Review
Pyrethroids: Exposure and health effects – An update

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Abstract

Synthetic pyrethroids are present in numerous commercial insecticide formulations and have extensive indoor and outdoor applications worldwide, including agricultural, public, residential, and veterinary usages for pest control. Pyrethroid use has increased continuously in recent years. The aim of this review is to provide updated and comprehensive information on human exposure and potential hazards associated with this class of pesticides. An initial keyword search in the PubMed database was conducted to identify relevant articles. Were taken into considerations only the studies published in the last decade that have assessed exposure and health effects of pyrethroids in human populations. Literature review shows that exposure evaluations increasingly focus on biomonitoring and that a large number of recent epidemiological studies pertain to the effects of pyrethroids on male fertility and prenatal development.

The main metabolites of pyrethroids have frequently been detected in urine samples from the general population, confirming widespread exposure of children and adults to one or more pyrethroids. Non-occupational exposure to pyrethroids mainly occurs through ingestion of residues in food, or ingestion of or dermal contact with contaminated house dust or surface-adhering particles, following domestic use. Although clinical features resulting from acute accidental exposure to pyrethroids are well described (e.g., paraesthesiae, and respiratory, eye and skin irritation), information regarding their chronic effects at low concentrations is both limited and controversial. Several recent epidemiological studies have raised concerns about potentially adverse effects on sperm quality and sperm DNA, reproductive hormones, and pregnancy outcomes. Early neurobehavioural development after in utero exposure is discussed. Further research is needed to clarify the possible risks associated with long-term environmental exposure to pyrethroids.

Introduction

Pyrethroids are a class of synthetic insecticides. Their chemical structure is based on naturally occurring pyrethrins, which are found in the flowers of Chrysanthemum cineraraefolum. The basic pyrethroid structure consists of an acid and an alcohol moiety, with an ester bond. Changes have been progressively introduced to increase their insecticidal potency and decrease their sensitivity to air and light. Most pyrethroids are chiral molecules and exist as mixtures of enantiomers. Pyrethroids are among the most frequently used pesticides and are found in many formulations used in agriculture to control insect pests in crops, forestry, horticulture, and in gardens. They are also widely used as insecticides in indoor environments such as households, warehouses, and farm and public buildings. They are found in pet shampoos, medication used for treating for scabies, and topical louse treatments. Some pyrethroids, such as permethrin, can be impregnated into clothing and fabric (e.g., carpets, blankets, uniforms) as arthropod contact repellants. They often replace home and agricultural use of certain restricted or banned insecticides, such as organophosphates (Horton et al., 2011a, Power and Sudakin, 2007, Williams et al., 2008). The main commercially available pyrethroids include allethrin, bifenthrin, cyfluthrin, lambda cyhalothrin, cypermethrin, deltamethrin, permethrin, d-phenothrin, resmethrin, and tetramethrin.

Because of the numerous applications and increasing worldwide use of pyrethroids during the last decade, the objective of this review was to provide a compilation of recently published findings of human health observations and biomonitoring exposure measurements, from 2003 to the present.

Section snippets

Method of search

An electronic search in the National Library of Medicine (PubMed) database was performed using the key-words “human” and “pyrethroid, bifenthrin, cyfluthrin, cypermethrin, deltamethrin, fenvalerate, or permethrin”. Selected articles were systematically reviewed and were then further filtered to include only those dealing with pyrethroid toxicology and/or exposure assessments in human populations. Several relevant reports that had been identified manually were also included (e.g., CDC surveys).

Human toxicity

In mammals and insects, the primary target of pyrethoids is the nervous system (Weiner et al., 2009, Wolansky and Harrill, 2008, Wolansky and Tornero-Velez, 2013). Pyrethroids are generally divided into two groups depending upon their acute neurobehavioural effects in rodents and the absence (Type I) or presence (Type II) of a cyano group at the α-carbon of the alcohol moiety. Regardless of the group or species, they primarily act by disrupting sodium channels in the axons. In laboratory

Conclusion

Numerous ambient monitoring data and analyses of pyrethroid metabolites in urine samples have shown widespread exposure to pyrethroids within the general population. Insecticide residues in food and in indoor residential environments are major sources of exposure. Recently published human studies have raised concerns about the potential developmental and male reproductive toxicity of pyrethroids at environmental concentrations. Additional studies are necessary to further evaluate the long-term

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