Is DEET a dangerous neurotoxicant?

Comparison of the cytotoxicity and zebrafish embryo toxicity of insect repellent ingredients: p-Menthane-3,8-diol synthesized by green chemistry from Eucalyptus citriodora and N,N-diethyl-meta-toluamide

Bio-sourced insect repellents are becoming more popular due to their safer applications. Known for its strong fly-repellent property, Cis, trans-para-menthane-3,8-diol (PMD) is the main component of the lemon eucalyptus essential oil and is synthesized from citronellal. In April 2005, US Centers for Disease Control approved two fly repellents that do not contain N,N-diethyl-meta-toluamide (DEET), including PMD. Due to the intentional and pervasive human exposure caused by DEET as insect repellent, concerns have been raised about its toxicological profile and potential harm to people. We hypothesized PMD would have a different toxicological profile than DEET. We synthesized PMD from Eucalyptus citriodora using green chemistry methods and analyzed its structures by 1H-NMR,13C-NMR, and GC/MS spectral methods. We used MTS assay to determine the percentage inhibition of PMD and DEET on keratinocyte (human epidermal keratinocyte [HaCaT]) cells. The xCelligence system was used and followed at real time. Effects of PMD and DEET on zebrafish embryo development were monitored and levels of lipid peroxidation, glutathione-S-transferase (GST), superoxide dismutase (SOD), and acetylcholinesterase (AchE) were evaluated at 72 h post-fertilization using spectrophotometric methods. Our results showed that while DEET inhibited human keratinocyte cell growth, while imporved cell viability and proliferation was exposed in PMD exposed group. In zebrafish embryos, PMD was less toxic in terms of development, oxidant-antioxidant status, and AChE activities than DEET. Based on these results we suggest an efficient method using green chemistry for the synthesis of PMD, which is found to be less toxic in zebrafish embryos and human keratinocyte cells.

Repellent activity of essential oils to the Lone Star tick, Amblyomma americanum

BACKGROUND

The Lone Star tick, Amblyomma americanum is important to human health because of a variety of pathogenic organisms transmitted to humans during feeding events, which underscores the need to identify novel approaches to prevent tick bites. Thus, the goal of this study was to test natural and synthetic molecules for repellent activity against ticks in spatial, contact and human fingertip bioassays.

METHODS

The efficacy of essential oils and naturally derived compounds as repellents to Am. americanum nymphs was compared in three different bioassays: contact, spatial and fingertip repellent bioassays.

RESULTS

Concentration response curves after contact exposure to 1R-trans-chrysanthemic acid (TCA) indicated a 5.6 μg/cm2 concentration required to repel 50% of ticks (RC50), which was five- and sevenfold more active than DEET and nootkatone, respectively. For contact repellency, the rank order of repellency at 50 μg/cm2 for natural oils was clove > geranium > oregano > cedarwood > thyme > amyris > patchouli > citronella > juniper berry > peppermint > cassia. For spatial bioassays, TCA was approximately twofold more active than DEET and nootkatone at 50 μg/cm2 but was not significantly different at 10 μg/cm2. In spatial assays, thyme and cassia were the most active compounds tested with 100% and 80% ticks repelled within 15 min of exposure respectively and was approximately twofold more effective than DEET at the same concentration. To translate these non-host assays to efficacy when used on the human host, we quantified repellency using a finger-climbing assay. TCA, nootkatone and DEET were equally effective in the fingertip assay, and patchouli oil was the only natural oil that significantly repelled ticks.

CONCLUSIONS

The differences in repellent potency based on the assay type suggests that the ability to discover active tick repellents suitable for development may be more complicated than with other arthropod species; furthermore, the field delivery mechanism must be considered early in development to ensure translation to field efficacy. TCA, which is naturally derived, is a promising candidate for a tick repellent that has comparable repellency to commercialized tick repellents.

Development and laboratory validation of a plant-derived repellent blend, effective against Aedes aegypti [Diptera: Culicidae], Anopheles gambiae [Diptera: Culicidae] and Culex quinquefasciatus [Diptera: Culicidae]

Mosquitoes of the genera Aedes, Anopheles and Culex vector a wide range of pathogens seriously affecting humans and livestock on a global scale. Over-reliance on insecticides and repellents has driven research into alternative, naturally-derived compounds to fulfil the same objectives. Steam distilled extracts of four plants with strong, yet attractive, volatile profiles were initially assessed for repellency in a dual-port olfactometer using Aedes aegypti as the model species. Picea sitchensis was found to be the most repellent, proving comparable to leading products when applied at 100% (p = 1.000). Key components of conifer-derived volatile profiles were then screened via electroantennography before those components eliciting an electrophysiological response were assayed individually in the olfactometer; according to WHO protocol. The most promising 5 were selected for reductive analyses to produce an optimised semiochemical blend. This combination, and a further two variations of the blend, were then progressed to a multi-species analysis using the BG-test whereby bite-attempt frequency on hands was assessed under different repellent treatments; assays were compared between Aedes aegypti, Anopheles gambiae and Culex quinquefasciatus. Efficacy was found against all three species, although it was found that Ae. aegypti was the most susceptible to the repellent, with An. gambiae being the least. Here, a novel, naturally-derived blend is presented with weak spatial repellency, as confirmed in laboratory assays. Further work will be required to assess the full extent of the potential of the products, both in terms of field application and species screening; however, the success of the products developed demonstrate that plant metabolites have great capacity for use in the repellent sector; both to improve upon known compounds and to reduce the usage of toxic products currently on the market.

Association between N, N-diethyl-m-toluamide exposure and the odds of kidney stones in US adults: a population-based study

Background

Currently, there is limited research on the specific relationship between N, N-diethyl-m-toluamide (DEET) exposure and the odds of kidney stones. We aimed to investigate the relationship between DEET exposure and the prevalence of kidney stones.

Methods

We included 7,567 qualified participants in our research from the 2007-2016 NHANES survey. We carried out three logistic regression models to explore the potential association between DEET exposure and the odds of kidney stones. Spline smoothing with generalized additive models (GAM) was utilized to assess the non-linear relationship and restricted cubic spline (RCS) curves was to determine the dose-response association. Multivariate regression models were used to conduct stratified analysis and sensitivity analysis.

Results

Baseline characteristics of study participants presented the distribution of covariables. Regression analysis revealed that the odds of kidney stones were positively associated with the main metabolites of 3-diethyl-carbamoyl benzoic acid (DCBA) (log2) (OR = 1.05, 95% CI 1.02 to 1.08). The fourth quartile of urine DCBA showed a greater risk of kidney stones in the fully adjusted model (OR = 1.36, 95% CI 1.08 to 1.72). Another DEET metabolite of N, N-diethyl-3-hydroxymethylbenzamide (DHMB) was used to confirm the accuracy and stability of the results. The spline smoothing curve represented two main DEET metabolites had similar no-linear relationships and a positive trend with kidney stones proportion. RCS implied that the incidence of kidney stones rose with increasing levels of DEET exposure. High-risk groups on kidney stones were exhibited by stratified analysis under DEET exposure.

Conclusion

Our study suggests that DEET exposure is positively associated with odds of kidney stones. Further investigation into the underlying processes of this association is required to guide the prevention and treatment of kidney stones.

Exposure to N,N-diethyl-m-toluamide and cardiovascular diseases in adults

Although growing evidence suggests that N,N-diethyl-m-toluamide (DEET) has adverse effects on public health, the relationship of DEET with cardiovascular disease (CVD) is still largely unknown. The purpose of this study was, therefore, to evaluate the association between DEET exposure and total and specific CVD among the US adults. In this cross-sectional study, a total of 5,972 participants were selected from the National Health and Nutrition Examination Survey (NHANES) 2007-2014. CVD was defined as a combination of congestive heart failure (CHF), coronary heart disease (CHD), angina, heart attack, or stroke. Logistic regression models were used to evaluate the association between DEET metabolites and the risks of total and specific CVD. Compared to the lowest quartile, 3-(diethylcarbamoyl) benzoic acid (DCBA) in the highest quartile was associated with the increased risks of CVD (odds ratio [OR]: 1.32, 95% CI: 1.03-1.68, P for trend = 0.025) and CHD (OR: 1.57, 95% CI: 1.10-2.25, P for trend = 0.017), after adjustment for potential covariates. Nevertheless, exposure to DCBA was not significantly associated with heart attack, CHF, angina, and stroke. Further studies are required to confirm these findings and identify the underlying mechanisms.

Update on mosquito bite reaction: Itch and hypersensitivity, pathophysiology, prevention, and treatment

Mosquito bites are endured by most populations worldwide. Reactions to mosquito bites range from localized wheals and papules with associated pruritus to rare systemic reactions and anaphylaxis in certain populations. The mechanism of itch is due to introduction of mosquito saliva components into the cutaneous tissue, although the exact pathophysiology is unclear. Histamine is thought to be a key player through mosquito saliva itself or through activation of mast cells by IgE or through an IgE-independent pathway. However, other salivary proteins such as tryptase and leukotrienes may induce non-histaminergic itch. Some individuals have a genetic predisposition for mosquito bites, and people with hematologic cancers, HIV, and other conditions are susceptible to robust reactions. Prevention of mosquito bites is key with physical barriers or chemical repellents. Treatment consists of second-generation antihistamines and topical corticosteroids. Further research on topical treatments that target neural-mediated itch is needed.

Nanogels Containing Foeniculum vulgare Mill. and Mentha piperita L. Essential Oils: Mosquitoes’ Repellent Activity and Antibacterial Effect

Foeniculum vulgare Mill. and Mentha piperita L. are two common medicinally important plants with a wide range of biological activities such as insecticide and antibacterial effects. In this study, the chemical composition of their essential oils was investigated using GC-MS analysis. After that, their nanoemulsions were prepared; optimum samples with droplet sizes of 74 ± 7 and 136 ± 5 nm were gelified. The viscosity of the prepared nanogels and the successful loading of the essential oil in them were investigated. The efficacy of the nanogel containing M. piperita essential oil as a repellent and antibacterial agent was more potent than the nanogel containing F. vulgare essential oil. Its completely protected time against Anopheles stephensi, the main malaria mosquito vector, was 120 ± 8 min. Moreover, the growth of Escherichia coli and Staphylococcus aureus after treatment with 5000 µg/mL of nanogel containing M. piperita essential oil was reduced by 100 and 65%, respectively. Considering natural constituents, a straightforward preparation method, and high efficacy, the nanogel containing M. piperita essential oil could be introduced for further investigation against other mosquitoes and bacterial species.

Polymeric Nanorepellent Systems Containing Geraniol and Icaridin Aimed at Repelling Aedes aegypti

Repellents are among the leading products used against diseases transmitted by the Aedes aegypti mosquito. However, their indiscriminate use or high concentrations can cause severe adverse reactions, particularly in children and pregnant women. To protect them, nanotechnology is a promising tool to encapsulate active compounds against degradation, increase their effectiveness, and decrease their toxicity, as it can promote the modified release of the active compound. This study aimed to develop polymeric nanocapsules containing the repellent actives geraniol and icaridin using low concentrations of the active component, with the objective of promoting effective activity and greater safety against adverse reactions. The nanocapsules were developed by the interfacial deposition method, and the physicochemical properties of the nanocapsules were evaluated using dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), zeta potential, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), release kinetics assay, and mathematical modeling. Cell viability was assessed by the MTT assay and genotoxicity analysis using the comet assay. The developed nanocapsules containing geraniol and icaridin showed mean diameters of 260 nm and 314 nm, respectively, with a polydispersity index < 0.2. The nanocapsules showed encapsulation efficiency values of 73.7 ± 0.1% for icaridin and 98.7 ± 0.1% for geraniol. Morphological analysis showed spherical nanocapsules with low polydispersity. The kinetic parameters calculated using the Korsmeyer−Peppas model indicated an anomalous release profile. Cell viability and genotoxicity analyses showed that the nanocapsules did not alter cell viability or damage DNA. The results demonstrate a promising nanostructured system with good physicochemical characteristics and good stability, with repellent activity against Aedes aegypti.

Assessment of Environmental Pollution and Human Exposure to Pesticides by Wastewater Analysis in a Seven-Year Study in Athens, Greece

Pesticides have been used in large amounts around the world for decades and are responsible for environmental pollution and various adverse effects on human health. Analysis of untreated wastewater can deliver useful information on pesticides’ use in a particular area and allow the assessment of human exposure to certain substances. A wide-scope screening method, based on liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry, was applied, using both target and suspect screening methodologies. Daily composite influent wastewater samples were collected for seven or eight consecutive days in Athens between 2014 and 2020 and analyzed for 756 pesticides, their environmental transformation products and their human metabolites. Forty pesticides were quantified at mean concentrations up to 4.9 µg/L (tralkoxydim). The most abundant class was fungicides followed by herbicides, insect repellents, insecticides and plant growth regulators. In addition, pesticide transformation products and/or metabolites were detected with high frequency, indicating that research should be focused on them. Human exposure was evaluated using the wastewater-based epidemiology (WBE) approach and 3-ethyl-carbamoyl benzoic acid and cis-1,2,3,6-tetrahydrophthalimide were proposed as potential WBE biomarkers. Wastewater analysis revealed the presence of unapproved pesticides and indicated that there is an urgent need to include more transformation products in target databases.

Volatile Organic Compounds in the Azteca/Cecropia Ant-Plant Symbiosis and the Role of Black Fungi

Black fungi of the order Chaetothyriales are grown by many tropical plant-mutualistic ants as small so-called “patches” in their nests, which are located inside hollow structures provided by the host plant (“domatia”). These fungi are introduced and fostered by the ants, indicating that they are important for the colony. As several species of Chaetothyriales tolerate, adsorb, and metabolize toxic volatiles, we investigated the composition of volatile organic compounds (VOCs) of selected domatia in the Azteca/Cecropia ant-plant mutualism. Concentrations of VOCs in ant-inhabited domatia, empty domatia, and background air were compared. In total, 211 compounds belonging to 19 chemical families were identified. Ant-inhabited domatia were dominated by ketones with 2-heptanone, a well-known ant alarm semiochemical, as the most abundant volatile. Empty domatia were characterized by relatively high concentrations of the monoterpenes d-limonene, p-cymene and β-phellandrene, as well as the heterocyclic sulphur-containing compound, benzothiazole. These compounds have biocidal properties and are primarily biosynthesized by plants as a defense mechanism. Interestingly, most of the latter compounds were present at lower concentrations in ant inhabited domatia than in non-colonized ones. We suggest that Chaetothyriales may play a role in reducing the VOCs, underlining that the mutualistic nature of these fungi as VOCs accumulation might be detrimental for the ants, especially the larvae.

Insights into the Use of Phytoremediation Processes for the Removal of Organic Micropollutants from Water and Wastewater; A Review

Greater awareness of micropollutants present in water and wastewater motivates the search for effective methods of their neutralization. Although their concentration in waters is measured in micro- and nanograms per liter, even at those levels, they may cause serious health consequences for different organisms, including harmful effects on the functioning of the endocrine system of vertebrates. Traditional methods of wastewater treatment, especially biological methods used in municipal wastewater treatment plants, are not sufficiently effective in removing these compounds, which results in their presence in natural waters. The growing interest in phytoremediation using constructed wetlands as a method of wastewater treatment or polishing indicates a need for the evaluation of this process in the context of micropollutant removal. Therefore, the present work presents a systematic review of the effectiveness in the removal of micropollutants from polluted waters by processes based on plant used. The article also analyzes issues related to the impact of micropollutants on the physiological processes of plants as well as changes in general indicators of pollution caused by contact of wastewater with plants. Additionally, it is also the first review of the literature that focuses strictly on the removal of micropollutants through the use of constructed wetlands.

Isolation of Volatile Compounds with Repellent Properties against Aedes albopictus (Diptera: Culicidae) Using CPC Technology

The present work describes the use of Centrifugal Partition Chromatography (CPC) for the bio-guided isolation of repellent active volatile compounds from essential oils. Five essential oils (EOs) obtained from three Pinus and two Juniperus species were initially analyzed by gas chromatography–mass spectrometry (GC/MS) and evaluated for their repellent properties against Aedes albopictus. The essential oil from needles of P. pinea (PPI) presented the higher activity, showing 82.4% repellency at a dose of 0.2 μL/cm². The above EO, together with the EO from the fruits of J. oxycedrus subsp. deltoides (JOX), were further analyzed by CPC using the biphasic system n-Heptane/ACN/BuOH in ratio 1.6/1.6/0.2 (v/v/v). The analysis of PPI essential oil resulted in the recovery of (−)-limonene, guaiol and simple mixtures of (−)-limonene/β-pheladrene, while the fractionation of JOX EO led to the recovery of β-myrcene, germacrene-D, and mixtures of α-pinene/β-pinene (ratio 70/30) and α-pinene/germacrene D (ratio 65/45). All isolated compounds and recovered mixtures were tested for their repellent activity. From them, (−)-limonene, guaiol, germacrene-D as well the mixtures of (−)-limonene/β-pheladrene presented significant repellent activity (>97% repellency) against Ae. albopictus. The present methodology could be a valuable tool in the effort to develop potent mosquito repellents which are environmentally friendly.

Narrative Review on Health-EDRM Primary Prevention Measures for Vector-Borne Diseases

Climate change is expanding the global at-risk population for vector-borne diseases (VBDs). The World Health Organization (WHO) health emergency and disaster risk management (health-EDRM) framework emphasises the importance of primary prevention of biological hazards and its value in protecting against VBDs. The framework encourages stakeholder coordination and information sharing, though there is still a need to reinforce prevention and recovery within disaster management. This keyword-search based narrative literature review searched databases PubMed, Google Scholar, Embase and Medline between January 2000 and May 2020, and identified 134 publications. In total, 10 health-EDRM primary prevention measures are summarised at three levels (personal, environmental and household). Enabling factor, limiting factors, co-benefits and strength of evidence were identified. Current studies on primary prevention measures for VBDs focus on health risk-reduction, with minimal evaluation of actual disease reduction. Although prevention against mosquito-borne diseases, notably malaria, has been well-studied, research on other vectors and VBDs remains limited. Other gaps included the limited evidence pertaining to prevention in resource-poor settings and the efficacy of alternatives, discrepancies amongst agencies' recommendations, and limited studies on the impact of technological advancements and habitat change on VBD prevalence. Health-EDRM primary prevention measures for VBDs require high-priority research to facilitate multifaceted, multi-sectoral, coordinated responses that will enable effective risk mitigation.

Association between Prenatal Exposure to Household Pesticides and Neonatal Weight and Length Growth in the Japan Environment and Children's Study

The effects of prenatal exposure to household pesticides on fetal and neonatal growth have not been fully clarified. The present study aims to determine the effects of prenatal exposure to pesticides on neonates’ body size and growth during the first month. This study included 93,718 pairs of pregnant women and their children from the Japan Environment and Children’s Study. Participants completed self-reporting questionnaires during their second or third trimesters on their demographic characteristics and frequency of pesticide use during pregnancy. Child weight, length, and sex were obtained from medical record transcripts. Birth weight and length, as well as weight and length changes over the first month, were estimated using an analysis of covariance. Frequency of exposure to almost all pesticides had no effects on birth weight and length. However, we found small but significant associations (i) between the use of fumigation insecticides and decreased birth weight, and (ii) between frequencies of exposure to pyrethroid pesticides, especially mosquito coils/mats, and suppression of neonatal length growth. Prenatal exposure to household pesticides, especially those containing pyrethroids, might adversely influence fetal and postnatal growth trajectories.

Exposure to N,N-Diethyl-Meta-Toluamide Insect Repellent and Human Health Markers: Population Based Estimates from the National Health and Nutrition Examination Survey

N,N-diethyl-meta-toluamide (DEET) is one of the most commonly used insect repellants in the United States, yet the existing literature regarding DEET's potential deleterious impact on humans is mixed and is based mostly on case reports. The primary aim of this study was to address this lack of population-based evidence of the effects of DEET exposure on human health in the United States. Our primary outcome measures were biomarkers related to systemic inflammation (high sensitivity C-reactive protein), immune function (lymphocyte), liver function (aspartate aminotransferase, alanine aminotransferase, and γ-glutamyl transferace), and kidney function (estimated glomerular filtration rate). We analyzed data from the population-based National Health and Nutrition Examination Survey, 2015-2016, and identified 1,205 patients (age 20+ years) who had DEET metabolite levels recorded at or above detection limits. A Pearson correlation was used to assess the relationship between DEET metabolite, and each biomarker found there was no significant correlation. Thus, there is no evidence that DEET exposure has any impact on the biomarkers identified.