Environ. Sci. Techno/. 1995, 29, 1246-1254
Introduction
Diiierent Witers under Various S Y L V A I N B . LARTIGES A N D PHILIPPE P. G A R R I G U E S * URA 348 CNRS, Universitk d e Bordeaux I, 33 405 Talence, Cedex. France
The evolution of a mixture containing 19 organophosphorus (OP) and organonitrogen (ON) pesticides at ppb level was studied over a 6-month period in differentwater types (ultrapure water, natural seawater, river water, filtered river water) and under various conditions. The degradation kinetics were monitored in closed bottles in darkness at two temperatures ( T = 6 and 22 "C) and in a system exposed to natural sunlight (variable temperature). The mixture was analyzed by gas chromatography coupled with a nitrogen phosphorus detector (GC/NPD). Energy activation (E,) and half-lifetimes (t,/*) were determined. Very different degradation behavior with respect to physicochemical conditions and molecular structures of the pesticides was observed. These experiments confirm that half-lives of OP pesticides can be more than several months and consequently lead to lasting environmental pollution.
Organophosphorus (OP) pesticides are widely used in agriculture for crop protection and fruit tree treatment (1). These extremely toxic and specific molecules, acting on acetylcholinesterase activity (21, are tending to replace the organochlorine pesticides that are more or less prohibited for use because of their persistence in the environment and their bioaccumulation along the food chain (3).It has been suggested that OP insecticides degrade faster and are not too lipophilic. Nevertheless, it has been shown that they may persist in the environment, for instance, halflives of t112 = 120 and 170 day in water (pH = 6.1, T = 20 "C) have beeen reported for chlorpyrifos and parathion, respectively (4, and t 1 / 2 = 200 day in an estuarine water (pH = 7.8, room temperature) for parathion (5). The aim of this study was to monitor the degradation kinetics of a mixture of pesticides in water and to estimate which factors were predominant among the three general degradation processes proposed: chemical (hydrolysis) (6), biological (7), and photochemical (8) degradation. In order to obtain an overview of the degradation behavior of OP pesticides, 16 compounds with different chemical structures were chosen. Some pesticides exhibited very similar structures such as ethyl parathion and methyl parathion and fenitrothion and fenthion. In addition to the OP insecticides, three organonitrogen (ON) compounds (two triazines and one carbamate) were used to allow comparison of three different classes of pesticides under the same experimental conditions. Individual pollutant concentrations in the ppb range (0.5-2.OpglL) close to natural conditions were used in preference to higher concentrations in the ppm range (1 mglL) often used in previous literature. The analysisofthe mixture was done by GCINPD,which is one of the most selective and sensitive techniques for the trace analysis of OP and ON pesticides. This enabled the disappearance of the study compounds to be checked.
Experimental Section Materials. The pesticides used were at least 95% pure; they were purchased from different suppliers. Azinophosethyl, azinphos-methyl coumaphos, dimethoate, ethyl parathion, methyl parathion, phosmet, and triazophos were from OS1 (Paris, France). Atrazine, bromophos, carbaryl, chlormephos, cyprazine, and dichlorvos were from Promochem (Strasbourg, France). Diazinon, fenthion, fenitrothion, and malathion, provided by Dr. J. B. Berg6 (I.N.R.A., Antibes, France). Isofenphos was from Bayer (Puteaux, France). Quinoline and benzoV]quinoline, used as internal standards, were obtained from Janssen-Chimica (Noisy le Grand, France). Acetonitrile, cyclohexane, and dichloromethane of pesticide grade were purchased from S.D.S. (Peypin, France). Evaporated dichloromethane (initial volume: 50 mL) was checked by GC/NPD for purity. The standard solutions (around 5 ppm) were prepared in cyclohexane. Whatman GFlF filters (290 mm diameter, 0.7 pm porosity)and 3-mLWaters-Millipore Florisil cartridgeswere purchased from OS1 (Paris,France);sodium sulfate (99.5% purity) was from Prolabo (Paris, France).
1246 1 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 5,1995
0013-936X/95/0929-1246$09.00/0
0 1995 American
Chemical
Sociev
TABLE 1
Characteristics of the Different Water Types water type
ultrapure water (MQ) river water filtered river water seawater
abbrev
pH
other characteristics
MQW 6.1 resistivity > 18 MQ RW 7.3 9.2 mg of particulates/L FRW 7.3 SW 8.1 salinity 25 g/L
Degradation Conditions. This study was carried out over 6 months (February-July 1993, Bordeaux, France) on a pesticide mixture (16 OP compounds, two triazines, and one carbamate) in water at ppb level. Water samples were spiked in the followingway: 1mL of the pesticide mixture/L of water was placed in a F'yrex container (2.5-10 L) and evaporated to dryness under a gentle nitrogen stream, The container was then fdled with the water, and the solution was mixed. Four types of water were used for the experiments: ultrapure water from a Millipore apparatus (MilliQ water = MQW), natural seawater (SW) from Arcachon Bay, river water (RW) from the Eau Bourde (smallriver near Bordeaux), and the same river water filtered (FRW) on 0.7-pm porosity filters to eliminate the particulates (see Table 1). The influence of temperature ( T = 6.0 f 0.5 "C and T = 22.0 f 1.5 "C) and light (darkness or natural sunlight) were evaluated using a set of 10 samples (Table 2). The temperatures under natural degradation studies ranged from T = -2 "C to T = 25 "C (environmental conditions). Aliquots of 50 mL were periodically taken from the samples, filtered in the case of the RW, solvent extracted with dichloromethane, and analyzed by GC/NPD. At the end of the experiments, the remainder of the water was analyzed, and the RW particulates were Soxhlet extracted with dichloromethane. Extraction Procedure. Water. Samples of 50 mL of water were taken from each of the 10homogenized samples, filtered on GF-F filters in the case of the RW (samples3-5), and solvent extracted with three 5-mL dichloromethane portions. The extracts were dried on sodium sulfate and evaporated to dryness under a gentle nitrogen stream, and 100 mL of cyclohexane was added. After 6 months, the water was extracted in the same way. Particulates. At the end of the experiments, the particulates were collected, dried, and Soxhlet extracted with dichloromethane over 24 h. The extracts were cleaned on Florisil cartridges (elution with 5 mL of acetonitrile) and treated as for the water extracts. Chromatographic Analysis. A gas chromatograph Shimadzu GC-14A equipped with an OCI-14 on-column injector and a FTD-14 nitrogen phosphorus detector (NPD) was used with the following gas flows: air (150 mL/min), hydrogen (3-4 mL/min), and helium as makeup gas (40 mL/min) and as carrier gas (2-3 mllmin). Data treatment was processed with a CR-4A Shimadzu integrator. Temperature program: injector (45-300 "C at 30 "C/ min, maintained for 15 min), oven (40-280 "C at 5 "C/min, maintained for 20 min), and detector at 300 "C. Two columns of different polarity were employed: a 50 m x 0.25 mm i.d. fused-silica capillary column (film thickness 0.12 pm) coated with 5% phenyl methyl silicone (CPSIL-8-CB,Chrompack)and a 50 mx0.25 mm i.d. fusedsilica capillary column (film thickness 0.40pm) coated with 14% phenyl methyl silicone (CPSIL-l3-CB, Chrompack).
Injection volumes of 1 pL were used in each analysis. The sensitivity of the detector ranged from 10 to 30 pg/pL for OP pesticides and over 200 pg/pL for ON compounds as mentioned previously (9). Kinetics Experiments. A total of 50 mL of water was sampled at the beginning (time to = 01, after 2,4, and 6 days and then once a week for a period of 2 months. The sampling was next performed at intervals of 3-4 weeks for a total period of six months. After each sampling, the volume of the container was adjusted to its initial value by adding the same amount of water (Le.,50 mL of RW replaced by 50 mL of RW) in order to maintain a constant volume and a certain equilibrium in the bottles (with respect to the quantity of air), but with a dilution effect on the concentration of pesticides. For the open systems, the water level was adjusted to the initial 4-L volume after each samplingsince the systems were exposed to both evaporation and precipitation. The use of such a system also raises the problem ofvolatilization of compounds and the introduction of bacteria and water of a different type (rainwater); however, these conditions mimic those found in the environment. Due to the time-consuming sample handling and treatment (sampling,solvent extraction, drying, reconcentration, analysis),no replicates were performed. Triplicate analyzes were nevertheless carried out at the initial time, indicating relative standard deviations (RSD) of 10-15% (further details in the Results). As previously reported (IO),the chemical degradation can be described using a first-order degradation curve (Ct = Coe-K3,with Ct as the concentration of the pollutant at time t, Co as its initial concentration, and K as the rate constant. The half-lifetime, t1/2,corresponds to a period of time at which the pesticide concentration is equal to half of the initial concentration, given by t1/2 = ln(2/K). By plotting the log (% residual pesticide) versus time, a straight line can be obtained, and the rate constant Kmay be derived from it. In addition to half-lives, it is also possible to calculate the activation energies Ea using the Arrhenius equation K =Ae-€JRT,where Tis temperature,A is the frequencyfactor, and R is the gas constant. The rate constants have been calculated at two temperatures ( T = 6 and 22 "C). It gives access to Ea (in kcal/mol) and to A (day-') for the four water types (MQW, RW, FRW, and SW). The E, values demonstrate the influence of temperature on degradation: the greater the E, value is, the greater the dependence on temperature, i.e., the degradation kinetics speed up with temperature increase. The activation energy may then be used to assess the environmental fate of pesticides in the environment ( 1 1 ) .
Results and Discussion The experiments performed in this study enabled the influence of the following factors to be compared: Temperature: Two temperatures comparable to environmental conditions (winter and summer) were considered ( T = 6 "C in a temperature-controlled cold room and T = 22 "C in an air-conditioned room). pH: The pH values varied from 6.1 (MQW) to 8.1 (SW) with an intermediate value of 7.3 for RW and FRW. Photodegradation: This factor is considered by certain authors as being one of the most important, especially in shallowwaters(12).The photodegradationin natural water VOL. 29, NO. 5,1995 /ENVIRONMENTAL SCIENCE &TECHNOLOGY
1247
TABLE 2
Description of the 10 Systems sample
water
PH
T("C)
light
system
water amount (L)
1 2 3 4 5 6 7
MQW MQW RW RW RW FRW FRW
6.1 6.1 7.3 7.3 7.3 7.3 7.3 8.1 8.1 8.1
6 22 6 22 variable 6 22 6 22 variable
darkness darkness darkness darkness sunlight darkness darkness darkness darkness sunlight
closed 2.5-L amber bottle closed 2.5-L amber bottle closed 2.5-L amber bottle closed 2.5-L amber bottle open IO-L container closed 2.5-L amber bottle closed 2.5-L amber bottle closed 2.5-L amber bottle closed 2.5-L amber bottle open 10-L container
2 2 2 2 4 2 2 2 2 4
sw sw sw
8 9 10
TABLE 3
Recovery Percentages of Water Solutions Spiked with Pesticides" compound atrazine azinphos-ethyl azinphos-methyl bromophos carbaryl chlormephos coumaphos cyprazine diazinon dichlorvos dimethoate fenitrothion fenthion isofenphos malathion ethyl parathion methyl parathion phosmet triazophos a
o/'
R (MOW)
61 f 18 89 f 11 77 f 16 71 i 18 67 i 2 66 f 5 93 f 18 63 i 12 67 i 6 59 f 12 91 f 15 81 f 5 77 f 9 77 f 12 71 f 9 89 f 8 78 f 10 81 f 6 87 f 16
Yo R(RW)
% R (FRW)
70 f 16 101 f 9 89 f 3 36 f 12 79 f 14 49 f 30 81 f 14 75f8 77 f 4 46 f 37 99 f 20 90 f 5 77 f 8 72f9 90 f 5 84 f 3 96 f 2 ND 99 f 6
6 3 i 15 8 8 i 14 82 f 23 81 i 16 9 2 i 15 3 2 i 12 89 f 21 75 f 11 73 f 17 20 f 4 9 3 f 11 8 6 f 14 7 6 % 15 81 f 14 7 6 f 15 72 f 10 86 f 7 39 f 4 8 9 f 17
% R(FRW+)
% R(SW)
74 95 96 52 90 15 93 65 63 13 105 94 71 79 80 81 93 20 92
59 f 7 104 f 7 91 f 22 82 f 12 9 0 f 15 55 f 9 119 f 15 7 8 % 11 6 6 % 16 5 4 f 19 117 f 17 74 f 21 82 i 14 7 7 f 16 71 f 10 7 8 f 11 8 6 f 13 49 f 6 107 i 18
%R, percentage of recovery; FRW*, FRW submitted to filtration after spiking (same procedure as for RW); ND, not detected.
may be due to direct photolysis (131,but in many cases the humic acids act as photosensitizers (14). The differences if any between RW containing particulates and humic substances and a clearer SW can thus be evaluated. It should be pointed out that in the case of an open system, volatilization of the compounds could certainly occur (13. Adsorption onto Particulates: In order to observe the influence of particulates in water, RW was filtered to give FRW (filtered river water) in which no adsorption should occur, though the colloids may play a role. It is important to know the distribution of the pollutant in all the compartments of the aquatic system. The adsorption onto particulates correlated to their log KO, (16) may greatly influence the fate of the contaminants as transport (13, bioavailability (18) and degradation are affected. This phenomenon leads to different behaviors: the pesticide may be stressed to a faster degradation (biological or chemical) on these active sites ( 4 ) , or on the contrary, the pesticide may be protected and exhibit a longer half-life. It could also be released slowly from the particles into the water as observed for the chlorpyrifos (19). It must be pointed out that the water types differ also in their chemical composition [e.g., influence of the ionic strength (3,fulvic and humic acids (20), and microbial activity (311, No comparison between sterile and nonsterile water was performed in this study as many studies have already dealt with this phenomenom (7,21,22): they have shown that biodegradation increases the total rate of 1248
ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 5 , 1995
degradation. For parathion, biodegradation is predominant over chemical degradation, whereas the contraryis true for chlorpyrifos (21). Percentagesof Recovery. One hour after the spiking of the water samples (to = 0) triplicate analyzes were carried out for each water type (MQW, RW, FRW, and SW). In order to validate the filtration procedure, one blank sample was performed with 50 mL of FRW submitted to the same treatment as RW samples. The results are shown in Table 3: for most of the pesticides, whatever the water type, good recovery of 7090% was obtained with RSD around 10-15%. However, chlormephos and dichlorvosgave bad results (recoveryfrom 15 to 66% with RSD up to 37%) due to their volatility (uncontrolled loss during evaporation and reconcentration steps). Phosmet and bromophos were rapidly adsorbed onto particulates and onto the filter: for bromophos, a loss of approximately 30% occurred on filtering. Moreover, the recovery for phosmet was low except for MQW this could be explained by the very rapid degradation of this compound (see below). Consequently, four compounds were difficult to quantify: chlormephos and dichlorvos because of their high volatility, and phosmet and bromophos due to their adsorption. Influence of Environmental Factors on HaKLives and Activation Energies. The half-lifetimes t 1 / 2 and the activa-
TABLE 4
Half=Livesf1n (day) of Studied Compoundsa pH 1.3
4n ( R W
pH 6.1 4,q (MOW)
4n FRW)
pH 8.1 4n (SW) 22°C sun
class
compound
6°C
22°C
6°C
22°C
sun
6°C
22°C
6°C
triazine triazine carbamate organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus organophosphorus
atrazine cyprazine carbaryl azinphos-ethyl azinphos-methyl bromophos coumaphos diazinon dimethoate fenitrothion fenthion isofenphos malathion ethyl parathion methyl parathion phosmet triazophos chlormephos dichlorvos
NOD NOD NOD 204 415 170 218 144 423 202 189 265 212 120 237 33 179 P P
NOD NOD 37 173 115 38 156 69 193 62 71 174 42 84 46 5 83 DA47 DA81
235 191 31 171 278 Ads 165 181 171 103 149 Ads 55 120 95 VFD 154 P DA81
164 190 11 65 42 Ads 59 80 43 31 42 Ads 19 86 23 VFD 41 DA47 DA55
59 37 9 9 8 5 5 43 29 4 2 21 8 8 11 VFD 21 DA2 DA55
NOD 160 45 186 506 88 225 132 173 143 104 175 53 122 173 VFD 183 P DA81
130 254 0
u
a,
FRW6"C FRW22OC
40
a
20
0
1 I
I
I
I
I
I
1
0
30
60
90
120
150
180
Tlme
(days)
FIGURE 2. Degradation curves in the case of a strong adsorption on particulates. Example of isofenphos: (a) river water (RW); (b) filtered river water (FRW).
range from Ea = 0.1 kcal/mol (methyl-azinphosin FRW) to Ea = 11 kcal/mol (ethyl parathion in SW). A comparison with data found in the literature indicated that only a few studies have dealt with the degradation of numerous OP insecticides (4, 6, 11) and even less have compared the degradation of OP compounds with other classes of pesticides [synthetic pyrethoids (3),organo1292 1 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 5,1995
chlorine, and carbamate pesticides (21)]. Only a few OP pesticides have been well-studied [parathion (4- 7,10,11, 21,26-321, malathion (4,6,11,24,27),ethyl-chlorpyriphos (3,4, 11, 19, 21), and methyl-parathion (3, 6, 11,2.31, and little work has been carried out on the identification of transformation products [diazinon (24), fenitrothion (331, malathion ( 7 ) , and parathion (5,26,27)1.
Ethyl-parathion
Methyl-parathion
1 Fenthlon
Fen1t r o t h i o n
FIGURE 3. Structures of a few OP pesticides.
Half-lifetimes found in this study were often in good agreement with those found in the literature. For instance, 8 day for parathion in a coastal nonsterile water (24 ppt, pH = 8.2) at T = 28 "C (10)with respect to 6 day in our experiments (SW, pH = 8.1, T = 22 "C, darkness). A halflifetime of 3 day has been reported in water at pH = 8 and T = 20 "C (28) comparable to a half-lifetime of less than 2 day in our experiments (SW,pH = 8.1; T = 22 "C, darkness). Generally greater Ea values have been reported in the literature: 9.9 kcallmol for methyl-parathion in water at pH = 11 (25) and activation energies from 14 kcal/mol to 22 kcallmol for seven OP pesticides in water at pH = 7.4 (4).
Some differences are nevertheless noticeable due to various physicochemical conditions (pH,temperature,light, etc.) and biological activities (sterile or nonsterile media). The concentration range (0.5-2pglL) used inthese studies may be an important factor since 102/103times this value has been used in previousworks. Eventual synergic effects due to the use of a compound mixture could also be mentioned. Behavior Differences for OP Pesticides with Respect to Molecular Structure. Studied OP pesticides were either dithionates or thionates. The data contained in Tables 4 and 5 did not enable us to confirm the general remarks reported elsewhere (6, 24), i.e., the increasing rate of hydrolysis with the decreasing sulfur content in the OP compounds. However, the decrease in stability when replacing ethoxy groups by methoxy groups (24) was confirmed when comparing azinphos-ethyl with methylazinphos and ethyl parathion with methyl parathion. As shown in Figure 3, methyl parathion differs from ethyl parathion by the replacement of ethoxy by methoxy groups. For fenitrothion, a methyl group is added in the meta position, and for fenthion, the nitro group NO2 in the para position is replaced by a sulfomethyl group SMe. It has already been noted that there is greater stability in compounds containing an ethoxy group compared to those containing a methoxy group (ethyl parathion versus methyl parathion). The addition of the methyl group or the replacement of NO2 by SMe does not change greatly the stability of the molecule but does modify the behavior of the molecule under photolysis: fenthion and fenitrothion are much more sensitive to photodegradation (C1l2 = 2-5 day with respect to t112 = 8 to 34 day for methyl parathion and parathion). The presence of a sulfomethyl group also leads to a slight adsorption onto particulates as illustrated for fenthion in Figure 1.
Conclusion As shown by the results presented in this study, many factors influence the behavior of OP and ON pesticides in water
(pH,temperature, chemical composition,particulates,light, etc.). One of the major results is the great difference in degradationbehaviorbetween river water (RW and filtered river water (FRW). The molecular structure of the pesticide itself (substituents) plays an important part in determining its behavior with respect to adsorption on particulates or absorption of light. The carbamate carbaryl degrades quickly as opposed to triazines, which may partly explain the fact that they are easily detected in the aquatic environment (34, 35). For organophosphorus pesticides, half-lives range from a few hours for phosmet up to 100 day for isofenphos (T= 22 "C, in darkness). It is consequently difficult to predict the persistence of OP insecticides in the environment: the modeling of the behavior of pollutants has already been attempted in aquatic systems (301,but the results provided have to be carefully interpreted (36). There is also a need to standardize the experiments in order to compare the results of different laboratories as has been done for biodegradability studies (37). For instance, it is difficult to extrapolate the photodegradation results obtained with a few centimeter water column to real aquatic systems. Further studies need to be carried out in order to identify the transformation products. It would be of interest to analyze the samples directly either by liquid chromatography coupled with mass spectrometry (LCIMS) to determine the polar metabolites or by gas chromatography coupled with MS for the less polar and thermolabile products. All these experiments would enable a better understanding of degradation pathways.
Acknowledgments We thank Touzart & Matignon for the loan of the GClNPD as well as the Aquitaine Region, CNRS, IFREMER (Grants 91-5440-039 and 94-3430-log), and the French Research Ministry (MRT 91.T.0539) for their financial support. M. Huxham is acknowledged for reviewing this manuscript.
Literature Cited (1) Barcelo, D.; Porte, C.; Cid, 7.; Albaigbs, J. Int. I. Environ. Anal. Chem. 1990,38, 199. (2) Bussiere, J. L.; Kendd, R. 7.; Lacher, T. E., Jr.; Bennett, R. S. Environ. Toxicol. Chen. 1989,8,1125. (3) Schimmel, S. C.; Garnas, R. L.; Patrick, J. M., Jr.: Moore, J. C. J. Agric. Food Chem. 1983,31,104. (4)Freed,V. H.; Chion, C. T.; Schmelding, D. W.J. Agric. Food Chem. 1979,27 (4),706. (5) Weber, S. K. Water Res. 1976,10,237. (6)Cowart, R.P.; Bonner, F. L.; Epps, E.A., Jr, Bull. Environ. Contam. Toxicol. 1971,6 (31,231. (7) Walker, W. W. J. Environ. Qual. 1976,15 (21, 210. (8)Durand, G.; Barcelo, D.; Albaiges, J.; Mansour, M. Chromatographia 1990,39 (3/4), 120. (9)Lartiges, S . B.; Garigues, P. Analusis 1993,21,157. (10)Wang, T.C.; Hoffman, M. E. 1.Assoc. Off: Anal. Chem. 1991,74 (51,883. (11)Wolfe, N. L. Chemosphere 1980,9,571. (12)Mansour, M.;Mamouni, A.; Meallier, P. MethodologicalAspects of the Study of Pesticide Behavior in Soil, Workshop Proceedings; Janet, P., Ed.; INRA: Paris, France, 1987;p 87. (13)Miller, G. C.; Zepp, R. G. Residue Rev. 1982,85,89. (14)Zepp, R. G.; Schlothauer, P. F.; Sink, R. M. Environ. Sci. Technol. 1985,19 (l),74. (15) Schomburg, C.J.: Glotfelty, D. E.; Seiber, J. N. Enuiron. Sci. Technol. 1991,25, 155. (16)Bowman, B.T.;Sans, W. W.J.Environ. Health 1983,E18 (61,667. (17)O'Neill, E. J.; Ripe, C. R.; Mueller, L. H.; Connolly, J. P.; Pritchard, P. H. Environ. Toxicol. Chem. 1989,8, 759. (18)Landrum, P.F.; Nihart, S. R.; Eadie, B. J.; Herche, L. R. Environ. Toxicol. Chem. 1987,6,11. (19) Riskallah, M. R.; El-Sayed, M. M.; Hegazy, M. E.; Takla, N. S.; Hindi, S. A. Agric. Res. Rev. 1981,59 (11,187. (20)Porschmann, J.; Stottmeister, U. Chrornatographia 1993,36,207.
VOL. 29, NO. 5, 1995 /ENVIRONMENTAL SCIENCE &TECHNOLOGY
1
1263
(21) Sharom, M. S.; Miles, J. R.; Haris, C. R.; McEwen, F. L. WaterRes. 1980,14,1089. (22) Ripe, C. R.; O’Neill,E. J.; Woods, M. E.; Gilliam, W. T.; Pritchard, P. H. Environ. Toxicol. Chem. 1989,8, 747. (23) Barcelo, D. 1. Chromatogr. 1993,643,117. (24) Faust, S. D.; Gomaa, H. M. Environ. Lett. 1972,3 (3), 171. (251 . . Badaw, M. I.: El-Dib, M. A. Bull. Environ. Contam. Toxicol. 1984,i3,40. (26) Fisher, S. W.; Lohner, T. W. Arch. Environ. Contarn. Toxicol.1987, 16,79. (27) Lydy, M. J.; Lohner, T. W.; Fisher, S. W.Aquat. Toxicol. 1990,17, 27. (28) Fisher, S. W.; Lohner, T. W.Arch. Environ. Contam. Toxicol. 1986, 15,661. (29) Readman, J. W.; Wee Kong, L. L.; Mee, L. D.; Bartocci, J.; Nilve, G.; Rodriguez-Solano, J. A,; Gonzalez-Farias, F. Mar. Pollut. Bull. 1992,24 (81, 398. (30) Yu, C. C.; Sandborn, J. R. Bull. Environ. Contam. Toxicol. 1975, 13, 543.
1264
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 5, 1995
(31) Rajasekhar Reddy, B.; Sethunathan, N. SoilBiol. Biochem. 1985, 17 (2), 235. (32) Sethunathan, N.1.Agric. Food Chem. 1973,21 (41, 602. (33) Durand, G.; Abad, J. L.; Sanchez-Baeza,F.; Messeguer,A.; Barcel6, D. 1.Agric. Food Chem. 1994,42,814. (34) Bodo, B. A. Environ. Toxicol. Chem. 1991,10,1105. (35) Pereira, W. E.; Hostettler, F. D. Environ. Sci. Technol. 1993,27, 1542. (36) Metcalf, R. L. Annu. Rev. Entomol. 1977,22,241. (37) Nyholm, N. Environ. Toxicol. Chem. 1991,10, 1237.
Received for review July 25, 1994. Revised manuscript received January 18, 1995. Accepted January 26, 1995.@
ES940465N @
Abstract published in Advance ACS Abstracts, March 1, 1995.
