Assessing Risks to Endangered and Threatened Species from Pesticides (2013) / Chapter Skim
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3 Exposure
3 Exposure
Pages 49-90
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From page 49... ...
Finally, the committee discusses some important uncertainties associated with exposure analysis and the need to propagate uncertainty through the analysis. EXPOSURE-MODELING PRACTICES If pesticides are to be used without jeopardizing the survival of listed species and their habitats, the estimated environmental concentrations (EECs)
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From page 50... ...
. Approaches and Models Used by the Agencies In Step 1 of the ESA process, EPA uses a program called DANGER to determine which listed species or their habitats coincide geographically and temporally with areas of pesticide use (EPA 2012a)
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From page 51... ...
The resulting estimated concentrations in soil, water, and sediment yield estimates of the pesticide exposure of receptors of interest, including listed species. For terrestrial species, EPA models pesticide exposure with the Terrestrial Residue Exposure (T-REX)
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Given the current practices in exposure analysis and the need to estimate pesticide exposures and the associated spatial-temporal variations experienced by listed species and their habitats, the committee envisions the following stepwise approach to exposure modeling.
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To that end, the models would use site-specific input values -- for example, actual pesticide application rates, locally relevant geospatial data to characterize such quantities as wind speed and organic contents of soils, and time-sensitive life stages of listed species. The exposure analysis would be completed with propagated errors on exposure estimates.
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From page 54... ...
The monitoring reports, however, are not associated with specific applications of pesticides under well-described conditions, such as application rate, field characteristics, water characteristics, and meteorological conditions. General monitoring data cannot be used to estimate pesticide concentrations after a pesticide application or to evaluate the performance of fate and transport models.
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GEOSPATIAL DATA FOR HABITAT DELINEATION AND EXPOSURE MODELING Geospatial data are critical for exposure modeling and for describing species' habitats. The committee was asked to consider what constitutes authoritative geospatial data.
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Regardless of method, the size of a species' range, and the specificity of its resource requirements, greater access to and reliability of geospatial data have made it easier to delineate and characterize habitat and habitat quality for a given species in space and time. The data also have improved the ability to model chemical fate and potential exposure of organisms.
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From page 57... ...
. Authoritative geospatial data should meet three criteria: they should be available from a widely recognized and respected source; they should be publicly available, whether freely or for purchase; and, for applications in the United States, they should be accompanied by metadata consistent with the standards of the National Spatial Data Infrastructure (NSDI)
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From page 58... ...
Among the types of geospatial data most useful for delineating habitat and estimating exposure and effects of pesticides on listed species and their ecosystems are those on topography, hydrography, meteorology, solar radiation, soils, geology, and land cover. Although those data are not mutually exclusive, they generally are represented with different spatial-data layers.
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From page 59... ...
. Hydrographic Data Watershed features are relevant to habitat delineation of terrestrial and aquatic species and to assessment of potential pesticide exposure of these species.
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A map of the inventory areas also serves as a graphical user interface to access many types of data associated with the biology and management of listed species (WA Department of Ecology 2012)
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From page 61... ...
can affect the distributions and population dynamics of organisms and their resources. Chemical fate and transport also are affected by meteorological variables, such as temperature, precipitation, and wind speed and direction.
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From page 62... ...
might allow one to determine the variability of the light intensity at the relevant wavelengths -- those at which a given compound has high absorptivity. If exposure analysis suggests that photolysis is highly relevant to chemical fate, characterizing that variability would probably be valuable.
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From page 63... ...
Geological Data Geology strongly influences the chemistry of surface materials and shallow groundwaters that interact with pesticides. Authoritative geospatial data on geology in the United States are provided by USGS via its Mineral Resources Online Spatial Data (USGS 2012c)
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From page 64... ...
. The National Agricultural Statistics Service provides spatial data and metadata on the distribution of 133 classes of land cover, including major crop types, across the country (NASS 2010)
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From page 65... ...
Environmental mixtures are the results of previous applications of tank mixtures -- sometimes many tank mixtures applied at different times to different areas in a watershed or other locale of concern. In addition, environmental mixtures include other environmental contaminants not related to pesticide applications in the media of concern.
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From page 66... ...
Pesticide Formulations and Tank Mixtures Pesticide formulations typically contain chemicals other than the active ingredients that often do not have a direct effect on the target species. The term inert is used to designate a chemical that is not classified as an active ingredient.
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From page 67... ...
If components of a tank mixture or formulation do not substantially affect the fate and transport of other components, the exposure analysis methods used for single chemicals can be applied to tank mixtures. In cases in which additives, such as surfactants, could affect the fate and transport of active ingredients in a formulation, uncertainties in exposure analysis could be substantial unless the effect of additives can be quantified in exposure modeling.
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From page 68... ...
Approaches to estimating exposures to environmental mixtures are at least conceptually similar to those associated with pesticide formulations or tank mixtures. If the exposure factors are known -- that is, the pesticide and environmental components, their concentrations, and their locations at a specific time -- exposure-analysis methods can be used to assess exposures to the environmental mixture.
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From page 69... ...
(2007, p.81) , an analysis of the co-occurrence of pesticides might be useful in identifying environmental mixtures that have the greatest probability of adversely affecting listed species, and these investigators provide a preliminary assessment of the most commonly occurring mixtures of two to seven pesticides (Belden et al.
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From page 70... ...
For now, pesticide use is probably an inaccurate input for exposure analysis; registration and labeling are not well suited for solving this exposure-analysis bias. Other Fate-Modeling Parameters Even if release rates per unit area of all the pesticide components were well quantified, other phenomena add uncertainty to estimates of exposure of various environmental surfaces, such as plant surfaces, soil surfaces, and surface water.
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From page 71... ...
In addition to inaccuracies and imprecisions in initial pesticide loadings on soil, parameters used in chemical-fate models, such as PRZM and EXAMS, have associated uncertainties, particularly because pesticides often contain or are applied with other chemicals that can affect some fate processes. Data sources for assigning values to parameters range from empirical observations reported by pesticide registrants to information extracted from peer-reviewed journal publications that sought to elucidate underlying process mechanisms.
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From page 72... ...
for a specific soil or sediment, calculated by using the foc of that solid, can be known almost as precisely as the pesticide's Koc values because site-specific foc measures can be made with great precision. However, if model calculations use a generic value for foc or even a value based on regional soil mapping (see section "Geospatial Data for Habitat Delineation and Exposure Modeling" above)
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From page 73... ...
. A second case of an inappropriate use of the focKoc model involves situations in which black carbon sorbents play an important role in addition to the rest of the organic carbon.
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. However, when substantial data were available, biodegradation rates varied widely, often by more than a factor of 10 (Table 32)
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. To summarize, pesticide-exposure analysis should be pursued by using enough biotransformation information to establish whether the rates are normally or log-normally distributed, and then the data should be analyzed to obtain the mean rate coefficient and its variance for use in fate modeling.
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From page 76... ...
Lower panels: Distribution of observed bacterial-numbernormalized biodegradation rates (L/organism-hour) of the butoxyethyl ester of 2,4-D as reported for 33 test surface waters by Paris et al.
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As discussed in Chapter 2, the committee recommends taking a probabilistic approach and assigning appropriate distributions to the input parameters instead of single values. The committee notes that EPA has been working on probabilistic exposure modeling for many years (see, for example, Burns 2001)
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From page 78... ...
b From Guidance for Chemistry and Management Practice Input Parameters for Use in Modeling the Environmental Fate and Transport of Pesticides, dated February 28, 2002. Abbreviations: EFED, Environmental Fate and Effects Division of EPA; KBACS, firstorder rate constant for pesticide's bacterial degradation in sediment (day-1)
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From page 79... ...
To estimate pesticide exposure concentrations at various stages, the committee proposes a stepwise approach to exposure modeling. Step 1 would determine whether a pesticide and listed species overlap geographically and temporally.
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From page 80... ...
Uncertainties Any exposure analysis involving pesticide applications should at least qualitatively describe the potential effect of inerts on the environmental fate of an active ingredient. If the available information suggests that inerts (or adjuvants)
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From page 81... ...
More sorption data are needed to characterize nonlinear isotherms over concentration ranges and under conditions that are applicable to relevant agricultural settings, such as pH, ionic composition, and solid-phase mineralogy. Likewise, more data are needed to determine biodegradation coefficients, whether biodegradation rates are normally or log-normally distributed, and under which circumstances lag periods are important.
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From page 82... ...
2004. Exposure Analysis Modeling System (EXAMS)
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From page 83... ...
: Development and Use of GENEEC Version 2.0 for Pesticides, Aquatic Ecological Exposure Assessment, May 1, 2001. Environmental Fate and Effects Division, Office of Pesticide Programs, U.S.
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2007. National Spatial Data Infrastructure [online]
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1995. EPA guidelines for environmental fate studies: Meaningful data for assessing exposure to pesticides.
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. NMFS (National Marine Fisheries Service)
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National Marine Fisheries Service, Silver Spring, MD. June 30, 2011 [online]
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2012. Likelihood analysis of species occurrence probability from presence-only data for modeling species dis tributions.
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Water Resources NSDI [National Spatial Data Infrastructure] Node [online]
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2003. Enhanced pesticide sorption by soils containing particu late matter from crop residue burns.
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