Optical Brightener Screening for Sewage Contamination of Water Table Aquifers in Southeastern Minnesota, USA

Abstract

Novel screening methods for detecting optical brighteners, fluorescent organic blue dyes principally used in laundry detergents for whitening fabrics, have been developed for the monitoring of water table aquifers impacted by septic systems. Four rural residential communities characterized by private water supply and sewage systems were selected in southeastern Minnesota. Developments were chosen with a variety of saturated and unsaturated zone materials and thicknesses, water table and well depths, and topographic and cultural settings. Sampling sites were enrolled if wells were completed above regional aquitards. Sanitary surveys of sampling sites were completed with attention to drinking water usage and waste/wastewater disposal practices to uncover sources of crosscontamination. Water supplies were sampled and analyzed to determine aquifer sources, sanitary quality and natural backgrounds and anthropomorphic contributions of physicochemical and microbiological parameters of interest (e.g., nitrate, chloride and coliform bacteria). Filter holders containing untreated cotton, activated carbon and polysulfone/polyethersulfone membrane filters were installed as immersion-type detectors in toilet reservoirs. Syringe filter capsules comprised of polyethersulfone membranes were utilized for direct sampling. Exposure times ranged from minutes to months, and exposed filter media were analyzed in solid phase utilizing a scanning spectrofluorophotometer. Spectral data were computer-processed to objectively match peaks with the spectra obtained from pure fluorescent dyes and laundry detergent formulations. Detections were positive if matched peaks at 440 nm appeared above background fluorescence. Water supply test data and site survey information indicative of septic system contamination were moderately correlated with positive optical brightener detections.