Distribution characteristics and ecotoxicological risks of typical organic flame retardants and plasticisers in the Amazon River basin around Manaus, Brazil

Current understanding of potential anthropogenic/environmental drivers and ecotoxicological risks of emerging contaminants in the Amazon Basin, particularly organic flame retardants and plasticisers, is limited. We collected sediment samples from Amazonian Rivers near Manaus city/Amazonas State, Brazil, and measured concentrations of 39 organic flame retardants and plasticisers, namely: polybrominated diphenyl ethers (PBDEs), novel brominated flame retardants (NBFRs), dechlorane plus (DP), hexabromocyclododecane (HBCDD), organophosphate esters (OPEs), and polychlorinated biphenyls (PCBs). Concentrations of Σ₉PBDEs, Σ₉NBFRs, Σ₂DPs, Σ₃HBCDDs, Σ₇OPEs, and Σ₉PCBs ranged between <0.26 and 5.1, 2.0 - 18, <0.075 - 290, <0.0014 - 0.29, 2.2 - 15, and 0.18 - 3.0 ng/g dw in sediments, respectively. Distribution of legacy BFRs (PBDEs and HBCDD), DPs, and OPEs in sediments was primarily driven by domestic sources; distribution of NBFRs was mainly driven by industrial sources; while distribution of PCBs was primarily modulated by organic matter. We also measured PBDEs in paired surface water samples collected from the Amazon basin near Manaus, with concentrations of Σ₉PBDEs ranging between 0.18 and 3.4 ng/L. In contrast to sediments, PBDE concentrations in water were primarily controlled by short-term aggregation and sedimentation enhanced by organic matter. Comparisons of our observations with PNEC (predicted no-effect concentration) values imply high ecotoxicological risks presented by DP, bis(2-ethyl hexyl) tetrabromophthalate (BEH-TEBP), PCB-11, and tris(1-chloro-2-propyl) phosphate (TCIPP) in sediments, and low to medium risks by other pollutants. This is especially striking for DP for which the maximum RQ (Risk Quotient) value was 24.7 at sampling point 1, possibly due to the impact of domestic waste disposal and intensive boat traffic.