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HomeMy WebLinkAboutNYS Fertilizer & Pesticide DemoSOUTHOLD DEMONSTRATION SITE New York State Fertilizer and Pesticide Demonstration Project Aldicarb Calculations October 1983 Center For Envlronmimtll Research Holliater Hall Cornell University Ithac~a, N.Y. 14853 Aldicarb Calculations Southold Demonstration Site New York State Fertilizer and Pesticide Demonstration Project October 1983 Center for Environmental Research 468 Hollister Hall Cornell University Ithaca~ New York 14853 ALDICARB CALCULATIONS Southold Demonstration Project In the final report for the Southold Demonstration Site of the New York State Fertilizer and Pesticide Demonstration Project, Table VI-2 presents the results of our simulation of aldicarb movement below the Depot Lane Transect in Southold, N.Y. Included are the dates when the simulation shows aldicarb entering the ground water and the average concentrations of these recharge plumes. The following explanation provides greater detail about the simulation, including the many simplifying assumptions inherent in its design. Table A-2 also provides the dates when the simulation shows aldicarb to decay below ? ppb along the Depot Lane transect under two different half life assumptions. These dates are meant merely to illustrate what may happen at this site if the assumptions are correct, not to predict with any accuracy what will occur. Because of the great uncertainty in the decay rate assumptions, these dates are not included in the Final Report of the Southold Demonstration Project. Depot Lane Trzn-~ect In 1980 the Suffolk County Department of Health Services had a series of geologic test holes and observation wells drilled along Depot Lane in Cutchogue in order to obtain information about ho~v aldicarb and other contaminants move through the North Fork's aquifer. The transect cuts across the North Fork from north to south and runs parallel to ground-water flow in both the northerly and southerly directions. Private wells were sampled by the County in the Spring of 1980, and the observation wells were tested a year later. Aldicarb contamination was found up to 100 feet below the water table near the center of the transect and at shallower depths {up to 40 feet below the water table) at the northern and southern extremities, with concentrations ranging from one to 149 ppb (Baler and Robbins, 198Z). Aldicarb Simulation The Depot Lane transect was divided into 13 areas (Figures 1 and Z), and the farmers were surveyeJ~ about their aldicarb use on fields within each of these regions. The aldicarb application rates for each field in an area were averaged, and fields where no aldicarb was applied were included in the averaging. Results are shown in Table 1. For our simulations, the adsorption partition coefficient was set at 0.09 in the root zone and at 0.0 below the root zone, indicating that only a small percent of the aldicarb contained in the soil water would be adsorbed to soil particles in the root zone, and none below this zone. These numbers were calculated from a linear regression relating adsorption coefficients to soil organic matter derived from the results of four field and laboratory experiments (Kain and Steenhuis, 198Z). The greatest uncertainty in modelling aldicarb is its rate of attenuation in the root zone, unsaturated zone, and saturated zone. The half-life, or time that it takes for half of the aldicarb to decay to nontoxic byproducts, -120. ,.~,, , , . . · · . , ~ _ ~,;::r/ '- \ DJst~nc~ fr~ N~th Share 11000 ltl Flpre 2. Simulated aldlclrb ~lume8 along t~ Depot LI~ tranm~t, S~thold, N.Y. 'fable 1 Aldicarb use on areas along the Depot Lane transect, 1975 to 1979 Area Aldicarb Applied (lb active ingredient/A) 1 0.5 0.0 0.0 0.0 0.0 0.5 Z Z.5 0.6 1.0 1.0 1.0 6.1 3 0.4 0.7 1.1 1.1 1.1 4.4 4 0.1 1.4 Z.3 Z.3 Z.3 8.4 5 1.1 1.9 Z.4 Z.4 Z.4 10.Z 6 0.5 1.8 Z.5 3.7 3.7 1Z.Z 7 0.0 0.0 0.0 0.0 0.0 0.0 8 1.7 Z.O Z.O 2.9 2.9 11.5 9 1.6 3.7 3.7 4.6 4.6 18.2 10 2.1 2.6 2.6 3.8 3.8 14.9 11 Z.1 '4.0 4.0 5.2 3.7 19.0 lZ 0.0 O.Z 0.2 O.Z 0.0 0.6 13 1.7 1.7 1.7 1.7 1.7 8.5 1975 1976 1977 1978 1979 Total is shortest in the root zone where ~nicrobial populations speed the decaying process, and longest in the saturated zone b,;cause of the lower temperatures and low rates of microbial activity. Unfortunately, laboratory and field experiments on these half-lives are few, and the results are inconclusive. A previous review summarizing studies on aldicarb degradation in a variety of soils showed ranges in half-lives from one to Z31 days (Kain and Steenhuis, 198Z). This review indicated that for Long Island soil types, a 50 day half-life was reasonable for the root zone, which was assumed to be 30 cm deep. This was increased to 100 days for the next 30 centimeters in depth because microbial populations diminish with increasing depth (Pacenka and Porter, 1981). For the remainder of the unsaturated zone, a half-life of 10 years was used. The 50 day root zone half-life is from Kain and Steenhuis (198Z). The other numbers were derived by calibrating our model with field data from a potato field on the North Fork studied by Intera (1980) and a deep soil core taken at the Long Island Horticultural Research Laboratory (unpublished data). The simulation results indicating the dates and concentrations of aldicarb leaching to the ground water are shown in Table Z. Dates of aldicarb decay are presented for two potential half-lives, three years and ten years, chosen somewhat arbitrarily to represent a range of possible half-lives for aldicarb in ground water. Aldicarb's half-life in ground water is highly speculative, however, because no laboratory data are available for its half-life at 15oc and pH of 6, conditions typical of Long Island's ground water (see Table 3}. ~rithout an accurate estimate of the half-life in ground water, any simulation of aldicarb's disappearance has to be based on speculation alone. Field and laboratory research currently underway will better define aldicarb's half-life under Long Island conditions. Until these data become available, simulations which predict specific dates of disappearance are likely to be misleading. We felt that the table of simulation results gives a false impression of accuracy. For this reason, the estimated dates of aldicarb decay presented in Table Z were not retained in the final report for the Southold Demonstration Site. As~umptio~a Implicit in the C, ro~nd-~ater Simulations The flow system. The velocities of the aquifer are calculated from data in the study conducted by the Suffolk County Department of Health Services (Baier and Robbins, 1982). These calculations assume that the aquifer is composed of uniform material. Variations in the material which undoubtedly occur will cause the actual flows to be slightly different. The Suffolk County Department of Health Services estimate that time of travel calculations would be accurate to within + 25 percent. Dispersion. The process of dispersion was modelled in the unsaturated flow where dispersion is quite significant. In the saturated zone dispersion was not explicitly accounted for. Instead, a simplifying assumption was made that all aldicarb within the plume is evenly distributed throughout the plume and therefore that the concentration in the plume is uniform. This is comparable to assuming that ali dispersion occurs within the unsaturated zone before the aldicarb enters the aquifer and that no dispersion occurs after that. The fact that these simplifyina assumptions only approximate reality means that the simulation results must be used carefully with an appreciation for their limitations. An additional word of caution needs to be made about the interpretation of the aldicarb decay dates in this table. These dates represent the times when the entire plume of aldicarb from each area along the transect would be expected to decay below 7 ppb, not the times for Are& Stream Tube Number 9 C D F G Table 3 Laboratory data on half-lifes (in days) of aldicarb and its degradation products in water at various pH's and temperatures. pH 5.5 6.0 7.0 7.5 8 8.5 Source Aldicarb 15oc ZSoc Aldicarb Sulfoxide 15oc ZSoc Aldicarb Sulfone 15oc ZSOC Sources: a) h) c) d) 3Z40 1900 170 b - Z66 Z45 - Z66 - a 440 - 360 10 b NA NA 73 - c 4ZZ1 4ZZ 4Z - d 679 161 23 - a NA 154 ZZ - c 450 - 1Z5 - 5 b NA Z7Z 52 c 1458 145 15 d 4Z0 77 10 a NA 84 10 c 597 60 6 d Chapman and Cole (198Z). Hansen and Spiegel (198Z). Hansen et al. (1983) (Note: Values labelled HNA" are not yet available but will be at the conclusion of the experiments). Lemley (1983) (Note: These data are extrapolated from experiments conducted at pH's 11 to 13). which wells at individual houses would be expected to exceed the standard. Aldicarb was applied to potato farms along the Depot Lane transect for the five years between 1975 and 1979. The plumes of aldi :arb contamination will advance thoug ~ the ground water underlying the transect, preceded and [ollowed by aldicarb-free water representing recharge from before and several years aft ~r the application period. Individual wells would therefore in most cases be expect ~.d to exceed the 7 ppb standard for a sl-orter period of time than tbe dates in ou' table, which represent aldicarb disappearance in the moving plume rather than at stationary sites along its path. The transect also portrays a wor~;e than usual case for aldicarb in $outhold's ground water because approximately half of the la_nd along Depot Lane is devoted to potato fart~mg~ whereas in Southold as a whole only approximately 41 percent of the land is used for any type of agriculture, r'or Eastern Long Islan4, farming accounts for less than Z0'>3 of thc total land use. 8 REFERENCES Baier, J.H., and S.F. Robbins. 198Z. Report on the Occurrence and Movement of Agricultural Chemicals in Groundwater: North Fork of Suffol~ County. Suffolk County Department of Health Services, Bu'~eau of Water Chapman, R.A., and C.M. Cole. 198Z. Observations ou the Influence of Water anl .~;oil pH on the Persistence of Insecticides. J. Environ. Sci. Health B17(5):487- 504. IIansen, J.L. and M.H. Spiegel. 1983. Long Term Hydrol),sis Studies of Aldicarb Sulfo'dde and Aldicarb Sulfone. Uni)n Carbide Corp., Unpublished Report. t-lansen, J.L., R.R. Romine and M.H. Spiegel. 198l. Hydrolysis Studies of Aldicarb~ Aldicarb Sulfoxide and Aldlcarb Sulfone. Environmental Toxicology and Chemistry l:147- 153. Kain, D.P. and T.S. Steenhuis. 1983. Adsorption Partition Coefficients and Degradation Rate Constants and Half-Lifes of Selected Pesticides Compiled from the Literature. Unpublished Manuscript. Cornell University, Ithaca, New York. Lemley, A.T. 1983. Unpublished Results. Department of Design and Environmental Analysis, Cornell University, Ithaca, N.Y. Pacenka, S. and K.S. Porter. 1981. Preliminary Regional Assessment of the Environmental Fate of the Potato Pesticid% Aldicarb~ Eastern Long Island~ New York. Center for Environmental Research, Cornell University, Ithaca, New York.