CALIBRATING THE PESTICIDE CAPTURE EFFICIENCY OF PASSIVE DOSIMETERS

A system has been devised for determining the absolute capture efficie ncy of passive dosimeters. The system is composed of three components: a wind tunnel, a tracer atomizer, and a capture efficiency test devic e (CETD). The CETD consists of a series of cylinders separated by nylo n screens to intercept and capture the spray containing a tracer. The decline in tracer at the screens was used to determine the tracer inci dent on the first screen. This in turn was used to estimate the tracer incident on a test dosimeter of washed muslin. The capture efficiency of the dosimeter was expressed as the ratio of tracer captured to tra cer incident on the dosimeter. The capture efficiency of the test dosi meter using the CETD was found to be independent of the time of exposu re and quantity of tracer captured. The approach presented is novel in that the method for documenting capture efficiency does not require p rior knowledge of the spray concentration. Elimination of this require ment allows the use of the device in a much larger array of test situa tions (e.g. field and greenhouse studies) than has been previously pos sible. Furthermore, the conceptual model can easily be modified to all ow for capture efficiency measurements from a range of structures and materials such as plants or whole leaves, as well as insects and non-t arget animal species. The CETD is simple and portable and could be use d to calibrate dosimeters in a variety of field situations.