Russell L. Jones

Characterizing the uncertainty of pesticide leaching in agricultural soils

Abstract A Monte-Carlo numerical simulation procedure for making regional assessments of pesticide leaching has been developed. This procedure uses probability density functions for organic matter, field capacity, and wilting point developed from information on approximately 3000 soils. Variations in climatic conditions were incorporated by random selection of yearly rainfall data. The procedure was demonstrated for aldicarb applied to corn grown in Ohio. A total of 2000 parameter sets were evaluated using the unsaturated zone model PRZM. The simulation results indicated that convergence of the 90th, 95th, and 99th percentiles for movement past 0.3, 0.6, 0.9, and 1.5 m was obtained after 500 simulations. The relative uncertainty associated with these percentiles was approximately 50% after 1500 simulations. The downward movement of aldicarb residues was most sensitive to changes in field capacity. These simulations, coupled with additional soil-specific simulations, indicated no significant movement of aldicarb residues beyond 1.8 m for applications to Ohio corn.

Movement and degradation of aldicarb residues in the saturated zone under citrus groves on the Florida ridge

Abstract A 1.7-ha section of citrus grove near Lake Hamilton was the site of a three-year field study designed to monitor the movement and degradation of the nematicide and insecticide aldicarb in the central ridge area of Florida. Soil cores were used to monitor the fate of aldicarb residues in the unsaturated zone and over 2,000 groundwater samples were collected from 174 monitoring wells to measure horizontal and vertical transport of aldicarb residues in the saturated zone. A simple saturated zone model was used to estimate the degradation rate of aldicarb residues and extrapolate findings to other ridge areas. The results of the study suggest that in the saturated zone aldicarb residues degrade at a rate corresponding to a half-life of approximately eight months. The predominantly horizontal movement of groundwater at this site limits aldicarb residues to the upper three to five meters of the saturated zone. Field data from this site together with unsaturated and saturated zone simulations suggest that in this area of Florida current restrictions on aldicarb used near potable wells are adequate to protect drinking water supplies.

A simulation procedure for groundwater quality assessments of pesticides

A procedure is described for making regional assessments of pesticide residue loadings and movement in groundwater underneath and downgradient from treated fields. A Monte-Carlo numerical simulation technique is used to generate model parameters for both the unsaturated and saturated zones. Simulations are performed using the Pesticide Root Zone Model linked to a simple groundwater solute transport model. The procedure is useful for evaluating the potential for producing pesticide residues in drinking water wells before actual field applications are made. Appropriate land management options, including restrictions on pesticide application, also can be developed using this procedure. The procedure was used to assess aldicarb levels in northeastern North Carolina groundwater resulting from application of the pesticide to peanuts. Probability density functions for selected soil characteristics were developed using a direct-access soils information data base. Probability density functions for selected groundwater characteristics were developed from available data for the study area. Simulation results indicated that mass fluxes to groundwater exceeded 0.01 and 0.1 kg ha−1 approximately 6.9 and 1.0 percent of the time, respectively. No fluxes exceeded 0.1 kg ha−1 at a distance of 60 m downgradient in any of the cases evaluated.

Laboratory Degradation Rates of 11 Pyrethroids under Aerobic and Anaerobic Conditions

Degradation of 11 pyrethroids was measured over approximately 100 days in three sediment/water systems under aerobic and anaerobic conditions at 25 °C in the dark. The three California sediments represented a range of textures and organic matter. Test compounds were bifenthrin, cypermethrin, ζ-cypermethrin, cyfluthrin, β-cyfluthrin, deltamethrin, esfenvalerate, fenpropathrin, γ-cyhalothrin, λ-cyhalothrin, and permethrin. A non-standard design was employed to keep conditions essentially the same for all compounds. The test compounds were applied as two test mixtures (six active ingredients per mixture, with bifenthrin common to both) at approximately 50 μg of test compound/kg of sediment (dry weight). Extracts of sediment/water were cleaned up by solid-phase extraction, concentrated, and analyzed by gas chromatography/mass spectrometry (except deltamethrin) against matrix-matched standards, with cyfluthrin-d6 as an internal standard. Deltamethrin was analyzed by liquid chromatography/tandem mass spectrometry using deltamethrin-phenoxy-(13)C6 as an internal standard. Similar degradation rates of bifenthrin and for related isomeric compounds (e.g., cyfluthrin and β-cyfluthrin) were generally measured in both mixtures for each sediment. First-order half-lives under aerobic conditions ranged from 2.9 to greater than 200 days, with a median value of 18 days. Under anaerobic conditions, the range was from 20 to greater than 200 days, with a median value of 70 days.

Summary of aldicarb monitoring and research programs in the U.S.A.

Since 1979, over 130,000 soil and water samples have been collected and analyzed for aldicarb in monitoring and research programs conducted in the U.S.A. Comprehensive field research studies have been conducted on 40 plots located in 14 states and involving eight different crops. In addition, exploratory studies have been conducted in eight states including three in which field studies were not conducted at a later date. Drinking water samples have been collected in 39 states. Many laboratory studies have been performed to better define degradation mechanisms and rates. Modeling simulations have been performed to interpret field data and to properly apply the results to other situations. The movement and degradation of aldicarb residues in the unsaturated and saturated zone in a complex process affected by soil and hydrogeological properties, climatic conditions, and agricultural practices. These studies show that in most areas aldicarb residues degrade in the upper portion of the unsaturated zone. In the few areas where aldicarb residues reach groundwater, the combined effects of the primarily lateral movement of groundwater and the continuing degradation usually constrain aldicarb residues to shallow groundwater neat treated fields. Most of the cases where aldicarb residues in drinking water have occurred in excess of the EPA (and WHO) health advisory level of 10 μg L−1 (a MCL of 7 μg L−1 is being proposed by the EPA) resulted from applications made at planting to potatoes. Generally, these instances of drinking water residues have been in the Northeast and Wisconsin: however, above guideline residues in drinking water wells have occurred as result of applications to lily bulbs in northern coastal California, sugar beets in Wyoming and citrus in central Florida. Management practices have been implemented to eliminate the occurrence of aldicarb residues in drinking water wells from future applications. These management practices have consisted of changes in application timing, application rates, and restrictions on applications near shallow drinking water wells in areas with vulnerable soils and shallow water tables. Almost all of the residues in drinking water wells currently exceeding guidelines are the result of applications made prior to the adoption of these management practices.

Field research studies on the movement and degradation of thiodicarb and its metabolite methomyl

Abstract The movement and degradation of thiodicarb and its metabolite methomyl were measured at three locations in the United States. At a site near Clayton, North Carolina, soil samples were used to determine the degradation rate of thiodicarb in surface soils and methomyl in both surface and subsoils. At sites near Palermo, New York, and Oviedo, Florida, the shallow groundwater was monitored following multiple foliar applications of thiodicarb. These groundwater monitoring studies were conducted under conditions favorable to movement of pesticides to groundwater since surface soils were loamy sand or sand, subsoils were sand, water tables ranged between 0.1 and 1.8 m, and rainfall was supplemented by irrigation to ensure that the sum of irrigation and rainfall was at least 1.5 times the normal monthly rainfall. In these studies the half-life of thiodicarb was only a few hours in surface soils, while the half-life methomyl was about two days in surface soils and about 0.5 to 1.6 months in subsoils. Although methomyl residues were detected in shallow groundwater in the Oviedo and Palermo studies (designed to be representative of worst case situations), these residues were present in only one well cluster and one sampling interval, and at concentrations substantially below the established health advisory level.

Changing aldicarb residue levels in soil and groundwater, eastern Long Island, New York

Abstract A study that involved repeated groundwater and soil-core sampling in four representative potato-growing areas of Long Island, New York was carried out between 1980 and 1984 to investigate the impact of the pesticide aldicarb on groundwater quality. Aldicarb residue concentrations in both the saturated and unsaturated zones were analyzed together with hydrologic data from the study sites. Results showed that the timing of initial residue delivery to groundwater was dependent on water-table depth. After arrival at the saturated zone, the rate of residue advance within the aquifer depended on the rate of groundwater movement, which is strongly associated in this area with location relative to regional groundwater divides. Residue concentrations in groundwater peaked earliest and highest in areas closest to the aldicarb application sites and later and lower in areas farther downgradient. Based on the observed patterns of residue distribution, the impact of the pesticide on the aquifer as a whole will be shorter in duration than some previous estimates. The continuing processes of groundwater flow, residue degradation, and dispersion will drop aldicarb residue concentrations in groundwater to below the New York State drinking-water guideline of 7 μg/L long before the associated groundwater leaves the aquifer through natural discharge.

MAJOR TRANSPORT MECHANISMS OF PYRETHROIDS IN RESIDENTIAL SETTINGS AND EFFECTS OF MITIGATION MEASURES

The major pathways for transport of pyrethroids were determined in runoff studies conducted at a full-scale test facility in central California, USA. The 6 replicate house lots were typical of front lawns and house fronts of California residential developments and consisted of stucco walls, garage doors, driveways, and residential lawn irrigation sprinkler systems. Each of the 6 lots also included a rainfall simulator to generate artificial rainfall events. Different pyrethroids were applied to 5 surfaces—driveway, garage door and adjacent walls, lawn, lawn perimeter (grass near the house walls), and house walls above grass. The volume of runoff water from each house lot was measured, sampled, and analyzed to determine the amount of pyrethroid mass lost from each surface. Applications to 3 of the house lots were made using the application practices typically used prior to recent label changes, and applications were made to the other 3 house lots according to the revised application procedures. Results from the house lots using the historic application procedures showed that losses of the compounds applied to the driveway and garage door (including the adjacent walls) were 99.75% of total measured runoff losses. The greatest losses were associated with significant rainfall events rather than lawn irrigation events. However, runoff losses were 40 times less using the revised application procedures recently specified on pyrethroid labels. Environ Toxicol Chem 2014;33:52–60.

Monitoring of aldicarb residues in Long Island, New York potable wells.

After aldicarb residues were detected in Long Island, New York ground water in 1979, the manufacturer agreed to provide carbon filters for potable wells exceeding the New York guideline of 7 μg/L. Analyses of samples taken from these wells in the past six years indicate aldicarb residue levels are declining in Long Island groundwater. Of the 1,218 wells which received carbon filters in 1980–1981, 55% no longer contain residues exceeding 7 μg/L (an additional 24% could not be sampled during 1984–1985). Although approximately 2,500 homes have received filters through October, 1986, the total number of wells with residues exceeding 7 μg/L is now about 1,400. The results suggest that by the end of the decade only a small number of potable wells will contain aldicarb residues above 7 μg/L.

Washoff of cypermethrin residues from slabs of external building material surfaces using simulated rainfall.

The use of pesticides by homeowners or pest-control operators in urban settings is common, yet contributions of washoff from these materials are not easily understood. In the present study, cypermethrin, formulated as Cynoff EC (emulsifiable concentrate) and Cynoff WP (wettable powder) insecticides, was applied at typical rates to 10 different building material surfaces to examine its washoff potential from each surface. Using an indoor rainfall simulator, a 1-h rainfall event was generated and washoff samples were collected from 3 replicates of each surface type. Washoff was analyzed for cypermethrin using gas chromatography-negative chemical ionization mass spectrometry. An analysis of variance for a split-plot design was performed. Many building materials had similar water runoff masses, but asphalt resulted in significantly reduced average water runoff masses (73% less). The Cynoff WP formulation generally produced greater cypermethrin washoff than the Cynoff EC formulation. In addition, results for both the WP and EC formulations indicated that smoother surfaces such as vinyl and aluminum siding had higher washoff (1.0–14.1% mean percentage of applied mass). Cypermethrin washoff from rough absorptive surfaces like concrete and stucco was lower and ranged from 0.1 to 1.3% and from 0 to 0.2%, respectively, mean percentage of applied mass. Both building material surface and formulation play a significant role in cypermethrin washoff. Environ Toxicol Chem 2014;33:302–307.