Journal of Environmental Quality 32:447-455 (2003)
© 2003 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
TECHNICAL REPORTS
Ecological Risk Assessment
Risk Assessment of Pesticide Runoff from Turf
Douglas A. Haith*,a and
Frank S. Rossib
a Biological and Environmental Engineering, Riley-Robb Hall, Cornell Univ., Ithaca, NY 14853
b Dep. of Horticulture, Plant Science Building, Cornell Univ., Ithaca, NY 14853
* Corresponding author (dah13{at}cornell.edu)
Received for publication December 19, 2001.
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ABSTRACT
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The TurfPQ model was used to simulate the runoff of 15 pesticides commonly applied to creeping bentgrass (Agrostis stolonifera L.) fairways and greens on golf courses in the northeastern USA. Simulations produced 100-yr daily records of water runoff, pesticide runoff, and pesticide concentration in runoff for three locations: Boston, MA, Philadelphia, PA, and Rochester, NY. Results were summarized as annual and monthly means and annual maximum daily loads (AMDLs) corresponding to 10- and 20-yr return periods. Mean annual pesticide runoff loads did not exceed 3% of annual applications for any pesticide or site, and most losses were substantially less than 1% of application. However, annual or monthly mean concentrations of chlorothalonil, iprodione, and PCNB in fairway runoff often exceeded concentrations that result in 50% mortality of the affected species (LC50) for aquatic organisms. Concentrations of azoxystrobin, bensulide, cyfluthrin, and trichlorfon in extreme (1 in 10 yr or 1 in 20 yr) events often approached or exceeded LC50 levels. Concentrations of halofenozide, mancozeb, MCPP, oxadiazon, propiconazole, thiophanate-methyl, triadimefon, and trinexapac-ethyl were well below LC50 levels, and turf runoff of these chemicals does not appear to be hazardous to aquatic life in surface waters.
Abbreviations: AMDL, annual maximum daily load • LC50, Concentration that results in 50% mortality of the affected species
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INTRODUCTION
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PESTICIDE RUNOFF HAZARDS associated with turf are uncertain. Chemical applications are intensive on highly managed turf systems such as golf courses, and proximity to ponds, streams, and other surface waters seemingly make pollution likely. However, the dense vegetation of turfgrasses and associated organic matter strongly favors water retention, and runoff from turf is much less common than from other urban and agricultural land uses. The issue is partially resolved by monitoring studies in urban watersheds from the U.S. Geological Survey National Water Quality Assessment (NAWQA), which indicate widespread presence of pesticides typically used in lawns, gardens, and golf courses (United States Geological Survey, 1999). Similarly, other monitoring has detected many pesticides in surface waters on or near golf courses, including nine pesticides that exceeded maximum allowable concentrations based on protection of aquatic species (Cohen et al., 1999). These results are supported by field experiments that have established that pesticide runoff losses can be substantial when large irrigation or precipitation events follow recent chemical applications (Cole et al., 1997; Evans et al., 1998; Hong and Smith, 1997; Ma et al., 1999; Smith and Bridges, 1996; Watschke et al., 2000).
Monitoring and experiments have demonstrated that surface water pollution from turf pesticides is possible, but our knowledge of the likelihood and severity of such contamination is meager. Pollution of surface waters is a random event produced by a combination of precipitation and chemical application, which may occur in only one or two days over several years. The rarity of these events limits our ability to draw direct conclusions from field experiments and monitoring.
Fate and transport models are a third tool that may be used for water pollution assessments. Compared with monitoring and field experiments, models are very efficient, because they can rapidly evaluate the effects of widely differing chemicals, weather, management, and site conditions. When the models are run with multiyear weather records, simulations can provide long-term estimates of pesticide runoff and frequencies or return periods of extreme events. The approach is reasonable only if a model has been shown to be an accurate description of the pesticide runoff process, as confirmed by testing with field data. In this fashion, the model becomes a means of efficiently using and extrapolating the results of field experiments.
This paper describes an application of simulation modeling to assess the runoff of pesticides commonly used on golf course turfs in the northeastern USA. The TurfPQ model (Haith, 2001, 2002) was used for these simulations. TurfPQ, which is a pesticide runoff model developed exclusively for turf, was tested using observed runoff data from 52 pesticide runoff events involving six pesticides measured in plot studies in four states. The current study had three objectives. The first was to determine the relative runoff susceptibility of pesticides labeled for use on golf courses in the northeastern USA. The second was to assess the severity of the pollution hazards by comparison of pesticide concentrations in runoff with levels that have been shown to be hazardous to aquatic species. The third was to evaluate the importance of regional variations in weather patterns on pesticide runoff loads and concentrations. Comparisons and evaluations were based on long-term mean values and on infrequent extreme events.
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MATERIALS AND METHODS
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Simulation Approach
The study simulated the runoff of 15 pesticides (Table 1) commonly applied to golf course greens and fairways in the northeastern USA. Simulations were repeated for three locations, Boston, MA, Philadelphia, PA, and Rochester, NY. One-hundred-year records of daily precipitation and temperature were produced for each of these locations by the weather generator developed by Hanson et al. (1994).
Mean historical temperatures and precipitation for the cities are shown in Table 2. Although these cities have similar humid temperate climates, there are significant climate differences that could be expected to influence pesticide runoff. For example, the nearly identical annual precipitation amounts in Philadelphia and Boston are distributed much differently during the year. Philadelphia has relatively more precipitation during the summer months, which coincide with most pesticide applications. Rochester is colder and has substantially less precipitation than the other cities, but summer precipitation is nearly the same as for Boston.
The TurfPQ model, which was used in the simulations, computes water and chemical mass balances on a one-day time step. Hydrology is determined from a curve number calculation for runoff volume. Pesticide in turf foliage and thatch is partitioned into adsorbed and dissolved components during a precipitation or irrigation event. Input requirements are daily precipitation and temperature, pesticide application dates and amounts, runoff curve number, pesticide organic carbon partition coefficient (Koc), and degradation half-life and turf organic matter content. Default values were developed for curve numbers and organic carbon contents based on grass height and turf thickness. Testing with field data indicated that the model typically produced conservative overpredictions of pesticide runoff, particularly with strongly adsorbed pesticides. Mean predicted pesticide runoff was 2.9% of application, compared with an observed mean of 2.1%. TurfPQ captured the dynamics of the pesticide runoff events well with R2 = 0.65 (see errata for Haith, 2001). The model, default parameter values, and testing results are described in more detail in Haith (2001).
Testing of the TurfPQ model as described in Haith (2001) was limited to irrigation and precipitation events, and the model's accuracy for the snowmelt conditions, which can occur in the three study cites, is uncertain. However, snowmelt runoff is modeled with the degree-day melt and curve number selection procedure used in the Generalized Watershed Loading Functions (GWLF) watershed model, and that approach has been shown to produce accurate winter streamflows (Haith and Shoemaker, 1987; Haith et al., 1992; Tung and Haith, 1995). A greater concern is probably in the influence of cold weather on chemical degradation. Temperature effects on pesticide decay are neglected in TurfPQ, and as a result, calculated winter pesticide levels are almost certainly too low. This would in turn produce underestimates of pesticide losses in snowmelt runoff.
Turf Conditions and Management
The curve number runoff model considers that soils fall into one of four hydrologic groups based on runoff potential: A (low runoff), B, C, or D (high runoff). New greens are typically sand-based, which would correspond to Group A. Fairways are formed from a site's existing soil, and could be any of the four groups. We assumed a sandy clay loam fairway, corresponding to hydrologic Group C. A May-through-October growing season was assumed at each location.
Grass type for greens and fairways was creeping bentgrass, maintained at heights of 3.5 mm for putting greens and 11 mm for fairways. Thatch thicknesses of 5 mm for greens and 8 mm for fairways were used. Based on the default values given in Haith (2001), these conditions produced runoff curve numbers of 35 for greens and 67 for fairways. Organic carbon contents were 6000 kg/ha for greens and 10 200 kg/ha for fairways.
Frequent irrigation with moderate water amounts is a standard management practice in this region, and we included daily watering of greens with 2.5 mm in June, July, and August. Irrigation of fairways was 6.4 mm every three days in June, July, and August. These irrigation amounts are likely to have two different effects on pesticide losses. First, as shown in Haith (2001), irrigation will leach chemicals from the turf into the soil, thus reducing the potential for pesticide runoff. Conversely, irrigation raises antecedent moisture, increasing the likelihood of significant water runoff from storm events.
Pesticide Applications and Properties
Characteristics of the 15 pesticides included in the study are listed in Table 3. Pesticide selection, application, and timing are consistent with label information (C & P Press, 2000) and are typical for managing creeping bentgrass on northeastern U.S. golf courses. The chemicals include insecticides, herbicides, fungicides, and one plant growth regulator. Half-lives and Koc values were taken from USDA Agricultural Research Service (2001) or Tomlin (2000). Half-life information for turf chemicals is problematic, and pesticide databases typically provide one or more of the following half-lives: soil dissipation, photolysis, and/or soil aerobic decomposition, none of which completely describes pesticide behavior on turf vegetation. Soil dissipation rates measure all loss mechanisms, including volatilization, leaching, and runoff. Photolysis could be applicable to the portion of chemical on the tops of grass surfaces, and aerobic soil rates, which depend on microbial processes, may be duplicated in the heavily organic and shaded thatch. We used the soil aerobic rates whenever possible, essentially assuming that application sprays or subsequent irrigation is sufficient to mix pesticide throughout the combined foliage and thatch layer, leaving relatively small amounts exposed to sunlight.
General ambient water quality criteria are not available for most of these pesticides, so runoff concentrations were compared with the LC50 levels shown in Table 3. These numbers are experimentally determined ambient water concentrations that result in 50% mortality of the affected species. Values were selected for rainbow trout (Salmo gairdneri) and water flea (Daphnia magna) since data for these species were the most commonly listed. Trout numbers were for 48- or 96-h durations, and all water flea values corresponded to 48-h durations. The LC50 concentrations have limitations as indicators of pesticide risk. They fail to measure chronic effects of lower-level concentrations and reported values often vary significantly from experiment to experiment. Also, regulatory water quality standards would typically be set at concentrations much lower than LC50 levels.
Outputs
Simulations produced a large amount of information that could be used for risk assessment. The basic results were runoff water volume and pesticide mass in runoff for each day in 100 different years. These were obtained for both greens and fairways with all pesticides at each location (2 x 15 x 3 = 90 different simulations). The information was summarized by annual and monthly means, and by extreme events, as measured by the annual maximum daily load (AMDL) of pesticide in runoff; that is, the largest one-day pesticide runoff mass produced in a year. All reported concentrations are flow-weighted; for example, mean annual concentration is mean annual mass load divided by mean annual runoff volume.
Means are useful in elucidating differences among chemicals, locations, and turf systems. They also can provide information on seasonal trends and the chronic effects on receiving waters. The AMDLs are indicators of shock loads or acute effects on surface waters. They are comparable with river flood flows, and their rarity is measured by return period, or the average number of years between occurrences. For example, a 1-in-20-yr AMDL would be expected to occur, on the average, once every 20 yr.
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RESULTS AND DISCUSSION
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Water Runoff
Mean monthly and yearly runoff volumes for the three locations are given in Table 4. Fairway runoff vastly exceeds runoff from greens because of the enhanced infiltration on the sand-based greens. Runoff totals and seasonal patterns differ greatly with location. Boston and Philadelphia have comparable greens runoff, but fairway runoff is substantially larger in Boston because of greater winter precipitation. Rochester precipitation is 80% of Boston and Philadelphia levels, and as a result, greens runoff is negligible in Rochester and fairway runoff is only about 50% of the values for Boston and Philadelphia. Precipitation and, hence, runoff is more uniformly distributed in Philadelphia than at the other two sites, producing larger water volumes during the growing season. These high flows are concurrent with most pesticide applications, and are a primary cause of large pesticide runoff loads at Philadelphia.
Mean Pesticide Runoff Loads and Concentrations
Mean annual loads and concentrations from greens are given in Table 5. No more than small fractions of a percent of annual pesticide applications are lost in runoff from greens. However, these minimal mass fluxes do not necessarily translate into insignificant concentrations. Concentrations of chlorothalonil, iprodione, PCNB, and trichlorfon all approach or exceed the LC50 levels for rainbow trout and/or water flea. The effects of these concentrations may be minor, however, since they are contained in very small amounts of runoff (Table 4). Such runoff would often be an insignificant component of the total water volume of a receiving water, resulting in considerable dilution.
Comparable results for fairways are shown in Table 6. Azoxystrobin, halofenozide, iprodione, and propiconazole are the chemicals most susceptible to runoff loss, as measured by percentages of application lost in runoff. These results are consistent with the chemical properties listed in Table 3, which indicate that these four pesticides are relatively soluble and persistent. Mean annual fairway pesticide loads are typically one or two orders of magnitude higher than for greens, with annual runoff losses approaching 1 or 2% for several pesticides. The much greater fairway losses are mainly due to the larger runoff volumes (Table 4). Regional differences in loads are also apparent, with Rochester loads always substantially less than those obtained for the other locations. Philadelphia runoff loads are higher than Boston's for most pesticides, due to the higher growing season runoff volumes, particularly June, July, and August. The pattern is different for a chemical such as PCNB, which is applied later in the year.
The concentrations of pesticides in fairway runoff are similar to those determined for greens, but they are associated with much greater runoff volumes. The annual mean chlorothalonil concentrations in fairway runoff at Boston, Philadelphia, and Rochester all substantially exceed LC50 levels and are contained in 67.9, 55.1, and 30.9 mm of water, respectively. Concentrations in greens runoff were similar, but the associated runoff values were only 2.0, 1.9, and 0.3 mm, respectively. Even with considerable dilution in surface waters, chlorthalonil runoff from fairways may significantly effect aquatic species. Similar concerns are apparent with iprodione, PCNB, and trichlorfon. Regional differences in mean concentrations are not as apparent as with mass loads. Although concentrations at Rochester are typically lower than the other two locations, this was not always the case.
Additional perspectives on runoff loads can be obtained from the mean monthly values shown for iprodione on greens in Table 7. Mean mass loads and concentrations differ greatly with season. Although iprodione is applied in June, July, and August, mass losses at Boston are actually higher in winter months due to the higher runoff volumes. Concentrations are much higher in the summer months at all locations, but may have limited effects due to the low runoff volumes.
The situation for fairways, as shown in Table 8, is somewhat different. Fairways have significant runoff during summer months, and as a result, mass runoff loads as well as concentrations are highest in this season. Iprodione concentrations in summer months greatly exceed annual averages and the LC50 for water flea. Receiving waters are often at low levels during this period, and these runoff discharges are likely to have major effects. The monthly results provide a different twist on regional differences. Although annual mean runoff, pesticide loads, and concentrations are lower at Rochester than the other locations, differences are much less in June, July, and August. In these months, discharges are very similar at Boston and Rochester, although both are much lower than Philadelphia.
Monthly fairway results for chlorothalonil are shown in Table 9. The LC50 concentrations for at least one and usually both of the indicator species are exceeded in each month at each location. Concentrations in summer months exceed both LC50 levels by more than an order of magnitude.
The mean results given in Tables 5 through 9 indicate that runoff of at least 4 (chlorothalonil, iprodione, PCNB, and trichlorfon) of the 15 chemicals are potential sources of adverse aquatic effects. The reasons for these potential effects differ with pesticide. Relatively small percentages of chlorothalonil are lost in runoff, but this chemical has a very high total application (9250 g/ha every 10 d in May–September), a moderate half-life (48 d), and is quite toxic (low LC50). Iprodione is significantly less toxic than chlorothalonil, but is much more likely to enter into solution, as indicated by Koc. The relatively high concentrations of PCNB seem to be due to its late-season application, just before major periods of runoff. Other studies have indicated that a high percentage of annual runoff from turf areas occurs during winter conditions (Kussow, 1995), therefore increasing the risk of significant runoff of materials applied late in the year.
Trichlorfon is a special case. Concentrations in runoff are minimal, but the listed water flea LC50 is so small (0.00096 mg L-1) that it is almost invariably exceeded. For all the other pesticides, the LC50 values for water flea and rainbow trout are of comparable magnitude, but the difference for trichlorfon is three orders of magnitude. The EXTOXNET database (Oregon State University, 2003) indicates a water flea LC50 of 0.18 mg L-1, so the much lower value from Tomlin (2000) may be suspect.
Cyfluthrin may be another special case. Although predicted mean concentrations sometimes exceeded the very small 0.0006 mg L-1 LC50 for rainbow trout, model precision is questionable for concentrations much below 0.001 mg L-1. Since all mean concentrations were below this threshold, effects are uncertain.
Annual Maximum Daily Loads
Extreme events in this study are defined as annual maximum daily loads, or the largest single-day pesticide runoff load occurring in any given year. Return periods were computed for these AMDLs for all pesticides and locations, and pesticide loads with their associated runoff and concentrations corresponding to 10- and 20-yr return periods (1-in-10-yr and 1-in-20-yr events) are provided for nine pesticides in Tables 10 and 11. The remaining six chemicals are omitted since concentrations for these events never reached 10% of the LC50 values.
The results for greens, which are given in Table 10, have different implications than the mean values discussed previously. Although mean concentrations in greens runoff sometimes approached or exceeded LC50 values, the associated runoff water was so small that it was difficult to infer any effects on surface waters. However, in many cases the AMDLs in Table 10 have concentrations that are substantially larger than the mean annual or monthly values. These concentrations occur with larger runoff volumes and hence may have severe short-term or acute effects. Six of the pesticides (azoxystrobin, bensulide, chlorothalonil, cyfluthrin, iprodione, and PCNB) have concentrations and runoff that could pose acute risks to receiving waters. Effects appear largest at Philadelphia and smallest at Rochester.
The most dramatic aspects of the fairway AMDLs shown in Table 11 are the very large runoff volumes associated with the 10- and 20-yr events. The same pesticides that were problematic for greens remain so for fairways, but are also joined by trichlorfon. Although as noted earlier, the very small water flea LC50 is suspect, concentrations for both the 10- and 20-yr events at Boston and Philadelphia greatly exceed the much larger rainbow trout LC50.
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CONCLUSIONS
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Simulated runoff of 15 pesticides from bentgrass greens and fairways in Boston, Philadelphia, and Rochester produced 100-yr daily records of water runoff, pesticide runoff, and pesticide concentration in runoff. These variables were summarized as annual and monthly means and AMDLs corresponding to 10- and 20-yr return periods. Based on analyses of these summary variables, we conclude the following.- Runoff losses of pesticides applied to turfgrass are relatively small. Mean annual pesticide runoff loads did not exceed 3% of annual applications for any pesticide or site, and most losses were substantially less than 1% of application. Pesticides with the largest percentage losses in runoff were azoxystrobin, halofenozide, iprodione, oxadiazon, and propiconazole.
- Pesticide runoff loads differ greatly with location, reflecting differences in annual and seasonal precipitation.
- Pesticide runoff loads are much greater from fairways than greens because of comparably greater volumes of water runoff.
- In spite of the relatively small pesticide runoff loads, concentrations of the chemicals in runoff often approach or exceed LC50 concentrations for aquatic organisms. In the case of greens, these high concentrations are contained in very small water volumes and may have limited effects on receiving waters. However, the much higher runoff volumes from fairways may produce significant aquatic effects.
- Annual or monthly mean concentrations of chlorothalonil, iprodione, and PCNB in fairway runoff often exceed LC50 concentrations, suggesting that these pesticides may routinely threaten the health of receiving waters.
- Concentrations of azoxystrobin, bensulide, cyfluthrin, and trichlorfon in extreme (1 in 10 yr or 1 in 20 yr) events approach or exceed LC50 levels. Thus, although these chemicals do not appear to pose routine dangers to receiving waters, they may occasionally produce serious effects.
- Runoff of halofenozide, mancozeb, MCPP, oxadiazon, propiconazole, thiophanate-methyl, triadimefon, and trinexapac-ethyl does not appear to be hazardous to aquatic life in surface waters.
These conclusions are predicated on the chemical application rates and timing listed in Table 3. To the best of our knowledge, these applications are typical for golf courses in the northeastern USA, but any given golf course may not use all of the chemicals, or may apply them less frequently. Similarly, care must be taken in extrapolating the results to residential lawns or parks, which may see smaller and less intensive sets of chemical applications.
In spite of the apparent hazards associated with several of the chemicals, it should be emphasized that the computed concentrations are for runoff and not receiving waters. Portions of the pesticides and/or the runoff may be intercepted and the remainders will often be diluted by cleaner waters on reaching streams, ponds, and lakes. Conversely, at least in the case of greens, an emphasis on runoff may understate the effects of turf pesticides on surface receiving waters. Substantial portions of applied chemicals are leached from the turf and enter the soil where they may subsequently be transported by percolation. TurfPQ calculates the chemical leaching but does not follow its subsequent transport in the soil. Particularly in the case of greens, these subsurface flows are typically intercepted by tile drainage, which is discharged into surface waters, bringing additional pesticide loads.
It is apparent from the simulation results that runoff hazards are related in commonsense fashion to three factors: chemical properties, application amounts and timing, and toxicity to aquatic organisms. Relatively soluble and persistent chemicals are typically susceptible to runoff. Similarly, pesticides that are applied frequently and in large amounts are most likely to appear in runoff, particularly if applications correspond to periods of heavy precipitation. Finally, the ultimate measure of runoff effects is the toxicity of the chemical. Relatively small amounts of a highly toxic chemical will pose greater risks than large amounts of a minimally toxic chemical.
In spite of the straightforward nature of these determinants, runoff risk for a particular pesticide at a specific site is not obvious. For example, consider the case of a soluble, toxic pesticide, applied frequently during months of high precipitation. If the turf is heavily thatched, infiltration will be high and the chemical will be retained by adsorption to the extensive organic matter. Also, if the heavy precipitation is in the form of frequent moderate storms, most pesticide leaving the site will be in the form of leachate and not runoff. In this case, pesticide runoff risk is more apparent than real. The difficulty in assessing risks associated with pesticide runoff from turf is not due to the uncertainty of causes. Rather, it is because the causes interact in complex ways, and a simulation model such as TurfPQ is the only practical means of determining the effects of these interactions.
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ACKNOWLEDGMENTS
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Research described in this paper was supported, in part, by Green Section Research, U.S. Golf Association.
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TOP
ABSTRACT
INTRODUCTION
runoff loads and concentrations in runoff from greens.