Environ. Sci. Technol. 1994, 28, 1159-1 163
Rapid Degradation of Fenitrothion in Estuarine Waters S h i a Lacorte and Dami; Barcelb'
Department of Environmental Chemistry, CID-CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain The degradation of fenitrothion under real environmental conditions was studied. Fenitrothion was applied in the irrigation ditches of the Ebre Delta (Tarragona, Catalonia) at an estimated concentration of 200 (situation 1)and 20 pg/L (situation 2 ) in order to eliminate the american crab (Procamburus clarkii). The evolution of the levels of fenitrothion and the formation of transformation products (TPs) were recorded during the 4 days after application. The TPs formed were 3-methyl-4-nitropheno1,fenitrooxon, and S-methyl isomer of fenitrothion. The concentration of fenitrothion decayed sharply in 2 h with 6% and 0.3% of the initial concentrations in situations 1and 2 , respectively, and reached a steady state within 10 h with a concentration of 4 and 0.01 pg/L, respectively, which was constant for the 4 days the experiment lasted. T P s were encountered a t a very low concentration, around 0.01 pg/ L. For the identification of fenitrothion and its TPs, solidphase extraction with CISEmpore extraction disks followed by GC-MS with E1 and NCI was used. Good sensitivity was obtained with both techniques, and qualitative information on the fragment ions of all the pesticides detected is given. Half-life of fenitrothion was of 13 h, with a disappearance rate of 0.053 and photolysis being the main pathway. In addition, the degradation of fenitrothion and the formation of T P s are closely related to the environmental conditions; in our experiment, a quick decay of the concentration of fenitrothion could be enhanced by the strong wind that usually affects the treated area.
Introduction
Fenitrothion [ 0,O-dimethylo- (3-methyl-4-nitrophenyl) phosphorothioate] is a powerful insecticide widely used because of its effectiveness against many insects and crustaceans. In the Ebre Delta (Tarragona, Catalonia), it is used in large quantities (43 t/year in 1990) for various purposes, mainly for the elimination of rice stem bores. Furthermore, punctual applications of this compound are performed in this area to eliminate the american crab (Procamburus clarkii), a non-autochthonous specimen that causes ecological and economical damage. Fenitrothion is known for its acute toxicity toward nontarget organisms, and after application, different types of degradation affect this pesticide, such as photolysis, hydrolysis, and biological degradation. Like fenitrothion, many transformation products (TPs), e.g., fenitrooxon and the S-methyl isomer of fenitrothion, may be even more toxic than the parent compound, with different biological activity (I). Therefore, it becomes necessary to monitor their presence in the environment. So far, several works concerning the decay of a variety of pesticides in diverse environmental matrices, e.g., diazinon, parathion, tetrachlorvinphos (2), fenthion (3), temephos (41,chlorpyrifos (51, fenitrothion (6),and triazine herbicides (7),have been carried out but only a few consider possible T P s formed; e.g., Coquart et al. (8) and Man0013-936X/94/0928-1159$04.50/0
0 1994 American Chemical Society
delbaum et al. (9)study the hydrolysis of atrazine in water, Greenhalgh et al. (10)report the hydrolysis of fenitrothion in natural waters, and Glotfelty et al. (11)report various organophosphorus pesticides and their oxygen analogues in the atmosphere. Numerous studies on the photochemical degradation of various pesticides in solution under laboratory conditions have been reported, e.g., carbamates (12), isoproturon (131,phosphorothioate pesticides (141, atrazine and diuron (15),and fenitrothion (15, 17),and provide data on GC-MS photolysis products. To our knowledge, no photodegradation studies on the evolution of fenitrothion under real environmental conditions that provide a complete overview of potential fenitrothion TPs have been undertaken. Studies on fenitrothion half-life under laboratory-controlled conditions are of importance since they provide qualitative information on the half-life of pesticides and their photoalteration products and establish the major photolytic decomposition routes (18). However, the results obtained under laboratory conditions may not be extrapolated to the field and lead to the unavoidable requirement to carry out studies on the degradation of pesticides in situ. The present study was executed by sampling water in two of the many irrigation ditches present in the area of the Ebre Delta, where fenitrothion was applied by manual spraying. The specific objectives of this study were (i) to evaluate the decay of fenitrothion, (ii) to monitor the presence and concentrations of possible T P s formed, (iii) to study the degradation and fate of fenitrothion under real environmental conditions, and (iv) to investigate whether photodegradation plays a significant role in the elimination of fenitrothion in estuarine waters. This paper presents qualitative and quantitative information on the photodegradation of fenitrothion under environmental conditions. This study is a continuation of a previous work (16) carried out by our group on the identification of fenitrothion photolysis products in water under laboratory conditions. Materials and Methods
Chemicals. Fenitrothion, fenitrooxon, and 3-methyl4-nitrophenol were obtained from Promochem (Wesel, Germany). Pesticide-grade ethyl acetate and methanol were purchased from Scharlau (Barcelona). Empore 3M CIS extraction disks were a gift from L. Beumer (J. T. Baker, Deventer, The Netherlands). Sampling Strategy. Sumithion 50 (Argos, Valencia), which contained 50 % fenitrothion, was applied by manual spraying on two separated irrigation ditches of the Ebre Delta at a concentration of 200 pg/L of active ingredient, referred to in this paper as situation 1, and of 20 pg/L, referred to as situation 2, respectively. Ordinarily fenitrothion is applied at a concentration of 200 pg/L of active ingredient to attain maximum efficiency of the treatment. The same procedure a t 20 pgIL was experimentally performed in order to study the evolution of fenitrothion and its degradation products a t this lower concentration Envlron. Sci. Technol., Vol. 28, No. 6, 1994 1159
and the effect of the treatment toward the crabs. Application was performed on December 2,1992, and water samples from each ditch of the Ebre Delta were collected before the treatment and a t 2, 4, 8, 24, 48, and 74 h. Sample Preparation. The cleanup technique consisted of the filtration of 1 L of water through filters of 0.45 pm (Millipore, USA) to remove the suspended particles. Extraction of analytes was done using SPE with Empore CISextraction disks. These disks were conditioned with 10 mL of ethyl acetate, 10 mL of methanol, and 10 mL of water, and extraction was done with 20 mL of ethyl acetate. This final volume was concentrated to 0.1 mL before GC-MS analysis. These proceedings have been used previously (20). Recoveries for the cited analytes were calculated by spiking estuarine water at a level of 1 pg/L for fenitrothion and fenitrooxon and at a level of 35 pg/L for 3-methyl-4-nitrophenol analyzed with GC-NPD. The standard of the S-methyl isomer of fenitrothion was not available. GC-MS Determinations. GC-MS-EI. AVarian 3400 GC interfaced to a TSQ-700 from Finnigan MAT (Walnut Creek, CA) was used. A DB-1701 (30 m X 0.25 mm i.d.) phenylcyanopropylmethyl fused-silica capillary column (J&W Scientific, Folsom, CA) was programmed from 75 to 90 "C at 30 "C/min and from 90 to 180 OC at 10 OC/min and to 280 "C at 8 "C/min. The ion source and analyzer were maintained at 250 "C. Helium was used as the carrier gas at 8 psi. The injection volume was 2 pL, and the splitless mode was used. Ionization potential was 70 eV. GC-MS-NCI. A Varian Star 3400 GC interfaced to a INCOS XL from Finnigan MAT (Walnut Creek, CA) was used. A DB-5 (30 m X 0.25 mm i.d.) column containing 5 % phenyl-95 % methylpolysiloxane (J&W Scientific, Folsom, CA) was introduced directly in the ion source. Methane was used as the reagent gas, and the analyzer was maintained at 0.055 Torr. The ion source was kept at 130 "C and the transfer line at 290 "C. Helium was used as the carrier gas at 10 psi. Chromatographic conditions were as described above. A sample of 2 pL was injected each time in the splitless mode.
Fenitrothion ISOMERIZATION
O / l \
CH, NO, O H*
3-methyl-4-nitrophenoI
Figure 1. Decomposition pathways of fenitrothion in estuarine waters.
i
E
3.2
r
f
GC-MS-E1
10
6.4
13.2
16.4
I
20
GC-MS-NCI
3.2
10
6.4
13 2
TIME (rnin)
Results and Discussion Quantitative Information. The mean recovery rates of fenitrothion and fenitrooxon were 100.06% and 95.11% , respectively, with a CV of 6.9 and 6.5 ( n = 5). Recoveries achieved for 3-methyl-4-nitrophenol were below 10% . These low values are due to the volatilization of this compound during manipulation and to the use of CISdisks as reported for other phenols (19). Quantification values were corrected for recovery. The LOD of the compounds under study were of 0.03 pg/L with E1 and 0.01 pg/L with NCI with a SIN of 3. Qualitative Information. Using GC-MS-EI, it was possible to identify fenitrothion and three of its TPs, fenitrooxon, fenitrothion isomer, and 3-methyl-4-nitrophenol. All these compounds have already been reported in the literature as possible photolysis products of fenitrothion (16). Figure 1 represents a scheme of decomposition of fenitrothion in estuarine waters, which indicates oxidation, isomerization, and hydrolysis as the main photolytic routes for fenitrothion degradation. Through oxidation, fenitrothion is converted to its oxo analogue, fenitrooxon. In general, the oxon is of concern because it is the activated form of fenitrothion and it has a much 1180
Environ. Sci. Technol., Vol. 28, No. 6, 1994
Figure 2. Total ion current (TIC) obtained using (A) GC-MS-E1 with a DB-1701 and (B)GC-MS-NCI with a DB-5 of a water extract collected from irrigationditches 4 hafter fenitrothion was applied which contained (1) 3-methyl-4-nitropheno1, (2) fenitrooxon, (3) fenitrothion, and (4) Smethyl isomer of fenitrothion.
higher acetylcholine esterase inhibition activity, so it is more toxic than the parent compound ( I ) . The S-methyl isomer of fenitrothion is formed by isomerization, which is induced by heat, thus taking place during synthesis and storage, or by light ( 1 7 ) . All these compounds can be hydrolyzed to generate 3-methyl-4-nitrophenol. The presence of fenitrooxon, S-methyl isomer, and 3-methyl4-nitrophenol indicates oxidation and hydrolysis as the main photolytic degradation of fenitrothion under environmental conditions, which yields water-soluble products. Figure 2 shows the total ion chromatogram obtained by GC-MS-E1 and GC-MS-NCI of an estuarine water extract collected 4 h after fenitrothion was applied. Both chromatograms illustrate fenitrothion as main peak, and three TPs were distinguished by both techniques. Better sensitivity was gathered with GC-MS-NCI for 3-methyl4-nitrophenol, fenitrothion, and the S-methyl isomer of fenitrothion.
Table 1. GC-MS-E1 Fragment Ions of Fenitrothion a n d Its TPs Formed in Estuarine Waters
m/z (relative intensity, % ) [characteristic ions] El NC1
compds
mol w t 153
3-methyl-4-nitrophenol
261
fenitrooxon
277
fenitrothion
277
S-methyl isomer of fenitrothion
77 (40) 136 (100) [M - OH]'+ 153 (50) [MI'+ 109 (47) 244 (100) [M - OH]*+ 261 (18) [MI'+ 109 (60) 125 (72) 260 (76) [M - OH]'+ 277 (100) [MI*+ 125 (100)
153 (100) [MI'125 (30) 261 (100) [MI*141 (55) 168 (100) [SC,H~NO~I'277 (50) [MI'141 (100) 152 (20) [M - 1251'262 (90) [M - CH31'277 (55) [MI..-
260 (97) [M - OH]'+ 277 (40) [MI'+
GC-MS-E1
I m/z.79
Ei05 8.138
Fenitrooxoii
rl
Hours after treatment
-
0.7 -
Fanitrothion isomer
4 - 3-msthyi-4nitrophenol
+- Fanitrooxon
3 u
3.2
6.4
10
13.2
16.4
20
0
10
20
30
40
50
60
70
80
Hours after treatment
TIME (min)
Flgure 3. Selected ion chromatograms obtained with GC-MS-E1 with a DB-1701 of an Ebre Delta water extract which contained (2) fenitrooxon. Fenitrooxon was monitored at m/z 261, 244, and 79. Chromatographic conditions as described in the text. Compound 3 is fenitrothion.
The typical fragment ions of these compounds by GC-MS-E1 are reported in Table 1. Each molecule was identified as minimum at three different ions, which is necessary for their unequivocal identification. The basis for the identification of fenitrothion TPs are the following: (i) all the compound detected have an intense peak at M-17, that corresponds to a loss of OH through a McLafferty rearrangement, which involves a proton extraction by an oxygen of the nitro group, and indicates the presence of a methyl group adjacent to a nitro group; (ii) the characteristic ion of fenitrooxon is no. 109, with no formation of no. 125 since an S group is not present a t the molecule. Ion 244 corresponds to a loss of OH and was chosen as a specific ion of fenitrooxon. The ion chromatogram is indicated in Figure 3; (iii) the S-methyl isomer of fenitrothion has the same molecular weight as its parent compound and exhibits as its most abundant ions nos. 260 and 125, which correspond to the same structures as fenitrothion. It is identified by the lack of ion 109 in the isomer since the structure (CH30)zPO (dimethoxyphosphate) does not exist and it elutes later GC-MS-EI.
Figure 4. Evolution of the levels of the concentration of fenitrothion [plotted In of concentration versus time, giving both measured values and calculated values, according to first-order rate equation (23)] and its TPs after the application of fenitrothion at a concentration of 200 pg/L (situation 1).
than fenitrothion; and (iv) 3-methyl-4-nitrophenol was characterized a t its molecular ion, a t [M - OH], and at ion 77, which belong to a loss of CHs, NOz, and OH from the aromatic moiety, respectively. GC-MS-NU. NCI offers better sensitivity for organophosphorus compounds and less noise as compared to E1 (20,22). The main processes for ion formation are the following,as remarked in ref 20: (i) the formation of [MI'as an abundant peak of all compounds detected is a consequence of its aromatic structure, which is stabilized under negative ion conditioned when a nitro group is present, (ii) the base peak of the S-methyl isomer corresponds to a diagnostic ion formed under NCI, and (iii) the ion a t mlz 168 as a base peak of fenitrothion is due to the transfer of the aromatic moiety from the oxygen to the sulfur atom. Environmental Levels. Fenitrothion and its degradation products were quantified using selected ion monitoring in GC-MS-EI. Calibration was carried out using external standards. Figures 4 and 5 represent the decay of fenitrothion in time and the evolution of its TPs from Environ. Sci. Technol., Vol. 28, No. 6, 1994 1161
J
-2 Hours after treatment
Figure 5. Evolution of the levelsof concentration of fenitrothion [plotted In of concentration versus time, giving both measured values and calculated values, according to first-order rate equation (241and its TPs after the application of fenitrothion at a concentration of 20 pg/L (situation 2).
situation 1 and situation 2. Fenitrothion was plotted in In of the concentration (In C) versus time, giving both the measured values and the estimated values, which were calculated using an exponential model (23), taking in consideration that In C of fenitrothion versus time was linear for a period of 20 h. From these figures, it can be observed that values distant from the linear fit do not follow the exponential model, indicating that the concentration of fenitrothion reached a steady state 20 h after treatment. From this curve, the disappearance rate or rate constant was calculated from both curves, being in all cases 0.05, indicating that the applied concentration did not affect the rate of disappearance. The values encountered are much higher than those of Greenhalgh et al. ( I O ) , who report rate constants 3 orders of magnitude lower in buffered distilled water at neutral pH and with light excluded, manifesting that environmental conditions enhance the degradation of fenitrothion. Even though fenitrothion was applied at a concentration of 200 and 20 pg/L, only 12 and 6 pg/L were found in water 2 h after treatment. This suggests that muchof the applied material did not reach the water. In principle, solubility in water was not the main reason of this quick decay since fenitrothion has a water solubility of 30 mg/L. The evolution of the concentration of fenitrothion in both situations demonstrated the same disappearance pattern (same rate constant), but the amounts encountered in situation 2 were 1order of magnitude lower than those at situation 1. When fenitrothion was applied at a concentration of 200 pg/L, a quick decay within the first 5 h can be observed and only 3.5% of the initial amount is found. Afterwards, the concentration reaches a steady state with 2% of the initial amount. Moreover, the evolution of the TPs was recorded, and levels around 0.05 pg/L are found with no high increase of any TPs. When fenitrothion was applied at 20 pg/L, both fenitrothion and fenitrooxon followed the same trend, with only 0.3% of the initial concentration 2 h after application, reaching a concentration of 0.01 pg/L. Similarly, the S-methyl isomer 1162
Environ, Sci. Technol., Vol. 28, NO. 6,1994
of fenitrothion and 3-methyl-4-nitrophenol were detected only during the same day of treatment. It can be remarked from Figures 4 and 5 that the halflife of fenitrothion in water is 12.1 and 12.8 h in situations 1and 2, respectively. Half-lives were calculated from the first-order rate equations (23)of each experiment. These results coincide with those of ref 24 where it is stated that the concentration of fenitrothion fell rapidly within 12 h after application and half-life was estimated around 6 h. From these results, it is possible to observe that the dissipation of fenitrothion was very rapid, occurring in a few hours after application. This phenomena can be explained by volatilization since the Henry's constant for fenitrothion has a value of 0.0036 P a m3/mol calculated at 20 "C(25),which is somewhat more than 10 times higher than atrazine and at similar levels as alachlor. Photolysis is an important route of fenitrothion degradation in natural waters, as reported by Mikami et al. (26)where hydrolysis is pH dependent, and at pH 5-9, commonly found in natural waters, hydrolysis was slow and appeared to be of minor importance compared to photolysis. Only when alkalinity increased was the hydrolysis rate of fenitrothion relevant. Other studies also reflect the same idea (27,28) indicating that fenitrothion is stable in drinking water at pH = 7 during 45 days. However, as pointed out by Greenhalgh et al. ( I O ) , microorganisms also play an important role in the degradative routes of fenitrothion in river and pond waters, and consequently Mikami et al. (25) agreed that both photolysis and microbial processes are the main routes for fenitrothion degradation in natural aquatic environment. Since in the Ebre Delta waters the pH is around 7 and 8, hydrolysis of fenitrothion is not relevant during the first days of the application period, during which water samples were collected to perform the present studies. Microbial degradation of fenitrothion is favored in this area, which is used for rice cultivation. Sediments located in the drainage canals and rice soils are very rich in organic matter (around 3 % ) due to the fact that rice straw is mixed with the soil sediment. We currently analyze rice soils and sediments of this area, and fenitrothion is rarely found. For this reason, sorption into sediment has been discarded due to previous experiments from various authors (18)and from our own studies (29) where half-lives of fenitrothion in sediment-soil samples of the Ebre Delta area were 2 days, similar to that reported in this paper for estuarine waters. Conclusions Formulated fenitrothion was applied a t two different concentrations, 200 and 20 pg/L. A quick decay of fenitrothion was observed in both situations, with 6.1% and 0.3 95 of the initial concentration 2 h after spraying, respectively, reaching a steady state at concentrations of 4 and 0.01 pg/L after the initial decay. TPs were detected in situation 1 for the 4 days the experiment lasted at concentrations around the LOD. In situation 2, they are found only during the same day of treatment. The degradation of fenitrothion under real conditions had not been reported previously, and this work provides a method by which degradation products of fenitrothion could be detected from estuarine water samples that had been treated with fenitrothion. Fenitrooxon, the S-methyl isomer of fenitrothion, and 3-methyl-4-nitrophenol were the only TPs formed under environmental conditions, and
they could be identified by both E1 and NCI. GC-MS both with E1 and NCI were sensitive enough for their detection. Further research recommends GC-MS with E1 or NCI and SIM to intensify sensitivity, and additional investigation is needed for the determination of more polar TPs for which GC-MS is not suitable. In this sense, more polar TPs could be formed but have not been detected with the present method. We are now carrying out experiments with on-line solid-phase extraction followed by liquid chromatography-diode array detection (LCDAD) to determine more polar TPs of fenitrothion as well as of other organophosphorus pesticides. On-line solidphase extraction with liquid chromatography and mass spectrometry will also be carried out. Such future work will bring us more information on the degradation of organophosphorus pesticides in natural waters. Acknowledgments
J. Abian and M. Carrascal (CID-CSIC) are thanked for their technical support using GC-MS facilities, the "Servei de Protecci6 de Vegetals" (Generalitat de Catalunya) for supplying climatological data, and CODE (Amposta, Tarragona) for sampling assistance. This work was supported by the Environment R&D Program 1991-1994 (Commission of the European Communities) (Contract EV5V-CT92-0105). S.L. gratefully acknowledges financial support from CICYT (Grant AMB92-0218). Literature Cited (1) Eto, M. Organophosphorus Pesticides: Organic and Biological Chemistry; CRC: Cleveland, OH, 1974; pp 1-287.
(2) Leistra, M.; Tuinstra, L. G. M. Th.; van der Burg, A. M. M.; Crum, S. J. H. Chemosphere 1984,13 (3), 403-413. (3) Wang,T. C.; Lenahan, R. A.; Tucker, J. W., Jr. Bull. Environ. Contam. Toxicol. 1987, 38, 266-231. (4) Lores, E. M.; Moore, J. C.; Moody, P.; Clark, J.; Forester, J.; Knight, J. Bull. Enuiron. Contam. Toxicol. 1985, 35, 308-313. (5) Knuth, M. L.; Heinis, L. J. J. Agric. Food Chem. 1992,40, 1257-1263. (6) Barcel6, D.; Solb, M.; Durand, G.; Albaigbs, J. Fresenius J. Anal. Chem. 1991,339,676-683. (7) Readman, J. W.; Liong Wee Kwong, L.; Gronding, D.; Batocci, J.; Villeneuve, J.-P.; Mee, L. D. Enuiron. Sci. Technol. 1993,27, 1940-1942.
(8) Coquart, V.; Garcia-Camacho, P.; Hennion, M. C. Int. J. Enuiron. Anal. Chem. 1993,52, 99-112. (9) Mandelbaum, R. T.; Wackett, L. P.; Allan, D. L. Environ. Sci. Technol. 1993,27, 1943-1946. (10) Greenhalg, R.; Dhawan, K. L.; Weinberger, P. J.Agric. Food. Chem. 1980,28, 102-105. (11) Glotfelty, D. E.; Majewski, M. S.; Seiber, J. N. Enuiron. Sci. Technol. 1990,24, 353-357. (12) Bertrand, N.; Barcel6, D. Anal. Chim. Acta 1991,254,235244. (13) Dureja,P.; Walia, S.; Sharma, K. K. Toxicol.Enuiron. Chem. 1991, 34, 65-71. (14) Chukwudebe, A.; March, R. B.; Othman, M.; Fukuto, T. R. J.Agric. Food Chem. 1989,37, 539-545. (15) Durand, G.; Barcelb, D.; Albaigbs, J.; Mansour, M. Chromatographia 1990, 29, 120-124. (16) Durand, G.; Barcel6, D. J.Agric. Food Chem. 1994,42,814821. (17) Wilkins, J. P. Pestic. Sci. 1990, 29, 163. (18) National Research Council Canada. NRCC 19073; NRCC: Ottawa, Canada, 1978; pp 105-134. (19) McDonnell, T.; Rosenfeld, J. J.Chromatogr. 1993,629,4153. (20) Lacorte, S.; Molina, C.; Barcel6, D. Anal. Chim. Acta 1993, 281, 71-84. (21) Stan, V. J.; Kellner, G. Biomed. Environ. Mass Spectrom. 1982, 9 ( l l ) , 483-492. (22) Durand, G.; Barcel6, D. Anal. Chim. Acta 1991,243,259271. (23) Frost, A. A.; Pearson, R. G. Kinetics and Mechanism, 2nd ed.; Wiley: New York, 1961. (24) Morrison, B. R. S.; Wells, D. E. Sci. Total Enuiron. 1981, 19, 233-252. (25) Suntio, L. R.; Shiu, W. Y.; Mackay, D.; Seiber, J. N.; Glotfelty, D. Rev. Enuiron. Contam.Toxicol. 1988,103,l-59. (26) Mikami, N.; Yshimura, J.; Katagi, T.; Yamada, H.; Miyamoto, J. J. Pestic. Sci. 1985, 10, 184-273. (27) Vitko, V.; Cunningham, T. D. Fish Mar. Seru. Tech. Rep. 1974, NO.458, 1-27. (28) National Research Council Canada. Fenitrothion: the effectsof its use on environmental quality and its chemistry; NRCC 14104; NRCC: Ottawa, Canada, 1975; pp 1-164. (29) Durand, G.; Barcel6, D. Toxicol. Enuiron. Chem. 1992,36, 225-234.
Received for review October 28, 1993. Revised manuscript received February 8, 1994. Accepted February 9, 1994." @
Abstract published in Advance ACS Abstracts, March 15,1994.
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