For decades, the worker's gardens in Gennevilliers, France, have been a peaceful place where families grow vegetables like leeks and tomatoes. These gardens, nestled in the greenery, offer a sense of normalcy. However, beneath the soil that now supports these crops lies a hidden history of industrial activity that dates back to the late 19th century. For more than seventy years, Paris's wastewater was spread over the fields of Gennevilliers as a natural filtration system. This practice left behind heavy metals such as lead, cadmium, and zinc, along with other micropollutants, which remain in the soil today. The practice of spreading wastewater began in response to a cholera outbreak in 1892, which claimed nearly 1,000 lives in Paris and its suburbs. At the time, chemical wastewater treatment was not yet developed, so city engineers devised an innovative, if controversial, solution: using agricultural fields as natural filters. In 1899, a dedicated pipeline was built to transport Parisian wastewater to the fields of Gennevilliers via the Clichy plant. This marked a symbolic shift in favor of engineers over hygienists, who had previously advocated for more cautious methods of handling sewage. Between 1900 and 1905, the system expanded significantly, with the pipeline extended to other areas such as Triel-sur-Seine, Méry-sur-Oise, and Achères. These fields, once known for their market garden produce that supplied much of Paris, became an extensive, open-air filtration system for the city's wastewater. Studies conducted between 1970 and 1975 confirmed the presence of heavy metals and other contaminants in the soil. Although the practice of spreading raw sewage was gradually phased out in 1974 with the opening of a sludge treatment plant in Achères, the pollution had already taken root. A key recommendation was to maintain permanent vegetation cover to prevent pollutants from migrating into groundwater. Today, regulations attempt to manage the risks associated with these contaminated soils. A decree from 1998 sets strict limits on the concentration of certain chemicals in treated sludge, including heavy metals and other pollutants. However, the regulation does not address an entire category of micropollutants, such as drug residues and detergents, which are known to be present in the sludge. Meanwhile, the administrative history of these lands is complex: the former spreading fields were once owned by the Seine department and later became the property of the City of Paris. Despite this, no major depollution plan has been implemented, leaving the soil still contaminated from over seventy years of use. The worker's gardens continue to be cultivated by families who are often unaware of the history beneath their feet. Similar concerns are now being raised in other areas, such as the Yvelines region, where residents fear the effects of sludge spreading from wastewater treatment plants. This issue affects over 55 communes in the department. The coexistence of industrial history and agricultural use raises a pressing question: who is responsible for the long-term consequences of a technical decision made over a century ago, still evident in the chemical composition of the soil today?