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| USGS Water Science Center, Minnesota |
Wet Atmospheric Deposition of Pesticides
in Minnesota, 1989-94
Originally published as Water-Resources Investigations Report 97-4026
Illustrations
Tables
Abstract
All of the rain samples during the growing season had
detectable quantities of at least one pesticide, but most of the pesticides
were only infrequently observed. The most frequently detected compounds
were the herbicides alachlor, atrazine, cyanazine, and metolachlor, and
in 1994, its first year of registration, acetochlor. Peak concentrations
of most herbicides in rainfall occurred shortly after their application
periods in the spring. Peak concentrations of most of the insecticides
occurred later in the summer.
The majority of the wet depositional flux of pesticides occurred between
early May and October. The annual wet depositional flux of pesticides is
5 orders of magnitude less than is the "annual flux" normally applied on
an agricultural field, although some of the pesticides in rain are deposited
in areas far removed from agricultural fields. The annual variability in
pesticide deposition can be explained by year-to-year differences in climate
and pesticide use patterns. The one sampling site (Lamberton) that was
in an area dominated by row crop agriculture showed a significantly greater
annual flux than the other four sampling sites that were in areas of either
urbanization or less intensive agricultural. Regional deposition, away
from a local source, can be inferred from these four sites because they
have annual pesticide fluxes that are very similar for any given year.
The observation of agricultural pesticides (not registered for home and
garden use) in rain and storm runoff in the urban area indicates their
transport from areas of agricultural use. Urban areas may be the best locations
for assessing changes in regional use and deposition of agricultural pesticides.
The pesticide fluxes in the streams out of the small three watersheds
was compared to the pesticide flux into the watersheds in rain. The data
indicate that flux into the watersheds from the rain is generally much
greater than the flux from the watersheds in the streams. Therefore, a
large fraction of the pesticides deposited in rain is retained within the
watersheds. For the urban area, this is on the order of 98 percent for
the four most commonly observed herbicides in rain and runoff.
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Introduction
Concerns about the contamination of the atmosphere by
organic chemicals have increased over the last four decades (Daines, 1952;
Eisenreich and others, 1981a,b; Richards and others, 1987; Kurtz, 1990;
Goolsby and others, 1993). Various pollutants, such as polychlorinated
biphenyls (Eisenreich and others, 1981b; Strachan and Eisenreich, 1990;
Chan and Perkins, 1989), polyaromatic hydrocarbons (Pankow and others,
1984; Ligocki and others, 1985a,b; Van Noort and Wondergem, 1985; Czuczwa
and others, 1988; Leuenberger and others, 1988), phenols (Leuenberger and
others,1985), and pesticides (Glotfelty and others, 1990; Brun and others,
1991; Goolsby and others, 1993) have been detected in atmospheric precipitation
samples. A wide variety of pesticides have been measured in the atmosphere
in air (Majewski and Capel, 1995), rain (Wu, 1981; Richards and others,
1987; Glotfelty and others, 1990; Capel, 1991; Nations and Hallberg, 1992;
Goolsby and others, 1993), snow (Czuczwa and others, 1988; Welch and others,
1991) and fog (Glotfelty and others, 1987; Glotfelty and others, 1990;
Capel and others, 1991; Schomburg and others, 1991; Valsaraj and others,
1993).
Since the 1960's, many of the studies of pesticides in the atmosphere
have focused on organochlorine insecticides, even though many have been
banned or their use greatly restricted in the United States. In the 1960's
and 1970's, air was the primary atmospheric matrix sampled and analyzed.
The more environmentally persistent pesticides, such as DDT, DDE, and a-HCH,
were detected in the atmosphere at low levels throughout the year (Bidleman
and others, 1987). Atmospheric transport distributes organochlorine pesticides
on a global basis (Patton and others, 1989; Tatsukawa and others, 1990,
Welch and others, 1991). Recently, research on wet deposition of pesticides
has expanded to a number of nations, including the United States (Glotfelty
and others, 1990; Goolsby and others, 1993), Canada (Brun and others, 1991;
Welch and others, 1991), Switzerland (Buser, 1990), Germany (Scharf and
others, 1992; Bester and others, 1995), and Japan (Haraguchi and others,
1995). In the United States, most of the focus of these recent studies
has been the Midwest including Minnesota (Richards and others, 1987; Glotfelty
and others, 1990; Capel, 1991; Nations and Hallberg, 1992; Goolsby and
others,1993).
Atmospheric contamination by pesticides occurs mainly through their
agricultural use. The physical and chemical properties of the pesticides
play an important role in the introduction to, movement in, and deposition
from the atmosphere. Pesticides enter the atmosphere during the application
process (spray drift), through volatilization, and through wind erosion
of soil particles to which the pesticides are sorbed (Majewski and Capel,
1995). In the atmosphere, the pesticides are redistributed among the vapor,
particulate, and aqueous phases. This distribution among phases depends
on their physical and chemical properties, such as vapor pressure and water
solubility, and the temperature, presence of liquid water, and properties
of particles (Tsal and Cohen, 1991). Pesticides that tend to associate
with fine particles or exist predominantly in the vapor phase tend to have
longer residence times in the atmosphere. These compounds can be transported
to areas far from their application sites (Glotfelty and others, 1990;
Goolsby and others, 1993). Pesticides are deposited through wet and dry
removal of gases and particles from the atmosphere. The relative contribution
of either process to total deposition depends on the amount and frequency
of precipitation, the equilibrium air-water partition coefficient (Henry's
Law constant), and the vapor-particle distribution in air (Bidleman, 1988).
One unintended aspect of pesticide use is the contamination of surface
water. Surface water can receive pesticides through a variety of mechanisms,
including field runoff, drainage of tiled fields, ground-water discharge,
direct application, and atmospheric deposition (Squillace and others, 1993;
Schlotter and others, 1992). For surface water that is remote from direct
inputs of pesticides from agricultural or urban runoff, atmospheric deposition
may be the major source of pesticides. Atmospheric deposition is considered
to be the main source of the organochlorine insecticide in many remote
areas (Eisenreich and others, 1981a,b; Patton and others, 1989; Welch and
others, 1991). The atmosphere is now recognized as a major pathway by which
pesticides, and other organic and inorganic compounds, are transported
and deposited in areas that are often far removed from their sources (Majewski
and Capel, 1995).
This report summarizes studies that have been conducted
in Minnesota from 1989-94 on the wet deposition of current-use pesticides
in rain and snow. (Studies from this time period on the deposition of organochlorine
insecticides, compounds that have been banned from agricultural use, are
not included in this report (Franz and others, 1991; Franz, 1994). The
early, preliminary study of pesticides in rain and snow was conducted in
1989 and 1990 in St. Paul and Rosemount, Minnesota (Capel, 1991). Based
on the findings of this study, a joint study among the U.S. Geological
Survey (USGS), Minnesota Department of Agriculture (MDA), University of
Minnesota (UM) and the Minneapolis Park and Recreation Board was undertaken
to further examine pesticides in rain throughout the state. This report
discusses the seasonal patterns in concentrations of pesticides in rain
in Minnesota, compares pesticide concentrations and loads in urban and
agricultural areas, and assesses the significance of wet deposition of
pesticides with respect to surface-water contamination.
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Pesticide Use
Pesticides have played a vital role in the production
of food and fiber and in the protection of the health of humans. The use
of herbicides to control weeds in crop production increased dramatically
during the 1960's and 1970's. The use of agricultural bicides in the United
States increased 480 percent between 1964 (38 million kg active ingredient
(AI) herbicides) and 1979 (221 million kg of AI herbicides). Since 1979,
herbicide use has remained steady and insecticide use has decreased slightly.
The annual total pesticide use after 1979 has remained relatively steady
(Eichers and others, 1968; Gilliom and others, 1985; Aspelin, 1994).
About 500 million kg of AI pesticides are used each year in the United
States in a wide variety of agricultural and nonagricultural settings.
The total agricultural use of pesticides accounts for 75 percent of this
total annual use (Aspelin, 1994). The use of herbicides accounts for 60
percent of the mass of pesticides used annually on cropland in the United
States. In 1993, total agricultural use of herbicides was approximately
208 million kg AI per year. Use on corn (93 million kg AI) and soybeans
(37 million kg AI) dominates the national totals accounting for about two-thirds
of the mass of herbicides used. In 1989, atrazine, alachlor, metolachlor,
EPTC, trifluralin, cyanazine, butylate, and pendimethalin were among the
most commonly used herbicides nationally
(fig.
1). These herbicides accounted for 63 percent of the total mass of
herbicides used in United States crop production. National non-cropland
use of herbicides was estimated by the U.S. Environmental Protection Agency
(USEPA) to be between 16 to 25 million kg AI per year (Aspelin, 1994).
This is about 10 percent of total use of herbicides in the United States
(Gianessi and Puffer, 1991).
Total annual use of herbicides in Minnesota was estimated at 13 million
kg AI during 1990 (Kelly and Hines, 1990). Minnesota ranked third in the
annual use of herbicides, after Iowa and Illinois. Use patterns in Minnesota
are somewhat different than in the United States as a whole, such as the
extremely high use of EPTC in Minnesota for 1989 (fig. 1). Total annual
use of insecticides in Minnesota in 1990 was 0.67 million kg AI. Minnesota
ranked 29th nationally in insecticide use (Gianessi and Puffer, 1992).
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Sampling Site Descriptions
Rain sampling locations have varied during the years
of this study, but together they cover various land use areas of Minnesota.
Land use in Minnesota ranges from dense forests in the northeast to intensive
row crops throughout the western and southern parts of the state. An intervening
transition zone has mixed cropland, woodland, and pasture. Land use is
affected by physiography, which varies from thin-soiled, crystalline bedrock
in the northeastern area to the rich prairie soils in the till and outwash
plains of southwestern Minnesota (Tornes, 1991). The sampling sites and
their respective sampling years are shown in
figures
2 and
3.
A brief description of each of the sampling sites follows.
The site near Blue Earth, in the south-central part of Minnesota, is
in an area of intensive row-crop agriculture. The site is located in the
East Fork of the Blue Earth River drainage basin. Rain was sampled in 1994.
Surface water from the East Fork of the Blue Earth River was also sampled
in 1994.
The site near Camp Ripley is located in the center of the state. It
is in an area of forest with some cropland and pasture. It was sampled
in 1991.
The site near Crystal Springs is located in the southeast part of the
state. This area is cropland mixed with pasture and forest and is in the
Whitewater River Basin. Rain was sampled from 1992 through 1994. Surface
water from the Middle Branch of the Whitewater River was also sampled in
1993 and 1994.
The site near Ely is located in the Superior National Forest in the
northeast part of Minnesota. This is an area of mostly forest. It was sampled
in 1991.
The site in Icelandic State Park is just across the Minnesota
state line, in extreme northeastern North Dakota, in an area of intensive
row-crop agriculture. It was sampled in 1991 and 1992.
The site near Lamberton is located at the UM Agricultural
Experimental Station in the southwest part of the State. This site is near
the center of corn and soybean production, and is located within the Minnesota
River Basin. It was sampled from 1991 through 1994.
The Minneapolis site is near Lake Harriet and is in an
urban, residential area. Rain was sampled from 1992 through 1994. Stormwater
from storm sewers draining into Lake Harriet was also sampled in 1993 and
1994.
The site near Marcell is located within the Chippewa
National Forest in north-central Minnesota. It is in an area of forest
and minor grazing and was sampled in 1991.
The site near Park Rapids is located in north-central
Minnesota in an area of forest with some irrigated cropland and some pasture.
It was sampled from 1992 through 1994.
The site near Princeton is located in east-central Minnesota
at an agricultural research site in an area of cropland mixed with pasture
and forest. It was sampled from 1991 to 1994.
The sampling site in Rosemount is located at the UM Agricultural
Experimental Station in east-central Minnesota. It is in an area of cropland
mixed with some pasture and forest. It was sampled in 1990 and 1991.
The site in St. Paul is in a residential area in the
northwestern portion of the city. It was sampled in 1989.
The sites near Lamberton, Camp Ripley, Marcell, Ely,
and Icelandic State Park were co-located at long-term precipitation sampling
sites sponsored by the National Atmospheric Deposition Program (Roberts
and Wojciechowski, 1986).
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Sampling Methods
Rain and Snow
For 1991-94, precipitation samples for pesticide analyses
were integrated for a period of one week and collected every Tuesday if
the amount of precipitation was greater than 0.635 cm (more than 300 milliliters
(mL)). Sampling occurred on a precipitation-event basis during March 1989
through June 1990. Based on results from these samples, the sampling period
was shortened to include pre-plant (late April/early May) to harvest (late
September/early October). The samples were obtained either by a local observer
or by the study investigators
(table
8).
The precipitation collector (Aerochem Metrics Inc., Model 301) was
a modified version of the collector that has been used by most of the major
atmospheric deposition monitoring networks in the United States
(fig.
4). It was chosen by the National Atmospheric Deposition Program (NADP)
and the National Trends Network (NTN) of the National Acid Deposition Assessment
Program (NADAP) for monitoring precipitation chemistry (National Atmospheric
Deposition Program, 1988). Recently, they have been used to collect precipitation
samples for herbicide analysis throughout the midwestern and northeastern
United States (Goolsby and others, 1993).
The precipitation collector was equipped with two 13-liter (L) high-density,
polyethylene buckets (diameter: 28.6 cm, depth: 23.2 cm, surface area:
640 cm2) that alternately collect wet or dry deposition.
The "dry side" bucket is uncovered between precipitation events and, thus,
collects only dry-deposited material. The "wet side" bucket is tightly
covered with a movable lid until precipitation begins. When water droplets
deposit on the electronic precipitation sensor, the sensing circuit activates
a motor which removes the lid from the "wet side" to the "dry side" to
collect a wet deposition sample. When precipitation ceases, the sensor
closes the lid to the "wet side" bucket until the next precipitation event.
The sensor base plate is heated during the wet cycle to increase the rate
of evaporation and, hence, reduce the open time after the cessation of
precipitation.
The precipitation collector was modified for this study
to minimize the potential for sorption and contamination of pesticides
by the plastic container, pesticide losses due to degradation, and the
inconvenience of transportation of precipitation samples. The modifications
to the precipitation collector were refined over time. During 1989 and
1991, a Teflon-lined, aluminum collection vessel with a Teflon outlet to
drain the rain water to a 4-L glass bottle was used. Starting in 1992,
the pesticides were isolated from the water in real-time by solid-phase
extraction (SPE). The modifications to the precipitation sampler during
this time period included a Teflon-lined aluminum collection vessel with
a Teflon outlet tube, a glass water-level sensor, a pump, and an in-line
solid-phase extraction column (EnviroPrep, Baxter Corp., 50 milligram (mg)
in 1992) or disk (Empore, 3M, diameter: 47 millimeter (mm) in 1993 and
1994) to provide the in-place filtration and extraction of pesticides from
the water. The SPE holder was easily mailed to the laboratory.
In 1993 and 1994, the Teflon-lined, 6-L aluminum vessel
(diameter: 25 cm, depth: 15 cm) was connected, through a Teflon tube, to
the glass water-level sensor
(fig.
5). The sensor was constructed with two pairs of platinum wire 3 cm
apart embedded in a glass tube (diameter: 2.5 cm, length: 12.5 cm). The
electrode sensed the water level and controlled the pump through an electronic
control board (
fig.
16). When the water level reached the upper pair of platinum wires,
indicating that rain was being collected, the pump turned on. When the
water level went below the lower pair of platinum wires, the pump turned
off. This design protected the pump from turning on and off frequently
during light precipitation. The inlet of the pump (FMI Lab, Model QSY,
Fluid Metering, Inc.) was connected to the sensor through a Michael-Miller
Teflon fitting (ACE Glass Inc.) and a 3.175 mm Teflon tube. The pump outlet
was directed through 3.175 mm Teflon tubing to the SPE device. The rainwater
was pumped at a rate of 15-20 milliliters per minute (mL/min) to an aluminum
in-line filter holder that held a 47 mm glass-fiber filter (Whatman GF/F)
and a C-18 SPE disk (Empore, 3M) that isolated the pesticides from the
water (fig. 4). The aluminum filter holder
(fig.
6) for the Empore disk was designed to reduce the residue of water
within the holder. The rainwater that passed through the SPE disk holder
was collected in a 6-L carboy waste container to measure the total volume
of rainwater that was extracted.
The SPE device was changed every Tuesday, if there was
rain during the week. Before replacing the SPE device, the Teflon-lined
aluminum vessel, Teflon tube, glass sensor, and pump were rinsed with "organic-free"
Milli-Q water (Millipore Corporation). SPE disks and glass fiber filters
were cleaned and activated by hexane/isopropyl alcohol (70 percent/30 percent,
by volume), methyl alcohol, and Milli-Q water in sequence in the laboratory
before they were deployed. This was done within the aluminum filter holder.
The filter holders, still filled with water and sealed at both ends with
Teflon plugs, were mailed to the sampling sites and deployed in the sampler.
A separate rain gauge was fixed on the side of the rain
sampler to make the measurement of precipitation. It was located at the
same height as the movable cover away from the precipitation sensor. A
large metal box, holding the sensor, pump, electronics, SPE disk holder,
Milli-Q water, and waste carboy, was located below the precipitation collector
and locked to prevent damage or tampering (fig. 4).
During the winter of 1989-90, snow was collected on an
event basis in St. Paul. The snow accumulated on a large, cleaned, Plexiglas
sheet. It was removed with a cleaned, 10-cm internal-diameter glass tube
and a 20-cm x 25-cm glass sheet and placed into a 4-L large-mouth, glass
jar for storage. The volume of snow was determined by the depth of the
snow and number of subsamples with the glass tube. The volume of melted
snow was determined by mass. All concentrations of pesticides in snow presented
here are on a snowmelt volume basis.
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Stormwater Runoff
Stormwater samples were collected near Lake Harriet in
Minneapolis using an ISCO model 3700 automatic sampler fitted with cleaned
glass bottles, Teflon tubing, and a stainless steel nozzle, and interfaced
to an ISCO model 3220 flow meter with a submerged probe. The equipment
was installed in a 1.37-m diameter concrete storm sewer about 60 m upstream
of Lake Harriet. Continuous flow measurements were taken at five-minute
intervals. The sampler collected stormwater based upon flow volumes recorded
by the flow meter. A 250 mL water sample was collected for each 28 m3
of runoff water. The samples were composited and then refrigerated until
they were analyzed. In 1992, 21 of 24 storm events (greater than 0.25 cm
of rain) were sampled. In 1993, 20 of 43 storm events were sampled.
Stormwater samples in the Blue Earth and Whitewater Rivers were collected
at automated monitoring stations equipped to monitor continuous rainfall,
temperature and river stage data. During storm events, an ISCO model 3700
sampler was activated by a Campbell Scientific model CR10 datalogger when
the river reached a predetermined stage. Samples were collected by the
ISCO sampler into precleaned glass bottles at equal time increments for
the duration of the storm runoff period. The samples were stored in ice
during the collection period and then stored in a refrigerator after collection.
Finally, samples were manually flow weighted by compositing an appropriate
volume of each sample based on the streamflow represented by that sample
as a percentage of the total streamflow over the entire storm event. The
final composited sample was submitted to the Minnesota Department of Agriculture
Laboratory Services for extraction and analysis.
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Analytical Methods
The analytical methods were modified from 1989 to 1994.
During this period, the number of target analytes increased from 4 to 35
(table
9). Each of the analytical methods are briefly described below.
The 1989 and 1990 precipitation samples were collected in 4-L glass
bottles. The pesticides were isolated from the water by SPE (C18, 5 mg)
within one week. The SPE columns were centrifuged to remove the residual
water. The pesticides were eluted from the SPE column with 4 mL of diethyl
ether. The extracts were passed through about 6 cm of anhydrous sodium
sulfate and collected in a glass centrifuge tube. The volume of diethyl
ether was reduced by a gentle stream of nitrogen and the solvent was switched
to hexane. The extract was analyzed by gas chromatography with a mass selective
detector in selective ion monitoring mode. The target analytes were atrazine,
alachlor, and cyanazine.
The 1991 and 1992 rain samples and the 1993 and 1994 stormwater samples
were analyzed by the MDA's Laboratory Service Division. In 1991, the method
employed liquid/liquid extraction of the rain samples with methylene chloride,
concentration of extract, and a solvent switch to hexane. The extract was
analyzed by gas chromatography with various specific detectors. In 1992,
the pesticides were isolated from the rain samples with SPE in the field.
The SPE columns were centrifuged to remove the residual water. The pesticides
were eluted from the SPE column with 4 mL of diethyl ether. The extracts
were passed through about 6 cm of anhydrous sodium sulfate and collected
in a glass centrifuge tube. The volume of diethyl ether was reduced by
a gentle stream of nitrogen in a 45°C water bath and the solvent was
switched to hexane. The extract was analyzed by gas chromatography with
various specific detectors. All positive detections were confirmed by gas
chromatography/mass spectrometry in the selective ion mode. The 1993 and
1994 stormwater samples were analyzed by this same method.
In 1993 and 1994, the analyses of pesticides in rain samples were performed
at the University of Minnesota. To eliminate contamination, all glassware
was cleaned with Liquinox detergent, rinsed with tap water, then Milli-Q
water (Millipore Corporation), and baked at 550°C for 6 hours in a
temperature-programmable muffle furnace (Paragon Electric Kiln, DTC 600).
Glass filters (Whatman GF/F, 4.7-cm internal diameter (ID)), glass wool,
and granular sodium sulfate were heated at 550°C for 6 hours and stored
in Pyrex glass beakers in an oven at 110°C. Precise measuring glassware
such as volumetric flasks, volumetric pipettes, and other laboratory items
such as forceps, spatulas, and filtration devices, which could not be baked,
were rinsed with methanol or acetone, hexane, and diethyl ether. The cleaned
items were allowed to air-dry in the fume hood, then placed in an oven
at 110°C for one hour. Autosampler vial inserts were rinsed with methanol,
hexane, and diethyl ether three times each in sequence and stored in a
covered beaker. All cleaned items were wrapped or covered with aluminum
foil. Organic-free Milli-Q water was used for blanks, recovery studies,
and activating the SPE disks. All were pesticide residue-grade solvents
(Burdick and Jackson). Surrogate compounds (terbuthylazine and butachlor)
used for standard solutions were "Pestanal" reagents obtained from Crescent
Chemical Company. The internal standard compounds (d-10 anthracene and
4,4-dibromo-biphenyl) were purchased from Supelco, Inc. Standard stock
solutions came from either the MDA laboratory or the USGS National Water
Quality Laboratory (Zaugg and others, 1995). These solutions were further
diluted to obtain a series of working standard solutions for calibration
curves.
Before being deployed in the field, the SPE disk was washed sequentially
with 5 mL of hexane/isopropyl alcohol (70 percent/30 percent, by volume),
5 mL of methanol, and 10 mL of Milli-Q water. The SPE disk holder was shipped
to the sampling site and deployed. After the filter holder with the used
SPE disk was received in the laboratory, it was dried by vacuum, then eluted
with 15-20 mL of 30 percent isopropyl alcohol in hexane in three aliquots.
Surrogates (terbuthylazine and butachlor) were spiked into the eluate to
quantify the analytical efficiency. The eluate was passed through an anhydrous
sodium sulfate column to remove trace residual water. The solvent was evaporated
to 100-150 microliters (mL) using an evaporation apparatus (Supelco 6-port
Mini-Vap) and quantitatively transferred to an autosampler vial. Internal
standards were added before it was tightly capped. Final analysis was performed
by gas chromatography/mass spectrometry in the selected ion monitoring
acquisition mode (HP 5890GC, Hewlett Packard). The analytical column for
gas chromatography was a J&W DB-5 column, 30 m x 0.25 mm ID, with a
film thickness of 0.25 mm. The temperature program was 100°C for 5
minutes (min), increased at 6°C/min to 300°C and held at that temperature
for 5 min. Injector and detector temperature were 250°C and 285°C,
respectively. The flow rate of carrier gas, helium, was set at 0.9 mL/min.
All target analytes were quantified by comparing retention
times, mass spectra, and ion intensities with those observed using standards.
For most of the sample analyses, the recoveries of surrogate standard compounds
varied from 70 to 120 percent. The reported concentrations of pesticides
have not been adjusted to 100-percent recovery. The recoveries of terbuthylazine
and butachlor are good indicators for the triazine and acetanilide herbicide
recoveries, respectively. The method detection limits were determined by
measuring a series of standard solution dilutions. For a 500 mL sample,
the detection limits for all target pesticides were 0.01
mg/L,
except for cyanazine, terbacil, lindane, methyl parathion, malathion and
azinphos methyl which were 0.02
mg/L.
Because the volumes of the rain samples varied appreciably, it was impossible
to establish a consistent detection limit.
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Wet Deposition of Pesticides
The results of 1989-94 are summarized in tables 1-6.
The summary tables include the common and brand name of each target analyte,
the percent of detections from all rain samples at all sites, the maximum
observed concentration, and the date and location of the maximum observed
concentration. The target analytes are grouped according to class: herbicides,
insecticides, fungicides and degradation products; and within each class
they are ranked in the order of decreasing percent detections. For pesticides
that were never detected above the method detection limit, the value of
the method detection limit (assuming rain sample volume of 500 mL) is preceded
by a less than symbol in the column for maximum observed detection. Tables
10-20 present a summary for each of the sampling sites from 1993 and 1994,
including the common and brand names, the percent of detections, and the
observed maximum and median concentrations.
[go to table
1] [go to
table 2] [go
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to table 4] [go
to table 5] [go
to table 6]
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to table 19] [go
to table 20]
Throughout this discussion it must be remembered that 1993 had an abnormally
wet late spring and summer in Minnesota. This caused many rivers to flood
and set many streamflow discharge records throughout Minnesota and much
of the midwestern United States.
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Annual Summaries of Detections and Concentrations
This study has changed over six years in an attempt to
better collect rain samples and to better quantify a wider variety of pesticides
at lower concentrations. As can be observed from tables 1-6, the changes
in the study have resulted in a greater number of compounds being detected
and more frequent detections of some compounds. As an example
(fig.
7), the frequency of detection of alachlor, atrazine, cyanazine, and
metolachlor in rain increased in 1993 and 1994 as compared to 1991 and
1992 due to the lower detection limits in the later two years. Sample frequency
distributions over the four year period were similar for concentrations
greater than 0.5 mg/L (fig. 7). Because 1993 and 1994 are the most complete
data sets, most of the following discussion will be based on these years.
Of the 30 pesticides that were targeted for analysis in 1993, 24 were detected
at least once. In 1994, 29 out of 32 targeted pesticides were detected.
The more limited results of 1989-92 agree with the results of these later
two years.
The pesticides targeted in this study have been divided into five groups
for purposes of this evaluation. These groups include:
(1) triazine herbicides (atrazine, cyanazine, metribuzin,
propazine, and simazine).
(2) acetanilide herbicides (acetochlor, alachlor, metolachlor,
and propachlor).
(3) soil-incorporated herbicides (benfluralin, butylate,
EPTC, ethalfluralin, pendimethalin, and trifluralin).
(4) "other" herbicides--compounds that generally have
low agricultural use in Minnesota (pebulate, prometon, propanil, tebuthiuron,
terbacil, and triallate), although triallate does have a significant use
in northwestern Minnesota.
(5) insecticides (see table 6 for list).
The percent of detections is graphed by group in
figure
8 for both 1993 and 1994. The percent of detections among the various
groups was similar between the two years. By far, the two highest percentages
were the triazine and acetanilide herbicides. These compounds generally
are applied to the soil surface as pre-emergent herbicides. This mode of
application appears to make them readily available to move from the soil
into the atmosphere (either through volatilization or wind erosion) and
eventually removed by rain. The group of soil-incorporated herbicides had
a substantially lower frequency of detection. These compounds are generally
quite volatile, so they are applied within the soil. The soil then acts
as a physical barrier to their loss to the atmosphere. The group of "other"
herbicides were detected quite infrequently, most likely a result of infrequent
use in the study area. The insecticides, as a class, are less frequently
detected than the herbicides. This difference is probably due to less use,
use later in the growing season when rains are less frequent, and in general,
shorter persistence in the environment.
The frequency of detections varied greatly among the
pesticides targeted in this study. The most frequently detected compounds
in 1994 were atrazine, alachlor, cyanazine, metribuzin, and metolachlor
(table 6). The results for 1993 were similar (table 5). Some compounds
were never or seldom detected (benfluralin diazinon, pebulate, and so forth,
tables 5 and 6). The frequency of detection of the various pesticides is
partly a function of the agricultural management practices used during
their application. One way to illustrate this is to calculate the percent
of the total possible number of times that pesticides, grouped by management
practices, were measured in rain. As an example (fig. 8), the soil-incorporated
herbicides (benfluralin, butylate, EPTC, ethalfluralin, pendimethalin,
and trifluralin) were measured 98 times in 107 samples (642 possible detections)
in 1994. This is an overall detection rate of 15.3 percent of possible
detections.
The percent detections for 19 herbicides from all sites
in 1993 and 1994 are plotted in comparison with their estimated use in
the United States and in Minnesota (fig. 1). Some of the most frequently
detected pesticides in rain were the surface-applied, pre-emergent herbicides:
atrazine, alachlor, cyanazine, and metachlor.
These are the same pesticides that are most frequently
detected in Minnesota's rivers and streams (Larson and others, 1995; Schottler
and others, 1992). Some of the other commonly used herbicides, such as
EPTC, trifluralin and butylate, were not as frequently detected in the
rain probably because they are incorporated into the soil and generally
have shorter soil half-lives (University of Minnesota, 1992). Some other
pesticides, such as metribuzin, pendimethalin, ethalfluralin, and propachlor
were detected frequently but at consistently low concentrations (fig. 1
and table 5).
Acetochlor was detected at all sites in 1994 at similar
concentrations and detection frequencies as other commonly used herbicides
(table 6 and tables 15-20). The detections in rain of this newly registered
(in the United States) herbicide in its first season of use is important
in several ways (Capel and others, 1995). Acetochlor is an acid amide,
similar in structure to alachlor and metolachlor. The USEPA has mandated,
as part of acetochlor's registration, that its use will reduce the use
of the sum of the six of the most common corn herbicides (alachlor, atrazine,
butylate, EPTC, metolachlor and 2,4-D) by 3 million kg during 1992-99,
adjusted for differences in planted acreage (U.S. Environmental Protection
Agency, 1994). Archived extracts of rain samples from 1993 were retrieved
and analyzed for acetochlor, but the compound was not detected. Acetochlor
appears to behave much like its analogs, alachlor and metolachlor, in its
movement from the field into the hydrologic system. The presence of acetochlor
in rain and surface water is expected based on the behavior of alachlor
and metolachlor (Capel and others, 1995). The presence of this new herbicide
in rain, in its first months of application, suggests that rain is a good
matrix to monitor pesticides in the environment, and that rain provides
a fast indicator of the movement of a pesticide from the site of application
to the broader environment. Atmospheric measurements, such as rain or air,
could be a valuable method to examine the short- and long-term presence
or absence of certain pesticides as they become registered or after their
current registration is withdrawn and they are no longer permitted to be
used.
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Seasonal Patterns in Detections, Concentrations,
and Fluxes
To assess the seasonal behavior of atmospherically deposited
pesticides, precipitation was continuously collected and analyzed (on a
rain- or snow-event basis) from March 1989 through June 1990 in St. Paul
or Rosemount (fig. 2). Three commonly used herbicides--alachlor, atrazine,
and cyanazine--were studied. All three had similar seasonal patterns, although
there were some minor differences
(fig.
9). All three had maximum concentrations in precipitation during the
spring of both years, immediately following application. Their concentrations
decreased within weeks following application. Alachlor and cyanazine were
at concentrations below the detection limit for most of the rain events
after July 1989. Atrazine was detected in most rain events and many snow
events throughout the year. This reflects the longer environmental persistence
of atrazine, compared to alachlor and cyanazine. The presence of atrazine
in snow, even when snow covered the ground locally, suggests either that
its atmospheric residence time is long or that there is a continual source
to the atmosphere and long-range atmospheric transport. It is possible
that both are true.
The majority of the rain samples from late April/early May through
the end of September had no detectable quantities of most of the target
pesticides, although during May and June, most of the rain samples had
detectable levels of some pesticides. The pattern of the highest concentrations
occurring in the spring has held true for many of the pesticides every
year. Data on the maximum concentration of each pesticide in rain, by sampling
site and for the entire state, are shown in tables 3-6, and in tables 10-20.
Most of the maximum concentrations occurred in May or June, just as was
observed in 1989 and 1990. For some compounds, the maximum concentration
occurred later, August or September. This occurred for a few infrequently
detected herbicides (table 5), some of which, such as prometon, have significant
nonagricultural use, and for several of the insecticides (see the site-specific
data, tables 10-20). This could be a result of late summer or autumn applications
of these compounds.
The importance of the spring in the atmospheric deposition of pesticides
can be seen in
figure
10. This graph presents the flux in micrograms per square meter per
time period (
mg/m
2/time
period) in rain for two time periods. The early time period (about May
through about June 15--the exact dates vary slightly between the two years
because of the Tuesday sampling schedule) encompasses the application period
for most herbicides and some insecticides in southern Minnesota. The later
time period (about June 15 through about October 1) encompasses most of
the remainder of the growing season when pesticides are applied less frequently.
An example of the differences in pesticide fluxes between these two periods
is shown by data for 1994. For all pesticide groups at all three sites,
the flux in the spring/early summer is much greater than in the late summer/fall.
In 1993, this pattern was not as definitive and even reversed for many
of the groups at the Minneapolis site. This could be due to the unusual
weather patterns (greater than normal amount of rain) and atypical timing
of some applications of pesticides that occurred that year because of the
wet spring.
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Temporal and Geographical Distribution of Fluxes
in Rain
Based on the data from 1989-90, it was determined that
the highest concentrations of pesticides and the majority of the annual
flux (greater than 99 percent) in rain occurred between May 1 and October
1 in Minnesota. Based on this conclusion, the duration of the sampling
period was reduced each year to the five months (May through September)
to decrease sampling and analysis costs. With the pesticide concentration
data from these five months and the volume of total rainfall for each sample,
total flux for the five month period was computed (
mg/m
2/five
months). From knowledge of the low levels of pesticide deposited during
the October-April time period, the May through September flux was assumed
to represent the annual flux (
mg/m
2/year)
for pesticides in precipitation in Minnesota. The weekly flux (mass per
unit area) for each pesticide was obtained by multiplying the concentration
of the pesticide in the rain by the amount of rainfall during that week
(volume per unit area). The annual flux (based on data from May through
September) was obtained by summing the weekly fluxes. The total yearly
flux of pesticides at each site was obtained by summing the annual fluxes
for all the pesticides (20 herbicides and 10 insecticides). The annual
fluxes of pesticides in rain for the sampling sites active during 1993
and/or 1994 are presented in
figure
11. Figure 11 can be used to compare the annual flux between the two
sampling years (1993 and 1994) and between selected sites in Minnesota.
Taken as a whole, the flux of pesticides in the rain in Minnesota is generally
in the range of 200 to 2,000
mg/m
2/year.
To put this flux in perspective, if a pesticide is applied yearly at the
rate of 0.45 kg AI/acre, then its "flux" to that field is about 1 x 10
8 mg/m
2/year. That
is, the purposeful application of a pesticide is about 200,000 times as
great as is deposited by rain, but the rain flux may be more significant
in areas that are not treated with pesticides. Pesticides are deposited
everywhere by the rain and have the potential to affect ecosystems for
which they were not intended.
At every site with 1993 and 1994 data, the yearly flux of total pesticides
was greater in 1994 than in 1993. This is due to the linked variations
in weather conditions and agricultural activities. In 1993, the spring
and early summer was extremely wet and cool. In some areas of the state,
crops were planted very late. The concentrations of pesticides measured
in many rivers were greater than normal, because the heavy rains caused
significant runoff from agricultural fields, carrying with it greater than
normal quantities of pesticides. Overall there may have been a smaller
source of pesticides available to the atmosphere in 1993 than in other
years. In contrast, 1994 was a much more typical year in terms of rainfall,
temperature, and agricultural practices. Compared to 1993, there was a
greater flux of total pesticides in the rain in 1994, but it is somewhat
surprising that this difference was largely due to one compound, cyanazine
(fig.
12 and table 7). The relatively high concentrations and fluxes of cyanazine
in rain was also observed by other investigators in 1994 compared to 1993
on Isle Royale in Lake Superior (E.M. Thurman, U.S. Geological Survey,
oral commun., 1996). It is unknown whether this simply reflects an increase
in the use of cyanazine in 1994 or whether it is due to other factors related
to its agricultural or geographical use.
There were geographical differences in total pesticide flux from rain
throughout the state that were consistent between the years (fig. 11 and
table 7). Lamberton, which is in one of the most intensive row crop areas
of the state, had the highest flux of any site sampled, both in 1993 and
1994. Its flux was 2.5 to 5 times higher than any other sampling site in
both years. The other sites (Park Rapids, Princeton, Minneapolis, and Crystal
Springs) all have similar pesticide fluxes in 1993 (200 to 410 mg/m2/year)
and 1994 (550 to 960 mg/m2/year).
These four sites are in areas of less intensive row-crop agriculture or
in an urban area. These results suggest that there is a significant content
of pesticides in rain regionally. The pesticides in the atmosphere are
from a large geographical area, and transported with the prevailing wind
currents. Other studies (Glotfelty and others, 1990; Goolsby and others,
1993) have shown that pesticides can be transported hundreds of miles before
they are deposited to the surface by rain or other depositional mechanisms.
This regional background occurrence of atmospheric pesticides is more reflective
of wide geographical use of pesticides than of their use in the immediate
area of the sampling site. Given this observation, it is notable that the
site in an intensive row crop agricultural area, Lamberton, had a total
pesticide flux that was considerably greater than the other sites. This
suggests that there is also a local influence on the pesticide content
of rain superimposed on the regional background. If there is a very strong
local source of pesticides to the atmosphere, then there can be increased
local deposition. The mechanisms through which pesticides enter the atmosphere
include both volatilization and wind erosion of soil particles with their
associated pesticides. The latter mechanism is a localized process because
soil particles, especially larger particles, are deposited close to their
source.
The observations of pesticides in rain in St. Paul (1989-90)
and in Minneapolis (1992-94) contribute to the understanding of the transport
and deposition of pesticides in the atmosphere. Most of the target compounds
(with the exception of diazinon, lindane, malathion, permethrin, simazine,
and trifluralin) are not registered for use in urban areas. The compounds
that were most frequently detected in rain in Minneapolis (alachlor, atrazine,
cyanazine, EPTC, metolachlor, and metribuzin) are not registered for use
in urban areas. The presence of these compounds in urban rain, stormwater,
and an urban lake (Wotzka and others, 1994) suggest that they are being
transported through the atmosphere from agricultural areas and deposited
by rain in the urban area. The total yearly flux of the four most frequently
detected herbicides are shown on figure 12. The flux appears more consistent
year to year in Minneapolis than in the more agricultural areas. Even the
drastic increase in the cyanazine flux observed for Lamberton is diminished
in Minneapolis. These data may indicate that an urban area may be an effective
monitoring location for assessing changes in the regional atmospheric burden
of agricultural pesticides deposited by rain.
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Potential Significance to Surface-Water Quality
Rain samples, during 1989-94, had maximum concentrations
of alachlor, atrazine and cyanazine of 22, 2.9, and 24 mg/L
(tables 2, 5 and 6, respectively). These compounds were the only three
pesticides with concentrations greater than 2 mg/L.
In general, the maximum concentrations of these three herbicides in rain
occurred in late May through June. These data from Minnesota agree with
results from Iowa (Nations and Hallberg, 1992) and the midwestern United
States (Goolsby and others, 1993). Although there is very little actual
connection between rain and drinking water, it is informative to compare
the rain concentrations with these benchmark values. For alachlor and atrazine,
the USEPA primary drinking water standards (maximum contamination level
(MCL)) are 2 and 3 mg/L, respectively
(Nowell and Resek, 1994). The maximum contamination level goal (MCLG) for
cyanazine is 1 mg/L (Nowell and Resek,
1994). Most of the measured concentrations of these herbicides in rain
are much lower than this, but the maximum concentrations in the spring
rain have exceeded the drinking water standards. There is some indication
that the volume of rain effects the concentration of the pesticides (Richards
and others, 1987). As an example from the present study, the rain event
that resulted in the maximum alachlor concentration of 22 mg/L
was from a very small storm (< 0.1 in. of rain). Capel (1991) reported
that within a single rain event, the maximum concentrations occur during
the first few millimeters of rainfall and these concentrations can be one
order of magnitude or greater than the concentrations measured in the complete
"integrated" rain event. This means that during the beginning of a rain
event the flora experience relatively high concentrations of pesticides.
These concentrations continually decreased throughout the rain event. The
environmental significance of this is unknown.
One way of assessing the potential significance of pesticides in rain
to surface-water quality is to compare the relative magnitudes of the pesticide
flux to a watershed from rainfall and the flux of pesticides from that
watershed in the river. This was done for the Middle Branch of the Whitewater
River (near Crystal Springs) in 1993 and 1994, for a small watershed that
discharges into Lake Harriet, Minneapolis in 1993 and 1994, and for the
East Fork of the Blue Earth River (near Blue Earth) in 1994. The comparative
fluxes for these three watersheds in stormwater runoff and rain are shown
for four herbicides in
figure
13. In almost every case the yearly flux in the rain is much greater
than the flux in the river (except in the Whitewater River Basin in 1993).
This implies that a large fraction of the pesticides deposited to the watershed
in the rain is retained within the watershed. If this is viewed on a weekly
basis, rather than the yearly sum, the observations are the same.
Figures
14 and
15
show the cumulative flux of example pesticides in the rain and the river
over time for the watershed discharging to Lake Harriet (Minneapolis) and
the watershed of the Middle Branch of the Whitewater River (near Crystal
Springs), respectively. Because the same area and time period were used
in the calculations for both the rain and the river, the cumulative fluxes
correspond to the fluxes from the rain to the watershed and to the river
from the watershed. The cumulative fluxes of the pesticides in both of
these systems show that contributions from the rain to the watershed occur
earlier in the year than do the contributions to the river from the watershed.
This suggests that the herbicides from the rainfall (evidence of long-range
transport) enter the watersheds earlier than the local application or that
pesticides applied in the basin take longer to go from the fields to the
stream as they are processed through the soils and drainage system.
The herbicides shown in figure 14 (alachlor, atrazine, cyanazine, and
metolachlor) are not used within the Lake Harriet watershed in the urban
area of Minneapolis. Thus, the source for all of these herbicides to the
basin is the atmosphere. The flux in rain generally was greater than the
flux in the river (stormwater) for all four herbicides in both years (fig.
13). The summed flux of the four herbicides in rain was about 40 and 210
times greater than in the stormwater in 1993 and 1994, respectively. (The
greater difference in 1994 can be almost entirely accounted for by cyanazine).
This implies that a large fraction of these herbicides, and probably all
pesticides, deposited to the urban watershed in the rain are retained and
degraded within the watershed. The urban landscape (less the impervious
fraction) is efficient at inhibiting the transport of the pesticides. If
the rain is assumed to be the total source of these herbicides to this
watershed, then the percent loss in runoff can be estimated. In 1993, only
1.6, 2.6, 1.7, and 1.7 percent of the alachlor, atrazine, cyanazine, and
metolachlor, respectively, and in 1994, only 0.4, 1.0, 0.01, and 2.8 percent
of the alachlor, atrazine, cyanazine, and metolachlor, respectively, that
was deposited in rain found the stormwater runoff. It is interesting to
note that these percentages are similar to those observed in the whole
of the Minnesota River Basin, an area of intense row crop agriculture (fig.
2). Schottler and others (1992) reported that 0.7, 1.3, 1.7, and 1.6 percent
of the alachlor, atrazine, cyanazine, and metolachlor, respectively, that
were used in the Minnesota River Basin were observed in the Minnesota River.
In the Whitewater River Basin, the flux of herbicides
in the river was generally much closer to the flux of herbicides in the
rain in 1993 (fig. 15), which was a year of abnormally large rainfalls
and high streamflows. Figure 15 illustrates the relation between alachlor
in the river and in rain. The upper plot represents the stream discharge
and herbicide concentration in the river. A typical pattern (Thurman and
others, 1991; Schottler and others, 1992; Larson and others, 1995) of low
concentrations in early spring is observed, followed by peak concentrations
with strong discharge events in late spring and early summer, followed
by low or nondetectable concentrations throughout the rest of the season.
The middle plot represents the rainfall amount and the herbicide concentration
from the weekly rain sample. The seasonal pattern of concentration in rain
is similar to the pattern observed in previous studies (Capel, 1991; Goolsby
and others, 1993). The peak concentrations in rain often precede or coincide
with the peak concentrations in the streams. The seasonal patterns of herbicides
in rain and in the stream are similar and both correspond with the local
use of herbicides with spring planting. The early peak concentrations in
rain suggest that either atmospheric removal is efficient or there is long-range
transport of these herbicides. The bottom plot presents a comparison of
the magnitude of these two transport processes: atmospheric deposition
(quantified as cumulative mass in rain) versus runoff from fields (quantified
as cumulative mass in the stream). The total water discharged from Middle
Branch of the Whitewater River and total rainfall to this watershed during
May through September 1993, were estimated to be about 1.0x10
7
and 4.5x10
7 m
3 , respectively. The cumulative mass of alachlor,
atrazine, cyanazine and metolachlor from precipitation to the watershed
are 2.7, 5.4, 1.9 and 0.7 kg, respectively. The cumulative mass of alachlor,
atrazine, cyanazine and metolachlor in the stream are 3.1, 6.1, 2.2 and
4.7 kg, respectively. They are all less than 1 percent of the same herbicides,
respectively, applied in Winona County (Kelly and Hines, 1990. Gianessi
and Puffer, 1991). For the herbicides alachlor, atrazine, and cyanazine
the magnitude of the masses are very similar between the stream and the
rain. The ratio of the masses between the rain and stream ranged from almost
equal for cyanazine and metolachlor to a factor of about five for alachlor.
That is, the amount of these herbicides falling in the rain within the
river's watershed is similar to the amount of the herbicides entering the
river through stormwater runoff. This is true even though the concentrations
in the river were about one order of magnitude greater than in the rain.
This is not to imply that the same molecules of a chemical that fall from
the sky enter the surface water; but that the magnitude of the two processes,
for these herbicides, are very similar. For the two years that were included
in this study, this similarity between the masses in the rain and stream
for the Whitewater River was different compared to the other two basins.
For all other sites in almost all years, the magnitude of the flux in the
rain to the basin was much greater than the flux in the river (fig. 13).
These data suggest that the importance of the atmosphere in distributing
the current-use pesticides throughout the hydrologic system is equal to
or greater than the importance of surface-water runoff, yet there has been
only limited investigations on the atmospheric transport and deposition
of pesticides.
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Summary and Conclusions
Rain was sampled across Minnesota for pesticides used
in the midwest during 1989. Snow was sampled during 1989 and 1990. The
number of sampling sites during any one year ranged from one to eight.
Most were located in the southern two-thirds of the State and included
a site located in a large urban area. The total number of compounds monitored
increased from 4 in (1989-90) to 32 (in 1994) and included both insecticides
and herbicides. In situ pesticide isolation from water was developed to
minimize loss and facilitate sample transport. Total volume of precipitation
was monitored to calculate the flux of pesticides in rainfall during each
sampling period.
All of the rain samples throughout the growing season had detectable
quantities of at least one pesticide, but most of the pesticides were only
infrequently observed. The most frequently detected compounds were the
herbicides alachlor, atrazine, cyanazine, and metolachlor, and in 1994,
its first year of registration, acetochlor. Peak concentrations of most
herbicides in rain occurred shortly after their application periods in
the spring. Peak concentrations of most of the insecticides occurred later
in the summer.
The vast majority of the wet depositional flux of total pesticide occurred
between early May and October. The annual variability in pesticide deposition
can be explained by year-to-year differences in climate and pesticide use
patterns. The one sampling site (Lamberton) that was in an area dominated
by row-crop agriculture showed a substantially greater annual flux than
the other sampling sites that were in areas of either less intensive agriculture
or urbanization. Regional deposition, away from a local source, can be
inferred from the results for these other sites because they have annual
pesticide fluxes that are very similar for any given year. The observation
of agricultural pesticides (not registered for home and garden use) in
rain and stormwater runoff in the urban area indicates their transport
from areas of agricultural use. The regional deposition suggests that urban
areas may be effective monitoring locations for assessing changes in the
regional atmospheric burden of agricultural pesticides deposited by rain.
The data collected from Minneapolis for acetochlor and cyanazine support
this suggestion.
The study quantified and compared the pesticide flux in streams out
of small watersheds and the pesticide flux deposited to the watersheds
in rain. The data indicate that the flux into the watershed from the rain
is generally much greater than the flux from the watershed in the stream.
For the urban area, on the order of 98 percent of the flux in the rain
and runoff for the four most commonly observed herbicides is retained by
the watershed.
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References
Aspelin, A.L., 1994, Pesticides
industrial sales and usage, 1992 and 1993 market estimates: U.S. Environmental
Protection Agency, Washington, D.C., 733-K-94-001, 33 p.
Bester, K., Huhnerfuss, H.,
Neudorf, B., and Thiemann, W., 1995, Atmospheric deposition of triazine
herbicides in northern Germany and the German Bight (North Sea): Chemosphere,
v. 30, p. 1639-1653.
Bidleman, T.F., 1988, Atmospheric
processes--Wet and dry deposition of organic compounds are controlled by
their vapor-particle partitioning: Environmental Science and Technology,
v. 22, p. 361-367.
Bidleman, T.F., Wideqvist,
U., Jansson, B., and Soderlund, R., 1987, Organochlorine pesticides and
polychlorinated biphenyls in the atmosphere of southern Sweden: Atmospheric
Environment, v. 21, p. 641-654.
Brun, G.L., Howell, G.D.,
and O'Neill, H.J., 1991, Spatial and temporal patterns of organic contaminants
in wet precipitation in Atlantic Canada: Environmental Science and Technology,
v. 25, p. 1249-1261.
Buser, H.R., 1990, Atrazine
and other s-triazine herbicides in lakes and in rain in Switzerland: Environmental
Science and Technology, v. 24, p. 1049-1058.
Capel, P.D., 1991, Wet atmospheric
deposition of herbicides in Minnesota, in U.S. Geological Survey Toxic
Substances Hydrology Program--Proceedings of the Technical Meetings, G.E.
Mallard, and D.A. Aronson (eds), Monterey, California: U.S. Geological
Survey Water-Resources Investigations Report 91-4034, p. 334-337.
Capel, P.D., Leuenberger,
C., and Giger, W., 1991, Hydrophobic organic chemicals in urban fog: Atmospheric
Environment, v. 25A, p. 1346-1355.
Capel, P.D., Ma, L., Schroyer,
B.R., Larson, S.J., and Gilchrist, T.A., 1995, Analysis and detection of
the new corn herbicide Acetochlor in river water and rain: Environmental
Science and Technology, v. 29, p. 1702-1705.
Chan, C.H., and Perkins, L.H.,
1989, Monitoring of trace organic contaminants in atmospheric precipitation:
Journal of Great Lakes Research, v. 15, p. 465-475.
Czuczwa, J., Leuenberger,
C., and Giger, W., 1988, Seasonal and temporal changes of organic compounds
in rain and snow: Atmospheric Environment, v. 22, p. 907-916.
Daines, R.H., 1952, 2,4-D
as an air pollutant and its effect on various species of plants, in Air
Pollution: Proceedings of the United States Technical Conference on Air
Pollution, L.C. McCabe, (ed): McGraw-Hill Book Co., Inc., New York, p.
140-143.
Eichers, T., Andrilenas, P.,
Jenkins, R., and Fox, A., 1968, Quantities of pesticides used by farmers
in 1964: Agricultural Economic Report, 131, Economic Research Service,
U.S. Department of Agriculture, 31 p.
Eisenreich, S.J., Hollod,
G.J., and Johnson, T.C., 1981a, Atmospheric concentrations and deposition
of polychlorinated biphenyls to Lake Superior, in S.J. Eisenreich (ed.),
Atmospheric Pollutants in Natural Waters: Ann Arbor Science, p. 425-444.
Eisenreich, S.J., Looney,
B.B., and Thornton, J.D., 1981b, Airborne organic contaminants in the Great
Lakes ecosystem: Environmental Science and Technology, v. 15, p. 30-38.
Franz, T.P., 1994, Deposition
of semivolatile organic chemicals in snow: Ph.D. Thesis, University of
Minnesota, 397 p.
Franz, T.P., Eisenreich, S.J.,
and Swanson, M.B., 1991, Evaluation of precipitation samplers for assessing
atmospheric fluxes of trace organic contaminants: Chemosphere, v. 23, p.
343-362.
Gianessi, L.P., and Puffer,
C., 1991, Herbicide use in United States: National Summary Report, Resources
for the Future, Washington D.C., 128 p.
____1992, Insecticide use
in U.S. crop production: Resources for the Future, Washington D.C., 108
p.
Gilliom, R.J., Alexander,
R.B., and Smith, R.A., 1985, Pesticides in the Nation's rivers, 1975-1980,
and implications for future monitoring: U.S. Geological Survey Water-Supply
Paper 2271, 26 p.
Glotfelty, D.E., Majewski,
M.S., and Seiber, J.N., 1990, Distribution of several organophosphorus
insecticides and their oxygen analogues in a foggy atmosphere: Environmental
Science and Technology, v. 24, p. 353-357.
Glotfelty, D.E., Seiber, J.N.,
and Liljedahl, L.A., 1987, Pesticides in fog: Nature, v. 325, p. 602-605.
Glotfelty, D.E., Williams, G.H.,
Freeman, H.P., and Leech, M.M., 1990, Regional atmospheric transport and
deposition of pesticides in Maryland, in D.A. Kurtz (ed), Long Range Transport
of Pesticides: Lewis Publishers, Inc., Chelsea, Michigan, p. 199-222.
Goolsby, D.A., Thurman, E.M.,
Pomes, M.L., and Battaglin, W.A., 1993, Occurrence, deposition, and long
range transport of herbicides in precipitation in the midwestern and northeastern
United States, in Selected Papers on Agricultural Chemicals in Water Resources
of the Midcontinental United States: U.S. Geological Survey Open-File Report
93-418, p. 75-89
Haraguchi, K., Kitamura, E.,
Yamashita, T., and Kido, A., 1995, Simultaneous determination of trace
pesticides in urban precipitation: Atmospheric Environment, v. 29, p. 247-253
Kelly, P.L., and Hines, J.W.,
1990, Pesticide use in rural Minnesota: State of Minnesota, Department
of Agriculture, 45 p.
Kurtz, D.A.(ed), 1990, Long
range transport of pesticides: Lewis Publishers, Inc., Chelsea, Michigan,
432 p.
Larson, S.J., Capel, P.D., Goolsby,
D.A., Zaugg, S.D., and Sandstrom, M.W., 1995, Relations between pesticide
use and riverine flux in the Mississippi River Basin: Chemosphere, v. 31,
p. 3305-3321.
Leuenberger, C., Czuczwa, J.,
Heyerdahl, E., and Giger, W., 1988, Aliphatic and polycyclic aromatic hydrocarbons
in urban rain, snow and fog: Atmospheric Environment, v. 22, p. 695-705.
Leuenberger, C.L., Ligocki,
M.P., and Pankow, J.F., 1985, Trace organic compounds in rain. 4. Identities,
concentrations, and scavenging mechanisms for phenols in urban air and
rain: Environmental Science and Technology, v.19, p. 1053-1058.
Ligocki, M.P., Leuenberger,
C.L., and Pankow, J.F., 1985a, Trace organic compounds in rain. 2. Gas
scavenging of neutral organic compounds: Atmospheric Environment, v. 19,
p. 1609-1617.
----1985b, Trace organic compounds
in rain-3. Particle scavenging of neutral organic compounds, Atmospheric
Environment, v. 19, 1619-1626.
Majewski, M.S., and Capel, P.D.,
1995, Pesticides in the atmosphere, distribution, trends, and governing
factors: Ann Arbor Press, Chelsea, Michigan, 214 p.
National Atmospheric Deposition
Program, 1988, Instruction manual, NADP/NTN Site Operation: National Resource
Ecology Laboratory, Colorado State University, Fort Collins, Colorado,
56 p.
Nations, B.K., and Hallberg,
G.R., 1992, Pesticides in Iowa precipitation: Journal of Environmental
Quality, v. 21, p. 486-492.
Nowell, L.H., and Resek, E.A.,
1994 National standards and guidelines for pesticides in water, sediment,
and aquatic organisms--Application to water-quality assessments: Reviews
of Environmental Contamination and Toxicology, v. 140, p. 1-164.
Pankow, J.F., Isabelle, L.M.,
and Asher, W.E., 1984, Trace organic compounds in rain. 1. Sampler design
and analysis by Adsorption/Thermal Desorption (ATD): Environmental Science
and Technology, v. 18, p. 310-318.
Patton, G.W., Hinchley, D.A.,
Walla, M.D., and Bidleman, T.F., 1989, Airborne organochlorines in the
Canadian High Arctic: Tellus, v. 41B, p. 243-255.
Richards, R.P., Kramer, J.W.,
Baker, D.B., and Krieger, K.A., 1987, Pesticides in rainwater in the northeastern
United States: Nature, v. 327, p. 129-131.
Roberts, J.K., and Wojciechowski,
D., 1986, Directory of precipitation monitoring sites, Volume 1: National
Atmospheric Deposition Program, Fort Collins, Colorado, 247 p.
Scharf, J., Wiesiollek, R.,
and Bachmann, K., 1992, Pesticides in the atmosphere: Fresenius Zeitung
fur Analytische Chemie, v. 342, p. 813-816.
Schomburg, C.J., Glotfelty,
D.E., and Seiber, J.N., 1991, Pesticide occurrence and distribution in
fog collected near Monterey, California: Environmental Science and Technology,
v. 25, p. 155-160.
Schottler, S.P., Eisenreich,
S.J., and Capel, P.D., 1992, Atrazine, alachlor, and cyanazine in a large
agricultural river system: Environmental Science and Technology, v. 28,
p. 1079-1089.
Squillace, P.J., Thurman, E.M.,
and Furlong, E.T., 1993, Groundwater as a nonpoint source of atrazine and
deethylatrazine in a river during base flow conditions: Water Resources
Research, v. 29, p. 1719-1729.
Strachan, W.M., and Eisenreich,
S.J., 1990, Mass balance accounting of chemicals in the Great Lakes, in
D.A. Kurtz (ed), Long Range Transport of Pesticides: Lewis Publishers,
Inc., Chelsea, Michigan, p. 291-301.
Tatsukawa, R., Yamaguchi, Y.,
Kawano, M., Kannan, N., and Tanabe, S., 1990, Global monitoring of organochlorine
insecticides--An 11-year case study (1975-1985) of HCHs and DDTs in the
open ocean atmosphere and hydrosphere, in D.A. Kurtz (ed), Long Range Transport
of Pesticides: Lewis Publishers, Inc., Chelsea, Michigan, p. 127-141.
Thurman, E.M., Goolsby, D.A.,
Meyer, M.T., and Kolpin, D.W., 1991, Herbicides in surface waters of the
midwestern United States--The effect of spring flush: Environmental Science
and Technology, v. 25, p. 1794-1796.
Tornes, L.H., 1991, Stream water
quality--Minnesota, National Water Summary 1990-91: U.S. Geological Survey
Water-Supply Paper 2400, p. 335-342.
Tsal, W., and Cohen, Y., 1991,
Dynamic partitioning of semivolatile organics in gas/particle/rain phases
during rain scavenging: Environmental Science and Technology, v. 25, p.
2012-2023.
United States Environmental
Protection Agency, 1994, Prevention, pesticides and toxic substances, questions
and answers, Conditional Registration of Acetochlor: U.S. Environmental
Protection Agency, Washington, D.C., 18 p.
University of Minnesota, 1992,
Cultural and chemical weed control in field crop: Minnesota Extension Service,
Agriculture, University of Minnesota, ERG-BU-3157-S, 27 p.
Valsaraj, K.T., Them, G.J.,
Reible, D.D., and Thibodeaux, L.J., 1993, On the enrichment of hydrophobic
organic compounds in fog droplets: Atmospheric Environment, v. 27A, p.
203-210.
Van Noort, P.C.M., and Wondergem,
E., 1985, Scavenging of airborne polycyclic aromatic hydrocarbons by rain:
Environmental Science and Technology, v. 19, p. 1044-1048.
Welch, H.E., Muir, C.G., Billeck,
B.N., Lockhart, W.L., Brunskill, G.J., Kling, H.J., Olson, M.P., and Lemoine,
R.M., 1991, Brown snow--A long-range transport event in the Canadian Arctic:
Environmental Science and Technology, v. 25, p. 80-286.
Wotzka, P.J., Lee, J., Capel,
P., Ma, L., 1994, Pesticide concentrations and fluxes in an urban watershed,
in Proceedings of the American Water Resources Association's National Symposium
on Water Quality: American Water Resources Association Technical Publication
TPS-94-4, Herndon, VA, p. 135-145.
Wu, T.L., 1981, Atrazine residue
in esturine water and the aerial deposition of atrazine into Rhode River,
Maryland: Water, Air, and Soil Pollution, v. 15, p. 173-184.
Zaugg, S.D., Sandstrom, M.W.,
Smith, S.G., and Fehlberg, K.M., 1995, Method of analysis by the USGS/NWQL-determination
of pesticides in water by C-18 solid-phase extraction and capillary-column
gas chromatography with selective-ion monitoring: U.S. Geological Survey
Open-File Report 95-181, 65 p.
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Conversion Factors, Abbreviations, and Water-Quality Units
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Chemical concentrations are
given in metric units. Chemical concentrations of substances in water are
given in milligrams per liter (mg/L) or micrograms per liter (mg/L).
Milligrams per liter is a unit expressing the concentration of chemical
constituents in solution as mass (milligrams) of solute per unit volume
(liter) of water. One thousand micrograms per liter is equivalent to one
milligram per liter. For concentrations less than 7,000 mg/L, the numerical
value is the same as for concentrations in parts per million.
Use of trade names in this report
is for identification purposes only and does not constitute endorsement
by the U.S. Geological Survey.
