Elsevier

Chemosphere

Volume 144, February 2016, Pages 2427-2435
Chemosphere

Pyrethroids in indoor air during application of various mosquito repellents: Occurrence, dissipation and potential exposure risk

https://doi.org/10.1016/j.chemosphere.2015.11.025Get rights and content

Highlights

  • The types of mosquito repellents (MRs) affected indoor exposure to pyrethroids.

  • Pyrethroid levels increased 3–6 orders of magnitude after indoor MR application.

  • The gas-particle partitioning and dissipation of pyrethroids varied among MRs.

  • Vaporizing mat-emitted allethrin posed significant risk to children (<6 years old).

Abstract

Commercial mosquito repellents (MRs) are generally applied as mosquito coils, electric vaporizers (liquid and solid) or aerosol spray, with pyrethroids often being the active ingredients. Four types of MRs were applied individually in a 13-m2 bedroom to study the occurrence, dissipation and risk of pyrethroids in indoor environments. Total air concentrations (in gas and particle phases) of allethrin, cypermethrin, dimefluthrin and tetramethrin during MR applications were three to six orders of magnitude higher than indoor levels before the applications, and allethrin emitted from a vaporizing mat reached the highest concentration measured during the current study (18,600 ± 4980 ng m−3). The fate of airborne pyrethroids was different when the four MRs were applied. Particle-associated allethrin accounted for 95% of its total concentration from the aerosol spray, and was significantly higher than the vaporizing mat (67%), suggesting that the released phase of MRs and size distribution of pyrethroid-carrying particles played important roles in the gas-particle partitioning process. In addition, air exchange through open windows more effectively reduced the levels of indoor pyrethroids than ventilation using an air conditioner. The inhalation risk quotients (RQ) for allethrin derived from application of the vaporizing mat ranged from 1.04 ± 0.40 to 1.98 ± 0.75 for different age-subgroups of the population, suggesting potential exposure risk. Special attention should be given concerning indoor exposure of pyrethroids to these vulnerable groups.

Introduction

Indoor air pollution and its toxicological effects have become a growing concern, since humans spend more than 80% of their time in indoor environments, where they are potentially exposed to a variety of xenobiotics, e.g., insecticides (Hadnagy et al., 2003, Zhang et al., 2013). The increased use of insecticides in homes for pest control has drawn extra attention to the risk of indoor exposure to these substances (Davis and Ahmed, 1998, Yusà et al., 2014, Zhang et al., 2014). Specifically, spraying of insecticides at high levels has been recommended as an emergency vector-control practice during outbreaks of mosquito-borne illnesses, e.g. dengue fever, in subtropical countries (http://www.who.int/mediacentre/factsheets/fs117/en/); however, this practice may cause considerable exposure of humans to these insecticides (Jin et al., 2015, Zhang et al., 2013). Meanwhile, modern homes are often designed to be more airtight compared with older construction to improve energy efficiency. As a result, these buildings tend to have lower ventilation rates, which decreases the dispersion of indoor contaminants, thereby increasing the risk of indoor exposure (Jones, 1999, Keig et al., 2014, Zhang et al., 2013).

Synthetic pyrethroids are widely used as active ingredients in mosquito repellents (MR) owing to their relatively low toxicity to mammals (Narendra et al., 2008, Pauluhn, 1999, Vesin et al., 2013). Recent studies, however, showed that pyrethroids might cause behavioral and developmental neurotoxicity, with special concern revolving around infants and children, due to their potential exposure during a sensitive neurodevelopmental stage (Shafer et al., 2005). In addition, some pyrethroids are listed as endocrine disruptors and possible carcinogens (USEPA, 2006, Vesin et al., 2013).

Long-term exposure to pyrethroid-based MRs in indoor environments has been shown to cause chronic neurotoxicity, e.g. dysfunction of blood–brain barrier permeability, oxidative damage to the brain (Gupta et al., 1999, Sinha et al., 2004), and cholinergic dysfunction leading to learning and memory deficiencies (Sinha et al., 2006). Wu et al. (2013) assessed indoor exposure of pyrethroids in China using questionnaires and measured urinary levels of pyrethroid metabolites in infants, and found that application of MRs significantly increased levels of urinary metabolites. On the other hand, direct indoor exposure data, including air concentrations of pyrethroids during and immediately after MR application are limited. In one of the few studies examining this issue, Vesin et al. (2013) detected elevated concentration of transfluthrin in the gaseous phase during the indoor application of an electric vaporizer, but they found inhalation risk of airborne transfluthrin was low. The exposure levels and potential risk of pyrethroids during the applications of other types of commonly used MRs remain unknown.

The objectives of the current study were to evaluate the occurrence, dissipation and potential risk of pyrethroids in indoor air induced by the use of four pyrethroid-based MRs, including a traditional mosquito coil, two electric vaporizers (liquid vaporizer and vaporizing mat) and an aerosol spray. Specific objectives included (1) monitoring indoor air concentrations of the active ingredient pyrethroids during and immediately after the individual application of various MRs, (2) evaluating the partitioning of pyrethroids between gas and particle phases and the dissipation of indoor airborne pyrethroids, and (3) quantitatively estimating the risk from potential exposure to the indoor application of pyrethroid-based MRs.

Section snippets

Pyrethroid-based MRs, chemicals and reagents

Four types of MRs that are distributed under the brand name Raid® were used in the current study and included a mosquito coil, liquid vaporizer, vaporizing mat and aerosol spray. The MRs were purchased from a local supermarket in Guangzhou, China. Descriptions of the MRs and their active ingredients, as well as the application procedures are detailed in Table S1 in the Supplementary material (“S” represents figures and tables in the Supplementary material thereafter).

Neat standards of

Occurrence of pyrethroids in indoor air during MR applications

As shown in Table S1, allethrin, cypermethrin, dimefluthrin and tetramethrin were the active ingredients in the MRs studied, and their total air concentrations (particle and gas phases combined) before MR application in the room were 0.042 ± 0.028, 0.033 ± 0.039, 0.0096 ± 0.0028 and 0.052 ± 0.094 ng m−3, respectively. The use of MRs markedly increased the concentrations of pyrethroids in the indoor air, with the concentrations being three to six orders of magnitude greater than the levels

Acknowledgments

We thank Dali Sun and Yanli Wei for sample preparation. This research was supported by the National Science Foundation of China (41222024, 41473106 and 41503091) and the State Key Laboratory of Organic Geochemistry (SKLOG2015A01). This is contribution No. IS-2160 from GIGCAS.

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