Fluorescent tracer technique for measuring the quantity of pesticide deposited to soil following spray applications

At present methods for measuring soil deposits from pesticide applications are somewhat limited. As an alternative to using pesticide residue analysis, a simple tracer technique has been developed using the fluorescent dye Tinopal CBS-X to measure deposits directly on the soil. Because there are soil tracer interactions with Tinopal CBS-X, the technique allows for variations in organic matter content by making use of a sorption isotherm as a calibration line. Laboratory measurements showed that tracer deposits on soil were comparable to those on artificial surfaces placed on the soil at the same location. Measurements from laboratory spray simulations and field experiments showed that there was high level of variability in the quantity of tracer recovered on soil. This was due to deposit variability below the crop, across the swath, and between sample locations rather than from the sampling method indicating that shading by the crop canopy has a significant effect on deposition. Because soil samples can be taken without bias, it was concluded that a more accurate indication of the amount reaching the soil could be obtained from soil surface sampling than from the use of artificial surfaces mounted on tables. (C) 2002 Elsevier Science Ltd. All rights reserved.