MONITORING SUREDYE® DEPOSITION DURING
AN AERIAL APPLICATION
In the past, emergency eradication programs for the Mediterranean fruit fly
(Medfly) have involved the aerial application of a malathion-bait mixture over
large regions of farming and residential properties. Recently, promising results
have been found with applications of a food dye (SureDye®) and bait mixture as a
replacement for malathion in trials performed by the United States Department of
Agriculture (USDA) in Hawaii. On April 17, 1996, the California Department of
Food and Agriculture's (CDFA) Pest Detection and Emergency Projects branch
began a trial aerial application program of SureDye® and bait to assess its pesticide
efficacy. Prior to application, sterile Medflies were released in a selected orchard
in Orange County and the population was to be monitored through trapping. The
SureDye® mixture was applied weekly by helicopter as an ultra-low volume spray
for a total of 9 applications. The dye concentrations in the preliminary test are
much less than the malathion concentrations currently used in aerial bait sprays.
SureDye® is a mixture of Red Dye #28 and Yellow Dye #8, both of which are
xanthene dyes registered for use as a color additive in drugs and cosmetics by the
Food and Drug Administration. Scientists speculate that the red dye reacts with
light and is transformed into a substance that destroys the insects' digestive tracts.
The yellow dye is believed to increase the activity of the red dye (NIEHS 1996).
The SureDye® compounds degrade rapidly under sunlight and applications of
SureDye® are not likely to cause significant impacts on the environment. The
reported half life of the dyes are approximately one hour under sunlight. Neither
dye persists for more than a few hours in air or water due to rapid photodegradation
This monitoring study was conducted as a two-phase project. The first phase
involved the initial development of the appropriate sampling and analytical
methodologies. The second phase consisted of a comprehensive sampling during
application and analysis of samples.
Sampling and Analytical Methods Development
Analytical Methods Development
The primary analytical laboratory for this study was the CDFA Center for
Analytical Chemistry. Available methods for residue analysis of SureDye® were
expanded to include absorbent deposition sheets (Kimbies®). Method development
included the determination of reporting limits for both dyes, which were 10 ug per
sample for the yellow dye and 12 ug per sample for the red dye. Because the dye is
applied in a yeast and fructose bait, the dense mixture made it difficult to generate
reproducible and low level quantitative spikes. With extended investigation into
various mixtures and methods for the formation of laboratory spikes, the final
recommendation was to use the dye and bait mixture as formulated, with a final
filtration of the extract through 0.45 micrometer pore size filters to remove
particles. The reported average recoveries from the method validation study for the
red dye and yellow dye were 93 and 88 percent, respectively.
During the sixth application, on May 29th, 30 mass deposition sites within the
treatment area were sampled to determine the amount of pesticide reaching the
ground. Sites were selected in the middle "access rows", which were located every
five rows within the orchard to allow vehicles through the orchard. A 0.093 square
meter of absorbent Kimbie® material was placed 20 centimeters above ground
level on cardboard platforms. Application took approximately one hour.
Following application, the samples were collected when spray droplets were
sufficiently dry. The samples were then folded in aluminum foil, put into
envelopes and placed on dry ice for transport. The samples remained frozen until
analysis in the laboratory. Because of the rapid photodegradation of SureDye®, all
samples were covered and protected from exposure to sunlight.
The application was made to approximately 150 hectares of oranges in Orange
County. The SureDye® mixture was applied by helicopter approximately seven
meters above ground level, just above tree height. The application swath width was
approximately 12 meters, covering two rows of trees.
The results are presented in Figure 1. The application rate of 39.2 grams of ai per
hectare of total red and yellow dye is equivalent to a theoretical deposition rate of
3958 micrograms per cubic meter (ug/m2). The average of all the measured
concentrations was 1827 ug/m2. Measured concentrations of SureDye® ranged from 585.6 to 5916 ug/m2 (Table 1).
Figure 1. Results of deposition sampling for SureDye® application.
Overall, the samples were much lower in concentration than the theoretical
concentration of the application rate. As a measurement of precision, the
coefficient of variation (CV) is calculated as the standard deviation divided by the
average of all the calculations and multiplied by 100%. The CV's for the red and
yellow dye concentrations were 61.5% and 61.7%, respectively. The results
indicate a high variation between samples, or low precision.
The relative deviation of the concentrations indicated poor accuracy between the
samples and the theoretical application rate for the red and yellow dye. The overall
relative percent deviation [((observed - theoretical)/theoretical) x 100] is 53.8%.
Twenty-eight of the thirty samples fell well below the targeted value for red dye.
Twenty-nine of the thirty samples fell well below the target application rate for
yellow dye. The sample collected from location 10 was atypical in comparison to
other samples, with a measured concentration nearly 4 standard deviations away
from the average concentration measured.
Table 1. Summary of SureDye® deposition concentrations.
|Total Dye mixture
The low precision and accuracy of the measured concentrations could be due to the
nature of the application, and location of the samples. A visual inspection of the
dye coverage following the application indicated a good distribution of material.
The sampling media were located between the widest possible tree rows, but were
still probably influenced by the orchard canopy. The usual procedure for
deposition sampling requires placement of the sample from the closest obstacle to
be at least twice the distance of the height of the closest obstacle. The only other
possible location for the sampling media would have been on platforms placed at
tree height. The low clearance of the helicopter and high wind turbulence made the
Another possible explanation could involve the short half-life of the compound.
The rapid degradation rate of the compound under sunlight may have affected
some of the samples before they were collected. A non-analytical method, such as
droplet distribution on drop cards, may give a better measure of coverage.
Consistent and accurate application may also be difficult to achieve because of the
physical nature of the mixture, which was a thick and concentrated mixture of dye,
yeast, fructose and water. Distribution of the material may be variable due to
clogging of equipment, difference in droplet size, or pattern of dispersion. The
thickness of the mixture made it difficult for the chemist to reproduce accurate and
consistent droplets for spiking purposes. Measured droplets of the mixture varied
widely in weight. The comparison of concentrations within discrete areas from the
actual field application, such as measured with the kimbies, would also result in
Liquido, Nicanor. 1996. USDA Agricultural Research Service. Tropical Fruit and
Vegetable Research Laboratory. Hilo, HI. Personal Communication. March 28,
National Institute of Environmental Health Services. 1996. Environmental Health
Perspectives Innovations Web magazine. Vol 104, Number 2, February.