Assessing the Stability of Routine Wastewater Parameters and Chemical Biomarkers as Population-Normalization Proxies in Wastewater-Based Epidemiology

Wastewater-based epidemiology (WBE) is increasingly used to monitor public health trends and chemical consumption by analyzing biomarkers in untreated wastewater. As a complementary approach to traditional epidemiological surveillance, WBE provides insights into infectious disease spread, drug use, and pharmaceutical consumption. However, accurate population normalization remains a major challenge, because census-based population estimates often do not correspond to hydrologically defined wastewater catchments. This study evaluates whether routinely monitored wastewater quality parameters can serve as cost-effective population-normalization proxies in WBE. Using data from Latvia’s national COVID-19 wastewater surveillance program, the performance of conventional wastewater parameters (BOD5, COD, suspended solids, total phosphorus, and total nitrogen) was compared with endogenous and exogenous biomarkers, including 5-HIAA, caffeine, cotinine, ethyl sulfate, gabapentin, ibuprofen, and diclofenac. Population estimates based on census and operator data were assessed under varying weather conditions. The results indicate that routine wastewater parameters, particularly total nitrogen, may serve as suitable indicators for population normalization in WBE, with performance comparable to or exceeding that of commonly used biomarkers. These findings support the use of routinely monitored parameters as scalable and accessible tools for improving WBE reliability and strengthening public health surveillance and early warning systems.