Elevated Metal Levels in U.S. Honeys: Is There a Concern for Human Health?

Honey is a bioactive food used for millennia to improve health and treat diseases. More recently, researchers employ honey as a tool to assess local environmental pollution. Honeybees effectively 'sample' their environment within a ~ 7 km radius, actively collecting nectar, pollen, and water to bring to their hive. Foraging honeybees also sample the air as dust particles accumulate on their pubescence, adding to the hive's contaminant load. Many studies from around the world report elevated metal levels in honey, with the most reports from Iran, Italy, and Turkey, but only two reports have measured metal levels in honey from the United States (U.S.). We report levels of 20 metals from 28 honeys collected from 15 U.S. states between 2022-2023. We then focus on four toxic metals recognized as hazards in foodstuffs when the concentrations are above safety recommendations - lead, cadmium, arsenic, and mercury. Two of these metals (lead and mercury) are regulated in honey by the European Union (EU), though the U.S. currently lacks defined regulations for metal levels in honey. We consider the levels of these toxic metals by state, then compare the U.S. mean honey level for these metals against the provisional tolerable weekly intake (PTWI). Our results suggest U.S. honey have levels metal that exceed the PWTI and EU regulations and may be hazardous to human health. Further research is needed to determine if the effects of these toxic metal at measured levels outweigh the health benefits from consumption of honey.

Acute particulate hexavalent chromium exposure induces DNA double strand breaks and activates homologous recombination repair in rat lung tissue.

Hexavalent chromium [Cr(VI)] is an established human lung carcinogen, but the carcinogenesis mechanism is poorly understood. Chromosome instability, a hallmark of lung cancer, is considered a major driver of Cr(VI)-induced lung cancer. Unrepaired DNA double strand breaks are the underlying cause, and homologous recombination repair is the primary mechanism preventing Cr(VI)-induced DNA breaks from causing chromosome instability. Cell culture studies show acute Cr(VI) exposure causes DNA double strand breaks and increases homologous recombination repair activity. However, the ability of Cr(VI)-induced DNA breaks and repair impact has only been reported in cell culture studies. Therefore, we investigated whether acute Cr(VI) exposure could induce breaks and homologous recombination repair in rat lungs. Male and female Wistar rats were acutely exposed to either zinc chromate particles in a saline solution or saline alone by oropharyngeal aspiration. This exposure route resulted in increased Cr levels in each lobe of the lung. We found Cr(VI) induced DNA double-strand breaks in a concentration-dependent manner, with females being more susceptible than males, and induced homologous recombination repair at similar levels in both sexes. Thus, these data show this driving mechanism discovered in cell culture indeed translates to lung tissue in vivo.

Employing a Toxic Aging Coin approach to assess hexavalent chromium (Cr[VI])-induced neurotoxic effects on behavior: Heads for age differences.

We are facing a rapidly growing geriatric population (65+) that will live for multiple decades and are challenged with environmental pollution far exceeding that of previous generations. Consequently, we currently have a poor understanding of how environmental pollution will impact geriatric health distinctly from younger populations. Few toxicology studies have considered age differences with geriatric individuals. Critically, all top ten most prevalent age-related diseases are linked to metal exposures. Hexavalent chromium [Cr(VI)] is a metal of major environmental health concern that can induce aging phenotypes and neurotoxicity. However, there are many knowledge gaps for Cr(VI) neurotoxicity, including how Cr(VI) impacts behavior. To address this, we exposed male rats across three ages (3-, 7-, and 18-months old) to Cr(VI) in drinking water (0, 0.05, 0.1 mg/L) for 90 days. These levels reflect the maximum contaminant levels determined by the World Health Organization (WHO) and the U.S. Environmental Protection Agency (US EPA). Here, we report how these Cr(VI) drinking water levels impacted rat behaviors using a battery of behavior tests, including grip strength, open field assay, elevated plus maze, Y-maze, and 3-chamber assay. We observed adult rats were the most affected age group and memory assays (spatial and social) exhibited the most significant effects. Critically, the significant effects were surprising as rats should be particularly resistant to these Cr(VI) drinking water levels due to the adjustments applied in risk assessment from rodent studies to human safety, and because rats endogenously synthesize vitamin C in their livers (vitamin C is a primary reducer of Cr[VI] to Cr[III]). Our results emphasize the need to broaden the scope of toxicology research to consider multiple life stages and suggest the current regulations for Cr(VI) in drinking water need to be revisited.

Transcriptomic analysis reveals particulate hexavalent chromium regulates key inflammatory pathways in human lung fibroblasts as a possible mechanism of carcinogenesis.

Hexavalent chromium [Cr(VI)] is considered a major environmental health concern and lung carcinogen. However, the exact mechanism by which Cr(VI) causes lung cancer in humans remains unclear. Since several reports have demonstrated a role for inflammation in Cr(VI) toxicity, the present study aimed to apply transcriptomics to examine the global mRNA expression in human lung fibroblasts after acute (24 h) or prolonged (72 and 120 h) exposure to 0.1, 0.2 and 0.3 µg/cm2 zinc chromate, with a particular emphasis on inflammatory pathways. The results showed Cr(VI) affected the expression of multiple genes and these effects varied according to Cr(VI) concentration and exposure time. Bioinformatic analysis of RNA-Seq data based on the Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and MetaCore databases revealed multiple inflammatory pathways were affected by Cr(VI) treatment. qRT-PCR data corroborated RNA-Seq findings. This study showed for the first time that Cr(VI) regulates key inflammatory pathways in human lung fibroblasts, providing novel insights into the mechanisms by which Cr(VI) causes lung cancer.

Prolonged Particulate Hexavalent Chromium Exposure Induces DNA Double-Strand Breaks and Inhibits Homologous Recombination Repair in Primary Rodent Lung Cells.

Hexavalent chromium [Cr(VI)] is a known lung carcinogen and a driving mechanism in human lung cells for Cr(VI)-induced lung cancer is chromosome instability, caused by prolonged Cr(VI) exposure inducing DNA double-strand breaks, while simultaneously inhibiting the repair of these breaks. In North Atlantic right whales, Cr(VI) induces breaks but does not inhibit repair. It is unclear if this repair inhibition is specific to human lung cells or occurs in other species, as it has only been considered in humans and North Atlantic right whales. We evaluated these outcomes in rodent cells, as rodents are an experimental model for metal-induced lung carcinogenesis. We used a guinea pig lung fibroblast cell line, JH4 Clone 1, and rat lung fibroblasts. Cells were exposed to two different particulate Cr(VI) compounds, ranging from 0 to 0.5 ug/cm2, for 24 or 120 h and assessed for cytotoxicity, DNA double-strand breaks, and DNA double-strand break repair. Both particulate Cr(VI) compounds induced a concentration-dependent increase in cytotoxicity and DNA double-strand breaks after acute and prolonged exposures. Notably, while the repair of Cr(VI)-induced DNA double-strand breaks increased after acute exposure, the repair of these breaks was inhibited after prolonged exposure. These results are consistent with outcomes in human lung cells indicating rodent cells respond like human cells, while whale cells have a markedly different response.

A whale of a tale: whale cells evade the driving mechanism for hexavalent chromium-induced chromosome instability.

Chromosome instability, a hallmark of lung cancer, is a driving mechanism for hexavalent chromium [Cr(VI)] carcinogenesis in humans. Cr(VI) induces structural and numerical chromosome instability in human lung cells by inducing DNA double-strand breaks and inhibiting homologous recombination repair and causing spindle assembly checkpoint (SAC) bypass and centrosome amplification. Great whales are long-lived species with long-term exposures to Cr(VI) and accumulate Cr in their tissue, but exhibit a low incidence of cancer. Data show Cr(VI) induces fewer chromosome aberrations in whale cells after acute Cr(VI) exposure suggesting whale cells can evade Cr(VI)-induced chromosome instability. However, it is unknown if whales can evade Cr(VI)-induced chromosome instability. Thus, we tested the hypothesis that whale cells resist Cr(VI)-induced loss of homologous recombination repair activity and increased SAC bypass and centrosome amplification. We found Cr(VI) induces similar amounts of DNA double-strand breaks after acute (24 h) and prolonged (120 h) exposures in whale lung cells, but does not inhibit homologous recombination repair, SAC bypass, or centrosome amplification, and does not induce chromosome instability. These data indicate whale lung cells resist Cr(VI)-induced chromosome instability, the major driver for Cr(VI) carcinogenesis at a cellular level, consistent with observations that whales are resistant to cancer.

Characterization of the inheritance of field-evolved resistance to diamides in the fall armyworm (Spodoptera frugiperda) (Lepidoptera: Noctuidae) population from Puerto Rico.

The fall armyworm (Spodoptera frugiperda) is one of the most destructive pests of corn. New infestations have been reported in the East Hemisphere, reaching India, China, Malaysia, and Australia, causing severe destruction to corn and other crops. In Puerto Rico, practical resistance to different mode of action compounds has been reported in cornfields. In this study, we characterized the inheritance of resistance to chlorantraniliprole and flubendiamide and identified the possible cross-resistance to cyantraniliprole and cyclaniliprole. The Puerto Rican (PR) strain showed high levels of resistance to flubendiamide (RR50 = 2,762-fold) and chlorantraniliprole (RR50 = 96-fold). The inheritance of resistance showed an autosomal inheritance for chlorantraniliprole and an X-linked inheritance for flubendiamide. The trend of the dominance of resistance demonstrated an incompletely recessive trait for H1 (♂ SUS × â™€ PR) × and an incompletely dominant trait for H2 (♀ SUS × â™‚ PR) × for flubendiamide and chlorantraniliprole. The PR strain showed no significant presence of detoxification enzymes (using synergists: PBO, DEF, DEM, and VER) to chlorantraniliprole; however, for flubendiamide the SR = 2.7 (DEM), SR = 3.2 (DEF) and SR = 7.6 (VER) indicated the role of esterases, glutathione S- transferases and ABC transporters in the metabolism of flubendiamide. The PR strain showed high and low cross-resistance to cyantraniliprole (74-fold) and cyclaniliprole (11-fold), respectively. Incomplete recessiveness might lead to the survival of heterozygous individuals when the decay of diamide residue occurs in plant tissues. These results highlight the importance of adopting diverse pest management strategies, including insecticide rotating to manage FAW populations in Puerto Rico and other continents.

Trunk injection to control Xylosandrus germanus (Coleoptera: Curculionidae) in topworked apple trees.

Xylosandrus germanus (Blandford) is an invasive species of ambrosia beetle known to attack apple trees in North America. Xylosandrus germanus are attracted to ethanol produced by stressed and injured trees and can be a serious problem when grafting a new cultivar onto established fruit trees (topworking). The objective of this study was to evaluate the efficacy of 2 insecticides (emamectin benzoate and azadirachtin) and injection timing (fall and spring) on their ability to control X. germanus colonization in apple trees with simulated topworking. Our study shows evidence that both emamectin benzoate and azadirachtin injections can reduce X. germanus infestations; however, our results were inconsistent. The timing of injections influenced X. germanus, with spring injected azadirachtin being more effective than fall injections. Residue analyses of emamectin benzoate and azadirachtin showed the presence of residues in woody tissue comparable to those found in leaves.

Prolonged particulate hexavalent chromium exposure induces RAD51 foci inhibition and cytoplasmic accumulation in immortalized and primary human lung bronchial epithelial cells.

Hexavalent chromium [Cr(VI)] is a human lung carcinogen with widespread exposure risks. Cr(VI) causes DNA double strand breaks that if unrepaired, progress into chromosomal instability (CIN), a key driving outcome in Cr(VI)-induced tumors. The ability of Cr(VI) to cause DNA breaks and inhibit repair is poorly understood in human lung epithelial cells, which are extremely relevant since pathology data show Cr(VI)-induced tumors originate from bronchial epithelial cells. In the present study, we considered immortalized and primary human bronchial epithelial cells. Cells were treated with zinc chromate at concentrations ranging 0.05 to 0.4µg/cm2 for acute (24 h) and prolonged (120 h) exposures. DNA double strand breaks (DSBs) were measured by neutral comet assay and the status of homologous recombination repair, the main pathway to fix Cr(VI)-induced DSBs, was measured by RAD51 foci formation with immunofluorescence, RAD51 localization with confocal microscopy and sister chromatid exchanges. We found acute and prolonged Cr(VI) exposure induced DSBs. Acute exposure induced homologous recombination repair, but prolonged exposure inhibited it resulting in chromosome instability in immortalized and primary human bronchial epithelial cells.

Systemic insecticides for control of stem gall wasp in highbush blueberry.

The gall wasp, Hemadas nubilipennis Ashmead, is a pest of highbush and lowbush blueberry and can pose a challenge to control with foliar sprays due to adult activity being during bloom and because larval development is within plant tissues. We hypothesized that systemic insecticides that move within the blueberry vascular system would reach areas where H. nubilipennis eggs are laid, causing larval mortality. Three application methods, crown injection, soil drench, and foliar spray were applied to potted 'Jersey' blueberry bushes at 50% and 100% rates to quantify systemic residue concentrations in shoots and leaves. Additionally, systemic insecticides were evaluated for control of gall wasps using single-shoot bioassays and measuring larval mortality at 0.01%, 0.1%, 1%, and 10% of field rate provided within a floral pick. Systemic insecticides tested in both studies included imidacloprid, flupyradifurone, and spirotetramat. The potted bush residue study determined that insecticides moved from three tested sites of entry: the roots, crown cavity, and foliage. Results from the shoot bioassays found that the mean percent larval survival of H. nubilipennis was negatively correlated with the concentration of AI detected in galls. Imidacloprid and spirotetramat were found to have the greatest potential for control of H. nubilipennis due to mortality in the shoot bioassays and similar residue concentrations in the potted bush studies to shoot bioassays. Future research should evaluate systemic insecticides applied in highbush blueberry plantings for control of H. nubilipennis using the bioassay mortality assessment method developed in this study.

Among Gerontogens, Heavy Metals Are a Class of Their Own: A Review of the Evidence for Cellular Senescence.

Advancements in modern medicine have improved the quality of life across the globe and increased the average lifespan of our population by multiple decades. Current estimates predict by 2030, 12% of the global population will reach a geriatric age and live another 3-4 decades. This swelling geriatric population will place critical stress on healthcare infrastructures due to accompanying increases in age-related diseases and comorbidities. While much research focused on long-lived individuals seeks to answer questions regarding how to age healthier, there is a deficit in research investigating what aspects of our lives accelerate or exacerbate aging. In particular, heavy metals are recognized as a significant threat to human health with links to a plethora of age-related diseases, and have widespread human exposures from occupational, medical, or environmental settings. We believe heavy metals ought to be classified as a class of gerontogens (i.e., chemicals that accelerate biological aging in cells and tissues). Gerontogens may be best studied through their effects on the "Hallmarks of Aging", nine physiological hallmarks demonstrated to occur in aged cells, tissues, and bodies. Evidence suggests that cellular senescence-a permanent growth arrest in cells-is one of the most pertinent hallmarks of aging and is a useful indicator of aging in tissues. Here, we discuss the roles of heavy metals in brain aging. We briefly discuss brain aging in general, then expand upon observations for heavy metals contributing to age-related neurodegenerative disorders. We particularly emphasize the roles and observations of cellular senescence in neurodegenerative diseases. Finally, we discuss the observations for heavy metals inducing cellular senescence. The glaring lack of knowledge about gerontogens and gerontogenic mechanisms necessitates greater research in the field, especially in the context of the global aging crisis.

Hexavalent Chromium Targets Securin to Drive Numerical Chromosome Instability in Human Lung Cells.

Hexavalent chromium [Cr(VI)] is a known human lung carcinogen with widespread exposure in environmental and occupational settings. Despite well-known cancer risks, the molecular mechanisms of Cr(VI)-induced carcinogenesis are not well understood, but a major driver of Cr(VI) carcinogenesis is chromosome instability. Previously, we reported Cr(VI) induced numerical chromosome instability, premature centriole disengagement, centrosome amplification, premature centromere division, and spindle assembly checkpoint bypass. A key regulator of these events is securin, which acts by regulating the cleavage ability of separase. Thus, in this study we investigated securin disruption by Cr(VI) exposure. We exposed human lung cells to a particulate Cr(VI) compound, zinc chromate, for acute (24 h) and prolonged (120 h) time points. We found prolonged Cr(VI) exposure caused marked decrease in securin levels and function. After prolonged exposure at the highest concentration, securin protein levels were decreased to 15.3% of control cells, while securin mRNA quantification was 7.9% relative to control cells. Additionally, loss of securin function led to increased separase activity manifested as enhanced cleavage of separase substrates; separase, kendrin, and SCC1. These data show securin is targeted by prolonged Cr(VI) exposure in human lung cells. Thus, a new mechanistic model for Cr(VI)-induced carcinogenesis emerges with centrosome and centromere disruption as key components of numerical chromosome instability, a key driver in Cr(VI) carcinogenesis.

Triple-stage Quadrupole Mass Spectrometer to Determine Ubiquitously Present Per- and Polyfluorinated Alkyl Substances in Drinking Water at Part Per Trillion Levels Using Solid Phase Extraction Approach.

An accurate analytical method was developed to determine selected per- and polyfluorinated alkyl substances (PFAS) at the level of parts per trillion (ppt or ng/L) in drinking water. The method included a concentration step using solid phase extraction (SPE) approach in combination with a liquid chromatography-tandem mass spectrometry system (LC-MS/MS). This method was optimized and validated for the common PFAS contaminants in drinking water. An initial demonstration of capability was established with an acceptable initial calibration, minimum reporting limit (MRL), limit of detection (LOD), initial demonstration of low system background, and initial demonstration of precision (IDP). Isotopically labeled internal standards were used for quantification. Surrogate standards were used to monitor method performance. The current method will help in better understanding of PFAS crisis by providing an efficient measurement of PFAS in water. In this study, the recoveries of four surrogates were between 84 and 113%, and calculated limit of detection (DL) and minimum reporting limits (MRL) were generally 1.0-3.0 and 5-10 ng/L, respectively.

The intersection between toxicology and aging research: A toxic aging coin perspective.

We are imminently faced with the challenges of an increasingly aging population and longer lifespans due to improved health care. Concomitantly, we are faced with ubiquitous environmental pollution linked with various health effects and age-related diseases which contribute to increased morbidity with age. Geriatric populations are rarely considered in the development of environmental regulations or in toxicology research. Today, life expectancy is often into one's 80s or beyond, which means multiple decades living as a geriatric individual. Hence, adverse health effects and late-onset diseases might be due to environmental exposures as a geriatric, and we currently have no way of knowing. Considering aging from a different perspective, the term "gerontogen" was coined in 1987 to describe chemicals that accelerate biological aging but has largely been left out of toxicology research. Thus, we are challenged with a two-faced problem that we can describe as a "toxic aging coin"; on one side we consider how age affects the toxic outcome of chemicals, whereas on the other side we consider how chemicals accelerate aging (i.e. how chemicals act as gerontogens). Conveniently, both sides of this coin can be tackled with a single animal study that considers multiple age groups and assesses basic toxicology of the chemical(s) tested and aging-focused endpoints. Here, I introduce the concept of this toxic aging coin and some key considerations for how it applies to toxicology research. My discussion of this concept will focus on the brain, my area of expertise, but could be translated to any organ system.

Chromium distribution in an oropharyngeal aspiration model for hexavalent chromium in rats.

Hexavalent chromium [Cr(VI)] is a well-known and widespread environmental contaminant associated with a variety of adverse health effects, in particular lung cancer. The primary route of exposure in humans is through inhalation. Particulate forms of Cr(VI) are the most potent but in vivo studies are difficult. Intratracheal instillation requires highly trained surgical procedures which also limits the number of repeated exposures possible and thus requires high doses. Inhalation studies can deliver lower more chronic doses but are expensive and generate dangerous aerosols. We evaluated an oropharyngeal aspiration exposure route for zinc chromate particles in Wistar rats. Animals were treated once per week for 90 days. We found chromium accumulated in the lungs, blood, and reproductive tissues of all treated animals. Additionally, we found inflammatory indicators in the lung were elevated and circulating lymphocytes had increased chromosomal damage. These results show oropharyngeal aspiration provides a practicable exposure route for chronic and sub-chronic exposures of Cr(VI) particles.

Inflammatory effects of hexavalent chromium in the lung: A comprehensive review.

Besides smoking, lung cancer can be caused by other factors, including heavy metals such as cadmium, nickel, arsenic, beryllium and hexavalent chromium [Cr(VI)], which is used in multiple settings, resulting in widespread environmental and occupational exposures as well as heavy use. The mechanism by which Cr(VI) causes lung cancer is not completely understood. Currently, it is admitted chromosome instability is a key process in the mechanism of Cr(VI)-induced cancer, and previous studies have suggested Cr(VI) impacts the lung tissue in mice by triggering tissue damage and inflammation. However, the mechanism underlying Cr(VI)-induced inflammation and its exact role in lung cancer are unclear. Therefore, this review aimed to systematically examine previous studies assessing Cr(VI)-induced inflammation and to summarize the major inflammatory pathways involved in Cr(VI)-induced inflammation. In cell culture studies, COX2, VEGF, JAK-STAT, leukotriene B4 (LTB4), MAPK, NF-Ò¡B and Nrf2 signaling pathways were consistently upregulated by Cr(VI), clearly demonstrating that these pathways are involved in Cr(VI)-induced inflammation. In addition, Akt signaling was also shown to contribute to Cr(VI)-induced inflammation, although discrepant findings were reported. Few mechanistic studies were performed in animal models, in which Cr(VI) upregulated oxidative pathways, NF-kB signaling and the MAPK pathway in the lung tissue. Similar to cell culture studies, opposite effects of Cr(VI) on Akt signaling were reported. This work provides insights into the mechanisms by which Cr(VI) induces lung inflammation. However, discrepant findings and other major issues in study design, both in cell and animal models, suggest that further studies are required to unveil the mechanism of Cr(VI)-induced inflammation and its role in lung cancer.

Medical Research Charities and Biopharmaceutical Companies as Partners in Patient-Centred R&D.

Life science research and development (R&D) companies are all too aware of the importance of patient perspectives but also of the barriers to engaging directly with patients, not least compliance, complex technical and regulatory issues, and the need to meet multifaceted expectations. Medical research charities (MRCs), highly technical and professional organisations, work directly with patients; they represent an expert resource for the science of their field, for disease-related patient advocacy issues and to advise and assist R&D companies in devising meaningful trials. The Pistoia Alliance, a non-profit organisation facilitating life sciences R&D, gathered a number of UK MRCs focused on complex lifelong conditions. The group used workshops and an opinion questionnaire for a snapshot of how the charities believe their knowledge and patient experiences could contribute insights and efficiencies to commercial R&D. MRCs argued that for chronic conditions, the patient perspective is vital in facilitating and de-risking trials, promoting patient motivation, compliance and study viability. MRCs and the patients they represent want to see successful trials, and it is in everyone's interest that well considered studies can proceed. Today, with remote assessments, consumer wearables and digital health technologies, MRCs and patients are already collating substantial data sets that are relevant to quality-of-life benefits, regulatory and value assessments, all of great interest to biopharmaceutical companies. In turn, MRCs would benefit from the experience of biopharma in generating clinical data and implementing novel technologies.

Development of a Sequence Searchable Database of Celiac Disease-Associated Peptides and Proteins for Risk Assessment of Novel Food Proteins.

Celiac disease (CeD) is an autoimmune enteropathy induced by prolamin and glutelin proteins in wheat, barley, rye, and triticale recognized by genetically restricted major histocompatibility (MHC) receptors. Patients with CeD must avoid consuming these proteins. Regulators in Europe and the United States expect an evaluation of CeD risks from proteins in genetically modified (GM) crops or novel foods for wheat-related proteins. Our database includes evidence-based causative peptides and proteins and two amino acid sequence comparison tools for CeD risk assessment. Sequence entries are based on the review of published studies of specific gluten-reactive T cell activation or intestinal epithelial toxicity. The initial database in 2012 was updated in 2018 and 2022. The current database holds 1,041 causative peptides and 76 representative proteins. The FASTA sequence comparison of 76 representative CeD proteins provides an insurance for possible unreported epitopes. Validation was conducted using protein homologs from Pooideae and non-Pooideae monocots, dicots, and non-plant proteins. Criteria for minimum percent identity and maximum E-scores are guidelines. Exact matches to any of the 1,041 peptides suggest risks, while FASTA alignment to the 76 CeD proteins suggests possible risks. Matched proteins should be tested further by CeD-specific CD4/8+ T cell assays or in vivo challenges before their use in foods.

Trunk injection delivery of dsRNA for RNAi-based pest control in apple trees.

BACKGROUND: RNA interference (RNAi) is a promising new approach for controlling insect pests without the use of synthetic pesticides. Trunk injection is a delivery system for woody plants that harnesses the vascular system of the tree to transport materials to the tree canopy. Full size apple trees were injected with double-stranded RNA (dsRNA), and season-long leaf samples were taken to measure the vascular mobility and temporal persistence of dsRNA, using quantitative reverse transcription polymerase chain reaction (qRT-PCR). RESULTS: The qRT-PCR results revealed that the quantities of dsRNA in the apple leaves of treated trees were significantly greater than those in the leaves of untreated trees for both 2019 and 2020 studies. The peak dsRNA concentration in 2019 was 242 pg/30 mg of leaf tissue, and in 2020 was 16.4 pg/30 mg. The persistence of dsRNA in the apple tree canopy in 2019 was at least 84 days, and in 2020 was at least 141 days. CONCLUSIONS: The highest mean measurement of dsRNA on a single date in 2019 was 242 pg, which is approximately equivalent to 8 ng/1 g leaf tissue. The projection using the highest replicate concentration from the same date is approximately equivalent to 27 ng/1 g leaf tissue, which may be sufficient to be considered biologically active. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.