Design and Radiometric Modeling of a Portable EEM Fluorescence Sensor for ppb-Level Detection of Pesticide Mixtures in Water

Abstract

According to the U.S. Geological Survey (USGS), pesticide contamination of American waters is widespread, with typical samples containing mixtures of 10 to 20 active compounds. Recent studies show that agricultural runoff and seasonal application patterns are two of the most common sources of this contamination. Environmental monitoring studies help improve understanding of the distribution and persistence of pesticides in natural water systems. Enhanced detection tools are critical for environmental monitoring studies that target data collection and the analysis of water quality data. Traditional pesticide measurement methods include solvent extraction and chromatographic separation, which introduce problems such as: 1) high cost per sample, 2) slow turnaround time, and 3) limited suitability for field deployment. Recent advancements in fluorescence spectroscopy have allowed for the development of various portable measurement techniques in different applications. However, environmental agencies are still using laboratory-based analysis rather than portable optical measurement tools, which demonstrates that there is significant room for improvement in this field. The detection of pesticides using excitation-emission matrix (EEM) fluorescence requires accurate photon throughput calculation using component-based or radiometric modeling techniques. This thesis is a study of the design, modeling, and validation of an EEM fluorescence system based on multi-wavelength excitation theory. The system was designed, modeled, and evaluated in pesticide detection applications using three representative compounds: zeta-cypermethrin, myclobutanil, and glyphosate. The compounds were tested at five concentration levels to characterize the system across different detection scenarios. When compared to model predictions, the experimental results showed detection limits of 10-100 ppb for strongly fluorescent pesticides, approximately one order of magnitude above predicted values due to lower LED power than modeled. Based on the results and validation from the radiometric model, the use of compact EEM fluorescence systems in portable applications has potential to improve the frequency and cost-effectiveness of pesticide screening.