How does one know when either kind of drift has occurred? Swab samples are used to detect pesticide residues from spray drift if the samples can be taken rather quickly as sunlight and oxygen will break down the pesticide quickly if it is volatile. Swab sampling works best if done within hours of a spray drift incident. Volatilization drift is not detected by swab sampling though it can continue at fairly high levels for several days after an application. Because volatilized pesticides are in gas form, it is unlikely that you will find residues on surfaces. Volatilization drift can be detected using air monitoring devices, sometimes called "drift catchers", that sample the air at a given moment. Regulatory definition of drift ignores 80-95% of total drift for volatile pesticides.
For about 45% of total pesticides applied in California, the bulk of off-site pesticide movement occurs as the pesticide volatilizes after application. ARB (California Air Resources Board) monitoring data show that concentrations of pesticides in air peak between eight and 24 hours after the start of application, with concentrations declining over several days to several weeks. In outdoor settings, airborne pesticides are carried away from the application site by wind and on windblown soil particles. Drifting pesticides can travel for miles, resulting in widespread toxic air pollution. In indoor environments, vaporized pesticides can persist for weeks after an application, concentrating in the air closest to the floor -- where children spend more of their time -- and condensing on plastic items such as children's toys (4).
1. Image: www.btny.purdue.edu/.../PPP-35.conclusion.jpg
4. Secondhand Pesticides: Airborne Pesticide Drift in California