Transfluthrin: Comparative efficacy and toxicity of reference and generic versions

Invisible enemies: evaluating human health threats of mosquito repellents through animal studies

Mosquito-borne diseases continue to pose significant threats to human populations, especially in developing and underdeveloped regions, where access to effective preventive measures remains limited. Mosquito repellents represent a cornerstone in the arsenal against these diseases, providing a barrier against mosquito bites. Mosquito repellents come in various formulations, including topical ointments and commercial vaporizers, with varying compositions. Common constituents include deodorized kerosene (DOK) as a solvent, pyrethroids, amides, essential oils for fragrance, and synergists. Despite their widespread use, the toxicological profiles of these repellents remain inadequately understood, raising questions about their safety in prolonged or excessive exposure scenarios. However, while their efficacy in preventing mosquito-borne illnesses is well-established, concerns persist regarding their potential toxicity to humans and the environment. This review critically examines the existing literature on the toxicity of mosquito repellents, focusing on their adverse effects on human health and environmental sustainability. Through an extensive analysis of available research, this review aims to shed light on the potential health risks associated with mosquito repellents, such as dermatological irritation, respiratory complications, and allergic reactions in humans.

Entomological assessment of hessian fabric transfluthrin vapour emanators for protecting against outdoor-biting Aedes aegypti in coastal Tanzania

BACKGROUND

A low technology emanator device for slowly releasing vapour of the volatile pyrethroid transfluthrin was recently developed in Tanzania that provides robust protection against night biting Anopheles and Culex vectors of malaria and filariasis for several months. Here these same emanator devices were assessed in Dar es Salaam city, as a means of protection against outdoor-biting Aedes (Stegomia) aegypti, the most important vector of human arboviruses worldwide, in parallel with similar studies in Haiti and Brazil.

METHODS

A series of entomological experiments were conducted under field and semi-field conditions, to evaluate whether transfluthrin emanators protect against wild Ae. aegypti, and also compare the transfluthrin responsiveness of Ae. aegypti originating from wild-caught eggs to established pyrethroid-susceptible Ae. aegypti and Anopheles gambiae colonies. Preliminary measurements of transfluthrin vapour concentration in air samples collected near treated emanators were conducted by gas chromatography-mass spectrometry.

RESULTS

Two full field experiments with four different emanator designs and three different transfluthrin formulations consistently indicated negligible reduction of human landing rates by wild Ae. aegypti. Under semi-field conditions in large cages, 50 to 60% reductions of landing rates were observed, regardless of which transfluthrin dose, capture method, emanator placement position, or source of mosquitoes (mildly pyrethroid resistant wild caught Ae. aegypti or pyrethroid-susceptible colonies of Ae. aegypti and An. gambiae) was used. Air samples collected immediately downwind from an emanator treated with the highest transfluthrin dose (15g), contained 12 to 19 μg/m3 transfluthrin vapour.

CONCLUSIONS

It appears unlikely that the moderate levels of pyrethroid resistance observed in wild Ae. aegypti can explain the modest-to-undetectable levels of protection exhibited. While potential inhalation exposure could be of concern for the highest (15g) dose evaluated, 3g of transfluthrin appears sufficient to achieve the modest levels of protection that were demonstrated entomologically. While the generally low levels of protection against Aedes reported here from Tanzania, and from similar entomological studies in Haiti and Brazil, are discouraging, complementary social science studies in Haiti and Brazil suggest end-users perceive valuable levels of protection against mosquitoes. It therefore remains unclear whether transfluthrin emanators have potential for protecting against Aedes vectors of important human arboviruses.

Derivation of thresholds for inhaled chemically reactive irritants: Searching for substance-specific common denominators for read-across prediction

Emergency response planning guideline values are used to protect the public when there has been a short-term chemical release. These values serve the purpose of identifying areas where a hazard exists if the concentration of hazardous chemicals is exceeded for the specified exposure duration. This paper focuses on carbonyl chlorides, a class of highly irritant/corrosive chemical intermediates characterized by the reactive moiety R-COCl. Despite their unifying property of reacting with nucleophilic biopolymers/peptides lining the airways of the respiratory tract, their adverse outcome pathway (AOP), in addition to surface area dose, appears to be dominated by their site(s) of major deposition (liquid) or retention (gas) within the respiratory tract. Thus, the physicochemical properties "phase" and "lipophilicity" become more decisive for the AOP than the chemical structure. This complicates the grouping of portal-of-entry irritant chemicals for the read-across prediction of chemicals, especially those with semivolatile properties. Phosgene (COCl₂) served as a template to predict emergency response planning levels 2 (non-incapacitating, reversible injury) and 3 (nonlethal) for related chemicals such as SOCl₂, formates, and acid chlorides. A rationale and guide to the systematic characterization of uncertainties associated with the lung region, water solubility of the vapor phase, and chemical specificity is given. The approach described in this paper highlights the regional differences and outcomes that are phenotypically described as irritation of the respiratory tract. Especially for such a data-lean group of chemicals, reliable read-across predictions could reduce the uncertainty associated with the derivation of values used for emergency-related risk assessment and management. Likewise, the approach suggested could improve the grouping and categorization of such chemicals, providing a means to reduce animal testing with potentially corrosive chemicals. Overall, the course taken for read-across predictions provided valid estimates as long as emphasis was directed to the physicochemical properties determining the most critical regional injury within the respiratory tract.

Impact evaluation of marking Salmo trutta with Alizarin Red S produced by different manufacturers

Fish otolith marking with the alizarin dye is a commonly used tool in sustainable fishery management. However, the reported effects of this dye on fish health are rather controversial and are possibly linked to differences in the composition of different brands of Alizarin red S (ARS). Laboratory experiments designed to elucidate effects of different concentrations of theoretically the same ARS as indicated by the CAS (Chemical Abstracts Service) number on fish at different development stages were carried out. The acute toxicity of ARS to Salmo trutta was found to be concentration- and fish developmental stage-dependant. Our study results showed that S. trutta sensitivity to ARS varies depending on its developmental stages as follows: fry (50-days after hatching) > alevins (30-days after hatching) > alevins (1-day after hatching). One of the tested ARS brands (purchased from VWR International LLC (Matsonford Road, USA)) was found to be several times more toxic to fish than another (purchased from Sigma-Aldrich (St. Louis, USA)), although according to the certificates of analysis, the tested substances were identical. Survival and growth of the S. trutta fry, which was marked with different ARS brands and stocked in the same natural stream, was investigated for two consecutive years. The results obtained indicate remarkable differences (p < 0.05) in the effects produced by the tested ARS brands, thus confirming our laboratory findings. The performed elemental analysis of the tested ARS dyes revealed significant differences in chemical impurities that these dyes contain. This study has, for the first time, expressed concern about the probable long-term impact of some ARS brands on the marked fish and their potential to bias the results of the studies dealing with ARS-marked fish.

Mutagenicity evaluation of pesticide analogs using standard and 6-well miniaturized bacterial reverse mutation tests

The Ames test is widely used in the mutagenicity evaluation of new and existing chemicals as a part of a compound selection strategy, regulatory control, the equivalence assessment, carcinogenic potential measurement etc. Intensification of the chemical industry and synthesis of plenty of new molecules has led to the necessity of tests with a higher throughput capacity. The 6-well miniaturized bacterial reverse mutation test and the standard Ames test were compared using 14 technical grade active ingredients (TGAIs) of pesticides. With some exceptions, the responses obtained in the miniscreen Ames are similar to those seen in the standard method: 4 overall test outcomes were negative and 9 were positive in both test versions, but 1 discordant result between the miniscreen and standard version. Comparison of the standard and the miniscreen Ames test resulted in 98% of concordance across five strains and conditions (±S9). The overall judgment is that the miniscreen Ames test can be used to assess the mutagenicity of pesticide analogs. It has the advantage of decreasing the number of materials and animals (for S9) and keeping a high-test performance.

Exposure to Mosquito Repellents Causes Profound Development Defects and Induces Oxidative Stress in Zebrafish

Objective The study was designed to investigate the effects of commercially available mosquito repellents on embryonic development of zebrafish.

Materials and Methods Transfluthrin is a type I pyrethroid present in all commercial mosquito and insect repellents. Pyrethrins are neurotoxins that target the nervous system of insects. Three popular brands of liquid vaporizer repellents coded as compound A, B, and C that contained transfluthrin, ranging from 0.88 to 1.6% w/w, were used in this study. The effects of these compounds on the embryonic development of zebrafish were investigated. In addition, the ability of transfluthrin to induce oxidative stress was examined by analyzing the generation of reactive oxygen species in exposed embryos.

Results The exposure to mosquito repellents resulted in extensive morphological defects in zebrafish embryos. The severity of the anomalies correlated with the concentration of transfluthrin in the repellents. Exposure to pure transfluthrin generated high levels of reactive oxygen species in zebrafish embryos, suggesting the induction of oxidative stress.

Conclusion Liquid vaporizer repellents are generally used for control of mosquitos and are common in many households. This study demonstrated that its exposure to mosquito repellents causes severe morphological defects and embryonic lethality in zebrafish. The study also showed that transfluthrin, the active insecticide in these repellents, induces oxidative stress in zebrafish.

Gas chromatography/negative chemical ionization mass spectrometry of transfluthrin in rat plasma and brain

RATIONALE

Transfluthrin is a relatively non-toxic rapid-acting synthetic pyrethroid insecticide. It is widely used in household and hygiene products. A sensitive and accurate bioanalytical method is required for quantification of its concentration in plasma and its potential target organ, the brain for studies to assess its health effects and toxicokinetics in mammals.

METHODS

The samples were prepared by liquid-liquid extraction. Gas chromatography mass spectrometry (GC/MS) analysis was performed for the determination of transfluthrin in biological samples with an overall method run time of 15 min. Transfluthrin was quantified using selected-ion monitoring (SIM) in the negative chemical ionization (NCI) mode. Chromatographic separation was achieved using a Zebron® ZB5-MS GC column operating with 1 mL/min constant flow helium. Cis-Permethrin was used as the internal standard.

RESULTS

The method was validated to be precise and accurate within the linear range of 1.0-400.0 ng/mL in plasma and 4.0-400.0 ng/mL in brain homogenate, based on a 100 μL sample volume for both matrices. This method was applied to samples following administration of a 10 mg/kg oral dose to male adult rats. The plasma concentrations were observed to be 11.70 ± 5.69 ng/mL and brain concentrations 12.09 ± 3.15 ng/g when measured 2 h post-dose.

CONCLUSIONS

A rapid GC/NCI-MS method was demonstrated to be sensitive, specific, precise and accurate for the quantification of transfluthrin in rat plasma and brain. The optimized method was successfully used to quantify the rat plasma and brain concentrations of transfluthrin 2 h after the oral dosing of Sprague-Dawley rats.