Environ. Sci. Technol. 2001, 35, 63-69
Occurrence and Spatial and Temporal Distribution of Pesticide Residues in Groundwater of Major Corn-Growing Areas of Greece (1996-1997)
latter compounds were selected among those pesticides most commonly used in corn-growing areas of Greece. The objectives of this study were to (a) survey the concentrations of the selected pesticides in groundwater of the major corn-growing areas of Greece, (b) examine the spatial and temporal distribution of pesticides in groundwater and identify the areas of groundwater contamination problems, and (c) tentatively identify groundwater contamination sources.
ASTERIOS PAPASTERGIOU AND EUPHEMIA PAPADOPOULOU-MOURKIDOU* Pesticide Science Laboratory, Aristotle University, P.O. Box 1678, 54006 Thessaloniki, Greece
Experimental Section
During 1996-1997, residues of selected pesticides were monitored, at 3-month intervals, in 80 wells, including both irrigation and drinking water wells, distributed among the main corn-growing areas (Pieria, Thessaloniki, Serres, Kavala, and Evros) of Greece. Pesticide residues were found in 48% of the wells; however, in most cases residues were very low ranging from LOQs (quantification limits of the analytical methods) to DEA > alachlor ) metolachlor; however, the order of descending concentrations was atrazine > metolachlor > DEA > alachlor. The occurrence and the spatial and temporal distribution patterns of pesticide residues indicate that at the present the situation of groundwater quality is favorable throughout the corn-growing areas of Greece with the exception of the Ardas Valley.
Introduction The presence of pesticides in groundwater has been documented in North America more than 20 years ago, and since then numerous reports demonstrated the worldwide severity of the problem (1-6). Atrazine, alachlor, metolachlor, and simazine are among the most routinely found pesticides in groundwater (4-11). In Greece, atrazine alone or in combination with alachlor (Lasso-at) or metolachlor (Primextra) is used mainly for weed control in cornfields. Applications are usually made preemergence during April to early May and before establishing the crop. Application rates range from 600 to 1200, 900 to 1800, and 1200 to 2000 gr/ha for atrazine, metolachlor, and alachlor, respectively. To the best of our knowledge no pesticide monitoring data have been reported so far for groundwater quality of Greece even though such studies have been conducted since the early 1990s (12). For the first time, a monitoring study of groundwater quality in major corngrowing areas of Greece was conducted during 1996-1997, and these data will be presented and discussed here. In this study, along with atrazine, DEA (deethylatrazine), DIA (deisopropylatrazine), hydroxyatrazine, alachlor, and metolachlor, 10 additional compounds were monitored; the * Corresponding author phone/fax: 0030 31 471478; e-mail:
[email protected]. 10.1021/es991253z CCC: $20.00 Published on Web 12/02/2000
2001 American Chemical Society
Materials. All solvents used were of Pesticide Residue and HPLC Grade (acetonitrile) purchased from Merck (Darmstadt, Germany). Lichrolut EN and C18 cartridges were purchased from Merck and Millipore (Bedford, MA), respectively. PRP-1 HPLC guard columns were purchased from Hamilton (Reno, NE). An HPLC Lichrospher C18, 250 × 4.6 mm, 5 µm analytical column was purchased from AZ-Analytical (Amtsgericht, Mainz, Germany. Pesticide analytical standard materials were either purchased from Promochem (Augsburg, Germany) or were donated by Novartis (Bassel, Switzerland). Instrumentation. A Tracker/Magnum ion trap mass spectrometer (ITMS) (Finnigan MAT, San Jose, CA) associated with a Varian (Varian Instruments, Sunnyvale, CA), Model 3300, gas chromatograph equipped with a split/splitless injector operated in the splitles mode under isothermal conditions (230 °C) was used. The analysis was carried out on a 30 m × 0.25 mm i.d. DB-5-MS, 0.25 µm film thickness capillary column (J&W Scientific, Folsom, CA). Injections of 2 µL were made by use of an autosampler, Model A200S (Finnigan Mat). Chromatographic and operational conditions of the mass spectrometer have been previously described (13). A semiautomated online-SPE-HPLC-PDA system was used for the analysis of hydroxyatrazine. This system has been previously described (14). Water Sampling. Each well was pumped for 15 min before samples were taken. Triplicate samples in 2.5 L amber glass bottles were taken from each well on each sampling date. Samples labeled and stored in ice boxes were transported to the laboratory where then they were refrigerated until processed; processing was carried out within 1-2 days upon arrival at the laboratory. On each sampling date water samples in triplicate were also taken form the rivers Strimonas, Nestos, Evros, and Ardas. These samples were handled as the rest of the samples. Analysis. One liter sample aliquots were processed by SPE on tandem C18-Lichrolut EN cartridges. Pesticides were eluted with 10% methanol in ethyl acetate at 2 × 5 mL portions. The eluates dried over anhydrous sodium sulfate were concentrated to dryness by use of a nitrogen stream; the residues reconstituted in 100 µL of ethyl acetate were analyzed by GC-MS. River water samples were filtered through 0.45 µm filters before processed by SPE, as described above. The filtration cakes extracted with acetone (50 mL acetone/filter) and the extracts combined with the respective SPE extracts were analyzed by GC-MS. The analyte list of the GC-MS method applied for the analysis of the surface water extracts included 130 pesticides from a variety of chemical and biological classes (13). The GC-MS method applied for the analysis of the groundwater extracts included only 15 compounds which are 13 pesticide parent compounds, DEA, and DIA. An online-SPE-HPLC-PDA system was used for the analysis of hydroxyatrazine. In the same method atrazine, chlorpyrifos ethyl, DEA, DIA, prometryne, and simazine were VOL. 35, NO. 1, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Map of Macedonia-Thrace, Greece with the sampling sites.
TABLE 1. Description of the Sampling Wells
location Pieria Thessaloniki Kavala Serres Evros total
no. of wells with depth (m) >100 50-100 80% at 0.1-0.05 µg/L level; the mean recoveries of molinate and trifluraline were around 60%, due to volatilization losses of these compounds during concentration of the SPE extracts, and the recovery of metamitron was 73% due to breakthrough. The limits of detection (LOD) and quantification (LOQ) were in the range of 0.001-0.010 and 0.005-0.010 µg/L, respectively, except for simazine and chloridazon with LOQs 0.050 µg/L. For the online SPE-HPLCPDA method the respective mean recovery values were in the 48-81% range, and the respective LODs and LOQs were in the 0.02-0.05 and 0.02-0.1 µg/L ranges, respectively. The RSDs (relative standard deviations) of the mean recovery values of both methods and at all fortification levels were LOQs a
LOQ (µg/L)
max. concn found
no. of wells exceeding MRL
0.005 0.005 0.010 0.010 0.005 0.010 0.005 0.005 0.005
0.347 1.508 0.456 0.014 0.547 3.699 0.028 0.005 0.005
2a 7b 6c 0 3d 1e 0 0 0
One in Thessaloniki and one in Kavala.
b
no. of wells with quantifiable residues (>LOQs) Pieria Thessaloniki Kavala Serres Evros 4 2 1 0 1 0 0 0 0 5
4 6 5 1 3 1 0 0 0 8
Two in Thessaloniki and five in Evros. c Six in Evros.
DIA, and hydroxyatrazine), and 2 insecticides (lindane and chlorpyrifos ethyl) were monitored in groundwater of the five major corn-growing areas of Greece. Five sampling periods were undertaken and during the first three samples from 75 wells were collected, while during the rest the number of wells increased to 80 by including five more wells in the area of Evros (Ardas Valley). Among the compounds monitored, only nine compounds were found at least once at concentrations equal to or higher than the respective LOQs of the analytical methods employed. A summary of the data generated during this study is presented in Table 2. In 48% (38 wells) of the monitored wells pesticides were found at least once at concentrations equal to or higher than the respective LOQs. However, the frequency of detections (percent of wells with pesticide residues present at trace levels) was much higher (64%) (data are not shown). Only in nine wells were found pesticide concentrations higher than 0.1 µg/L, which is the MPL (maximum permissible level, µg/L) of the EU Drinking Water Directive EE 83/98 (15). Among the compounds found at concentrations > MPL, atrazine had the highest site frequency of occurrence followed by DEA, metolachlor, alachlor, and metamitron (footnote of Table 2). However, the highest concentration was exhibited by metamitron, followed by atrazine, metolachlor, DEA, and alachlor. Atrazine and DEA were found at quantifiable concentrations in 35 and 26% of the wells, respectively, and alachlor and metolachlor in 17% each. Pendimethalin was found only in three wells, and metamitron, propanil, and triflluraline were found in one well each. DIA was found only in two wells and at concentrations not exceeding 0.02 µg/L. Atrazine and DEA were also reported having the highest frequency of detections in shallow groundwater of 20 major hydrologic basins of U.S.A. (10), while alachlor was detected in 3.3% of the samples (11). To examine the relationship of the occurrence of pesticides in groundwater with ancillary parameters such as well depth, distance from corn fields, and type of aquifers, all the sampling wells were separated into respective groups, and the concentrations of the most frequently found compounds (atrazine, DEA, metolachlor, and alachlor) were averaged over the wells of each group (Tables 3-5). With respect to the well depth variable, it appears that the averaged concentrations of all compounds are higher in the 50-100 m depth group (Table 3). This difference is more pronounced when the sums of averaged concentrations of the groups are considered (the sum of the 50-100 m group is 3-4 times higher). At present, there is no plausible explanation for this difference; the expected result was to find higher averaged concentrations of pesticides in the group of the shallowest wells.
2 3 1 0 0 0 0 0 0 5 d
0 0 1 0 0 0 0 0 1 2
total no. of wells
7 16 13 1 13 0 3 1 0 18
17 27 21 2 17 1 3 1 1 38
Three in Evros. e One in Thessaloniki.
TABLE 3. Concentrations (ng/L) of the Most Frequently Found Pesticides Averaged over the Wells Classified by Variable Depth well depth (m) >100 (n ) 43) 50-100 (n ) 27) 0.050 is not significant.)
the five sampling dates) and the wells classified by depth, distance from corn fields, and aquifer type were calculated (Table 6). With respect to variable dept, the occurrence of individual pesticides is the same in all three groups of wells classified by depth, the probability (P) for CHISQ (χ2) approximation of Kruskal-Wallis test being 0.2502, 0.0505, 0.2604, and 0.1183 for atrazine, DEA, metolachlor, and alachlor, respectively (P > 0.05 is not significant). Thus the probability of occurrence of any of the four pesticides in the wells of either group, classified by depth, is the same. However, when the occurrences of all four pesticides in each well are considered, the three groups of wells are significantly different (P ) 0.0342, Kruskal-Wallis test, and 2 degrees of freedom). Thus, since the null hypothesis is rejected, apparently the wells of the 50-100 m depth group are significantly different from the rest, and consequently the sums of pesticide averaged concentrations are significantly higher than the respective sums of the other groups (shown in Table 3). The distance from corn fields does not seem to have any relationship with the occurrence of pesticides in groundwater, the probability for (χ2) approximation of Wilcoxon-2 sample test being >0.05 for all four pesticides either when they are considered individually or all together (Table 6). This is probably due to the fact that all monitored wells were selected to be among those located as close as possible to corn fields, and thus the differences in distance from corn fields are not significant to differentiate the two groups. However, the lack of a relationship between the detection frequencies of atrazine in groundwater and the distance to the nearest crop has been reported (6). In the latter case, however, a significant relationship was found for alachlor. With respect to the type of aquifer the probability of (χ2) approximation of Wilcoxon-2 sample test is higher than 0.05 (not significant) for all compounds examined individually. However, when all pesticides are considered together, the two groups are significantly different (P ) 0.0191) (Table 6). Water samples detected positive for atrazine, DEA, or DIA by the GC-MS method were also analyzed by an onlineSPE-HPLC-PDA system to investigate the presence of hydroxyatrazine. In none of these samples was hydroxyatrazine detected (residues < 0.02 µg/L which was the LOD for hydroxyatrazine). The analytical data for the rest of the analytes were in general agreement with the respective data provided by the GC-MS method. The absence of hydroxyatrazine in groundwater should have been expected on the basis of the strong adsorption of this compound onto the soil material and thus limiting leaching potential (16). However, in recent studies the presence of hydroxyatrazine in surface aquatic systems has been reported (17, 18). Spatial Distribution. The distribution of wells in each corn-growing area found at least once with pesticide levels equal to or higher than the respective LOQs is shown in Table 2. In Pieria, in 10 out of 15 monitored wells pesticide residues were detected (data are not shown); however, in only five 66
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TABLE 7. Concentrations of the Most Frequently Found Pesticides Averaged over the Wells Classified by Variable Corn-Growing Area area Pieria Thessaloniki Kavala Serres Evros
average concentrations (ng/L) sum of n atrazine DEA metolachlor alachor averages 15 15 15 15 20
0.31 35.84 1.89 0 88.04
0.17 3.84 1.01 0.21 60.78
0.12 1.51 0 0 45.37
0.64 2.81 5.92 0 2.25
1.24 44.08 8.83 0.21 196.43
wells pesticide concentrations ranged from the LOQ to 0.018 µg/L. In Thessaloniki, in only two wells were no detectable levels of pesticide residues (data are not shown); however, in only eight wells were pesticide concentrations at quantifiable levels, while in only two wells the respective concentrations were occasionally > 0.1 µg/L (Table 2). Among the 15 wells monitored in the two main corngrowing areas of Kavala (Tenagi of Fillippi and Chrysoupolis) in only five wells pesticide residues were detected and also found at quantifiable levels (Table 2). The most frequently found compounds were atrazine and alachlor; however, the concentrations of atrazine were low ( 0.1 µg/ L. The most frequently found compound was atrazine with the respective concentration levels ranging from traces to 0.030 µg/L. DEA was found only once in the rivers Ardas and Evros, while metolachlor was also found once in the rivers Ardas and Nestos. Other pesticides found were alachlor, pendimethalin, molinate, and diazinon. In none of the surface water samples was found hydroxyatrazine. In alluvial aquifers it has been estimated that the flux of atrazine from a river ranges from 60 to 3000 µg/day/m2, and this rate was reported to be one to three times greater than the standard flux via leaching beneath a typical soil (19). However, the opposite phenomenon has been also reported, that is, alluvial groundwater has been identified as the source of atrazine and DEA found in an adjacent river (20). The aquifers of Ardas Valley are alluvial aquifers, and, since pesticide concentrations in the Ardas River never exceeded the 0.1 µg/L level, it is postulated that none of the above transport mechanisms are in effect in the Ardas Valley. However, this needs to be proven by research and data collection before such a possibility is excluded. Differences in farming practices among the five major corn-growing areas exist, and these should also be considered to explain the differential behavior of atrazine and metolachlor in these areas (the distribution of alachlor is not different among the five areas according to the Kruskal-Wallis test, Table 8). Despite the apparent lack of relationship between the distance of a certain well from cornfields and the presence of corn pesticides in groundwater the fact that groundwater contamination is significant only in the Ardas Valley, which is the most intensively corn producing area of Greece, is not surprising. In this area corn has been almost a monoculture for the last 20 years, and only lately, however, very rarely, rotational crops such as sunflower and asparagus have been installed. A relationship between the presence of atrazine in groundwater with the frequency and distribution of corn production in a certain area has been established (9).
TABLE 9. DAR Units [(Mol of DEA/L)/(Mol of Atrazine/L)] in Selected Wells Monitored in Evros (Ardas Valley) sampling dates well no. 1 2 5 7 8 9 11 12 13 15 16a 17a 19a 20a
July 1996
Sept 1996
Jan 1997
June 1997
Sept 1997 0.65 0.46
1.98
1.38
1.38
0.38 1.16
0.67 3.13 0.86 0.73 0.83
0.62 3.27 0.58 0.63
0.13 2.95 0.78 0.62
2.66 0.79 0.72 3.33 0.73 0.40
1.16 9.20 0.78 10.24 0.83 0.76 1.02 3.96 0.68 0.32 0.70
a These wells were included in the monitoring study after the third sampling period.
In the same study the highest atrazine concentrations were associated with continuous corn production, whereas other parameters such as the type of aquifer rock, depth of the water table, and aquifer recharge rate were concluded not to be important. Another major difference between Evros and the rest of the areas is the fact that in Evros, especially in the Ardas Valley, atrazine applications are followed by heavy flooding before corn is sown and after corn herbicides are applied. Certainly, this practice favors pesticide transport in soil, and in clayey soils preferential flow might be enhanced. Further studies, including geological characterization of the Ardas Valley soil horizons, water movement, and groundwater vulnerability to contamination are currently in progress to elucidate the mechanism(s) of groundwater contamination of the Ardas Valley. The DAR units (ratio of molarities of DEA/atrazine) for some of the Evros wells (Ardas valley) are shown in Table 9. For a number of wells, specifically those containing atrazine at concentrations >0.1 µg/L, the respective DAR units are in the range of 0.13-0.86. This is an indication that atrazine reached the groundwater table bypassing the deethylation catabolic activity of soil (7, 21, 22). Since this area has clayey soils, it is probable that preferential flow might be the transport mechanism of atrazine to some aquifers. In the wells with DAR units >1.0, leaching of atrazine and DEA from corn-growing soils is the probable cause of contamination (7, 21-23). Temporal Distribution. The temporal distribution of pesticides in the wells of the study areas was examined by applying the Box and Whisker Plot Test for the difference of pesticide concentrations found in each well at the last minus the first sampling period. Such plots for the temporal distribution of pesticides in the wells of Thessaloniki and Evros are shown in Figures 2 and 3, respectively. Respective plots for Pieria, Serres, and Kavala are not shown because, as discussed before, the data for these areas are limited, and thus the respective plots have very little or inconclusive information. For Thessaloniki, the median value of the temporal differences, as defined above, and most of the rest of values of such concentration differences and for all compounds are close to or almost equal to zero (Figure 2). This indicates that there is a steady-state situation with respect to the presence of pesticide residues in the wells of this area. However, there are two outlier values for atrazine and one for alachlor. Indeed high concentrations (1.0 and 1.508 µg/L) of atrazine were found in two wells, and alachlor at 0.133 µg/L was also found VOL. 35, NO. 1, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 4. Temporal concentration patterns of atrazine and DEA in a well located in Kavala. FIGURE 2. Box and Whisker plot of differences of pesticide concentrations found in the last minus the first sampling of each well monitored in Thessaloniki. In this case the median (or the 50th percentile) of differences is shown (thick line) and outlier values (square spots).
FIGURE 5. Temporal concentration patterns of atrazine and DEA in a well located in Evros (Ardas Valley).
FIGURE 3. Box and Whisker plot of differences of pesticide concentrations found in the last minus the first sampling of each well monitored in Evros. In this case the median (or the 50th percentile) of differences is shown (thick line) in the box, the low and upper edge of the box mark the 25th and 75th percentiles (or quartiles), the narrow boxes extending from the box are the whiskers (the whiskers extend to the farthest concentration differences but not farther than 1.5 times the distance between the quartiles), and the square spots are the outlier concentration differences. once in one of the above two wells. In one of these two wells metamitron (not considered in the box and whiskers plot test) was also found once at 3.699 µg/L. Repeat sampling of both wells, a month later, showed atrazine levels 2 µg/L. The temporal distribution of pesticide concentrations in the wells of Evros is shown in Figure 3. The median of the concentration differences, as defined above, for all the compounds is positive; the range of values, however, is narrow for all compounds except for DEA, and there are three high positive outliers for atrazine and one negative outlier for metolachlor. More specifically the information presented in Figure 3 indicates that for atrazine, metolachlor, and alachlor there is a limited temporal variation of concentration levels with a small tendency of decrease, especially for atrazine (values are in the 25th percentile and low whisker), slight temporal increase for metolachlor, and a steady condition for alachlor. The three outliers for atrazine indicate that in 68
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three wells the concentration of atrazine increased disproportionally during the last sampling which can happen as a result of point sources. The same is true for metolachlor; however, the event happened before the first sampling. Atrazine and DEA have equal median values; however, for DEA the differences of concentrations (the last minus the first sampling) for most of the wells are in the upper 75th percentile and farther (whisker) indicating a temporal tendency of increase. There are no outliers for DEA which is reasonable. Recent data (data are not shown) indicate that the trend of atrazine concentration decrease in the wells of Evros (Ardas Valley) is continued. Recently, conclusive temporal decreases of atrazine concentrations were reported for Iowa’s groundwater (5). The highest changes were found in alluvial aquifers, and these were consistent with the patterns of use and application rates of atrazine. This is probably also true for the Ardas Valley alluvial aquifers since lately, more frequently than before, corn monoculture has been interrupted by other crops such as sunflower and asparagus. These temporal variations of pesticide concentrations were also evident in individual wells of the study areas. Two such cases are presented in Figures 4 and 5. Figure 4 shows the temporal variation of atrazine and DEA concentrations in a well of Kavala. This is the only well in Kavala in which consistently quantifiable concentrations of both compounds were found at each sampling period. The concentrations of both compounds are still at low levels; however, the slight tendency of increase is evident. Figure 5 shows the temporal variation of atrazine and DEA concentrations in a well of the Ardas Valley. Both compounds show a decreasing trend; however, as expected the rate of decrease is higher for atrazine than for DEA. Among the 16 compounds (11 herbicides, 2 insecticides, and 3 conversion products of atrazine) monitored in selected wells of the five main corn-growing areas of Greece only nine compounds at concentrations equal to or higher than
the respective LOQs were found at least once; atrazine, DEA, alachlor, and metolachlor were the most frequently found. Pesticides were found in 48% of the monitored wells; however, in only 11% of the wells were residue levels > 0.1 µg/L (EU MPL level). Some of these exceedances of EU drinking water MPL level were transitory, most probably caused by point contamination sources located at the sites of these wells and related to inappropriate pesticide handling. However, for a few others, located in Evros (Ardas Valley), it is probable that preferential flow and to some extent leaching of pesticides from soils of corn-growing areas are the main causes of more persistent groundwater contamination. A few pesticides, at very low concentration levels, were found in rivers of the study areas. Thus the situation of ground and surface water quality is favorable throughout the corn producing regions of Greece with the exception of the Ardas Valley. However, in the latter area the temporal distribution patterns of pesticides in groundwater indicate a tendency toward a slight decrease in atrazine concentrations.
Acknowledgments This work was financially supported by the Greek Ministry of Agriculture via the Interreg II program and a research fund by Novartis, Crop Protection, Switzerland. The authors would like to express their appreciation to George Mastoridis of Novartis, Greece for his valuable assistance in the Evros samplings. The authors thank Dr. Christina Ligda for her valuable help in completing the statistical analysis of the data. The work was presented, as poster, at the 9th IUPAC Congress of Pesticide Chemistry, August 1998, London.
Literature Cited (1) Cohen, S. Z.; Creeger, S. M.; Carsel, R. F.; Enfield, C. G. In Treatments and Disposal of Pesticide Wastes; Krueger, R. F., Seiber, J. N., Eds; ACS Symposium Series No. 259, American Chemical Society: Washington, DC, 1984; pp 297-291. (2) Isenbeck-Schroter, M.; Bedbur, E.; Kofod, M.; Korig, B.; Schramm, T.; Mattheb, G. University of Bremen Monograph No. 91, 1997; Bremen, Germany. (3) European Crop Protection Association. Pesticides in groundwater: A critical assessment of residues in selected European Countries; Final Report; 1998.
(4) Riparbelli, C.; Scalvini, C.; Bersani, M.; Auteri, D.; Azimonti, G.; Maroni, M.; Salamana, M.; Carreri, V. In The Environmental Fate of Xenobiotics; Del Re, A. A. M., Capri, E., Evans, S. P., M. Trevisan, M., Eds.; Proceedings of the X Symposium Pesticide Chemistry, Sept 30-Oct 2, 1996; pp 559-566. (5) Kolpin, D. W.; Sneck-Fahrer, D.; Hallberg, G. R.; Libra, R. D. J. Environ. Qual. 1997, 26, 1007-1017. (6) Mass, R. P.; Kucken, D. J.; Patch, S. C.; Peek, B. T.; van Engelen, D. L. J. Environ. Qual. 1995, 24, 426-431. (7) Pasquarell, G. C.; Boyer, D. G. J. Environ. Qual. 1996, 25, 755765. (8) Blanchard, P. E.; Donald, W. W. J. Environ. Qual. 1997, 26, 16121621. (9) Pionke, H. B.; Glotfelty, D. E.; Lucas, A. D.; Urban, J. B. J. Environ. Qual. 1988, 17, 76-84. (10) Kolpin, D. W.; Barbash, J. E.; Gilliom, R. J. Environ. Sci. Technol. 1998, 32, 558-566. (11) Kolpin, D. W.; Thurman, E. M.; Goolsby, D. A. Environ. Sci. Technol. 1996, 30, 335-340. (12) Greek Department of Agriculture. Reports on Axios River Basin monitoring studies; 1993; 1995; 1998. (13) Patsias, J.; Papadopoulou-Mourkidou, E. J. Chromatogr. A 1996, 740, 83-98. (14) Papadopoulou-Mourkidou, E.; Patsias J. J. Chromatogr. A 1996, 726, 99-113. (15) EEC Drinking Water Directive 83/98. L330/32; EEC: Brussels, 1998. (16) Moreau-Kervenan, C.; Mouvet, C. J. Environ. Qual. 1998, 27, 46-53. (17) Muller, S. R.; Berg, M.; Ulrich, M. M.; Schwarzenbach, R. P. Environ. Sci. Technol. 1997, 31, 2104-2113. (18) Lerch, R. N.; Blanchard, P. E.; Thurman, E. M. Environ. Sci. Tecnol. 1998, 32, 40-48. (19) Burkart, M. R.; Simpkins, W. W.; Squillace, P. J.; Helmke, M. J. Environ. Qual. 1999, 28, 69-74. (20) Squillace, P. J.; Thurman, E. M.; Furlong, E. T. Water Resources Res. 1993, 29, 1719-1729. (21) Adams, C. D.; Thurman, E. M. J. Environ. Qual. 1991, 20, 540547. (22) Flury, M. J. Environ. Qual. 1996, 25, 25-45. (23) Mills, M. S.; Thurman, E. M. Environ. Sci. Technol. 1994, 28, 600-605.
Received for review November 8, 1999. Revised manuscript received October 9, 2000. Accepted October 17, 2000. ES991253Z
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