Passive air sampling (PAS) involves the diffusive uptake of gas-phase target analytes into a sorbent over time. Some advantages of PAS include its low cost and simplicity to assemble and deploy. With these features, PAS has widely become the leading method for the collection of air samples for long-term global background air quality monitoring studies. In the current study, we sought to investigate whether the PAS technique could be applied as a forensics tool for detecting off-target pesticide exposure. The location for this study was central west NSW – a significant cotton-growing region. In cotton farming, a common practice before harvest is the application of a defoliant to encourage the cotton leaves to drop to improve harvest efficiency. Community reports of specific evergreen tree species losing their leaves occurs annually within the region and coincides with the cotton defoliation period. Vegetation sampling to date has not yielded evidence of pesticide exposure among affected trees. In this study, we have used a multiple lines of evidence approach to investigate off-target pesticide exposure. The techniques included deposition sampling using passive polyurethane foam (PUF) samplers (deployed for consecutive one-month intervals), bulk deposition sampling (weekly), and leaf sampling (weekly). While PAS can detect the occurrence of off-target pesticide application, given its coarse spatial and temporal resolution it cannot be used to pinpoint the precise source of the pesticide overspray where multiple users are present. PAS is however a suitable environmental forensics tool for providing a proactive response to understanding aerial dispersal profiles of pesticides, providing a useful line of evidence (e.g. high-risk periods, regions and pesticide applications) from which evidence-based decisions can be made about the need for more targeted investigation or management.