A narrative review of converging evidence addressing developmental toxicity of pyrethroid insecticides

Abstract

Pyrethroid insecticides are broadly used in agriculture and household products throughout the world. Exposure to this class of insecticides is widespread, and while generally believed to be safe for use, there is increasing concern regarding their effects on neurodevelopment. Due to the critical roles that molecular targets of pyrethroids play in the regulation of neurodevelopment, particular focus has been placed on evaluating the effects of in utero and childhood pyrethroid exposure on child cognition and behavior. As such, this narrative review synthesizes an assessment of converging study types; we review reports of neonatal pyrethroid levels together with current epidemiological literature that convergently address the risk for developmental toxicity linked to exposure to pyrethroid insecticides. We first address studies that assess the degree of direct fetal exposure to pyrethroids in utero through measurements in cord blood, meconium, and amniotic fluid. We then focus on the links between prenatal exposure to these insecticides and child neurodevelopment, fetal growth, and other adverse birth outcomes. Furthermore, we assess the effects of postnatal exposure on child neurodevelopment through a review of the data on pediatric exposures and child cognitive and behavioral outcomes. Study quality was evaluated individually, and the weight of evidence was assessed broadly to characterize these effects. Overall, while definitive conclusions cannot be reached from the currently available literature, the available data suggest that the potential links between pyrethroid exposure and child neurodevelopmental effects deserve further investigation.

Keywords:

• Pyrethroid
• neurodevelopment
• review
• epidemiology
• developmental toxicity
• insecticide
• attention deficit hyperactivity disorder
• autism

Acknowledgments

The authors are grateful for critical internal review of this paper by Diane Rohlman Ph.D., of the University of Iowa College of Public Health, and Jonathan Doorn Ph.D., of the University of Iowa College of Pharmacy. The authors also acknowledge the valuable comments offered by the external reviewers who were selected by the Editor and anonymous to the authors.

Declaration of interest

This manuscript was prepared as a component of the first author’s PhD thesis, introducing a set of experiments investigating the impact of pregnancy cypermethrin on offspring brain using mouse models. These studies and also the time dedicated to preparing this manuscript was funded by pilot/seed grants to the authors from the University of Iowa Center for Health Effects of Environmental Contamination (established through the 1987 Iowa Groundwater Protection Act) and the University of Iowa Environmental Health Science Research Center (EHSRC: funded by National Institute of Environmental Health Science P30 ES005605). The funders had no participation in the preparation of the manuscript; the University of Iowa faculty members who reviewed drafts of this work are both affiliated with the EHSRC. The authors have no previous or anticipated participation in legal or regulatory activities related to the contents of the paper. Hanna Stevens is an author on a policy brief, prepared through the University of Iowa Public Policy Center, to the 2022 Iowa Legislative session advocating for reevaluation of pyrethroid pesticide regulation.

Additional information

Funding

This work was supported by the National Institute for Environmental Health Sciences through the University of Iowa Environmental Health Sciences Research Center (EHSRC) under grant NIEHS/NIH P30 ES005605. This work was also supported by a pilot grant from the University of Iowa’s Center for Health Effects of Environmental Contamination (CHEEC) and a Microfinance Research Grant from the Pappajohn Biomedical Institute. This publication’s contents are solely the responsibility of the authors and do not necessarily represent the official views of the funders.