Naled is an organophosphate pesticide that is applied aerially to control mosquito-borne disease transmission as well as areas with high bite rates by nuisance mosquitoes. During the summer of 2016 the use of naled in urban areas received considerable attention due to its use to control the first documented Zika virus outbreak in the continental U.S. Concerns were raised about the persistence of the pesticide in the environment and how this information can be used to develop protection strategies for humans and non-target organisms. The objective of this study was to evaluate the fate of naled, and its degradation product dichlorvos, in natural waters to assess the persistence during actual aerial spray scenarios. To evaluate the influence of changing environmental conditions, laboratory experiments were designed to measure the influence of hydrolysis, naturally occurring nucleophiles, temperature, and light on degradation rates.   Two representative water samples (a freshwater and a marine water) were utilized for experimentation, in addition to deionized water used as a control. Water samples were also measured in the field to document levels observed immediately after the spray activities.  Results show that the naturally occurring nucleophiles were necessary to promote degradation as experiments with deionized water resulted in the prolonged persistence of naled (half-life of many weeks).  The half-life in natural waters which excluded light sources was determined to be on the order of 6 hours. With light exposure, this reaction was accelerated and yielded more dichlorvos. Levels measured in the field after aerial sprays were 13 µg/L in freshwater and 19 µg/L in marine water.

Degradation of naled in natural waters collected from areas impacted by aerial spray activities

2019 Spring National Meeting

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