Cities concentrate a wide range of environmental, social, and lifestyle-related exposures that can influence human health. Chemical contaminants, microorganisms, and antibiotic resistance genes are all part of this complex environment and can vary considerably even between neighborhoods within the same city. Understanding this variability and determining the extent to which it translates into differences in human exposure is one of the major challenges in current exposome research.

Wastewater offers a particularly valuable opportunity to study this phenomenon. Each sample aggregates contributions from hundreds or thousands of individuals and can provide a snapshot of a community’s chemical and biological characteristics. This approach, known as Wastewater-Based Epidemiology (WBE), makes it possible to study populations anonymously, repeatedly, and at different spatial scales, complementing the information obtained through traditional epidemiological and human biomonitoring studies.

In this context, EXPOWASTE – “Integrating human biomonitoring and wastewater-based epidemiology to assess exposure to harmful chemicals and biological agents” was launched as a project coordinated by ICRA-CERCA. It integrates two complementary subprojects: one led by ICRA-CERCA and another led by the Institute of Environmental Assessment and Water Research (IDAEA-CSIC). The project also involves Dipsalut, the Public Health Agency of the Girona Provincial Council, which contributes expertise in public and environmental health and helps connect the project with the population of Girona.

EXPOWASTE is funded through the 2022 Knowledge Generation Projects call by MCIN/AEI and the European Regional Development Fund (ERDF), European Union, and brings together expertise in environmental microbiology, antimicrobial resistance, analytical chemistry, exposomics, human biomonitoring, and public health.

One of the project’s scientific starting points is the study of the microbiome, resistome, and mobilome of wastewater from different neighborhoods in Girona. The results obtained so far show that the microbiological signal in wastewater is not homogeneous across the city. The composition of bacterial communities, antimicrobial resistance genes, and mobile genetic elements can differ between urban areas with distinct socioeconomic characteristics.

This observation raises a fundamental question: to what extent do the patterns detected in wastewater actually reflect the characteristics and exposures of the people living in those communities?

Answering this question is one of the central challenges of EXPOWASTE. The project aims to move beyond simply describing differences between neighborhoods by directly linking environmental signals with information obtained from the people contributing to the wastewater.

To achieve this, EXPOWASTE is built around Girostudi, a population-based cohort established in the Girona region that provides individual-level information on sociodemographic characteristics, lifestyles, health status, and environmental exposures. This infrastructure enables the continuation of the initial wastewater studies while supporting a particularly innovative study design: the paired analysis of human samples and wastewater samples collected from the same communities.

This approach makes it possible to compare two levels of information that are usually studied separately. On the one hand, wastewater provides an integrated signal representing an entire community. On the other hand, human samples and Girostudi data make it possible to characterize exposure and biological features at the individual level. Comparing these two sources of information will help identify which wastewater markers are capable of reproducing patterns observed in people.

The project addresses this challenge from two complementary perspectives. The subproject led by ICRA-CERCA focuses on biological components, including the microbiome, resistome, and other microbiological markers, while the subproject led by IDAEA-CSIC investigates the chemical exposome using advanced mass spectrometry techniques. Integrating both perspectives will enable the joint study of chemical and biological exposures and their relationship with environmental, social, and lifestyle factors.

EXPOWASTE is currently entering a crucial phase. Environmental samples collected from Girona’s sewer network are already being analyzed, and the project is progressing in the collection of human samples selected through Girostudi. The availability of these two sources of information will enable the next major step: a direct comparison between wastewater signals and the characteristics of people living in the same communities.

The ultimate goal is to determine the extent to which wastewater can function as a collective sensor of the exposome and the health status of urban populations. If specific chemical or biological indicators measured in wastewater can reliably reproduce patterns observed at the individual level, this approach could open new opportunities to complement conventional epidemiological surveillance and public health monitoring systems.

Rather than continuously monitoring thousands of individuals one by one, wastewater could make it possible to track selected health and exposure indicators at the community level, identify differences between areas, and detect changes over time. EXPOWASTE aims to establish the scientific foundations needed to determine when such inference is possible, for which markers, and with what degree of representativeness.