Depositional history of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and poly cyclic aromatic hydrocarbons (PAHs) in an Amazon estuary during the last century

摘要

Highlights•The depositional history of OCP, PCB and PAH was studied in the Amazon.•It is possible to distinguish two depositional periods, before and after 1965.•OCP showed trends corresponding to the production, usage and prohibition in Brazil.•Before 1965, PAH concentration portrays the region's baseline.•The increase in PAH concentration after the 1960s is mainly due to forest fires.Graphical abstractGraphical abstract showing two depositional periods along the cores. The first period occurred before extensive anthropogenic effects were registered in the sediments, while the second reflects the intensification of human influence in the area, when the introduction of OCPs, PCBs, and PAHs increased over time.Display OmittedAbstractThe sources and depositional history of OCPs (organochlorine pesticides), PCBs (polychlorinated biphenyls) and PAHs (polycyclic aromatic hydrocarbons) over the last 100years were determined in two sediment cores collected in the Amazon region. It was possible to distinguish two depositional periods along the cores. The first period occurred before extensive anthropogenic effects were registered in the sediments. During this time interval, the concentrations of all OCPs and PCBs were below the detection limits (DL), and the PAH concentrations were low and essentially constant (58.19–124.28ngg−1). The second period starts in the mid-1960s and reflects the increased human influence in the area. The concentrations of OCPs, PCBs, and PAHs increased towards the top of the cores, varying between

−1,

−1and 331 to 2341ngg−1, respectively. In general, OCP results showed trends corresponding to the production, usage and prohibition periods of POPs in Brazil. Compounds related to wood treatment, such HCHs and chlordanes, were predominant among the OCPs, which may be associated with many sawmills located in this region. The increase in PAH concentration after the 1960s is mainly due to forest fires, caused by the implementation of large-scale cattle ranches, which burned forests to create pastures. The background PAH concentrations before the 1960s are probably related to natural diagenetic processes.