Pesticides in the Atmosphere of the Mississippi River Valley, Part I — Rain

Pesticides in the atmosphere of the Mississippi River Valley, Part I — Rain By Michael S. Majewski, William T. Foreman, and Donald A. Goolsby ABSTRACT Weekly composite rainfall samples were collected in three paired urban and agricultural regions of the midwestern United States and along the Mississippi River during April - September 1995. The paired sampling sites were located Mississippi, Iowa, and Minnesota. A background site, removed from dense urban and agriculture areas, is located near Lake Superior in Michigan. Herbicides were the predominant type of pesticide detected at every site. Each sample was analyzed for 47 compounds and 23 of 26 herbicides, 13 of 18 insecticides, and 3 of 3 related transformation products were detected in one or more sample from each paired site. The detection frequency of herbicides and insecticides were nearly equivalent at the paired Iowa and Minnesota sites. In Mississippi, herbicides were detected more frequently at the agricultural site and insecticides were detected more frequently at the urban site. The highest total wet depositional amounts (µg pesticide/m² per season) occurred at the agricultural sites in Mississippi (1,980 µg/m²) and Iowa (490 µg/m²) and at the urban site in Iowa (696 µg/m²). Herbicides accounted for the majority of the wet depositional loading at the Iowa and Minnesota sites, but methyl parathion (1,740 µg/m²) was the dominant compound contributing to the total loading at the agricultural site in Mississippi. Atrazine, CIAT (a transformation product of atrazine) and dacthal were detected most frequently (76, 53, and 53 percent, respectively) at the background site indicating their propensity for long-range atmospheric transport. INTRODUCTION human health have grown steadily. A wide variety of pesticides have been More than 500 million kg (kilograms) of detected in the atmosphere throughout the pesticides are used each year in the United world (Grover, and others, in press; Majewski States to control many different types of weeds, and Capel, 1995). Pesticides become airborne insects, and other pests in a wide variety of through volatilization and wind erosion of agricultural and urban settings (Aspelin, 1994). particles both during and after the application The highest density of agricultural activity and process. Volatilization is a continuous process harvested cropland in the United States is in the and can be a major dissipative route for many upper Midwest and along the lower Mississippi pesticides (Glotfelty, 1978; Majewski, 1991; River. A wide variety of herbicides and Seiber and Woodrow, 1995). Once airborne, the insecticides are used on many of the diverse pesticide can be carried by wind and deposited crops grown in this region. Although increased in unintended areas by dry (gas and particle) and pesticide use has resulted in increased crop wet (fog and precipitation by rain and snow) production, concerns about the potential depositional processes. These deposited adverse effects of pesticides and pesticide residues can revolatilize, re-enter the transformation products on the environment and atmosphere, and be transported and redeposited downwind repeatedly until they are transformed 0.5 km [kilometer] from cotton field), at the or accumulate, usually in areas with cooler Cedar Rapids, Iowa, airport (sampler located climates (Risebrough, 1990; Wania and ca. 15 m [meters] from corn field), and at the Mackay, 1996). This same process also can U.S. Department of Agriculture’s MSEA occur for the products from abiotic or biotic (Management Systems Evaluation Area) near transformations of pesticides. For some Princeton, Minn., (sampler located ca. 300 m persistent compounds, this deposition and from MSEA fields). A background site revolatilization process can continue for removed from large urban and agriculture areas decades. was located at Eagle Harbor, Mich. This site is A six-month study was conducted that was part of the IADN (Integrated Atmospheric designed to characterize the atmospheric Deposition Network) for Lake Superior. occurrence, temporal patterns, transport, and Sampling began during the first week of deposition of a variety of pesticides used in April and continued through September, 1995. agricultural and urban environments in three The precipitation samples were collected using geographically different regions of the a modified automatic wet-dry precipitation Mississippi River Valley. Weekly composite air collector. Modifications to the collector (gas and particle phase) and precipitation (rain) included replacing the plastic collection bucket samples were collected. with a 31-cm (centimeter) diameter, Teflon Two principal study objectives were 1) to coated, metal funnel connected by Teflon tubing document the occurrence and detection to a 3-L (liter) glass carboy inside a small frequency of a wide variety of herbicides, refrigeration unit located beneath the deposition insecticides, and selected transformation collector. Teflon sheeting also lined the cover products in the various atmospheric matrices of the collector, which was placed over the (gas phase, particle phase, and precipitation) at funnel during dry periods. Each sample was a urban and agricultural areas over one growing composite of the precipitation events that season, and 2) to compare the types of occurred during a one-week period. If more pesticides detected among three geographically than one liter of liquid was collected during a different areas of the Mississippi River Valley. sampling period, the total volume was recorded The results of the study in relation to the and a 1-L sub-sample was taken for analysis. If precipitation data are reported in this paper. less than 75 ml (milliliter) of rainwater was collected at the end of the 1-week sampling Sampling Sites period, it was left in the container and the sampling period was extended for another week. Each monitoring site was chosen to be If at the end of a 2-week period there was not within or near an existing NAWQA (U.S. sufficient rainwater for an appropriate Geological Survey National Water Quality extraction, the liquid was discarded, the carboy Assessment program) study unit. The urban and cleaned, and a new collection period was begun. suburban sampling sites (Figure 1) for this study were located at Jackson, Miss. (Mississippi Each sample was extracted using C-18 Embayment NAWQA study unit), Iowa City, solid-phase extraction followed by selected ion Iowa (Eastern Iowa Basins NAWQA study GC/MS (gas chromatographic/mass unit), and Minneapolis, Minn. (Upper spectometric) analysis for 47 herbicides, Mississippi River Basin NAWQA study unit). insecticides, and selected transformation The agricultural sampling sites were located products (Zaugg, and others, 1995). The near Rolling Fork, Miss. (sampler located ca. concentration of each pesticide compound in microgram per liter (µg/L) was divided by the extensively in the production of corn, soybeans, actual rainfall amount in cm (centimeter) to sorghum, and to a lesser extent, cotton. Their obtain the total depositional flux (µg/m² state-wide use in Iowa and Minnesota range [microgram per square meter] per sample and from 1 to 4 million kg each annually with an per growing season). This was done to facilitate order of magnitude less used in Mississippi the comparison between each sampling period (Gianessi and Anderson, 1995). In Mississippi, and sampling site. the rice herbicides molinate, propanil, and thiobencarb were among the most frequently Results and Discussion detected pesticides at both the agricultural and the urban sites. An average of 18 samples were collected at Atrazine, CIAT, and dacthal were the most each location — 16 at each of the Mississippi frequently detected compounds (76, 53, and 53 sites, 18 at Iowa City, Iowa, 20 at Cedar percent, respectively) at Eagle Harbor, Mich., Rapids, Iowa, 20 at Minneapolis, Minn., 17 at the background site. These findings indicate Princeton, Minn., and 17 at Eagle Harbor, Mich. that of the 47 pesticides analyzed for in this Six herbicides (alachlor, atrazine, CIAT [2- study, these three are relatively stable in the chloro-4-isopropylamino-6-amino-s-triazine, a atmosphere and are subject to at least regional- transformation product of atrazine], cyanazine, atmospheric transport. Atmospheric transport dacthal, and metolachlor) were detected at every and deposition often are the major or only input site in at least one sample. Six other herbicides mechanisms for the movement of these types of (acetochlor, EPTC, pendimethalin, prometon, pesticides into remote, pristine environments. simazine and trifluralin) were detected at six of Five insecticides (carbaryl, carbofuran, the seven sites in at least one sample. chlorpyrifos, diazinon, and parathion) were Herbicides were the predominant type of frequently detected at most of the paired sites. pesticide detected at every site. Of the Many of the insecticides were detected at pesticides analyzed for, 23 of 26 herbicides, 13 comparable frequencies at both the agricultural of 18 insecticides, and 3 of 3 transformation and the urban sampling locations, but the products were detected. depositional amounts at the agricultural sites The general trend in pesticide occurrence generally were higher with the exception of and detection frequency in rain samples at the malathion, carbaryl, diazinon, and chlorpyrifos. three paired sampling sites was that nearly every These four compounds are used extensively in pesticide detected at the agricultural site was the urban environment

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