Monitoring Diazinon Ground Application Under Controlled Conditions in Sacramento, California, 1993

Report Number EH 95-1

California Enviornmental Protection Agency

Environmental Monitoring and Pest Management Branch

Environmental Hazards Assesement Program

1020 N Street, Sacramento, California 95814-5624

ABSTRACT

A study was conducted by the Environmental Hazards Assessment Program (EHAP) scientists of the Department of Pesticide Regulation to monitor the levels and estimate the changes in concentration of diazinon and diazoxon over time on surface soil and turfgrass. Diazinon was applied to barren soil and turfgrass three times, 14 days between applications, at a rate of 5 lb active ingredient/acre. Soil and turf samples were collected immediately before and after diazinon application, then after incorporation with sprinkler irrigation. The average amount of water applied was 0.54 cm. Additional soil and turf samples were collected up to eight days after the first application and up to 45 days after the third application. Dissipation curves for diazinon and diazoxon were determined by first-order exponential decay equations for both media. The dissipation half-lives for diazinon in soil when all pre-water and post-watering-in samples were analyzed were 2.4 days and 11.3 days following applications one and three, respectively. Diazoxon in soil was detected in two of four samples on only one sampling day following application one. The average concentration of diazoxon found in soil two days following application one was <0.01 ug/g. Following application three, diazoxon was detected on four sampling days. The mean concentration of diazoxon per day during this sampling period was <0.01 ug/g. Dissipation half-lives for dislodgeable diazinon residues on turf were 3.4 days following application one and 9.5 days following application three. Dissipation half-lives for total diazinon residues on turf were estimated to be 5.1 days following application one and 12.8 days following application three. Dislodgeable and total diazoxon residues on did not show a significant decline over the sampling period following application one. Following application three, dissipation half-life for dislodgeable diazoxon residues on turf was estimated to be 14.1 days. Following application three, dissipation half-life for total diazoxon residues on turf was estimated to be 18.8 days.

The average diazinon mass deposition on soil for applications one, two and three was 47.27, 51.27 and 51.8 ug/cm2, respectively. For application one, two and three, the mean diazinon mass deposition on turf was 52.56, 48.77 and 49.85 ug/cm2, respectively (Table 6).

The tank samples contained diazinon concentrations which ranged from 0.43 to 0.46%. Diazoxon was not detected in any of the samples.

ACKNOWLEDGMENTS

We would like to thank the following individuals for their cooperation and assistance with this project:

Soil Composition Analysis: Cindy Garretson

Pesticide Application: Bob Sano and Alfredo Da Silva

A very special thanks to Roger Sava, Senior Environmental Research Scientist, and Clarice Ando and Frank Schneider, Associate Environmental Research Scientists.

DISCLAIMER

The mention of commercial products, their source or use in connection with material reported is not to be construed as an actual or implied endorsement of such product.

TABLE OF CONTENTS

ABSTRACT i
ACKNOWLEDGMENTS iii
DISCLAIMER iii
TABLE OF CONTENTS iv
LIST OF TABLES vi
LIST OF FIGURES vi
INTRODUCTION1
MATERIALS AND METHODS 2
Study Design 2
Diazinon Ground Treatment 2
Soil Monitoring 3
Turf Monitoring 3
Mass Deposition Samples 4
Tank Samples 4
Chemical Analyses and Quality Control 4
Statistical Analysis 6
RESULTS AND DISCUSSION 6
Dissipation of Diazinon at the Bare Soil Site 6
Dissipation of Diazinon at the Turf-Thatch Site10
Mass Deposition Samples 20
Tank Samples 20
Quality Control 21
CONCLUSIONS AND RECOMMENDATIONS 25
PREFERENCES 27
APPENDICES28
Appendix A - Chemical Analytical Methods
Appendix B - Sacramento, California - Diazinon Field Data Results
Appendix C - Laboratory Quality Control

LIST OF TABLES

Table 1. Dissipation of diazinon in soil with values expressed on a dry weight basis 8
Table 2. Dissipation of dislodgeable diazinon on turf with values expressed on a wet weight basis12
Table 3. Dissipation of total diazinon (dislodgeable and penetrated) for turf with values expressed on a wet weight basis14
Table 4. Dissipation of dislodgeable diazoxon on turf with values expressed on a wet weight basis 16
Table 5. Dissipation of total diazoxon (dislodgeable and penetrated) for turf with values expressed on a wet weight basis 18
Table 6. The amount of diazinon deposited on soil and turf on three separate application days 20
Table 7. Inter-laboratory soil split sample results 23

LIST OF FIGURES

Figure 1. Diazinon dissipation in soil with time. Means are connected by straight lines9
Figure 2. Dislodgeable diazinon dissipation on turf with time. Means are connected by straight lines13
Figure 3. Total diazinon dissipation on turf with time. Means are connected by straight lines15
Figure 4. Dislodgeable diazoxon dissipation on turf with time. Means are connected by straight lines17
Figure 5. Total diazoxon dissipation on turf with time. Means are connected by straight lines19

INTRODUCTION

The Mediterranean fruit fly is a destructive pest known to attack more than 290 fruits and vegetables. To prevent this pest from becoming established in the State of California, the Department of Food and Agriculture (CDFA) staff apply diazinon by ground to eradicate prepupal or adult stages of the fruit fly as various life stages enter or emerge from the soil. One treatment consists of three diazinon applications made at 14 day intervals.

Diazinon is an insecticide belonging to the organophosphate family. Its chemical name is O,O-diethyl O-[6methyl-(1-methylethyl)-4pyrimidinyl]phosphorothioate. It has a vapor pressure of 0.097 mPa at 200C, a specific gravity of 1.116-1.118 at 200C, and its solubility in water at 200C is 40 mg/L. It is a non-systemic insecticide and acaricide with contact, stomach, and respiratory action through cholinesterase inhibition (Royal Society of Chemistry, 1993).

In 1992 and 1993, EHAP staff monitored diazinon levels in soil and turfgrass to document levels of diazinon and diazoxon in both media (Ando et al., 1993; Leyva, 1993). Diazinon was applied by CDFA at a rate of 5 lb active ingredient (ai)/acre (5.7 kg ai/ha) and then watered in immediately after application. Samples of soil and turf were collected after watering-in. The results were variable from application to application so it was not possible to evaluate dissipation.

A controlled study was conducted to measure the amount of diazinon applied to the ground, the volume of water applied to the treated sites immediately after pesticide application, and to estimate dissipation. Environmental Hazards Assessment Program staff applied diazinon in September 1993 and monitored diazinon and diazoxon, a breakdown product, under controlled conditions in Sacramento, California. Dissipation of diazinon and diazoxon was measured in soil and turf samples collected from September to December 1993.

MATERIALS AND METHODS

Study Design

Study objectives were to determine diazinon and diazoxon residues in the top one cm of surface soil, to determine dislodgeable and total residues in turf-thatch, and to determine the dissipation half-lives of diazinon and diazoxon in each media.

In September 1993, one bare soil and one turf site were selected in Sacramento, California. The soil site measured 18.58 m2 and was divided into four equal subsites, each measuring 4.65 m2. The turf site measured 58.06 m2 from which four subsites were selected, each subsite measuring 5.81m2 (7.62 m X 0.762 m).

The pesticide was applied to entire sites; samples were collected from the subsites. Background levels of diazinon were measured by collecting soil and turf samples prior to each diazinon application (denoted as day -1). Samples were collected immediately two times after application: 1) prior to and 2) approximately one hour after sprinkler incorporation. At the first application, samples were collected 1, 2, 4 and 8 days after application. At the second application, samples were collected only before and after application but at the third application samples were collected 1, 2, 4, 8, 11, 15, 31, and 45 days after application.

Diazinon Ground Treatment

Diazinon AG500® (emulsifiable solution containing 1.81 kg ai per 3.79 L) was applied by EHAP staff to the two sites. Diazinon was applied to the turf site on September 27 and October 11 and 25, and to the soil site on October 11, 25, and November 8; the interval between each application was 14 days. The target application rate was 5.6 kg ai/ha. A pesticide concentrate of 82.6 ml was added to 8710 ml of water per 58.06 m 2 resulting in a targeted rate of 68.24 ug diazinon/cm2. A new tank mix was prepared at each site for all application days. Applications were made with a CO2 constant-pressure backpack sprayer outfitted with two nozzles on a 0.49-m length boom. Shortly after application, diazinon was moved into the upper layers of soil at both sites by applying an average of 0.54 cm of water with an automatic sprinkler system.

Soil Monitoring

Soil cores were collected using a stainless steel cylinder with of 6.3 cm id. Three soil cores were randomly selected from each subsite. The steel cylinder was inserted to a one cm depth from the soil surface. Soil samples at each subsite were composited and placed into a 1-pint glass mason jar and sealed with an aluminum-lined lid. Soil samples were split for comparative analysis by the primary and quality control laboratories on days 0, 1, 2, 4, and 8 of the first application, on background and day 0 of the second application, and on day 4 of the third application. Six soil cores instead of three were collected from each subsite for the interlaboratory splits. All samples were thoroughly mixed, placed on dry ice for shipping, and kept frozen until extraction for chemical analysis. Diazinon and diazoxon residues were calculated on a dry weight basis (ug/g of soil) and reported on a ground surface area basis (ug/cm2).

Organic carbon content, soil pH, and soil texture were determined on additional soil samples collected from the top 1 cm of soil prior to the first application.

Turf Monitoring

A stainless steel cylinder with an internal diameter of 6.3 cm was used to randomly sample turf and thatch. A core consisting of turf and soil was randomly selected and removed from the ground at each subsite. The cylinder contents were gently removed by holding the cylinder in a vertical position (turf side up) and pushing a smaller diameter rod upward from the soil portion of the chamber. Once the core was exposed, the turf and thatch were cut directly from the core into a 1-pint glass mason jar. Turf samples were composited from each subsite until 25 g of vegetative material was collected. Samples were sealed in jars with aluminum foil-lined lids, transported on wet ice, and maintained at 4oC until extraction for chemical analysis. Turf samples were extracted by CDFA's Center for Analytical Chemistry personnel to determine dislodgeable residue and total residue (the sum of the amount in dislodgeable and penetrated analyses) of diazinon and diazoxon. Residue results were calculated on a wet weight basis (ug/g of turf and thatch) and on a ground surface area basis (ug/cm2).

Mass Deposition Samples

Prior to each application, three half-pint canning jars were randomly placed in each of the four subsites at the soil and turf locations. Each jar was sunk into the ground so that the opening was flush with the soil surface or level with the top of the grass. Sample jars were sealed immediately with Teflon®-lined lids and transported to the laboratory on wet ice. Diazinon deposition was measured by analyzing the amount of diazinon deposited in each jar (id 7.6 cm). The average value was compared to the theoretical diazinon deposition rate of 5.6 kg ai/ha. The volume of chemical applied to the ground was estimated by measuring the volume of pesticide mix in the sprayer before and after application.

Tank Samples

One tank sample from each site was collected on each application day to measure the percent diazinon in the tank mix. Each sample container was sealed with a Teflon®-lined lid, double bagged, and placed in an ice chest on wet ice for transportation. This ice chest contained only tank samples.

Chemical Analyses and Quality Control

Soil texture, pH and organic carbon analyses were performed by EHAP's Soil Laboratory in Fresno, California (Bouyoucos, 1962; California Fertilizer Association; and Hausenbuiller, 1972). Chemical analyses for diazinon and diazoxon in soil were conducted by CDFA's Center for Analytical Chemistry in Sacramento, California (Appendix A). CDFA staff used ethyl acetate to extract diazinon and diazoxon in soil. Residues were analyzed using gas liquid chromatography with a flame photometric detector (phosphorous mode) for both compounds. The minimum detection limit was 0.005 ug/g for diazinon and diazoxon.

Split soil samples were analyzed by Enseco Laboratory for quality control (Appendix A). Enseco used methylene chloride:acetone to extract diazinon in soil. Analysis was only performed for diazinon. The determination of diazinon in soil was completed by gas chromatography with a thermionic specific detector. The minimum detection limit for diazinon was 0.05 ug/g.

Turf samples were analyzed by CDFA's Center for Analytical Chemistry for dislodgeable and penetrated diazinon and diazoxon (Appendix A). Dislodgeable diazinon and diazoxon residues were removed from turf with a mixture of water and a surfactant. Pesticides present in aqueous solution were then extracted with ethyl acetate. Penetrated diazinon and diazoxon were separated from turf by blending with ethyl acetate and by filtration. The minimum detectable level was 0.005 ug/g for both dislodgeable and penetrated diazinon and diazoxon. Diazinon and diazoxon concentrations were subsequently determined using gas chromatography with flame photometric detector.

Mass deposition samples were analyzed by CDFA's Center for Analytical Chemistry (Appendix A). Residues of diazinon and diazoxon were extracted with ethyl acetate and an aliquot of the solution was concentrated for the determination of diazoxon. Analyte detection was performed by gas chromatography equipped with a flame photometric detector. The minimum detection limit was 0.2 ug/sample (0.004 ug/cm2).

Statistical Analysis

Diazinon's dissipation was described by first-order kinetics. Linear regression analysis on logarithmically transformed diazinon data was used to estimate dissipation half-lives.

The means for diazinon and diazoxon concentrations in soil are presented as ug/g and ug/cm2 on a dry weight basis and in turf as ug/g and ug/cm2 on a wet weight basis. Sample results reported as not detected were assigned one-half the value of the reporting limit in order to complete calculations. Standard deviations of the means, confidence intervals for the means, and estimated dissipation half-lives were determined. Confidence intervals provide additional information which may be useful in estimating exposure. The lower and upper confidence intervals define a range in which the true mean is expected to lie, with 95% certainty.

RESULTS AND DISCUSSION

Dissipation of Diazinon at the Bare Soil Site

Soil at this site was classified as a loam. The average proportion of sand, silt, and clay was 36, 46, and 18%, respectively. Due to sprinkler incorporation after each application, soil moisture was as high as 24% by weight during sampling. The mean organic carbon content was 2.2% and soil pH was 6.0.

Raw data are presented in Appendix B. Since there were no differences in the dissipation when expressed in either unit of measurement, results will be discussed on a ug/g basis (dry weight measurements) rather than ug/cm2. Diazinon was detected prior to the first application at an average concentration of 0.11 ug/g. The highest average diazinon soil concentration, 36.86 ug/g, occurred immediately following application three prior to sprinkler incorporation. The average diazinon soil concentrations following applications one and two (pre-water) were 27.81 ug/g and 27.66 ug/g, respectively (Table 1, Figure 1).

Dissipation half-life for diazinon at the third application was 11.3 days (r2 = 0.60) which was greater than the half-life value of 2.4 days (r2 = 0.95) estimated after the first application. Diazinon residue was detected 45 days after the third and final application at a mean concentration of 0.53 ug/g (Table 1, Figure 1). During the dissipation study, the site was covered with plastic sheeting during heavy rainfall events but on day 30 after the third application, the site was uncovered and received 2.42 cm of rain.

The breakdown product, diazoxon, was detected on only one sampling day after application one (post-watering). The average concentration of diazoxon found in four samples on the second day following application one was <0.01 ug/g. After application 3, diazoxon was found on four sampling days. The mean concentration for diazoxon was <0.01 ug/g (n = 4) within each day when positive samples were reported (Appendix B). Biggar and Seiber (1987) indicated that diazoxon was not typically found in soil and they conclude that diazinon degradation to diazoxon was not a major degradation pathway in soil. The results of this study agree with these previous findings. Data were insufficient to estimate half-lives.

The inclusion of pre-incorporation data did not affect the half-life estimate. The larger half-life of diazinon at the third application was probably caused by the increase in concentration between applications. Concentration has been shown to affect dissipation half-life (Zimdahl et al., 1993).

Table 1. Dissipation of diazinon in soil with values expressed on a dry weight basis.
Appl Sample Diazinon Standard 95% Confidence Intervals Estimated Estimated
# Daya Mean Deviation Lower Upper Half-lifeb Half-lifec
------------------------------ug/g---------------------------- ------------days------------
1 -1 0.11 0.10 0.0d 0.27 2.3 2.4
1 B0 27.81 1.68 25.14 30.48
1 A0 26.09 3.89 19.90 32.28
1 1 29.26 4.99 21.32 37.20
1 2 27.52 2.59 23.40 31.64
1 4 10.05 4.86 2.32 17.78
1 8 3.26 1.01 1.65 4.87
2 -1 2.31 1.39 0.10 4.52 --- ---
2 B0 27.66 9.04 13.28 42.04
2 A0 6.24 2.53 2.21 10.27
3 -1 5.76 2.78 1.34 10.18 13.9 11.3
3 B0 36.86 8.60 23.18 50.54
3 A0 9.92 3.05 5.07 14.77
3 1 5.68 3.29 0.45 10.91
3 2 6.79 2.30 3.13 10.45
3 4 1.82 0.65 0.79 2.85
3 8 2.02 2.19 0.0d 5.5
3 11 3.47 3.60 0.0d 9.2
3 15 1.16 0.70 0.05 2.27
3 31 1.63 1.75 0.0d 4.41
3 45 0.53 0.16 0.28 0.78
a - Four soil samples taken per day; B0 = Application day soil samples taken before
watering in, A0 = Application day soil samples taken after watering in.
b - Post-water data used to determine dissipation curve for diazinon on soil.
c - Pre- and post-water data used to determine dissipation curve for diazinon on soil. 

d - Calculated value was below minimum detectable limit of 0.25 ug.

Dissipation of Diazinon at the Turf-Thatch Site

Diazinon was not detected in any of the background turf-thatch samples for application one. The highest mean concentration of 45 ug/g of dislodgeable diazinon and 138 ug/g of total diazinon in turf-thatch was detected before sprinkler incorporation at the second application (Tables 2 and 3, Figures 2 and 3).

If the background level is subtracted, the mean total diazinon level for the pre-water sample for application three was low when compared to applications one and two. The theoretical tank mix diazinon percentage was 0.46% and the measured diazinon percentage in the tank mix for the third application was 0.44%. The theoretical diazinon mass deposition was 68.24 ug/cm2 whereas the measured diazinon mass deposition for third application was 49.85 ug/cm2 (73% of theoretical). Analyte recovery for spiked dislodgeable and penetrated turf-thatch averaged 100% for both. Therefore, the low level may be explained by the sampling method variability.

Dissipation half-lives for dislodgeable diazinon residues when pre-incorporation samples were included were 3.4 days (r2 = 0.89) at application one and 9.5 days (r2 = 0.95) at application three (Table 2, Figure 2). Dissipation half-lives for total diazinon residues when pre-incorporation samples were included were 5.1 days (r2 = 0.85) at application one and 12.8 days (r2 = 0.97) at application three (Table 3, Figure 3). After the third application, mean dislodgeable and total diazinon values decreased over time, yet were detected during the remainder of the monitoring period. Forty-five days after the last application, mean residue levels of 0.84 ug/g of dislodgeable diazinon and 6.54 ug/g of total diazinon were reported.

In Kuhr and Tashiro (1978), the dissipation half-life for diazinon from grass with no thatch present was about one week. Diazinon residues after six weeks from only one application of 6.72 kg/ha ranged from 0.17 ug/g to 0.65 ug/g. In Sears and Chapman (1979), residue analyses were performed on samples of turfgrass treated with diazinon when applied under optimum conditions at rates normally recommended for control of soil insects which damage turf. Diazinon degraded rapidly, disappearing almost completely in 14 days.

Dislodgeable and total diazoxon were also detected 45 days after the last application at 0.02 ug/g and 0.07 ug/g, respectively (Tables 4 and 5, Figures 4 and 5). The measured rainfall for the 74-day monitoring period extending from the first application to the last sampling date was 9.2 cm. Since each rainfall event during this monitoring period was light, the site was not covered. The total amount of water applied to maintain the turf over the same period was 17.5 cm.

It was not possible to estimate half-lives, because concentrations of dislodgeable and total diazoxon residues on turf-thatch, and collected pre-and post-watering samples did not significantly decline over the sampling period following the first application. The best predictor for dissipation of dislodgeable and total residues during this period was estimated by the mean concentration. The average concentration of dislodgeable diazoxon residues following application one, including pre-watering and post-watering for four days, was 0.19 ug/g (Table 4). The average concentration of total diazoxon residue after application one during the same period of time was 0.40 ug/g (Table 5). The dissipation curves for dislodgeable and total diazoxon residues following application three fit an exponential decay function. Estimated dissipation half-lives (pre-water samples included) were 14.1 days (r2 = 0.90) for dislodgeable and 18.8 days (r2 = 0.93) for total diazoxon (Tables 4 and 5, Figures 4 and 5).

The inclusion of pre-incorporation data did not affect the half-life estimate. The larger half-life of diazinon at the third application was probably caused by the increase in concentration between applications.

Table 2. Dissipation of dislodgeable diazinon on turf with values expressed on a wet weight basis
 
 
Mean
 
Appl Sample Dislodgeable Standard 95% Confidence Intervals Estimated Estimated
 
# Daya Diazinon Deviation Lower Upper Half-lifeb Half-lifec
 
------------------------------ug/g-------------------------- ------------days-----------
 
1 -1 ND d ND 0.0032 0.02 3.8 3.4
1 B0 35.34 22.50 0.0e 71.14
1 A0 18.00 4.16 11.38 24.62
1 1 22.52 2.82 18.03 27.01
1 2 20.12 5.81 10.88 29.36
1 4 11.77 2.46 7.80 15.62
1 8 5.30 1.63 2.71 7.89
2 -1 6.55 2.55 2.49 10.61 --- ---
2 B0 44.74 5.53 35.94 53.54
2 A0 15.99 4.26 9.21 22.77
3 -1 6.79 2.73 2.45 11.13 9.5 9.5
3 B0 24.69 7.63 12.55 36.83
3 A0 31.80 7.35 20.11 43.49
3 1 18.45 6.26 8.49 28.41
3 2 20.13 8.83 6.08 34.18
3 4 18.71 6.83 7.84 29.58
3 8 8.88 3.06 4.01 13.75
3 11 7.58 2.71 3.27 11.89
3 16 6.05 2.91 1.42 10.68
3 29 3.95 1.70 1.25 6.65
3 45 0.84 0.41 0.23 1.49

a - Four turf samples taken per day; B0 = Application day turf samples taken before
 
watering in, A0 = Application day turf samples taken after watering in.
b - Post-water data used to determine dissipation curve for diazinon on turf.
 
c - Pre- and post-water data used to determine dissipation curve for diazinon on turf. 

d - Calculated value was below minimum detectable level of 0.25 ug.

 
Table 3. Dissipation of total diazinon (dislodgeable and internal) for turf with values expressed on a wet weight basis.
Mean
Appl Sample Diazinon Standard 95% Confidence Intervals Estimated Estimated
# Daya Content Deviation Lower Upper Half-lifeb Half-lifec
---------------------------ug/g-------------------------- --------days-------
1 -1 NDd ND --- --- 5.7 5.1
1 B0 99.08 46.37 25.31 172.85
1 A0 59.34 10.12 43.24 75.44
1 1 75.57 9.21 60.92 90.22
1 2 65.59 7.82 53.15 78.03
1 4 51.86 11.89 32.94 70.78
1 8 26.41 4.37 19.46 33.36
2 -1 28.19 9.54 13.01 43.37 --- ---
2 B0 138.34 27.29 94.92 181.76
2 A0 56.49 13.73 34.65 78.33
3 -1 32.37 6.91 21.38 43.36 12.9 12.8
3 B0 94.36 37.68 36 152.72
3 A0 90.19 16.46 64 116.38
3 1 67.98 12.52 48.06 87.90
3 2 85.55 27.91 41.15 129.90
3 4 68.32 16.75 41.67 94.97
3 8 51.06 12.42 31.30 70.82
3 11 44.23 6.20 34.37 54.09
3 16 40.7 10.29 24.33 57.07
3 29 23.23 8.16 10.25 36.21
3 45 6.54 2.64 2.34 10.74
a - Four turf samples taken per day; B0 = Application day turf samples taken before
watering in, A0 = Application day turf samples taken after watering in.
b - Post-water data used to determine dissipation curve for diazinon on turf.
c - Pre- and post-water data used to determine dissipation curve for diazinon on turf.
d - Not detected.

Table 4. Dissipation of dislodgeable diazoxon on turf with values expressed on a wet weight basis
Mean
Appl Sample Dislodgeable Standard 95% Confidence Intervals Estimated Estimated
# Daya Diazoxon Deviation Lower Upper Half-lifeb Half-lifec
----------------------------ug/g------------------------ ------------days-----------
1 -1 NDd ND --- --- nse ns
1 B0 0.10 0.05 0.02 0.18
1 A0 0.10 0.03 0.05 0.15
1 1 0.32 0.07 0.21 0.43
1 2 0.34 0.08 0.21 0.47
1 4 0.20 0.03 0.15 0.25
1 8 0.09 0.02 0.06 0.12
2 -1 0.07 0.02 0.04 0.10 --- ---
2 B0 0.25 0.06 0.15 0.35
2 A0 0.10 0.02 0.07 0.13
3 -1 0.12 0.02 0.09 0.15 13.4 14.1
3 B0 0.14 0.05 0.06 0.22
3 A0 0.21 0.04 0.15 0.27
3 1 0.22 0.05 0.14 0.30
3 2 0.24 0.08 0.11 0.37
3 4 0.21 0.07 0.10 0.32
3 8 0.12 0.03 0.07 0.17
3 11 0.11 0.04 0.05 0.17
3 16 0.07 0.02 0.04 0.10
3 29 0.07 0.03 0.02 0.12
3 45 0.02 0.01 0.00 0.04
a - Four turf samples taken per day; B0 = Application day turf samples taken before
watering in, A0 = Application day turf samples taken after watering in.
b - Post-water data used to determine dissipation curve for diazoxon on turf.
c - Pre- and post-water data used to determine dissipation curve for diazoxon on turf.
d - Not detected.
e - ns = regression not significant, half-life not calculated.

Table 5. Dissipation of total diazoxon (dislodgeable and internal) for turf with values expressed on a wet weight basis.
Mean
Appl Sample Diazoxon Standard 95% Confidence Intervals Estimated Estimated
# Daya Content Deviation Lower Upper Half-lifeb Half-lifec
----------------------------ug/g-------------------------- ---------days---------
1 -1 NDd ND 0.01 0.04 nse ns
1 B0 0.31 0.17 0.04 0.58
1 A0 0.27 0.08 0.14 0.40
1 1 0.64 0.13 0.43 0.85
1 2 0.55 0.13 0.34 0.76
1 4 0.37 0.06 0.28 0.47
1 8 0.23 0.05 0.15 0.31
2 -1 0.18 0.07 0.07 0.29 --- ---
2 B0 0.57 0.14 0.35 0.79
2 A0 0.27 0.07 0.16 0.38
3 -1 0.26 0.02 0.23 0.29 17.7 18.8
3 B0 0.30 0.12 0.19 0.41
3 A0 0.40 0.07 0.29 0.51
3 1 0.47 0.06 0.38 0.57
3 2 0.44 0.14 0.22 0.66
3 4 0.38 0.08 0.25 0.51
3 8 0.29 0.08 0.16 0.42
3 11 0.28 0.05 0.20 0.36
3 16 0.23 0.06 0.05 0.24
3 29 0.17 0.06 0.08 0.27
3 45 0.07 0.02 0.04 0.10
a - Four turf samples taken per day; B0 = Application day turf samples taken before watering in, A0 = Application day turf samples taken after watering in.
b - Post-water data used to determine dissipation curve for total diazoxon on turf.
c - Pre- and post-water data used to determine dissipation curve for total diazoxon on turf.
d - Not detected.
e - ns = regression not significant, half-life not calculated.

Mass Deposition Samples

The theoretical diazinon mass deposition was 68.24 ug/cm2. The average diazinon mass deposition on soil for applications one, two and three was 47.27, 51.27 and 51.18 ug/cm2, respectively. For applications one, two and three, the mean diazinon mass deposition on turf was 52.56, 48.77 and 49.85 ug/cm2, respectively (Table 6).

Tank Samples

The theoretical diazinon percentage is 0.46%. The six tank samples contained diazinon concentrations which ranged from 0.43 to 0.46%. Diazoxon was not detected in any of the samples and the minimum detection limit for the diazoxon was 1 mg/L.

Quality Control

For continuous quality control (Appendix C) by CDFA's Center for Analytical Chemistry and Enseco Laboratory during analyses, a blank matrix and a spiked matrix sample were analyzed with each set of field samples. CDFA's overall continuing quality control for diazinon recovery in soil was 95% (SD=5.4, CV=5.6%). CDFA's recovery value for diazoxon in soil was 91% (SD=8.0, CV=8.8%). Enseco's overall continuing quality control for diazinon recovery in soil was 83% (SD=7.5, CV=9.2%).

During the study, soil samples were collected from each of the four subsites within the soil site on nine separate occasions. As an inter-laboratory comparison, these 36 samples were split and sent to two different laboratories (CDFA and Enseco) for analysis. Soil moisture determination between both laboratories was very similar. Diazinon soil concentrations in the split samples ranged from 0.89 to 37 ug/g on a dry weight basis (Table 7). Regression analysis was used to investigate differences between the two sets of results. The precision of the two laboratories was compared prior to calculating the regression line. To determine whether the relative precision of Enseco results was significantly different from the relative precision of CDFA results, a comparison was made between the coefficients of variation within each of the nine subsets of data. A test of the equality of coefficients of variation indicated there were no significant differences (p>0.05) in relative precision between the two laboratories for seven out of nine subsets. The coefficients of variation for the remaining two subsets could not be tested because they were greater than 0.50. The previous test is not recommended for coefficients larger than 0.50. These two subsets were collected in connection with application two. An examination of the within-laboratory variance indicated that precision varied with concentration for both CDFA and Enseco. However, the pattern of variance relative to concentration did not follow a simple functional form and could not be estimated appropriately. Therefore, unweighted regression procedures were used assuming that precision did not vary with concentration. A regression of Enseco concentrations on CDFA concentrations indicated that the calculated slope did not differ significantly from 1 and the calculated intercept did not differ significantly from 0 at the 5% level of significance. The correlation coefficient was 0.90. The sample collected from subsite one (CDFA = 14.4 ug/g, Enseco = 2.5 ug/g) and the sample collected from subsite two (CDFA = 34.2 ug/g, Enseco = 12 ug/g) immediately after application two (prior to watering) were flagged as observations having large standardized residuals in comparison to other samples. On further investigation, the within subsite regression analysis of Enseco results on CDFA results indicated that the sample collected at this time was unusual compared to other samples for each of the four subsites. It was determined that these four samples collected in connection with application two were processed differently than the remaining samples. These samples were collected on October 25, 1993 but were not analyzed by Enseco until approximately six weeks later on December 4, 1993. Some degradation may have occurred resulting in lower and/or more variable concentrations reported by Enseco for these four samples. The regression analysis, without these observations, indicated there was no evidence of systematic differences between the two sets of results for concentration of diazinon in soil on a dry weight basis. Two observations were flagged indicating they were unusual compared to the remaining observations. The sample collected from subsite two after application one (prior to watering) (CDFA = 28.3 ug/g, Enseco = 37 ug/g) and the sample collected from subsite one on the day following application one (CDFA = 24.3 ug/g, Enseco = 16 ug/g) were investigated. These samples did not appear to be treated differently compared to other samples. No errors in recording the data were determined and they were not removed from the regression analysis. These analyses were repeated for soil concentrations expressed on a wet weight basis. Wet weight results were nearly identical to dry weight results.

Table 7. Inter-laboratory soil split sample results
 
 
Diazinon Soil Concentration
 
 
Appl Sample Dry Weight Wet Weight
 
# Day CDFA Ensecoa CDFA Ensecoa
 
------------ug/g------------- ----------ug/g---------
 
1 B0b 25.7 32.00 20.5 27.00
1 B0 27.6 33.00 22.5 28.00
1 B0 29.8 33.00 24.7 28.00
1 B0 28.0 31.00 23.4 27.00
1 0 20.7 25.00 15.9 20.00
1 0 28.3 37.00 21.7 30.00
1 0 25.8 31.00 19.8 26.00
1 0 29.5 37.00 23.3 30.00
1 1 29.2 33.00 23.2 28.00
1 1 35.8 37.00 28.6 31.00
1 1 28.5 33.00 22.8 28.00
1 1 23.6 24.00 19.0 20.00
1 2 24.3 16.00 19.8 14.00
1 2 30.6 29.00 25.3 25.00
1 2 27.8 28.00 23.0 24.00
1 2 27.4 31.00 22.8 27.00
1 4 4.3 5.00 3.6 4.30
1 4 7.7 9.50 6.4 7.90
1 4 14.7 14.00 12.6 12.00
1 4 13.5 12.00 11.0 10.00
1 8 1.9 1.50 1.6 1.30
1 8 3.5 3.30 3.0 2.90
1 8 4.4 4.80 4.0 4.40
1 8 3.2 2.40 2.9 2.20
2 -1 1.0 1.40 0.9 1.20
2 -1 3.4 2.10 3.2 2.00
2 -1 3.6 4.10 3.4 3.90
2 -1 1.2 0.89 1.1 0.83
2 B0 14.4 2.50 12.1 2.20
2 B0 34.2 12.00 31.6 11.00
2 B0 32.4 29.00 30.7 28.00
2 B0 29.7 26.00 28.2 25.00
3 4 1.2 1.10 1.0 0.93
3 4 2.4 1.70 2.1 1.50
3 4 2.4 1.30 2.1 1.20
3 4 1.3 0.96 1.1 0.84

aEach value contains two significant digits. Non-significant digits have been added for clarity.

bB0 = application day soil samples taken before watering in.

For turf, continuing quality control was conducted during chemical analyses and the overall mean dislodgeable diazinon results for spike matrix recovery was 100% (SD=6.13, CV=6.13%). The overall mean recovery for internal diazinon spike matrix samples was 102% (SD=9.82, CV=9.65%). Overall mean recovery for continuing quality control results was 102% (SD=8.52, CV=8.38%) for dislodgeable diazoxon on turf and 101% (SD=7.47, CV=7.37%) for internal diazoxon.

For mass deposition samples, continuing quality control was conducted during chemical analyses and the overall mean diazinon results for spike matrix recovery was 100% (SD=2.86, CV=2.86%). Overall mean recovery for continuing quality control results was 99% (SD=3.36, CV=3.41%) for diazoxon on mass deposition samples.

CONCLUSIONS AND RECOMMENDATIONS

Conclusion 1: In soil, the estimated dissipation half-life of diazinon measured after three applications that were spread 14 days apart was 11.3 days. Diazoxon dissipation could not be determined because residues were detected infrequently. Diazoxon concentrations were less than or equal to 0.01 ug/g for individual samples and were similar to observations made by Ando et al. (1993).

Recommendation: Because diazoxon is rarely detected, it is recommended that diazoxon be excluded from further soil monitoring when diazinon application rates do not exceed 5.7 kg ai/ha.

Conclusion 2: In turf, the estimated dissipation half-lives of total diazinon and total diazoxon measured after three applications that were spread 14 days apart were 13 days and 19 days, respectively.

Recommendation: Low diazinon levels were reported for the pre-water sample at the third application which may have been caused by sample collection methods. In order to achieve better estimates of diazinon concentrations after an application, the variability in the sampling method could be reduced by analyzing the represented matrices deeper in the core. Directly cutting the turf, thatch, and specified soil layer into individual sample containers could account for more of the pesticide applied and thereby reduce uncertainties.

Conclusion 3: Previous attempts to determine the dissipation half-life of diazinon in the Mediterranean fruit fly Eradication Soil Treatment Program were unsuccessful because of large variability in the field data. In this study, the use of uniform soil and turf types and the addition of consistent amounts of water after pesticide application tended to reduce variability.

In past monitoring studies for fruit fly eradication projects, samples were not collected immediately after application (pre-watering). In this study pre-watering samples confirmed that the applications were precise and uniform.

Recommendation: Collect more information, such as: 1) calculate surface area receiving the application, 2) collect and analyze deposition samples, (3) collect a sample immediately after application (prewatering), and (4) measure the amount of water added after pesticide application which are important factors in evaluating dissipation.

In future monitoring of diazinon ground treatments, pre-watering samples should be included in the sampling schedule to more accurately estimate deposition.

REFERENCES

Ando, C., J. Leyva, and C. Gana. 1993. Monitoring diazinon in the Mediterranean fruit fly eradication soil treatment program, Los Angeles County, California, 1992. California Department of Pesticide Regulation. EH 93-01.

Biggar, J. and J. Seiber. 1987. Fate of pesticides in the environment - proceedings of a technical seminar. Division of Agriculture and Natural Resources, University of California. Oakland, California.

Bouyoucos, George John. 1962. Hydrometer Method Improved for Making Particle Size Analysis of Soils. Agronomy Journal.

California Fertilizer Association, Organic Matter (O.M.) Dichromate Reduction. Method S: 18.0. California Soil Testing Procedures Manual. Sacramento, California.

Hausenbuiller, R.L. 1972. Soil Science Principles and Practice. 3rd ed. Wm. C. Brown Co., Dubuque, Iowa.

Kuhr, R.J. and H. Tashiro. 1978. Distribution and Persistence of Chlorpyrifos and Diazinon Applied to Turf. Bull. Environm. Contam. Toxicol. 20:652-656.

Leyva, J. 1993. Memorandum of Results of Diazinon Monitoring in Soil and Turf During the Medfly Eradication Program in Granada Hills, California and Rosemead, California. California Department of Pesticide Regulation.

Sears, M.K. and R.A. Chapman. 1979. Persistence and Movement of Four Insecticides Applied to Turfgrass. J. Econ. Entomol. 72:272-274.

The Royal Society of Chemistry. 1993. The Agrochemicals Handbook. 3rd ed. Thomas Graham House, Cambridge, England.

Zimdahl, R. L., Cranmer, B. K., and Stroup, W. W. 1993. Use of Empirical Equations to Describe Dissipation of Metribuzin and Pendimethalin. Weed Science 42:241-248.