Monitoring Pesticide Runoff and Leaching from ... - ACS Publications

Chapter 2

Monitoring Pesticide Runoff and Leaching from Four Farming Systems on Field-Scale Coastal Plain Watersheds in Maryland 1

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D. R. Forney , J. Strahan , C. Rankin , D. Steffin , C. J. Peter , T. D. Spittler , andJ.L.Baker Downloaded by COLUMBIA UNIV on September 20, 2012 | http://pubs.acs.org Publication Date: April 3, 2000 | doi: 10.1021/bk-2000-0751.ch002

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DuPont Agricultural Products, Chesapeake Farms, Chestertown, MD 21620 Cornell Analytical Laboratories, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456 Iowa State University, Ames, IA 50011

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Losses of herbicides in runoff and leachate were measured in four different production systems. These production systems varied in the amounts and types of herbicides used, from preemergence applications of products used in the kg/ha, to selective use of postemergence herbicides used in g/ha. The highest herbicide concentrations in runoff samples were found in the first runoff event after application. Herbicides used at higher use rates were found in higher concentrations in both runoff and leachate samples. Incorporation of herbicides greatly reduced runoff losses. Herbicides used at similar rates but with shorter half-lives were found at lower concentrations in leachate samples. No-till treatments resulted in the highest concentrations in the leachate. Crop protection from insects, diseases, nematodes, and weeds is a critical component of agricultural sustainability (i). Synthetic pesticides are among a suite of technologies that have afforded tremendous gains in agricultural productivity, profitability, and efficiency in the last 50 years. While consumers are increasingly concerned about environmental consequences of production methods, pesticides remain the primary means of controlling pests. Off-site movement of agricultural chemicals into surface and groundwaters is a common consequence of their use (2). Perfecting the use of pesticides is an ongoing need in the development of environmentally sound, economically viable, and socially acceptable production systems (/). Concerns about pesticides in surface and groundwater have spawned numerous studies over the years to quantify the amounts of different materials leaving treated fields and to characterize the pesticide concentrations of receiving waters (3-8). Studies have focused on the more widely used compounds, and those that appear to represent a 20

© 2000 American Chemical Society

In Agrochemical Fate and Movement; Steinheimer, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

21 threat to human or aquatic ecosystem health based on their physical, chemical, and biological properties. Herbicides are the most widely used class of pesticides, and have received considerable attention. Their losses in surface runoff water have been observed to be highly dependent on their properties, notably soil adsorption and persistence, together with rate, timing, and method of application (9). Also, the timing of runoff producing rainfall events, and factors such as tillage and buffer or filter strips that influence the movement of water and sediments from fields, influence pesticide movement.

Downloaded by COLUMBIA UNIV on September 20, 2012 | http://pubs.acs.org Publication Date: April 3, 2000 | doi: 10.1021/bk-2000-0751.ch002

Herbicides Used Among the herbicides used in U.S. crop production, triazines have long been a focus of concern due to their widespread use, relatively high rates of application, extended persistence, and moderate soil adsorption characteristics. Among these, atrazine is the pesticide most often detected in surface and groundwater resources today (6). With application rates in the range of 0.5 to 2.0 kg/ha, it was used on 71% of surveyed U.S. corn acres in 1996 at an average rate of 1.2 kg/ha, with corn applications totaling 24.3 million kg (10,11). It is the second most widely used pesticide in the Chesapeake Bay watershed (12). It is sold in a number of formulations, all of which are classified as "Restricted Use Pesticide" due to ground and surface water quality concerns. Like atrazine, but less persistent, cyanazine is a widely used corn herbicide that also has been the focus of water quality concerns. Uncertainty as to its regulatory fate in the U.S. in light of water quality and toxicological concerns led to an agreement between DuPont and the U.S. EPA for a gradual withdrawal of cyanazine from the marketplace, with all uses to be canceled by 2003. It is sold in a number of formulations, all of which are classified as "Restricted Use Pesticide" due to toxicological and ground and surface water concerns. In 1996, it was used on 13% of surveyed U.S. corn acreage at an average use rate of 2.6 kg/ha, with corn applications totaling 9.4 million kg (//). Metribuzin, a triazine herbicide used on soybeans, has declined in importance due to the introduction of other new herbicides, but was still used on 9% of surveyed soybean acreage in 1996, at an average use rate of 0.34 kg/ha, with soybean applications totaling 1.9 million kg. The acetanilide, or chloroacetamide herbicides, including alachlor and metolachlor, are frequently cited among compounds of concern for aquatic or toxicological risk (8). They are widely used due to their utility in both corn and soybean production. While alachlor is being phased out in recent years in favor of acetochlor, it was still used in 1996 on 9% of surveyed corn acreage and 5% of surveyed soybean acreage. Average use rates were 2.4 kg/ha in corn and 1.8 kg/ha in soybeans, with U.S. corn and soybean applications totaling 6.9 million kg (//). It is sold in a number of formulations, all of which are classified as "Restricted Use Pesticide" due to oncogenicity. Metolachlor was used in 1996 on 30% of surveyed corn acres and 5% of surveyed soybean acres, at average use rates of 2.2 and 2.0 kg/ha, respectively, with corn and soybean applications totaling 20.5 million kg (11). Together with the triazines, atrazine and In Agrochemical Fate and Movement; Steinheimer, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

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cyanazine, the acetanilides alachlor and metolachlor are routinely detected in surface and subsurface waters draining from agricultural lands (13). In addition, they are routinely detected at sub-ppb levels in precipitation. Precipitation may deposit more alachlor in the Mississippi River Basin than is transported out of the basin in stream flow (6). These herbicides are most often applied to the soil at or right before planting time to provide residual control of weeds. Triazines and acetanilides were among the earliest truly selective and widely effective herbicides available to U.S. corn and soybean farmers, and have been in use in U.S. crop production for approximately 20 to nearly 40 years. During this period, pesticide discovery and development efforts have brought new chemistries with new characteristics to the market. At least two new classes of herbicides, imidazolinones and sulfonylureas, have been widely adopted. In soybeans, imidazolinones, imazethapyr and imazaquin widely replaced metribuzin and the acetanilides in the late 1980s and 1990s. With far lower use rates typical of newer pesticides, these two materials were used on 43% and 15% of surveyed U.S. soybean acres in 1996 at use rates of 0.07 and 0.10 kg/ha, respectively, with applications totaling 0.54 and 0.32 million kg (11). Along with the adoption of imidazolinones, sulfonylureas have also had a tremendous impact on the quantities of pesticides used because of their low use rates. Worldwide, substitution of sulfonylureas for older, higher-use-rate materials in cereals has afforded an estimated reduction in herbicide use of approximately 99 million kg, with an associated reduction of perhaps 3 billion kg of manufacturing waste (14). While much is known about the physical, chemical, and biological properties of sulfonylureas and their degradation, mobility, and sorption processes, little water quality monitoring data have appeared in the literature for these compounds(/5, 16). Losses of 1.1 to 2.3% of applied nicosulfuron and chlorimuron were reported for a rainfall simulated runoff study, similar to the percentage losses typically reported for other higher use rate herbicides (17). In corn, nicosulfuron is used as a postemergence (foliar) spray for annual and perennial grasses and select broadleaf weeds, at rates of 35 to 70 g/ha (18). Following first commercial use in 1990, its use has grown to 12% of surveyed corn acres, with a total of 111 thousand kg applied, in 1996 (11). Chlorimuron ethyl has both preemergence and postemergence uses, with rates of approximately 35 and 10 g/ha respectively. It was used on 14% of surveyed U.S. soybean acres, with applications totaling 65 thousand kg (//). Thifensulfuron methyl is used in soybeans, corn and winter cereals, and tribenuron methyl is used in winter cereals (among other uses) at rates of approximately 5 to 35 g/ha. They would appear to pose minimal threat to surface and ground water quality due to their very short persistence (15,16).



23 Many approaches are used to estimate or determine the contamination of surface and groundwater by pesticides. In the U.S., EPA registration of a pesticide under FIFRA requires the demonstration that the active ingredient is not likely to accumulate in water at levels that pose unreasonable risk to human health or aquatic ecosystems. Methods employed include model predictions based on known physical and chemical properties, laboratory soil-column leaching studies, small-scale prospective ground water monitoring studies, natural or artificial rainfall field-edge runoff monitoring, whole watershed studies, and monitoring of receiving waters. Each approach offers its own benefits and limitations. Modeling efforts offer the opportunity to simulate wide ranges of conditions but can be limited in accuracy based on the assumptions that must be made when knowledge of the precise impact of variables is not known. Field studies are site-specific with regard to soils, hydrology, agronomy, and prevailing weather. Evaluating environmental impacts of agricultural production practices, including pesticides, has evolved toward a more systems-oriented holistic approach in recent years, in accord with recommendations put forth by the National Research Council (19). In the Midwest, the Management Systems Evaluation Areas (MSEA) program represents an ambitious regional approach that includes the goals of identifying and evaluating agricultural management systems that can protect water quality, and assess the impact of agricultural chemicals and practices on ecosystems associated with agriculture (20). This program recognizes that field studies are necessarily site specific and that a diversity of conditions are encountered from site to site, but also that results of multiple projects sharing common objectives will form a powerful tool in solving regional problems. Materials and Methods "A Sustainable Agriculture Project at Chesapeake Farms" is a watershed-focused long-term comparison of four cash grain farming systems relevant to the mid-Atlantic region of the U.S. The project arose out of discussions among representatives of DuPont Agricultural Products and a number of progressive thinkers from diverse perspectives concerned about agricultural sustainability. Collaborators include environmental and agricultural non-profit organizations, government agencies, academia, agri-business, and a group of concerned farmers. Each contributes specific talents, diverse thinking, and resources needed to ensure the project's success and give the project the depth of thought needed to help meet the groups' common challenges. A Farmer Advisory Board guides all decisions, assists with outreach, and ensures compliance with local concerns. Chesapeake Farms encompasses 1335 ha of agricultural and wildlife habitat lands on the Eastern Shore of the Chesapeake Bay near Chestertown, MD. Soils range from gravelly upland soils to low-lying hydric soils. Predominant agricultural soils are silt loams, with management concerns including crusting and drainage. The predominant soil type in the area under investigation is Mattapex Variant silt loam (fine-loamy, mixed, mesic Aquic Hapludult), considered deep and moderately well-drained, formed in silty loess deposited by wind on older, clayey soil. The AP horizon (approximately In Agrochemical Fate and Movement; Steinheimer, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

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28 cm) has about 2% organic matter, CEC of around 8.0 meq/lOOg, and pH is maintained in the 6.0 to 7.0 range by liming. The four farming systems at Chesapeake Farms are subject to distinct rotation schemes, tillage practices, fertility programs, and methods of pest control, all options currently in use on farms in the mid-Atlantic region of the U.S. Each system covers approximately 4 ha and occupies a discreet watershed so that runoff water, soil, nutrients, and pesticide losses can be monitored. Grass waterways and berms manage surface runoff for each watershed, and a flume with automated monitoring equipment is used to measure and samples runoff water (Figure 1). The systems demonstrate varying reliance on rotational diversity and in-season management and labor; make optimal use of fertilizers, crop protection chemicals, and other purchased input; and employ Best Management Practices to keep sediments, nutrients, and pesticides on the field and out of the water. A replicated, small-plot experiment based on the four cropping systems in the watershed study is being conducted in an adjacent field of similar soil type. Comparisons are made on yield, soil tilth, fertility, and pest populations, as well as nutrient and pesticide movement through the soil profile via both passive and suction soil-water samplers. Cropping Systems. Each cropping system is managed using commercial farming equipment, with all procedures being performed as close to the ideal time, considering prevailing conditions, as possible for optimum crop production. Pesticide applications were made with commercially formulated products, in water or liquid fertilizer, by either custom applicators or on-farm equipment. System A. System A consists of continuous no-till corn, with rye cover crop (A2) and without rye cover crop (Al). Systems A l and A2 employ a "programmed" approach to pest and nutrient management, in which crop protection is accomplished largely through pre-planned applications of products known to control the anticipated pests. System A employs approximately 3600 g/ha of pesticides annually, including atrazine and cyanazine for burndown of existing vegetation at planting time (together with 2,4-D, as well as paraquat for added burndown of the rye cover crop). Insecticide is included in furrow at planting time (tefluthrin in 1994 and 1995, chlorethoxyfos in subsequent years), and es-fenvalerate is included in the "burndown" herbicide application (for which the carrier is a nitrogen fertilizer solution). A combination of nicosulfuron and dicamba is applied postemergence for perennial weeds. Within this program approach, the triazines were applied in 1994 and 1995 at rates designed to provide season-long annual weed control, the program then being completed with a spot application of the nicosulfuron/dicamba mixture, which was applied to 30% of the field in 1994. By 1995, however, due to a long history of triazine use on the farm, escaping triazine-resistant weeds required treatment on 80% of the field. For subsequent years, a planned approach was employed with a reduced rate of the triazines and a postemergence broadcast application of the nicosulfuron/dicamba mixture. Pesticide runoff monitoring efforts for this system have focused primarily on the triazines and nicosulfuron (Tables I and II).



Figure 1. A Sustainable Agriculture Project at Chesapeake Farms.


26 Table I. Annual Herbicide Concentrations and Losses for Watershed A


Herbicide 1994 Atrazine Cyanazine Nicosulturon 1995 Atrazine Cyanazine Nicosulturon 1996* Atrazine Cyanazine Nicosulturon

Avg. Cone. (ug/L)

Max. Cone. Oig/L)

DAA days (event)

Loss (%)

Loss (g/ha)

Amount applied (g/ha)

5.16 25.54 0.002

240.00 >1000 0.07

2(1) 2(1) 20(1)

1.25 1.96 0.04

8.79 43.46 0.003

701.8 2213.5 8.8

19.62 20.04 0.672

327.00 212.00 10.55

1(1) 11(4) 5(1)

14.29 4.67 10.40

100.26 103.45 2.45

701.8 2213.5 23.6

120.97 53.93 2.03

77.33 501.3 8(2) 280.00 15.43 550.00 1581.1 68.10 7(1) 4.31 29.4 3.85 1.37 4.67 3(1) * Includes estimated flow and loss for 2nd event after application, a major event when sampler failed. Flow and loss were estimated based on measured flow for this event in other watersheds and their known relationships to this watershed, and pesticide concentrations in similar events the same week in this watershed.

Table II. Annual Herbicide Concentrations and Losses for Watershed A2 Herbicide 1994 Atrazine Cyanazine Nicosulturon 1995 Atrazine Cyanazine Nicosulturon 1996 Atrazine Cyanazine Nicosulturon

Avg. Cone. (ug/L)

Max. Cone. (ug/L)

DAA days (event)

Loss (%)

Loss (g/ha)


43.22 84.79 0.01

680.00 1035.00 0.13

1(1) 1(1) 34(2)

3.64 2.26 0.12

15.94 31.28 0.003

438.4 1382.8 2.6

7.86 8.48 0.18

114.00 162.00 1.28

11(2) 9(1) 19(1)

3.87 1.32 3.36

16.04 17.31 0.43

414.6 1307.9 12.9

50.18 43.48 1.17

150.00 290.00 7.37

7(1) 7(1) 3(1)

11.60 2.97 4.97

31.91 25.72 0.81

275 867.3 16.2

System B. This system employs a two-year corn and soybean rotation with deep-tillage prior to corn, and full-season no-till soybeans. System B also relies on programmed pest and nutrient management. System B employs approximately 3400 g/ha of pesticides annually. For corn, these include atrazine, cyanazine, and metolachlor applied and incorporated into the top 5 cm of the soil prior to planting corn. Spot applications of a nicosulfuron/dicamba mixture are made to control perennial weeds. The rotation with soybeans, with the herbicides used there, has prevented any buildup of triazine-resistant weeds. The programmed approach for soybeans includes a planting-time application of a mixture of metribuzin, chlorimuron ethyl, and alachlor, together with glyphosate if needed for additional "burndown", In Agrochemical Fate and Movement; Steinheimer, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.


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Table III. Annual Herbicide Concentrations and Losses for Watershed B Herbicide 1994 Alachlor Metolachlor Atrazine Cyanazine Metribuzin Chlorimuron ethyl Nicosulfuron 1995 Alachlor Metolachlor Atrazine Cyanazine Metribuzin Chlorimuron ethyl Nicosulfuron 1996 Alachlor Metolachlor Atrazine Cyanazine Metribuzin Chlorimuron ethyl Thifensulfiiron methyl

Avg. Cone. (Hg/L)

Max. Cone.

DAA Days (event)

Loss (%)

Loss (g/ha)


4.23 2.35 2.85 1.39 0.01 1.08 0.02

36 11 8 12 0.12 12 0.08

0(1) 3(1) 8(2) 3(1) 54(4) 0(1) 21(3)

0.15 0.25 0.83 0.13 0 2.61 0.33

2.60 1.44 1.75 0.85 0.01 0.62 0.01

1733.1 578.9 210.3 663.3 133.9 23.9 4.2

0.72 0.41 0.7 0.3 0.01 0.18 0.07

2.97 8.6 8.08 11.7 0.52 5 0.53

54(4) 29(4) 29(4) 29(4) 25(3) 12(2) 21(2)

0.11 0.08 0.38 0.05 0.03 1.76 1.72

1.23 0.70 1.20 0.51 0.02 0.26 0.11

1161.3 863.9 313.8 989.9 89.8 14.9 6.3

2.89 2.5 2.08 0.85 0.62 0.41

Monitoring Pesticide Runoff and Leaching from ... - ACS Publications

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