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a U.S. Geological Survey, 5231 S. 19th St., Lincoln, NE 68512
b U.S. Geological Survey, Placer Hall–6000 J St., Sacramento, CA 95819
c U.S. Geological Survey, 122 CivEng. Bldg., 500 Pillsbury Dr. SE, Minneapolis, MN 55455
* Corresponding author (jrvogel{at}usgs.gov).
Received for publication February 12, 2007.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMaterials and MethodsResults and DiscussionREFERENCES |
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Abbreviations: DEA, deethylatrazine • OA, oxygen analog
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionREFERENCES |
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The pesticide content in rain has been studied in a number of environments around the world and has been reviewed through 1992 and 1998, respectively, by Majewski and Capel (1995) and Van Dijk and Guicherit (1999). Many other studies in North America have been reported recently (Miller et al., 2000; Thurman and Cromwell, 2000; Park et al., 2001, 2002; Carlson et al., 2004; Aulagnier and Poissant, 2005; Goel et al., 2005; Waite et al., 2005), as have studies in Europe (Charizopoulos and Papadopoulou-Mourkidou, 1999; Polkowska et al., 2000; De Rossi et al., 2003; Asman et al., 2005).
This paper compares the spatial and temporal patterns of the occurrence of a large number of current-use pesticides and selected degradates in rain during two growing seasons at four locations across the USA (Capel et al., 2008). Study locations in the East and Midwest (Maryland, Indiana, Nebraska) are dominated by corn and soybean row crops, whereas cropland in the West (California) is dominated by almonds and vineyards with some corn and dairy. A more complete description of the watersheds can be found in Capel et al. (2008). The target chemicals (42 parent pesticides and 40 degradates) represent broad spectrums of pesticide classes, physical/chemical properties, usage amounts, and application rates and methods. This is the first study of current-use pesticides in rain that includes a large number of degradates as target chemicals. For each of the studied watersheds, the loads of individual pesticides in the rain were calculated and compared with the estimated application amounts of the same pesticides in the watersheds at three different scales (local, intermediate, and broad) to illustrate the importance of the atmosphere in the overall mass transport of pesticides in the environment.
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Materials and Methods |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionREFERENCES |
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Rain samples were filtered through a Supor (Pall Corporation, East Hills, NY) membrane filter (0.45 µm pore diameter), split, and transferred to amber glass bottles that were shipped on ice overnight to USGS laboratories for analysis. The pesticides were isolated from the water by solid-phase extraction and analyzed using gas chromatography–mass spectrometry and high-performance liquid chromatography–mass spectrometry. The target chemicals included 21 insecticides, 18 herbicides, three fungicides, and 40 degradates (see Capel et al. [2008] for a complete listing of parent and degradate pesticides and selected pesticide properties). The surrogates diazinon-d10 and alpha-HCH-d6 were spiked into each rain sample at the laboratory, with mean recoveries of 102% and 90%, respectively. More complete details on the sampling, analytical, and quality-control methods can be found in Capel et al. (2008).
Pesticide use estimates were compiled for each of the study areas for three different areal scales (Capel et al., 2008). The areas comprising the three different scales in Indiana, Nebraska, and California corresponded to nested watersheds surrounding the sampling site and were deemed appropriate to represent pesticide use because of the consistent agricultural land uses in these areas. In Maryland, county-level and multiple county-level pesticide use represented the intermediate- and broad-scale areas because of the varied land-use patterns at larger scales. At the Eastern and Midwestern sites (Maryland, Indiana, and Nebraska), pesticide use in the local-scale watershed (1.5–33 km2) was estimated by interviewing the individual farmers about the crops they planted and what pesticides they applied and when during 2003 and 2004. Pesticide use in the intermediate scale (about 250–1000 km2) and broad scale (about 500–30,000 km2) watersheds that encompassed the sampling locations was estimated using the 1997 county-wide use estimates (Thelin and Gianessi, 2000) for Maryland, Indiana, and Nebraska. In Maryland, pesticide use for Kent County was used for the intermediate-scale data, and the summed pesticide use for Harford, Baltimore, Cecil, Kent, and Queen Anne's Counties were used for the broad-scale data. Although pesticide use patterns may have changed and many new pesticides may have been introduced between 1997 and the timing of this study, the county-wide estimates represent the most recent widespread pesticide use data available. These data were based on average usage for different crop types within an area and may not necessarily represent agricultural practices at a specific location. For California, the pesticide use estimates were obtained from the California Department of Pesticide Regulation pesticide use database (California Department of Pesticide Regulation, 2004). Because the upper part of the Merced River basin is forested, only the lower part downstream from McSwain Dam was used for calculating the intermediate-scale pesticide use data. More complete details on the pesticide use can be found in Capel et al. (2008).
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Results and Discussion |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionREFERENCES |
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Maryland
Agricultural products in the Maryland study area were a mixture of dairy, corn, sweet corn, soybean, and alfalfa. Metolachlor, atrazine, and simazine were the only herbicides reportedly used in the immediate area around the rain sampler (Capel et al., 2008). Metolachlor was detected in every sample, with the largest concentrations occurring during late April through the end of May, concurrent with the planting of corn and soybeans (Fig. 1
; Table 2A
). This same seasonal pattern occurred for atrazine and simazine. The concentrations of simazine in rain were much lower than those of metolachlor or atrazine despite similar reported use amounts of these three herbicides in the local-scale watershed. This can be explained primarily by the vapor pressure of simazine (2.95 x 10–6 Pa at 25°C), which is three orders of magnitude lower than metolachlor's (4.19 x 10–3 Pa at 25°C) and one order of magnitude less than atrazine's (3.85 x 10–5 Pa at 25°C).
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Three other herbicides used on corn and soybeans—pendimethalin, acetochlor, and alachlor—were detected in the rainfall. Although no applications were reported in the local-scale watershed during the study, all three of these herbicides were used on the intermediate- and broad-scale watersheds. The maximum concentrations for all of these herbicides followed the same temporal trends as were seen with metolachlor, atrazine, and simazine, with the highest concentrations occurring in April and May of each year, concurrent with the planting of crops in the area.
Dacthal had no reported agricultural use in the local-scale area and only minimal agricultural use (0.15 Mg yr–1 was reported in the broad-scale area, but there may have been unreported usage in commercial nurseries near the study site). Dacthal was detected in 74% of the samples but at low concentrations (maximum: 0.009 µg L–1; median: 0.002 µg L–1 [estimated]; laboratory reporting limit = 0.003 µg L–1) (Tables 1 and 2A).
Indiana
The primary crops in the Indiana study area were corn, soybeans, and alfalfa. The rain sampling site was in an agricultural area on a fence-line between a corn field and a soybean field (rotated oppositely in each field). Pesticide use in the local-scale watershed in 2003 consisted primarily of atrazine (245 kg) and chlorpyrifos (103 kg) with minor amounts of metolachlor (5 kg) and acetochlor (3 kg). None of these and none of the other targeted pesticides that were analyzed was reportedly used in the local-scale area in 2004.
The herbicides atrazine, acetochlor, and metolachlor were detected in >80% of all samples (Table 2B) and in every sample collected in 2003. The greatest concentrations were detected between mid-April and mid-June, which corresponded to the period of application (Fig. 2 ; Table 2B).
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Three other herbicides that had no reported use in the local-scale watershed but had >50 Mg yr–1 use in the broad-scale watershed were pendimethalin, alachlor, and dimethenamid. Pendimethalin was detected in only 31% of the samples, mostly in 2003, and was detected only twice in 2004 (Table 2B). Concentrations of pendimethalin were considerably lower than those of atrazine or acetochlor, with the exception of the 29 Apr. 2003 sample (0.48 µg L–1). Because pendimethalin is usually incorporated into the soil, it is less available for volatilization into the atmosphere than surface-applied chemicals like atrazine, acetochlor, and alachlor. Alachlor was detected in 58% of rain samples but at concentrations that were generally one to two orders of magnitude lower than the locally applied pesticides atrazine and acetochlor. Although intermediate- and broad-scale watershed use of alachlor (1.5 and 99 Mg yr–1, respectively) was less than half that of pendimethalin (3.6 and 220 Mg yr–1, respectively), alachlor's detection frequency and median concentration were greater (Table 2B), probably because of the difference in their physical/chemical properties. This means that pendimethalin sorbs more strongly to soil and is less likely to volatilize. It also means that airborne pendimethalin is more likely to partition onto particles. Dimethenamid was not detected in 2003 and was detected only twice in 2004. There is little information available in the literature on the physical and chemical properties or the environmental fate of dimethenamid.
Chlorpyrifos was the only insecticide reportedly used in the local-scale watershed in 2003 (103 kg yr–1). Overall, chlorpyrifos was detected in 54% of all samples collected (Table 2B). The number of chlorpyrifos detections in 2004 (when there was no reported use in the local-scale watershed) dropped off significantly, with detections in 21% of the samples. These data indicate that chlorpyrifos may not be transported as far as atrazine and acetochlor partially because of photochemical degradation. Several other insecticides that had no reported use in the local-scale watershed were detected in rain, including malathion (54%), diazinon (31%), carbaryl (25%), and phosmet (20%) (Table 2B).
Nebraska
The primary crops grown in the Nebraska study area were corn, soybeans, and alfalfa. Two herbicides (acetochlor and atrazine) and one insecticide (chlorpyrifos) had reported use at all three study-area scales in 2003 and 2004. Metolachlor, atrazine, and acetochlor were the most heavily used herbicides in the broad-scale watershed (473, 462, and 204 Mg yr–1, respectively). Compared with 2003, the amounts of atrazine and acetochlor used in the local-scale watershed were greater in 2004 (15 kg compared with 12 kg and 38 kg compared with 31 kg, respectively). This usage was reflected in the detection frequency and concentrations of these herbicides in rain (Fig. 3
). The acetochlor concentrations in April and May 2004 were the highest recorded at any of the four sites in this study (maximum of 4.39 µg L–1) (Table 2C). The highest concentrations of atrazine and acetochlor were observed in a small rain event that occurred shortly after herbicide application to nearby fields.
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California
The California site contrasted with the other three study sites in that a wide variety of crops were grown (grapes, almonds, corn). Additionally, the growing season and associated pesticide use were reported throughout the year. As is typical, December through March was the rainy season, and rainfall rarely occurred during the summer months. A third difference was that three sites (referred to as upper, middle, and lower, corresponding to their position in the watershed) were sampled instead of one, and the rain samples were event samples rather than weekly composites. For purposes of discussion in this paper, samples from 1 Feb. 2003 through 30 Apr. 2003 are considered to represent the 2003 rainy season (samplers were not operating until February), and samples from 1 Dec. 2003 through 30 Apr. 2004 are considered to represent the 2004 rainy season. Insecticides were used more frequently than herbicides in this study area, although both were used extensively. Nine pesticide parent compounds were detected in more than 50% of the samples: four herbicides, three insecticides, and two fungicides (Table 2D).
Simazine had the highest reported use of the herbicides at all watershed scales in 2003 and 2004. This usage was also reflected in simazine's detection frequency (100%) and the maximum (15.6 µg L–1) and median (0.040 µg L–1) concentrations. Metolachlor and trifluralin had similar amounts applied in 2003 in the local-scale watershed, but trifluralin had the higher use at the intermediate- and broad-scale watersheds. Trifluralin was detected in 39% of the samples with a median concentration of <0.009 µg L–1, which was much lower than the other highly used herbicides. Trifluralin is relatively volatile (vapor pressure, 0.0147 Pa at 25°C), is usually incorporated into the soil at the time of application, and is photoreactive (Woodrow et al., 1978; Mongar and Miller, 1988; Soderquist et al., 1975; Woodrow et al., 1983), which may account for its low detection frequency and concentrations in rain.
Pendimethalin and dacthal had no reported use in the local-scale watershed, but both were used in the intermediate- and broad-scale areas. Pendimethalin had the second-highest use of all herbicides in the broad-scale area (30 Mg yr–1) and was detected frequently (78%), with a median concentration of 0.021 µg L–1. Dacthal use was considerably lower (4.6 Mg yr–1) but was detected in every rain sample, with a median concentration of 0.009 µg L–1.
Of the herbicides commonly used on corn and soybeans and detected at the other three study sites (acetochlor, alachlor, atrazine, and metolachlor), none were reportedly used in the local-scale watershed, and there was minimal or no reported use in the intermediate- and broad-scale watersheds. Atrazine was detected in only one sample, and alachlor and acetochlor were detected in none of the samples. Metolachlor was detected in 61% of the rain samples collected from the California site but at low concentrations (only 17% of samples >0.01 µg L–1).
The insecticides diazinon, chlorpyrifos, and carbaryl were detected in more than 70% of the samples; diazinon was present in all of them. All three of these insecticides are typically applied on various crops throughout the year. Major applications of diazinon and chlorpyrifos occurred in January and February for over-wintering insect control in dormant orchards. Chlorpyrifos and carbaryl typically are applied to other crops during this time. Chlorpyrifos was the most-applied insecticide in the local-, intermediate-, and broad-scale study areas. Diazinon was not used in the local-scale watershed, and its total use in the broad-scale area was about one third that of chlorpyrifos, yet concentrations of diazinon in rain were almost always greater. Diazinon and chlorpyrifos have moderate vapor pressures (3.33 x 10–4 and 2.27 x 10–3 Pa at 25°C, respectively [Capel et al., 2008]), and both are estimated to have short half-lives in air (4.1 and 6.3 h, respectively [Howard et al., 1991]). Diazinon typically has a longer soil half-life than does chlorpyrifos (30 compared with 100 d), which would make it available to move into the atmosphere over a longer period of time. Carbaryl is used as a dormant orchard insecticide but is also used on rice, fruit trees, vegetables, grapes, and in nonagricultural areas (California Department of Pesticide Regulation, 2004). The vapor pressure of carbaryl is similar to diazinon (1.60 x 10–4 Pa at 25°C), but carbaryl has a shorter typical soil half-life (10 d). Carbaryl undergoes photochemical degradation at a much slower rate than do the other two insecticides (Brahmia and Richard, 2003). Carbaryl was observed in every air sample over a growing season in an agricultural area (grapes, fruit trees, and corn) in Washington (Ohrt et al., 2006).
The fungicides iprodione and myclobutanil were used in California to a much greater extent than in the other study areas (Capel et al., 2008). Only iprodione had any reported use in the local-scale watershed and was detected in 83% of the samples (Table 2D). The highest concentrations occurred during February of both years (Fig. 6 ), with an estimated median concentration of 0.074 µg L–1. Myclobutanil, which was not used in the local-scale watershed, was detected in 74% of the rain samples but only in February through April because it is used only after the almond trees bud. The median concentration of myclobutanil was 0.014 µg L–1. The physicochemical properties of both fungicides are similar (Capel et al., 2008). Iprodione was applied in greater quantities than myclobutanil at all watershed scales.
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The samples collected in this study were analyzed for 40 degradates. The most frequently detected were deethylatrazine (DEA) (from atrazine), chlorpyrifos oxygen analog (OA), diazinon OA, malathion OA, and 1-napthol (primarily from carbaryl). Three distinct patterns emerged from analysis of the degradate data. First, DEA was detected in about two thirds of the samples collected at the Midwestern and Eastern study sites (Maryland, 59%; Indiana, 73%; and Nebraska, 75%), but DEA was detected only once in California. The occurrence of DEA in rain samples mirrors the use of atrazine at the study sites. Second, detections of the OAs of chlorpyrifos, diazinon, and malathion occurred primarily in California. Malathion OA also was detected in samples from Indiana (36%) and Nebraska (18%), but chlorpyrifos OA was rarely detected at the Midwestern and Eastern sites, and diazinon OA was not detected. The detection frequencies and concentrations of the detected OA degradates usually reflected the amount of the parent compound used. Third, degradates of the acetanilide herbicides (acetochlor, alachlor, and metolachlor) were rarely detected in rain. The ethane sulfonic acid, oxanilic acid, and the sulfynil acetic acid degradates of the acetanilide herbicides are frequently found in surface and ground waters at relatively high concentrations (Scribner et al., 2004). The formation of these degradates is a microbially mediated process (Barbash, 2003) that would not be expected to occur in the atmosphere or falling rain droplets. Because these compounds are organic acids, they do not undergo volatilization in their ionic forms from soil or surface water.
The degradate fraction is the molar ratio of a degradate to its parent compound plus all degradates. The degradate fraction is calculated using Eq. [1] and molar units for all concentrations. This equation assumes a stoichiometric degradation and makes no assumptions about how the parent compound degrades.
 | [1] |
Figure 7 shows the degradate fraction for DEA in the Maryland, Indiana, and Nebraska rain samples and the cumulative rainfall amounts in 2003 and 2004. Deethylatrazine was detected in only one California rain sample and is not included in this graph. Deisopropyl atrazine and other atrazine degradates were not analyzed in this study and are not included in the DEA fraction calculation. The DEA fraction tended to gradually increase after the herbicide applications in the spring and peaked near mid-summer, then decreased rapidly or was no longer detected. The peak DEA fraction for Maryland, Indiana, and Nebraska samples in 2003 was measured on 8 July 2003 (degradate fraction, 0.50; last detection of atrazine and DEA), 15 July 2003 (0.57), and 29 July 2003 (0.71), respectively. In 2004, peak DEA fractions for Maryland, Indiana, and Nebraska samples were measured on 15 June 2004 (0.55), 8 June 2004 (0.36), and 20 July 2004 (0.68), respectively. Compared with 2003, the peak DEA fraction occurred sooner at about the same magnitude in 2004 in Maryland, occurred sooner with a lower peak value in 2004 in Indiana, and occurred at a similar time with similar magnitude in 2004 in Nebraska. The interannual differences may reflect different cropping patterns, precipitation, timing of application, or other climate variables. The largest DEA fraction was observed in Nebraska during both years. The gradual upward trend in the DEA fraction was not readily observable in a plot of DEA concentration values (not shown) in which concentrations began to decline shortly after the application period in most instances.
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Pesticide Deposition
The total weekly (or rain event in California) wet deposition of each pesticide analyzed in the study was calculated using the measured concentrations and total precipitation amounts (Table 2). Total wet deposition of pesticides in California was calculated using data from the middle site only. The total wet deposition at the Maryland, Indiana, and Nebraska sites was dominated by herbicides, which accounted for at least 91 to 98% of the total pesticide mass deposited (Fig. 9
). This was not unexpected because herbicide use greatly exceeded insecticide use at these sites where corn and soybeans were the predominant crops. The largest contributors to the depositional mass of herbicides at these three sites were atrazine, acetochlor, and metolachlor (plus pendimethalin in Maryland). Carbaryl, malathion, malathion OA, and chlorpyrifos were the insecticide compounds composing the largest percentage of the insecticide mass deposited by the rain. At the middle site in California, 21% of the total pesticide wet deposition consisted of herbicides in 2004, compared with 94% of total pesticide deposition in the partially monitored season of 2003 (most of this herbicide deposition was from one event and was probably caused by drift from a local application). In California in 2004, the herbicides simazine (11%) and pendimethalin (4%) accounted for about three fourths of the herbicide component of the total deposited mass of pesticides in rain; however, insecticides accounted for 60% of the total wet deposition at the California site in 2004. Insecticides that contributed most of the total mass of pesticides in all wet deposition in California included diazinon, methidathion, and chlorpyrifos. Additionally, the fungicide iprodione ranked third in mean yearly wet deposition.
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Local versus Long-Range Sources
The data from this study show that proximity to application areas strongly influences the occurrence of pesticides in rainfall. For example, in Nebraska the local-scale use of trifluralin in 2003 resulted in high detection rates and concentrations in rain during the application season. Majewski et al. (1998) found similar results for trifluralin in airborne pesticide residues along the Mississippi River. The absence of local-scale pesticide use at the Indiana site in 2004 (for pesticides that were analyzed during this study) was likely largely responsible for a 70% decrease in atrazine wet deposition and 63% decrease in DEA wet deposition in 2004 compared with 2003. In fact, most pesticides having a detection frequency >10% were detected less frequently in 2004 than in 2003 at the Indiana site, where only prometon, malathion, and malathion OA were detected more frequently in 2004.
Although local pesticide use is a major determinant of the types and mass of pesticides present in wet deposition, regional- and long-range atmospheric transport may be responsible for a portion of the mass loading of some pesticides in some watersheds. Insecticides and herbicides were detected in rain samples in watersheds with no reported local-scale use of those compounds. Insecticides detected in samples from areas with no reported local-scale use included malathion, carbaryl, diazinon, and methidathion, indicating long-range atmospheric transport from use in the intermediate- or broad-scale watershed. Malathion and malathion OA were detected in Nebraska (sporadic, low-level detections) and in Indiana (consistent, low-level detections during July and August of both years) despite the absence of reported agricultural use of the insecticide at any scale in Nebraska and only broad-scale use reported in Indiana. Assuming accurate pesticide usage reports, the malathion and malathion OA detections were likely a result of long-range atmospheric transport of the insecticide into the study area. Carbaryl also had the third highest annual mean wet deposition of all insecticides in Nebraska (after chlorpyrifos and azinphos-methyl, both of which had greater intermediate- and broad-scale use), even though there was no reported local use of carbaryl.
In California, diazinon was detected in all rain samples collected, even though there was no reported local-scale use but substantial use at the intermediate scale. This result indicates that intraregional atmospheric transport throughout the rainy season was the source of diazinon in rain. Diazinon was detected in the stream water of Mustang Creek, which drains the local-scale area. Because there was no use in the watershed, the only measured or reported source of the pesticide in the watershed was from the rainfall (Domagalski et al., 2008). As evidence for intraregional transport, the highest concentrations in rain for carbaryl and methidathion at the California sampling sites occurred on 16 Dec. 2003 (Table 2D), well before the dormant orchard spraying normally begins in the local-scale area. These insecticides were used on other crops at the intermediate and broad scales and likely were transported atmospherically into the local-scale area.
Several herbicides were found in rain falling in areas with no reported local use of the compounds, including pendimethalin, acetochlor, and dacthal. Pendimethalin was found in multiple samples at all four study areas, even though no local use was reported for any of the sites. There was substantial use of pendimethalin at the intermediate scale of all four study areas; in mass, applied pendimethalin ranked fourth nationally among the pesticides analyzed in this study (Table 1). This result indicates that the mid- to long-range transport of pendimethalin is important. Similarly, acetochlor was detected in rain at the Maryland site where there was no reported local-scale use. There was, however, substantial use in the intermediate- and broad-scale watersheds. When compared with acetochlor concentrations in rain in the other corn/soybean areas in Indiana and Nebraska, however, the median acetochlor concentrations measured in Maryland were at least five to seven times lower, consistent with a longer transport distance from the source to the sampling site. Dacthal was detected at low levels at every site and in 70% of all samples. The low concentrations observed at all the study sites throughout each sampling season indicate that dacthal is well mixed in the atmosphere and likely undergoing long-range transport. Other studies have shown dacthal to be environmentally stable, widely detected in the atmosphere (Foreman et al., 2000; Majewski et al., 2000), and prone to long-range transport (Rice and Chernyak, 1997).
Timing of Pesticide Deposition
Figure 10
illustrates that a large percentage of the total wet deposition at these sites is often related to a few weekly samples or storm events. Generally, the substantial deposition is associated with large storms that occur shortly after pesticide applications in the local area. Most of the instances of this phenomenon at the four sites analyzed during this study involved herbicides (simazine, atrazine, acetochlor, metolachlor, and alachlor), although one storm in California in December 2003 deposited a large mass of two insecticides (diazinon and methidathion). During the week of 20 Apr. 2004, in Maryland, metolachlor and atrazine deposition (35 µg m–2) was 26% of the year's total wet deposition of pesticide at that site. In Indiana, wet deposition of atrazine and acetochlor during the week of 27 May 2003 accounted for 37% (171 µg m–2) of that year's wet deposition total. In Nebraska, wet deposition of atrazine, acetochlor, metolachlor, and alachlor during the weeks of 29 Apr. 2003, 4 May 2004, and 18 May 2004 contributed 66% (166 µg m–2), 37% (233 µg m–2), and 18% (114 µg m–2), respectively, of the year's total wet deposition of all pesticides. From individual storm data in at the middle site in California, simazine accounted for 93% (113 µg m–2) of total pesticide wet deposition between February and April 2003. From a single storm sample collected 16 Dec. 2003, the mass of the insecticides diazinon and methidathion accounted for 31% (25 µg m–2) of the total wet deposition of all pesticides during the rainy season of 2003 to 2004 (November through April).
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionREFERENCES |
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionREFERENCES |
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nik. 2000. Organic pollutants in precipitation: Determination of pesticides and polycyclic aromatic hydrocarbons in Gda
sk, Poland. Atmos. Environ.
34
:1233–1245.This article has been cited by other articles:
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  P. D. Capel, K. A. McCarthy, and J. E. Barbash National, Holistic, Watershed-Scale Approach to Understand the Sources, Transport, and Fate of Agricultural Chemicals J. Environ. Qual., May 1, 2008; 37(3): 983 - 993. [Abstract] [Full Text] [PDF]
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D. A. Alvarez, W. L. Cranor, S. D. Perkins, R. C. Clark, and S. B. Smith Chemical and Toxicologic Assessment of Organic Contaminants in Surface Water Using Passive Samplers J. Environ. Qual., May 1, 2008; 37(3): 1024 - 1033. [Abstract] [Full Text] [PDF]
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T. C. Hancock, M. W. Sandstrom, J. R. Vogel, R. M.T. Webb, E. R. Bayless, and J. E. Barbash Pesticide Fate and Transport throughout Unsaturated Zones in Five Agricultural Settings, USA J. Environ. Qual., May 1, 2008; 37(3): 1086 - 1100. [Abstract] [Full Text] [PDF]
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J. L. Domagalski, S. Ator, R. Coupe, K. McCarthy, D. Lampe, M. Sandstrom, and N. Baker Comparative Study of Transport Processes of Nitrogen, Phosphorus, and Herbicides to Streams in Five Agricultural Basins, USA J. Environ. Qual., May 1, 2008; 37(3): 1158 - 1169. [Abstract] [Full Text] [PDF]
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