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Marajó Island, an environmental protection area for sustainable use in the Brazilian Amazon, was the first region in Brazil to apply the pesticide DDT, a persistent organic pollutant (POP), to control malaria outbreaks. This study investigated background levels of various POPs, including o,p'- and p,p'-DDT and their primary metabolites (o,p'- and p,p'-DDE, o,p'- and p,p'-DDD), as well as hexachlorocyclohexane (α-, β-, γ-, δ-HCH), using estuarine surface sediments and sediment cores from areas influenced by urbanization and agriculture. All samples were collected during the dry season (September 2014). Surface sediments exhibited ΣDDT concentrations up to 2.71 ng g⁻1, with isomeric ratios indicating past DDT application and contributions from dicofol. Sediment profiles revealed alternating aerobic and anaerobic degradation processes of DDT. Other organochlorinated contaminants were not detected. The presence of γ-HCH as the main isomer (0.24 to 0.90 ng g⁻1) in surface samples suggests recent lindane application as a wood preservative or cattle parasite treatment. A dated sediment core revealed historical contamination of early DDT tests in the Amazon during the mid-1940s. Increasing ΣDDT concentrations (up to 12.3 ng g⁻1) were identified in the 1970s, coinciding with the intensification of DDT use for public health campaigns, which lasted until 2009 and reached the highest ΣDDT flux. Legal restrictions on the use and commercialization of POPs, along with natural degrading processes, likely led to decreased accumulation and limited ecological risks. Furthermore, the low concentrations of POPs suggested biodegradation and dispersion from northeast to southeast. [ABSTRACT FROM AUTHOR]