was to develop an online EC-LC-MS method that could predict the metabolism of fluopyram (fungicide) and chlorpyrifos (insecticide). Oxidation products were produced by using a boron doped diamond electrode and characterized by either online LC-MS or offline LC-MS/MS. After incubation with rat and human liver microsomes, different targeted and suspected metabolites were identified by LC-MS/MS and high resolution-mass spectrometry (HR-MS) and compared with the EC based methods. Additionally, conjugation reactions with a variety of biomolecules such as glucoside and glutathione were investigated by trapping the oxidized species before entering to mass spectrometry.
In summary, phase-I metabolism by N-dealkylation, O-dealkylation, P-oxidation, hydroxylation and dearylation and phase-II metabolism by conjugation with glutathione mechanisms were successfully mimicked by EC-LC-MS. Fluopyram is primarily metabolized to 7- and 8-mono- hydroxyl, 7,8-di-hydroxyl and 2-trifluoromethyl benzamide, and chlorpyrifos is metabolized to chlorpyrifos oxon, trichloropyridinol, diethylthiophosphate and diethylphosphate.