Citizen-Based\nWater Quality Monitoring: Field\nTesting a User-Friendly\nSensor for Phosphate Detection in Global Surface Waters

Widespread\nconcern over surface water pollution has led to interest\nin developing easy-to-use accurate tools for citizen-based measurements\nthat provide high spatial and temporal resolution while maintaining\naccuracy. Excessive anthropogenic phosphate significantly contributes\nto global eutrophication and necessitates regular on-site phosphate\nmonitoring in surface waters. Traditional instrumentation for quantifying\nphosphate is labor-intensive, expensive, and performed in laboratories.\nExisting on-site testing methods relying on phosphomolybdenum blue\n(PMB) have limited sensitivity and stability under ambient conditions.\nTo overcome these limitations, a novel low-cost, rapid, and user-friendly\nsensor for citizen-led phosphate monitoring in surface water is introduced\nand demonstrated with a global sampling campaign. The fast-flow microfluidic\ndevice provides user-friendly operation, achieving an environmentally\nrelevant limit of detection (LoD) of 190 ppb, which is near the EPA-recommended\nmaximum for phosphate. The dip-and-read operation reduces procedural\nsteps while delivering accurate sample volume, making it well-suited\nfor citizen-led science initiatives. This sensor exhibits high selectivity\nand prolonged stability for two months under ambient conditions. The\nsensor’s performance was validated using the industry-standard\nUV–Vis method with 90% correlation. More than 1000 sensors\nwere deployed in different continents, facilitating phosphate mapping\nin diverse water sources across multiple continents. The initiative\ncovered much of the globe, including Thailand, Nepal, Brazil, Chile,\nthe USA, and Germany. In some cases, phosphate levels exceeded legislative\nguidelines by 100-fold. Through the collaboration of citizen scientists,\nwe analyzed regional topography and socioeconomic practices near water\nsources, identifying potential sources that could contribute to eutrophication\nin these areas.