Indoor and Outdoor Pyrethroid Air Concentrations

Pyrethroids are used throughout the world in agricultural settings and inside and outside of residences to control pests. This has resulted in their increase in air concentration leading to inhalation, and to a lesser extent dermal, exposures to applicators, their families, and the general public. Applicators need to wear appropriate personal protection equipment (PPE) to avoid high exposures during or after spraying of crops. The various uses of the pyrethroids and pyrethrins are regulated and education often mandated to minimize potential exposures. Outdoor levels are predominantly influenced by agricultural applications which can result in drift of the pesticides to the surrounding residential communities. Drift contributions decrease with distance from application and depend upon wind conditions, temperature, and precipitation. Only a limited number of studies have directly measured pyrethroid air concentrations due to the effort involved. Rather, air concentrations and the resulting exposure estimates rely on mathematical modeling to predict the transport and distribution of pyrethroids and on biomarker measurements to determine uptake in individuals. Urinary metabolites are the most common biomarkers. However, most of the metabolites are not specific to individual pyrethroids; rather, they provide evidence that an individual or population were exposed to one or more pyrethroid pesticide. Recently, silicone bracelets have been deployed to evaluate relative personal inhalation exposures to pyrethroids as part of a scan for multiple semi-volatile organic compounds. When pyrethroids are sprayed indoors, they are absorbed onto surfaces and by house dust. The absorbed pyrethroids subsequently equilibrate with the indoor air and are distributed throughout the home resulting in multiple exposures over an extended time period. Inhalation of pyrethroids usually contributes only a small portion (<10%) of the total exposure in the general population, with ingestion of foods grown or stored with pesticides to increase crop yield having the largest contribution. Inhalation exposures can be significant though following the use pesticide application devices that release larger amounts into the air or if individuals enter a treated area without adequate ventilation or prior to the pyrethroid air concentration declining sufficiently.