Watershed Fluxes of Pesticides to Chesapeake Bay - ACS Symposium

Chapter 7

Watershed Fluxes of Pesticides to Chesapeake Bay 1

GregoryD.Foster and KatriceA.Lippa

Downloaded by NORTH CAROLINA STATE UNIV on September 20, 2012 | http://pubs.acs.org Publication Date: April 3, 2000 | doi: 10.1021/bk-2000-0751.ch007

Department of Chemistry,MSN3E2, George Mason University, Fairfax, VA 22030

Input mass budgets of pesticides and other organic contaminants in Chesapeake Bay are being used to identify the most important source areas for chemical contamination. The concentrations and fluxes of selected current-use pesticides, such as simazine, prometon, atrazine, and metolachlor, were determined above the fall lines of nine of the major tributaries of Chesapeake Bay during base flow hydrologic regimes in spring (May) and autumn (November) of 1994. The watershed fluxes of the pesticides showed a high degree of spatial variability across the Chesapeake Bay region. The greatest fluxes occurred for most of the pesticides above the river fall lines of the Choptank River, an eastern shore tributary, and the Susquehanna River, the largest tributary, in the spring and above the river fall line of the Patuxent River in autumn.

Chesapeake Bay is a collection of delicate ecosystems, many of which have been greatly perturbed through the mismanagement of resources within the Bay as well as by continued pollution of anthropogenic substances from the surrounding watershed. A critical step in understanding the effects of toxicants on the Bay's ecology is knowing the types and quantities of substances being delivered to the estuary. The fluxes of current-use pesticides above the river fall lines of the three largest tributaries of Chesapeake Bay have been quantified in various years since 1990 through the Chesapeake Bay Fall Line Toxics Monitoring Program (FLTMP). The fall line is defined as the physiographic boundary between the Piedmont and Coastal Plain Provinces in the eastern United States or above the head of tide in coastal streams. The primary goal of the FLTMP has been to estimate the annual riverine fluxes of contaminants to tidal Chesapeake Bay, including pesticides, from the noncurrent address: Department of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore, MD 21218

© 2000 American Chemical Society

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

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tidal riverine source areas above the fall lines (1-5). Riverine fluxes estimated through the FLTMP are used to determine mass budgets of contaminant inputs to the Bay from a variety of identified sources, including, among others,riverinedischarges, atmospheric deposition, and urban runoff (6). The focus of the FLTMP since its inception has been on the Susquehanna, Potomac, and James Rivers. Recentfindingsfrom the FLTMP have shown that the magnitudes of annual fluxes of several current-use pesticides, such as atrazine, metolachlor, and cyanazine, estimated for the three tributaries were variable but generally correlated with annual river discharges at the fall lines (3,5). To more comprehensively compare the spatial variability in fall line loadings throughout the Chesapeake Bay watershed, a number of additional bay tributaries were sampled synoptically in the spring and fall of 1994. The new tributaries included in the FLTMP, in addition to the three tributaries above, were the Patuxent, Rappahanock, Pamunkey, Mattaponi, Choptank, and Nanticoke Rivers located in Maryland and Virginia. The above nine tributaries provide approximately 80% of all the freshwater flow to Chesapeake Bay (7). The objective of the present report is to compare the fluxes of selected pesticides estimated for the nine major tributaries across the Chesapeake Bay watershed in 1994 through the synoptic sampling study. Materials and Methods River Fall Line Sampling. River water was collected from the nine tributaries twice during 1994 employing a synoptic sampling design. The first sampling occurred during the spring flush (May 5-12) and the second in autumn (November 18-22) when flows were lowest. Each tributary (Figure 1) was sampled along the fall line reach or just above the head of tide depending on the nature of the stream or river using a Fultz submersible pump (Fultz Pumps, Inc., Lewistown, PA). Surface water was collected from eachriverby immersing the pump at least one-third of a meter below the surface at the approximate center of flow of the river and pumping water into a 35-L stainless steel beverage container. The container was filled with river water, capped tightly, and transported to the laboratory. In the laboratory, the samples were immediately placed in a cold room (1 °C) and stored for no more than 48 hrs. prior to the analysis of nine pesticides (Table I). Sample Processing and Analysis. The surface water samples werefilteredusing a stacked arrangement of 15-cm disks of Whatman GF/D overlying GF/F glass fiber filters (Whatman Inc., Clifton, NJ), housed in a 142-mm Millipore (Millipore Corporation, Bedford, MA) stainless steel filtration apparatus, at 1 L/min using a positive displacement pump (Model QB, Fluid Metering Inc., Oyster Bay, NY). The filtered water was collected in separate precleaned 37.5 L containers and held for surrogate spiking and extraction. Thefilterswere wrapped in precleaned aluminum foil envelopes and stored at -25 °C for subsequent chemical analysis.



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Figure 1. Map of Chesapeake Bay showing locations of watersheds of the nine tributaries monitored in the synoptic study in 1994. (This map was provided courtesy of the USGS in Baltimore, MD.) Filtered water was extracted with dichloromethane (DCM) using a Goulden large-sample extractor (GLSE) to isolate the pesticides. The GLSE extraction procedures reported by Foster et al. (8) were used with the following modifications: (i) a customized distillation device was added to recover DCM from the waste stream of the GLSE for reuse in the extraction and (ii) the sample flow rate in the GLSE was decreased to 110 mL/min to accommodate the solvent recovery system. Sample volumes processed through the GLSE ranged from 25 to 35 L. Following extraction, DCM from the GLSE was passed through anhydrous sodium sulfate and solvent exchanged with w-octane during solvent-volume reduction to 0.5 mL by using rotary flash evaporation and nitrogen gas blowdown. The GLSE extracts were subsequently analyzed for the pesticides using GC/MS. The filters were intermittently analyzed for the pesticides but were below method detection limits in all cases.


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Table I. List of pesticides monitored in water samples collected from the tributary fall lines. Pesticide Abbreviation Chemical Class CAS Registry Number Simazine Prometon Atrazine Diazinon Alachlor Malathion Metolchlor Cyanazine Hexazinone

sima prom atra diaz alac mala meto cyan hexa

triazine triazine triazine organophosphorus chloroacetamide organophosphorus chloroacetamide triazine triazine

122-34-9 1610-18-0 1912-24-9 333-41-5 15972-60-8 121-75-5 51218-45-2 21725-46-2 51235-04-2

The pesticides were analyzed in the GLSE extracts using a 5890A HewlettPackard (HP) GC (Hewlett-Packard, Wilmington, DE) coupled to a Finnigan MAT Incos 50 mass spectrometer (Finnigan MAT, San Jose, CA). Sample injection (2 pL) was performed using an HP 7673A autoinjector in the splitless mode, with the split and purge vent flow rates adjusted to 30 and 3 mL/min, respectively. The GC/MS was fitted with a 30 m X 0.25 mm (id) DB-5 fused-silica capillary column (0.25 μηι film; J&W Associates, Folsom, CA) and operated using the following temperature program: 100° (5 min); 100°-120° at 77min; 120° (0.1 min); 120M80 at 1.257min; 180° (0.1 min); 180-290° at 207min; and 290 (10 min) for a total run time of 74.2 min. A l l GC/MS acquisitions were performed using multiple ion detection (MID) in the electron impact ionization mode (70 eV) with the electron multiplier voltage ranging from 1100-1300 V. Three characteristic ion masses were selected for each analyte in MID quantitation. Quantitation was accomplished using internal injection standards consisting of naphthalene-d8, phenanthrene-dlO, and chrysene-dl2, which were added to all the sample vials immediately before GC/MS injection. 0

Quality Assurance. Quality assurance (QA) samples included laboratory and field blanks and the addition of terbutylazine and fluoranthene-dlO as surrogate standards to each river fall line sample prior to GLSE extraction. The monitored contaminants were surrogate normalized to the overall mean surrogate recoveries for all the fall line samples when the surrogate recovery (%rec) in the sample was outside of the established range of performance (determined from numerous extractions of the surrogates as the mean %rec ± 0.15 X mean %rec for both surrogate standards). Method quantitation limits were determined as three times the signal found in the GC/MS chromatograms of laboratory blank samples, and ranged from 0.4 - 2.1 ng/L for the nine pesticides.


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Flux Estimates. Instantaneous fluxes of the pesticides were determined for each tributary as the measured concentration times the instantaneous river discharge at the point of sampling along the fall line. Fluxes were normalized by dividing instantaneous fluxes by the land areas within each tributary basin classified as agricultural. For pesticides which were below the method quantitation limits in the river fall line samples, fluxes were estimated using the method quantitation limit concentrations. Results and Discussion Hydrologie conditions during the spring and fall synoptic sampling were at base flow. No storms occurred during the river water collections in the spring although the fall line discharges were above their historical averages since sampling was near the end of a rainy spring season. River discharges measured during the 1994 spring and autumn synoptic collections are listed in Table II. The spring collection followed the heaviest pesticide field application period (between March to July in the Chesapeake Bay basin (9)) during the spring flush, providing a good potential to capture the effects of pesticide runoff in the rivers. Hydrologie conditions for the autumn synoptic collections were near base flow, which is typically the season with lowest river flows, but mild storms occurred during river water collections from the Virginia rivers (i.e., the Rappahannock and James Rivers). The influence of the storms did not markedly affect river flow conditions in these tributaries. The river discharges during the autumn synoptic study were lower than those in spring for all nine rivers. Concentrations of the pesticides measured in the river fall line samples are summarized in Table III for the nine tributaries monitored in the spring and autumn synoptic studies. The concentrations of the pesticides at the tributary fall lines showed a wide range of spatial variability. There have been many geologic, hydrologie, and geochemical variables postulated which affect the seasonal concentrations of pesticides in river runoff. Among those variables proposed to influence the fluvial transport of moderately polar pesticides such as those presented in this study include pesticide soil/water sorption constants (10,11), agricultural growing season (12,13), rainfall frequency and quantity (14,15), soil texture and moisture (13,15), watershed bedrock lithology (12), landuse (12,13), and cropping patterns (12,13). The limited synoptic sampling design in 1994 did not accommodate a statistical evaluation of these parameters. The Choptank and Nanticoke Rivers showed the highest concentrations of simazine and metolachlor in spring, and furthermore the Choptank River showed the highest concentrations of all monitored pesticides except hexazinone in non-tidal river water (Table III). The watersheds of these two eastern shore tributaries lie entirely in the Coastal Plain and the relatively high concentrations observed at their fall lines, especially in the Choptank River, arose, in part, from their low stream order (leading to less dilution), permeable soils (16), and close proximity to the agricultural fields. All of the monitored western shore tributaries flow through the Atlantic Piedmont to reach Chesapeake Bay and are higher order rivers than those on the eastern shore. Of the


120 western shore rivers the Susquehanna River showed the greatest concentrations of pesticides in the spring. There is extensive farming in the Piedmont region of the Susquehanna River basin, and most of the pesticide runoff occurs in this region of the basin (13).


Table II. Spring and autumn river discharges and basin areas above the fall lines of the nine monitored tributaries of Chesapeake Bay for 1994. Tributary

Spring River Discharge, m^/s

Autumn River

Agricultural

Discharge, m^/s

Land Area® km?

Pamunkey 25 980 6.9 Mattaponi 19 5.6 436 James 174 48 3726 Rappahannock 1835 43 10 Potomac 626 69 10870 Choptank 4.7 161 1.1 Nanticoke 5.3 0.96 195 Patuxent 414 8.8 4.0 21890 Susquehanna 1730 144 Land area within the watersheds designated as agricultural; area of the entire Nanticoke basin above the head of tide. b

b

In the autumn synoptic study, the highest or next highest concentrations for many of the pesticides were found in the Patuxent River (Table III). The Patuxent River basin has 35% of its watershed area classified as urban, which is considerably greater than any of the other eight tributary basins. Urban application of pesticides may provide considerable inputs into nearby rivers, and non-agricultural use of pesticides occurs from spring through winter (17), correlating with the high pesticide concentrations seen in the Patuxent River. Simazine and prometon concentrations in the river fall lines samples were greater in five of the nine tributaries and atrazine in four of the nine tributaries in fall relative to spring sampling, indicating the existence of important non-agricultural sources for these pesticides in autumn runoff. Pesticide fluxes estimated for each river basin are listed in Table IV. Areanormalized fluxes provided a more clear comparison of individual basin dynamics in watershed runoff because instantaneous loads (i.e., μg/s) were found to follow the order of descending stream discharges above the fall lines. The magnitude of instantaneous load estimates are governed predominantly by river discharge. Estimates of fluxes above the river fall lines provided a comparison among the Bay's major tributaries of the integrative effects of all source inputs on the scale of the individual watershed. A great deal of spatial variability was found in fluxes among the nine tributaries (including the Susquehanna River) for both spring and autumn


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Table III. Summary of pesticide concentrations measured in the river fall line samples collected through the spring and fall synoptic study. Tributary Pesticide


sima prom atra

diaz alac mala meto cyan hexa

Spring (26 April -- 6 May) Concentration in ng/L Pamunkey 20.3 7.0 20.6 1.3 2.3 2.9 Mattaponi 2.7 2.9 4.3 0.9 6.6 1.6 James 13.8 3,0 1.3 0.9 2.9 5.8 Rappahannock 14.1 1.3 0.9 2.9 13,3 6.2 Potomac 8.6 29.1 6.9 28.5 3.1 1.4 Choptank 171 37.2 630 31.2 177 23.8 Nanticoke 3.2 157 16.2 46.2 24.2 7.7 Patuxent 1.3 0.9 2.9 1.7 1.4 1.6 Susquehanna 89.3 8.0 99.9 4.9 23.1 2.9 Autumn (11 November -18 November) Pamunkey 7.8 30.1 7.0 12.2 1.0

Watershed Fluxes of Pesticides to Chesapeake Bay - ACS Symposium

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