Mapping Sources of Fine Metallic Particles Near Schools in Greater Paris Using Passive Biocaptors: transforming environmental monitoring practices

As of 2024, 100% of Parisian residents remain exposed to concentrations of fine particulate matter (PM₂.₅) that exceed the World Health Organization’s (WHO) guideline limit of 5 µg/m³. Despite gradual improvements in air quality, atmospheric pollution—particularly from fine particles and nitrogen dioxide (NO₂)—continues to pose a major public health challenge. Recent findings by the French association Respire revealed that 682 daycare centers and schools in Île-de-France (Administrative region of Paris) exceed WHO NO₂ thresholds, underscoring the urgent need for intervention and the increasing mobilization of local stakeholders.

In the Paris region, wood heating and road traffic are the primary sources of fine particulate matter. Ultrafine particles (<1 µm), often enriched in heavy metals and exhibiting magnetic properties due to their iron content, present significant health risks. Their high reactivity and association with toxic metals suggest a potential link to neurodegenerative diseases.

This study presents the first results from the interdisciplinary Nanomap project (based on the Ecorc’Air scientific protocol), launched in 2024 in Île-de-France. The project integrates researchers from social sciences, geosciences, and participatory science, collaborating with nine citizen associations. Its objective is to map fine and ultrafine metallic particles pollution near schools and daycare centers, with the aim of tracing and determining the variability of pollution sources in urban areas. Additionally, the project examines scientific practices and interactions between researchers and citizen groups.

The study employs plane tree bark as a passive pollution sensor, leveraging its annual renewal and widespread presence in cities (more than 42,000 plane trees in Paris) to enhance spatial and temporal resolution. In 2025, nearly 700 samples were collected by citizens, with half of which were situated near educational facilities. Magnetic susceptibility measurements revealed varying concentrations of metallic particles.

Samples collected near potential pollution sources (e.g., ring roads, high-traffic areas) are currently undergoing advanced chemical analysis (ICP-MS and spICP-MS) and detailed magnetic characterization. This integrated approach is essential for validating suspected sources before any public disclosure to the citizen groups involved in the Nanomap project.