Monitoring of Methyl Eugenol and DDVP in Fruit Near Fruit Fly Traps During a Pest Trapping Program
Abstract
In 1989, the California Department of Food and Agriculture undertook a monitoring program to determine if methyl eugenol and DDVP, two chemicals used in the Oriental Fruit Fly trapping program, could be detected in fruit growing near traps placed in trees. Methyl eugenol, a male attractant, and naled, an insecticide, were added to traps, and DDVP {also an insecticide) formed as a breakdown product of naled. Methyl eugenol is used as a food additive and occurs naturally in some fruit types. It is currently being evaluated for oncogenicity by the National Toxicology Program. DDVP is on the California Safe Drinking Water and Toxic Enforcement Act (Proposition 65) list of chemicals known to cause cancer. Both compounds had been detected in whole citrus fruit samples from trees containing traps in September 1988. Naled was not detected in any samples in 1988, so fruit was not analyzed for it in 1989. The 1989 monitoring was expanded to include apples and apricots as well as citrus {oranges).
Fruit samples were collected from trees containing Oriental Fruit Fly traps in Sacramento County between May and August, 1989. Traps were replaced (or rebaited) every 4-6 weeks during spring and summer. Sampling took place when traps were first replaced, and fruit was collected from trees in which traps had been in place at least 6 weeks. Samples were collected 4 h and 24 h after replacement of traps, at a distance of 31-61 cm from the traps, or from greater than 61 cm, if necessary. Fourteen trees of each fruit type were sampled.
For apples and apricots, the whole fruit was analyzed for methyl eugenol and DDVP. Neither chemical was detected in any apricot or apple samples. Methyl eugenol was found to occur naturally in orange rinds, so only the inner pulp of this fruit was analyzed. Methyl eugenol was detected in 14 of the 28 orange samples collected, at concentrations ranging from 28.8 ppb to 147.1 ppb. Since it was known to occur naturally in orange rinds, 14 control samples from trees not containing traps, but located in trapping areas, were collected and the inner pulp was analyzed. Methyl eugenol was detected in 8 of these 14 samples, at concentrations of 32.3 ppb to 289.0 ppb. Statistical tests performed on the data failed to find a significant difference between trapped and control samples.
DDVP was detected in 4 of the 28 orange samples collected from trapped trees, but was not detected in control samples. Concentrations ranged from 1.2 ppb to 1.6 ppb. Statistically, there was no difference between trapped and control samples. Although special precaution was taken to prevent sample contamination in the field and laboratory, the source of DDVP residues remains problematic. The DDVP found in orange pulp may have been due to ambient volatilization of DDVP from fruit fly traps or the result of sample contamination in the lab or field. Future research should determine the most likely source of these residues.