Persistence of aerially-sprayed naled in coastal sediments

Aerial sprays of the organophosphate pesticide, naled, were intensified over beach areas during the summer of 2016 to control the locally-acquired Zika outbreak in the continental U.S. Concerns were raised in beach frequented areas about contaminated sediments. The aim of this study was to evaluate the persistence and levels of naled and its byproduct, dichlorvos, in sediments obtained from the affected areas. Laboratory experiments were designed to simulate the effect of various natural conditions on the decomposition of naled in three sediment types (beach sand, marl, and calcinated beach sand). The three sediment samples were also exposed to field aerial sprays. After 30 min of exposure, more dichlorvos was detected in the sediments than naled, with 33 to 43% of the molar concentration initially applied as either naled or dichlorvos. Under dark conditions, trace levels of naled were observed after 24 h on sediments. Higher temperature accelerated the natural decomposition of both naled and dichlorvos in sediments. The half-life of naled ranged from 3 to 5 h at 22.5 °C and ranged from 1 to 3 h at 30 °C. Expedited decomposition of naled was observed under sunlight conditions with a half-life of naled of 20 min. In the field, only dichlorvos was detected in the sediment samples at concentrations between 0.0011 and 0.0028 μmol/g 1 h after aerial sprays. This data can be used towards a risk assessment that evaluates exposures to naled and dichlorvos through beach sands impacted by aerial spray activities.

Persistence of aerially applied mosquito-pesticide, Naled, in fresh and marine waters

Naled, an organophosphate pesticide, received considerable attention during 2016 as it was applied aerially to control the first mosquito-borne Zika virus outbreak in the continental United States. Stakeholders living in affected areas raised concerns about its environmental impacts. One factor influencing environmental impacts is the persistence of the chemical applied. The objective of this study was to evaluate the persistence of naled - and its degradation bi-product, dichlorvos - in natural waters. Initial naled concentrations were measured at ground level after full-scale aerial spray activities. Laboratory experiments were designed to evaluate factors (fresh versus marine water chemistry, temperature, and sunlight) that may promote the degradation of naled and dichlorvos in the environment. Results show that natural fresh and marine water chemistry promoted naled degradation as experiments with de-ionized water resulted in half-lives greater than 6 days. The half-life in natural waters without light ranged from 5 to 20 h with lower half lives at higher temperatures. Under light exposure, degradation was accelerated and yielded more dichlorvos. Detectable levels (0.05 μM for naled and 0.10 μM for dichlorvos) were measured in water samples collected from the field during aerial spray events. Results can be used in risk assessments that consider both naled and dichlorvos to better understand ecological impacts and to develop improved public health recommendations.

Managing Aedes aegypti populations in the first Zika transmission zones in the continental United States

The African Zika virus swept across the Pacific, reaching the New World in 2014. In July, 2016, Miami-Dade County, Florida became the locus of the first mosquito-borne Zika transmission zones in the continental United States. Control efforts were guided by the Centers for Disease Control and Prevention, including aerial and truck sprays of adulticides and larvicides. To improve our understanding of how best to fight Zika transmission in an urban environment in the developed world, trap counts of adult Aedes (Stegomyia) aegypti (L.) mosquitoes from the treatment zones were analyzed to determine efficacy of the different insecticide treatments. Analysis revealed that application of four different ester pyrethroid and one non-ester pyrethroid had no statistically significant effect on mosquito counts. Aerial application of naled, a potent organophosphate adulticide, produced significant but short-lived drops in Ae. aegypti counts in the first two applications in the first active transmission zone (Wynwood), then lost some efficacy with subsequent application. In the other active transmission zone (Miami Beach), naled produced no measurable effect in the first three applications, and only a small, transient, and marginally significant reduction in the fourth application. Repeated application of the larvicidal bacterium Bti was accompanied by steady declines of Ae. aegypti populations in both sites. Zika transmission ceased in the first transmission zone, but expanded in the second transmission zone during this period. Specific recommendations are proposed for future treatments of urban mosquitoes.

Poor qualitative analysis of Naled necessarily leads to incorrect quantitative analysis

This correspondence is in regards to a published article, titled "Prenatal Naled and Chlorpyrifos Exposure is Associated with Deficits in Infant Motor Function in a Cohort of Chinese Infants" Silver et al., Environ Int., 2017 Sep; 106:248-256. Upon careful review of this work we identified some significant issues in the mass spectral analysis of naled, specifically its identification and quantification. In this communication we address these issues and provide analytical data and rationale to support our criticism of the reported work. We collected mass spectral data for naled (analytical standard grade) under a variety of mass spectrometric conditions in an attempt to obtain a fragmentation pattern similar to what was reported in Silver et al., 2017. We however, could not reproduce a similar fragmentation pattern under any of the tested experimental conditions. Our results however were in excellent agreement with the National Institute of Standards and Technology (NIST) database, which is a very well established and widely accepted resource for such compounds. This leads us to conclude that naled was in all probability misidentified in the reported (Silver et al., 2017) study which consequently raises serious questions regarding the quantification of naled in the blood samples thus placing the whole statistical correlation of naled as a contributor to impairment of motor function in infants in question.

Identification of a carboxylesterase associated with resistance to naled in Bactrocera dorsalis (Hendel)

Compared to other organophosphate-resistant and -susceptible (S) lines of Bactrocera dorsalis, the carboxylesterase (CBE) BdE5 in the naled-resistant (nal-r) line has been found to possess remarkable quantitative elevation. Our study attempts to identify the role of BdE5 in naled resistance, and we discovered several points of interest. Firstly, activity staining on native PAGE revealed that the percentage of flies with intensive BdE5 bands in the nal-r line was substantially higher than in the S line, indicating that the BdE5 band correlates with naled susceptibility. Secondly, in vitro and in vivo inhibition assays showed that BdE5 was inhibited by naled in both lines; under diagnostic doses of naled, the overall extent of inhibition on CBEs was much greater in the S line than in the nal-r line. Thirdly, NanoLC-nanoESi-MS/MS analysis used the NCBI database to identify and annotate BdE5 as an esterase FE4-like (XP_011200445.1) in B. dorsalis. Fourthly, rapid amplification of cDNA ends was used to obtain the 2012-bp full-length BdE5 cDNA, which contained an open reading frame of 1770bp and encoded a putative protein of 590 amino acid residues. Phylogenetic analysis revealed that BdE5 is a secreted β-esterase (E clade) closely related to CG6414 (NP_570089), a CBE in Drosophila melanogaster. Finally, our relative quantification real-time PCR data showed a significant elevation in transcript levels of the BdE5 gene in nal-r line. Our results confirmed that BdE5 is correlated with naled resistance and provides further understanding about the identification and molecular characteristics of BdE5 in B. dorsalis.

Mosquito control insecticides: a probabilistic ecological risk assessment on drift exposures of naled, dichlorvos (naled metabolite) and permethrin to adult butterflies

A comprehensive probabilistic terrestrial ecological risk assessment (ERA) was conducted to characterize the potential risk of mosquito control insecticide (i.e., naled, it's metabolite dichlorvos, and permethrin) usage to adult butterflies in south Florida by comparing the probability distributions of environmental exposure concentrations following actual mosquito control applications at labeled rates from ten field monitoring studies with the probability distributions of butterfly species response (effects) data from our laboratory acute toxicity studies. The overlap of these distributions was used as a measure of risk to butterflies. The long-term viability (survival) of adult butterflies, following topical (thorax/wings) exposures was the environmental value we wanted to protect. Laboratory acute toxicity studies (24-h LD50) included topical exposures (thorax and wings) to five adult butterfly species and preparation of species sensitivity distributions (SSDs). The ERA indicated that the assessment endpoint of protection, of at least 90% of the species, 90% of the time (or the 10th percentile from the acute SSDs) from acute naled and permethrin exposures, is most likely not occurring when considering topical exposures to adults. Although the surface areas for adulticide exposures are greater for the wings, exposures to the thorax provide the highest potential for risk (i.e., SSD 10th percentile is lowest) for adult butterflies. Dichlorvos appeared to present no risk. The results of this ERA can be applied to other areas of the world, where these insecticides are used and where butterflies may be exposed. Since there are other sources (e.g., agriculture) of pesticides in the environment, where butterfly exposures will occur, the ERA may under-estimate the potential risks under real-world conditions.