Environmental Concentrations and Aquatic Toxicity Data on Diflubenzuron (Dimilin)

Abstract

The insecticide diflubenzuron (DFB) is commonly used in various mid-Atlantic states for suppression of gypsy moths in hardwood forests. DFB is potentially toxic to nontarget biota because it can enter aquatic systems through aerial application or runoff after precipitation events. Based on this concern, the objectives of this study were to: (1) compile, review, and synthesize literature on the fate, persistence, and environmental concentrations of DFB in both freshwater and saltwater environments; (2) compile, review, and synthesize acute and chronic aquatic toxicity data on DFB effects on freshwater and saltwater organisms; (3) assess possible risk to aquatic biota associated with the use of this insecticide in one specific area (Maryland); and (4) recommend future research based on the data gaps identified from this study. DFB has low solubility in water and exists as a technical grade (TG) and wettable powder (WP) formulation. The toxicity of both formulations is similar at concentrations less than 10 micrograms/l. Organic matter is a major factor influencing the adsorption and degradation of DFB in freshwater, saltwater, and sediment. The half-life of this insecticide in freshwater is approximately 3 days at a pH of 10 and temperature of 36 degrees C. At lower pH conditions of 6 and at the same temperature, DFB is more persistent since half-life values of approximately 9 days have been reported. The half-life of DFB in soil is less than 14 days when the particle size was approximately 2 microns. The half-life is generally greater in cool, dry soil than in hot, wet soil. Aquatic vegetation acts as a sink for DFB by gradually adsorbing the chemical and releasing it over a period of time. Freshwater organisms demonstrated a wide range of sensitivity to DFB. Sensitivity was dependent on body composition (i.e., exo- vs. endoskeleton), trophic level, and life stage. During acute exposures, aquatic invertebrates were more than 25,000 times as sensitive to DFB than fishes. The most acutely sensitive species tested was the Amphipod, Hyallela azteca (96-h LC50 = 1.84 micrograms/l). A mature Plecopteran, Skwala sp., was the most resistant invertebrate species tested in acute tests (96-h LC50 greater than 100,000 micrograms/l). In chronic tests, DFB concentrations of 1 microgram/l or greater were reported to eliminate populations of various Plecopteran (stoneflies) and Ephemeropteran (mayflies) species after 1 month of exposure. A 30-day LC50 of 0.1 micrograms/l DFB was also reported for the Tricopteran, Clistorinia magnifica.(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental Study on Diflubenzuron: Degradation in Freshwater and Bioconcentration in Mosquitofish Following Chronic Exposure

“…Dimilin is degraded in the environment mainly by photodegradation and hydrolysis [40], producing as major metabolites: 2,6-diflurobenzamide, 4-chlorophenylurea, 4-chloroacetanilide, 4-chloroaniline and N-methyl-4-chloroaniline [45]. Among them, 4-chloroaniline shows a higher toxicity to fish than the original product [46].…”

“…Low concentrations can persist for 7 weeks or longer in pond waters under low pH and temperatures [49]. Thus, a half-time of 3 days at pH = 10 in freshwater was reported [46] against a half-life of 1.5 to 2 weeks at pH between 8 -8.5 [50].…”

Comparative Effects of a Genetically Engineered Insect Virus and a Growth-Regulating Insecticide on Microbial Communities in Aquatic Microcosms

“…Dimilin has also been found to degrade in aquatic environments within 2 weeks of application (Sundaram et al, 1991). Regardless of the magnitude of e!ects on aquatic microbial communities they are likely to be of far less ecological signi"cance than the well-documented adverse e!ects of Dimilin on aquatic insects and crustaceans (Fisher and Hall, 1992).…”

Nontarget effects of a test application of diflubenzuron to the forest canopy on stream macroinvertebrates

“…Because of the unique mode of action of DFB, adverse effects are delayed until the molting process begins. Freshwater organisms have demonstrated a wide range of sensitivity to DFB, dependent on species, trophic level, and life stage [7].…”