Persistence of aerially-sprayed naled in coastal sediments

Area of Science:

• Environmental Chemistry
• Pesticide Science
• Public Health Entomology

Background:

• Aerial naled (organophosphate pesticide) spraying intensified in 2016 to combat Zika virus outbreaks in the U.S.
• Concerns arose regarding potential contamination of beach sediments by naled and its byproduct, dichlorvos.
• Understanding pesticide persistence in beach environments is crucial for public health risk assessment.

Purpose of the Study:

• To evaluate the persistence and levels of naled and dichlorvos in beach sediments.
• To investigate the impact of environmental factors (temperature, sunlight, sediment type) on naled decomposition.
• To provide data for risk assessment of exposure through contaminated beach sands.

Main Methods:

• Laboratory experiments simulating natural conditions on three sediment types (beach sand, marl, calcinated beach sand).
• Exposure of sediment samples to simulated aerial sprays and field aerial sprays.
• Analysis of naled and dichlorvos concentrations and decomposition rates over time.

Main Results:

• Dichlorvos was detected at higher concentrations than naled within 30 minutes of simulated exposure.
• Naled showed rapid decomposition, with half-lives of 1-5 hours at varying temperatures (22.5-30 °C).
• Sunlight significantly accelerated naled decomposition (half-life of 20 minutes); only dichlorvos was found in field samples post-spray.

Conclusions:

• Naled exhibits short persistence in beach sediments, particularly under sunlight and elevated temperatures.
• Dichlorvos is the primary detected residue in sediments following aerial naled application.
• Data supports risk assessment for human exposure to pesticide residues in beach sand environments.