Community health assessments based on measurement of biomarkers in untreated wastewater using wastewater-based epidemiology (WBE) are influenced by wastewater flow conditions. Combined sanitary and storm sewer systems, which remain an important part of urban water infrastructure, are sensitive to changes in flow resulting from weather-dependent precipitation. Stormwater flow during precipitation events may differentially impact consumption estimates depending on the in-sewer stability and use patterns of parent substances. Dilution of sanitary flow with stormwater causes apparent decreases in consumption. Conversely, reduced hydraulic retention times under high-flow conditions cause apparent increases in consumption for biomarkers susceptible to in-sewer transformation. Xenobiotics used by a consistent fraction of the population (i.e., population biomarkers) may provide a consistent standard to estimate the influence of wet-weather flow conditions on WBE biomarker measurements in combined sewers. Few studies have investigated the occurrence patterns of common population biomarkers in combined sewers during major precipitation events. Therefore, we monitored thirty population biomarkers in daily time-proportional 24-hour composite samples collected from geographically co-located sewersheds serving similar population sizes (110 and 140 thousand people), with variation in the fraction of sewershed served by combined sewers (5 and 20% combined, respectively). Population biomarkers were selected based on urinary excretion profiles and included a range of common prescription and over-the-counter pharmaceuticals and personal care products (e.g., artificial sweeteners, caffeine, nicotine) and their metabolites. During the thirty-day study period, precipitation was recorded on thirteen days, total daily precipitation ranged from 0.03 to 2.54 inches, and combined sewer overflow events were recorded on four days. Fourteen population biomarkers had detection frequencies greater than &gt;50% and had median measured concentrations ranging from 0.08-29.4 μg L-1. In this presentation we will evaluate the influence of precipitation events and chemical structure on population biomarker occurrence to inform selection of population biomarkers for normalizing consumption estimates for high-value WBE assay targets (e.g., drugs, pharmaceuticals).

Population biomarkers reveal the influence of precipitation events on consumption estimates in combined sewer systems using wastewater-based epidemiology

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