Photodegradation of Sufonylurea Herbicides in Aqueous Solutions under Natural Sunlight

Transcription

1 Photodegradation of ufonylurea Herbicides in Aqueous olutions under atural unlight John V. Headley 1, Jing-Long Du 1,2, Kerry M. Peru 1, Dena W. McMartin 2, Jane Elliot 1 and Allan J. Cessna 1 1 ational Water Research Institute, Environment Canada, askatoon 2 Faculty of Engineering, University of Regina, Regina

2 utline of the Talk Introduction to the environmental photochemistry Chemical and physical properties of U s Photodegradation of Thifensulfuron methyl Ethametsulfuron methyl Metsulfuron methyl Conclusions in the aqueous solutions

3 Products Excited tate inglet Excited tate Triplet 2 2 ΔE = hc/λ T 1 Ground tate inglet Quantum Yield = o 1 umbers of molecules transformed umbers of photons absorbed 1. inglet-inglet Absorption 2. Internal Conversion 3. Fluorescence 4. Intersystem Crossing 5. Phosphorescence 6. Intersystem Crossing

4 Photochemical Laws: 1. nly the radiation absorbed by a molecule can be effective in producing a photochemical change in the molecule. 2. Each photon absorbed can activate only one molecule in the primary step of a photochemical sequence. rganic Pollutants Degradation Products

5 Photo Products Herbicide* Herbicide* hν Herbicide Y = Photosensitizer Y* Y hν Y Y* + Herbicide

6 Light sources used in the environmental photochemical studies Low -pressure Hg lamp Medium- pressure Hg lamp High-pressure Hg lamp Low-pressure a lamp High- pressure a lamp atural sunlight Wavelength (nm)

7 High phytotoxicity Low application rates (5 to 40 g ha -1 ) Low mammalian toxicity Weak acids (pka values range from 3 to 5)

8 Thifensulfuron Methyl H 3 CC H H C CH 3 CH 3

9 Metsulfuron Methyl H 3 CC H H C CH 3 CH 3

10 Ethametsulfuron Methyl H 3 CC H H C HCH 3 C 2 H 5

11 Hydrolysis H 3 CC H H C CH 3 H 3 CC H 2 CH 3 H 3 CC H H C CH 3 H H 3 CC H H C C H H C C CH 3 Jean-Pierre Cambon, and Jean Bastide, J. Agric. Food Chem. 1996, 44,

12 Photolysis H 3 CC H H C CH 3 CH 3 hν H 3 CC H 2 H H 2 C CH 3 Major CH 3 H 3 CC H 2 CH 3 Minor CH 3 Laura crano, et. al. 3 rd European Conference on Pesticides and Related rganic Micro pollutants in the Environment, 2004, Halkidiki, Greece.

13 Controls Photocells

14 Photocells Controls Light ource

15 LC/M: Water 2695 LC Waters Xterra C18 (3.5 mm, 2.1 x 100 mm) Mobile phase: A: 90% water, 10% MeC B: 90% MeC; 10% water 0.1% formic acid + 2 mm ammonium acetate Isocratic 70%A + 30%B flow rate: 200 ml/min Injection volume: 10 ml. Micromass Quattro Ultima EI positive mode Capillary voltage: 4.39 kv Core voltage: 61 V ource temperature: 90 o C Desolvation temperature: 220 o C

16 Mass spectroscopic parameters for three herbicides Herbicide MRM Transition Coll. E (ev) Ret. Time (Min.) Thifen to Met to Eth to

17 Ethametsulfuron methyl CH H CCH 3 H C H FW = 410 C 2 H Metsulfuron methyl H 3 C CCH 3 H C H FW = 381 Me Thifensulfuron methyl H 3 C CCH 3 H C H FW = 387 Me

18 Concentration Dependence of Photolysis of Thifensulfuron methyl in Milli-Q Water under atural unlight ppb 2.01 ppb 2.89 ppb Concentration (ppb) Time (days)

19 Photolysis of Thifensufuron-methyl under unlight at Different Concetrations (fit to 24 days) ppb 2.01 ppb 2.89 ppb -1 ln (C/C 0 ) Time (days)

20 3 Plot of Concentration of Thifensulfuron methyl against time during the first 20 days Concentration (ppb) ppb 2.01 ppb 2.89 ppb C = C 0 e-kt Time (days)

21 4 Concentration Dependence of Photolysis of Metsufuron-methyl In Milli-Q Water under atural unlight ppb 3.06 ppb 3.33 ppb Concentrations (ppb) Time (days)

22 Photolysis of Metsulfuron-methyl under atural unlight at Diffrent Concentrations (fit to 42 days) ppb 3.06 ppb ppb -1 Ln (C/C 0 ) Time (days)

23 4 Plot of Concentration of Metsulfuron methyl againt time during the first 42 days 0.90 ppb ppb 3.33 ppb Concentration (ppb) Time (days)

24 4 Concentration Dependence of Photolysis of Ethametsulfuron-methyl in Milli-Q Water under atural unlight 0.76 ppb ppb 3.33 ppb Concentration (ppb) Time (days)

25 Photolysis of Ethametsulfuron-methyl under unlight in Milli-Q Water at Different Concentrations ( fit to 42 days) 0 Kinetic Constant (Days -1 ) 0.76 ppb 2.36 ppb ppb Ln(C/C 0 ) Time (days)

26 4 Plot of Concentration of Ethametsulfuron against time during the first 24 days 0.76 ppb 2.36 ppb ppb Concentration (ppb) Time (days)

27 8 ph Profile of ulfonylurea Herbicides Photolyzed by atural unlight Control 7 Thifen Met 6 Eth ph Time (days)

28 Kinetic Parameters Herbicide C a initial C b final %Loss c k(day -1 ) t 1/2 (d) R Thifen Met Eth a Initial concentration in ppb. b Final concentration of the controls after 126 days of experiment in dark. c Calculated based on [C a initial Cb final ]/Ca initial

29 6 Photolysis of 3 U Herbicides Using Photosyn at a Concentration of 4.8 ppb 5 Concentration (ppb) Thifensulfuron-methyl Metsulfuron-methyl Ethametsulfuron-methyl Time (days)

30 Charges on the sulfonylurea bridge Thifen Met Eth [C(1)] [(2)] [(3)] [(4)] [(5)] [C(6)] [(7)] [(8)] [C(9)]

31 Further investigation needs to be done to identify the degradation products. Conclusions All three Us were degraded under natural sunlight. C- The weakest bonds in the U bridge is the -H bond adjacent to the heterocyclic group. The rate of degradation for three Us are: Thifen > Eth > Met. ome degradation products cause the system more and more acidic. The acidity was probably caused by the formation of carboxylic acid due to the hydrolysis of methoxide group on the aryl part.