Environ. Sci. Technol. 2005, 39, 2952-2959
Gas-Phase Concentrations of Current-Use Pesticides in Iowa AARON M. PECK† AND KERI C. HORNBUCKLE* Department of Civil and Environmental Engineering, University of Iowa, Iowa City, Iowa 52242
Local and regional atmospheric transport of current-use pesticides is an important source of these compounds to nontarget plants and ecosystems. Current-use pesticides were measured at urban, rural, and suburban sites in eastern Iowa during 2000-2002. The most detected compounds were hexachlorobenzene and trifluralin, which were found in 89% and 78% of the samples, respectively. As expected, many pesticides showed a strong seasonal trend with the most detections and highest concentrations occurring during the spring and early summer. The average detected concentrations of five heavily used herbicides were 0.52 ng/ m3 for trifluralin, 4.6 ng/m3 for acetochlor, 2.3 ng/m3 for metolachlor, 1.1 ng/m3 for alachlor, 1.7 ng/m3 for pendimethalin, and 1.2 ng/m3 for atrazine. The most frequently detected insecticides were phorate and chlorpyrifos, which were found in 20% and 19% of the samples, respectively. The average phorate and chlorpyrifos concentrations were 25 ng/m3 and 1.0 ng/m3, respectively. The maximum phorate concentration, the highest measured for all pesticides, was 91.2 ng/m3. The most frequently detected current-use fungicides were chloroneb and etridiazole, which were found in 14% and 10% of the samples, respectively.
Introduction Intensive farming practices in Iowa include the use of synthetic pesticides. In 2002, approximately 11 000 tons of five of the most heavily used herbicides (atrazine, trifluralin, acetochlor, metolachlor, and pendimethalin) were applied to Iowa farmland (1). Some portion of the applied pesticides is expected to move offsite via leaching, runoff, and volatilization. Volatilization processes not only result in reduced efficiency in pest control, but also have the potential to adversely impact terrestrial and aquatic natural systems far from the intended target. Losses to the atmosphere occur during application and through volatilization from plant surfaces and soil after application. Volatilization losses depend on a variety of factors including physical-chemical properties of the pesticide (i.e., Henry’s law constant, vapor pressure, octanol-air partition coefficient, and aqueous solubility), soil properties (i.e., moisture and organic carbon content), farming practices (i.e., tillage and application techniques), and meteorological factors (i.e., precipitation, temperature, humidity, and wind speed) (2-7). Many reports have shown that loss to air can be significant. Rice and co-workers studied volatilization losses of several * Corresponding author phone: (319)384-0789; fax: (319)335-5660; e-mail:
[email protected]. † Current address: National Institute of Standards and Technology, Hollings Marine Laboratory, 331 Fort Johnson Road, Charleston, SC 29412. 2952
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pesticides from soil. After 21 days, they measured cumulative losses of 14.1% for trifluralin, 3.6% for atrazine, 6.5% for metolachlor, and 10.4% for chlorpyrifos (2). In a similar study, Glotfelty and co-workers found that pesticide volatilization losses could be predicted within an order of magnitude from the pesticides’ vapor pressure, aqueous solubility, and organic carbon partitioning coefficient. They measured cumulative volatilization losses of 18% for alachlor, 2% for atrazine, and 1% for simazine from soil (3). A 30% cumulative loss of trifluralin from soil was measured from a wind tunnel system after 8 days (4). The cumulative loss of atrazine and alachlor were shown to double when temperature increased from 25 to 35 °C in glass agrosystem chambers. After 35 days at 35 °C, 8% of the atrazine applied and 16% of the alachlor applied to bare soil were lost (5). Whang et al. reported that the volatilization losses of fonofos, chlorpyrifos, and atrazine were less for a conventionally tilled field (27, 12, and 1.9% losses) compared to a no-till field (62, 49, and 2.5% losses) (6). Prueger et al. found that after 10 days, 22% of broadcast applied metolachlor was lost from a central Iowa field while banded application reduced the loss to 6% (7). In that study, the metolachlor concentrations measured at 3 m above the field surface 2 h after application were ∼190 ng/m3 and ∼3000 ng/m3 over the banded and broadcast fields, respectively. After 7 days of volatilization, measured air concentrations of metolochlor were ∼12 ng/m3 and ∼90 ng/m3, over the same banded and broadcast fields, respectively. Iowa is one of the most intensively agricultural regions in the world, with ∼90% of the total land area dedicated to farming (16). Agricultural production in Iowa has involved the use of pesticides for at least 50 years. Despite this, few measurements of current-use pesticides in Iowa air have been reported and none for seasons other than spring and summer. In a study conducted April-September 1995, current-use herbicides were detected in air more frequently than insecticides at sites in Iowa City, IA and Cedar Rapids, IA (8). The most frequently detected herbicides in air were trifluralin, metolachlor, atrazine (and metabolites of atrazine), acetochlor, pendimethalin, and alachlor. In a study conducted from October 1996 to September 1997 in eastern Iowa, atrazine and cyanazine were detected in three spring and summer air samples (9). In a study on the Mississippi River, the most important factor controlling the atmospheric concentration of trifluralin, alachlor, and fonofos was the proximity to use regions. The highest pesticide concentrations were measured along the river over segments with the highest rates of use within 40 km on each side of the river (10). The objective of this study was to measure current-use herbicides, insecticides, and fungicides in the gas-phase at three sites in Iowa. To our knowledge, this is the first study to report these compounds in an agricultural area over this many seasons. A list of all 51 herbicides, insecticides, and fungicides are listed in Tables SI-1-SI-3 in the Supporting Information with chemical structures, trade names, application rates in Iowa, and primary target crops.
Methods Chemicals. All solvents were Fisher Pesticide Grade (Fair Lawn, NJ) with the exception of ethyl acetate, which was Fisher Optima (Fair Lawn, NJ). 100-200 mesh Florisil was obtained from Acros Organics (Fair Lawn, NJ). All pesticide standards were obtained from Chem Service (West Chester, PA). Deuterated polycylic aromatic hydrocarbons (d10fluoranthene, d10-acenaphthene, d10-phenanthrene, and d10pyrene) were obtained from Cambridge Isotope Laboratories (Andover, MA). 10.1021/es0486418 CCC: $30.25
2005 American Chemical Society Published on Web 03/16/2005
FIGURE 1. Sampling sites in eastern Iowa. Air Sampling. Air samples were collected at three sites in eastern Iowa (Figure 1). Samples were collected at the Iowa Air Monitoring Station (IA-AMS) in Iowa City, IA, from April 2001 to July 2002; at Metro High School in downtown Cedar Rapids, IA, from October 2001 to May 2002; and at The University of Iowa Observatory outside of Hills, IA, from September 2000 to September 2001. There were no samples collected during December 2000-January 2001 and JanuaryFebruary 2002. A total of 136 samples were analyzed from these sites. Eighty-five samples were from IA-AMS, 41 samples were from Hills, and 10 samples were from Metro. Each air sample passed through a Gelman Type A/E glass fiber filter (Ann Arbor, MI) and the gas phase was collected on ∼40 g Supelco Amberlite XAD-2 resin (St. Louis, MO). The average flow rates ranged between 0.2 m3/min and 0.8 m3/min. Samples were collected for approximately 24 h and the average volume of air sampled was 835 m3. XAD-2 resin is a styrene-divinylbenzene sorbent that retains all but the most volatile organic compounds (17). XAD has been previously used to collect a variety of pesticides including diazinon (18), chlorpyrifos (18, 19), diazinon (19), disulfoton (19), fonofos (19), mevinphos (19), phorate (19), terbufos (19), cyanazine (20), alachlor (20), metolachlor (20), simazine (20), atrazine (20-23), deethyl atrazine (23), deisopropyl atrazine (23), molinate (21, 22), hexachlorobenzene (21, 22), trifluralin (18, 21, 22), methyl parathion (24), dichlorvos (25), and isofenphos (26). In addition to these studies, considerable work has been done to evaluate the trapping efficiency of gas-phase organic contaminants on sorbents such as XAD-2 resin (17). Pankow and co-workers developed a model to predict compound specific safe sampling volumes for air sampling with styrene-divinylbenzene sorbents from the compound’s subcooled liquid vapor pressure and the mass of sorbent used (17). From the results of these estimation calculations, all of the compounds in this study were retained. Additional information on the estimated safe sampling volumes and prediction methods are provided in the Supporting Information.
The XAD-2 resin was precleaned with 24-h Soxhlet extractions with methanol, acetone, dichloromethane, hexane, and 50/50 hexane/acetone prior to sampling. The XAD-2 resin was put into stainless steel sampling cartridges in the laboratory. The resin-filled cartridges were stored in aluminum canisters sealed with Teflon tape and sealed plastic bags during transport to and from the sampling locations. Sample Extraction and Cleanup. The sample extraction method has been described previously (27, 28). Prior to extraction, 100 µL of a d10-fluoranthene surrogate standard solution (0.82 ng/µL) was added to each sample. The XAD-2 resin was extracted for 24 h in a Soxhlet apparatus with ∼350 mL hexane/acetone (50/50 v/v). The extract volume was then reduced to ∼100 µL using rotary evaporation followed by evaporation with nitrogen. Each sample extract was passed through a Pasteur pipet containing ∼0.75 g 100-200 mesh Florisil with 4 mL ethyl acetate to provide cleanup as described by Foreman et al. (8). After cleanup, the sample extract was reduced to ∼100 µL with nitrogen evaporation and 100 µL of an internal standard solution containing d10acenaphthene (2.5 ng/µL), d10-phenanthrene (2.4 ng/µL), and d10-pyrene (2.2 ng/µL). Instrumental Analysis. Each sample was analyzed with an HP6890 gas chromatograph coupled to an HP5973 mass selective detector with electron impact ionization (GC/EIMS) operating in selected ion monitoring (SIM) mode. A 30-m 5% phenyl methyl siloxane capillary column was used (HP-5MS; 250-µm I. D., 0.25-µm film thickness). Samples were injected splitless with an inlet temperature, pressure, and total flow rate of 250 °C, 9.96 psi, 63.7 mL/min, respectively. A constant 1.2 mL/min column flow rate was used. The oven temperature was ramped from 60 to 210 °C at 1.5 °C/min followed by a 13 °C/min ramp to 300 °C. The final temperature (300 °C) was held for 10 min. The MS transfer line temperature was 280 °C. The MS quadrupole and source temperatures were 150 °C and 230 °C, respectively. The electron energy was 70 eV. All analytes were identified by retention time and with two characteristic ions. One ion VOL. 39, NO. 9, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Average pesticide recoveries with standard errors through the Florisil cleanup method.
TABLE 1. Herbicide Concentrations in Iowa Air compound
median (ng/m3)a
range (ng/m3)
average ( 95% CI (ng/m3)b
detections
MRL (ng/m3)
trifluralin chlorthal metolachlor acetochlor alachlor atrazine pendimethalin prometon EPTC atraton DEA pebulate cycloate propyzamide butachlor tri-allate simazine propachlor vernolate propazine butylate molinate DIA chlorpropham napropamide ametryne simetryn metribuzin prometryne terbutryne diphenamid
0.040 0.0036
