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Title: Studies of the environmental fate of a popular antifouling booster biocide, Irgarol-1051
Other Titles: Guan yu guang fan shi yong fang wu sun sheng wu sha [i.e. sha] mie ji Irgarol-1051 zhi huan jing gui qu yan jiu
Guan yu guang fan shi yong fang wu sun sheng wu sha mie ji Irgarol-1051 zhi huan jing gui qu yan jiu
關於廣泛使用防污損生物刹 [i.e. 殺] 滅劑 Irgarol-1051 之環境歸趨研究
關於廣泛使用防污損生物殺滅劑 Irgarol-1051 之環境歸趨研究
Authors: Lam, Ka Ho (林家豪)
Department: Dept. of Biology and Chemistry
Degree: Doctor of Philosophy
Issue Date: 2006
Publisher: City University of Hong Kong
Subjects: Paint, Antifouling -- Additives -- Environmental aspects
Triazines -- Environmental aspects
Notes: CityU Call Number: QH545.T747 L35 2006
Includes bibliographical references.
Thesis (Ph.D.)--City University of Hong Kong, 2006
xxviii, 297 leaves : ill., maps ; 30 cm.
Type: Thesis
Abstract: Irgarol-1051 (2-methylthiol-4-tert-butylamino-6-cyclopropylamino-s-triazine) is a s-triazine compound specially developed for use as a booster algaecide additive in copper- and zinc-based antifouling paints. It is one of the new generation antifouling agents/additives to replace organotin-based antifoulants. It is a photosystem-II (PSII) inhibitor and is highly toxic to microalgae, but shows minimal toxicity to animals. Since its introduction in the mid-1980’s, considerable efforts have been devoted to the study of its occurrence and fate in the coastal marine environment around the world. It is well-established that Irgarol-1051 undergoes relatively rapid photodegradation in natural waters and 2-methylthio-4-tert-butylamino-6-amino-s-triazine, also commonly known as M1 or GS26575, is the major degradation product. In terms of toxicity, M1 is generally less toxic to aquatic phytoplankton but more toxic to root elongation of terrestrial plants than Irgarol-1051. M1 is also found to be a stable and terminal biotransformation metabolite of Irgarol-1051. In this thesis, I report a series of research work concerning the identification of several previously unknown s-triazine species in the coastal marine environment that are related to Irgarol-1051. These species are designated M2, M4 (both are new discovered degradation products of Irgarol-1051) and M3 (likely to be a by-product during the industrial synthesis of Irgarol-1051). A series of surveys in the coastal environment of Hong Kong and Pearl River Estuary reveal the presence of these newly identified Irgarol-related s-triaizine compounds in the natural coastal environment. The occurrence of M2 and M4 defies all the proposed degradation mechanisms of Irgarol-1051 in the literature. This indicates that the environmental fate of the antifouling booster biocide is more complicate than we expected. This has prompted me to further investigate the physicochemical properties of these new s-triazine species as well as the probable mechanisms leading to their formation in the natural aquatic environment. The first part of this thesis (Chapter 1) gives a general introduction to the problem of fouling (or biofouling) and the history of development of antifouling technology from the use of pitches, copper, wax, tar, lead, and asphaltum early Phoenicians and Carthaginians, more than 2000 years ago, to the development of synthetic antifoulants in modern times. The problem of environmental contamination by these synthetic antifouling chemicals, especially Irgarol-1051, is also discussed. The second part of this thesis (Chapter 2) reports the identification of a previously unknown s-triazine species present in commercially available Irgarol-1051. This new species is designated as M3. After careful isolation, purification and characterization by high resolution MS-MS and 1H NMR, the identity of M3 was found to be N,N’-di-tert-butyl-6-methylthiol-s-triazine-2,4-diamine. Concentrations of Irgarol-1051, its major degradation product (M1) and a newly identified (M3) ranged between 0.1 – 1.6 μg l-1, 36.8 – 259.0 μg l-1 and 0.03 – 0.39 μg l-1, respectively, in samples from the coastal waters of Hong Kong. My results indicate that M3 is relatively stable against photo- and bio- degradation and may pose considerable risk to primary producer communities in the coastal marine environment. The third part of this thesis (Chapter 3) reports the identification of another s-triazine compound in the natural coastal waters of Hong Kong and the Pearl River Estuary as well as from the mercuric chloride catalyzed hydrolysis of Irgarol-1051. Because of the fact that we have actually observed this new s-triazine compound in coastal water samples before our discovery of M3, we designate this s-triazine species as M2. After careful isolation, purification and characterization by high-resolution MS-MS and 1H NMR, the identity of this new species was found to be ([(4-tert-butylamino-6-methylthiol-s-triazin-2-yl)amino]propanal). M2 is an entirely new degradation product that does not conform to any of those proposed degradation pathways of Irgarol-1051 in the literature. From its structure, it is probable that M2 is formed from Irgarol-1051 via oxidative ring-opening of the N-cyclopropyl moiety. With an ion-pairing HPLC method, the concentrations of Irgarol-1051, M1, M2 and M3 in the coastal waters of the Pearl River Estuary is revealed (0.31 – 4.26 ng l-1, 0.28 – 2.61 ng l-1, 0.41 – 0.56 ng l-1 and 0.13 – 4.08 ng l-1 respectively). The fourth part of this thesis (Chapter 4) reports a mechanistic study of the photodegradation of Irgarol-1051 in natural seawater under simulated solar irradiation. Besides the degradation products M1 and M2, another previously unknown degradation product was identified. We designate this new product as M4. The identity of M4 is confirmed by HR-MS-MS to be [(4-tert-butylamino-6-methylthiol-s-triazin-2-yl)amino]propenol. The rate of degradation of Irgarol-1051 was found to be 4.02 x 10-4 hr-1 and the formation rate constant of M1 was found to be 4.6 x 10-5. Based on these degradation kinetic data and the identification of M4, a new degradation pathway was proposed. The last part of this thesis (Chapter 5) reports the measurement of the partitioning behaviours of all the s-triazine compounds that are involved in my study. Octanol – water partition coefficients, log KOW, and organic matter – water partition coefficients, log KOC, of these s-triazines are measured by reversed-phase HPLC and a triphasic SPME equilibrium model, respectively. The average log KOW (± S.D.) of the five s-triazine species were: 4.14 ± 0.12 (M3); 3.21 ± 0.12 (Irgarol-1051); 2.79 ± 0.12 (M2), 2.45 ± 0.11 (M1) and 2.27 ± 0.10 (M4), while the mean log KOC (± S.D.) of these species were: 2.47 ± 0.03 (M3); 2.16 ± 0.03 (Irgarol-1051); 1.97 ± 0.03 (M2), 1.79 ± 0.04 (M1) and 1.43 ± 0.04 (M4). These results were compared to reported physicochemical parameters of Irgarol-1051 in the literature. Partitioning behaviours of these s-triazine species in the coastal environment revealed by their KOW and KOC were also discussed.
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