Abstract: This dissertation general objective is to analyze the use of polluting chemical substances in Brazil and the technical, regulatory and political debates that cross it, using the approach of Science, Technology and Society (STS) studies and Actor-Network Theory (ANT).From the constitution of a substance as a 'pollutant', I seek to recover the ontological disputes around this substance and its broader social reverberations.The substance in question is perfluorooctane sulfonic acid (PFOS), a synthetic chemical that has been present in consumer products and industrial processes since the 1950s and which, in 2009, became part of the Stockholm Convention on Persistent Organic Pollutants.This decision, in addition to classifying it as a pollutant, sought to compose a global effort looking for its elimination, a measure that would also prevent the synthesis of countless other substances that become associated with the production of PFOS, including sulfluramid.The latter, however, had its use as a pesticide against leaf-cutting ants maintained in Brazil, even after the decision was taken in 2009.Therefore, the following question guided this research: how was it possible to preserve the use of sulfluramid in Brazil, despite its global ban and the scientific perception of these substances as persistent pollutants and dangerous to health?The main data were collected from a bibliographic and documentary research, focusing on scientific articles, documents and technical reports mobilized given the decision-making perspective under the Stockholm Convention.The time frame considered for this research was from July 2005 to May 2009, a period that covers the entire process of evaluating the PFOS candidacy to integrate the international agreement, from the submission of the proposal to decision making.The methodology adopted for analysis was ANT, which allowed the identification and organization of actors and associations involved in the constitution of these chemical substances, sometimes understood as safe, sometimes understood as pollutants, resulting in disputes about who they are and what they do.The results allowed us to discuss how the configuration of the final decision, based on the regulatory model of molecular identities, contributed to the fact that, despite the PFOS ban, sulfluramid did not reach the status of pollutant, nor did it sustain the safe condition.In addition, preserving it as permitted is pointed out as a result that had the joint mobilization of Brazilian bait producers, agribusiness, the government and researchers against the Stockholm Convention's interest in prohibiting it.The argument of economic impact is the most evident in favor of maintaining sulfluramid, however, it appears inserted in a particular logical construction that disputes the narrative not only about the measures to be adopted, but about the constitution of the mobilized entities.In this context, the establishment of doubt seems to be an important element for this configuration, as it allows the interest of industrial and economic actors to prevail to the detriment of the interest of other parts of society, maintaining production regimes potentially harmful to human and environmental health, as is happening in this case.