Spatiotemporal bioavailability of PCDD/Fs and dl-PCBs in wild mussels from the Portuguese Atlantic coast.

This study aimed to assess the spatiotemporal bioavailability of polychlorinated dibenzo--dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in wild adult mussels, collected along the Portuguese Atlantic coast between 2009 and 2020. The work is part of a national environmental monitoring program. The purpose was to evaluate the dioxins' temporal trends, the human and ecological risks, and the correlation between mussels' location and the main pollutant sources in Portugal. The levels and congener patterns of the most toxicity-relevant 17 PCDD/Fs and 12 dl-PCBs were determined, with the dl-PCBs dominant. The sum of ΣPCDD/Fs and Σdl-PCBs values ranged from 2.0 to 4.0 ng WHO-TEQ kg, (wet weight basis), below the limits established by the European Commission for contamination in fish and fishery products (6.5 ng per kg). The study included five years - 2009, 2010, 2016, 2018 and 2020 -, allowing to verify the impact of European Directive 2013/39/UE against the pollution of water in Portugal; it was observed that dioxin levels in mussels diminished over the time. Statistical analysis allowed verification of different spatial trends of dl-PCB profiles along the Portuguese Atlantic coast. The mono-ortho dl-PCB pentachlorinated congener IUPAC #118 prevailed in 2009 and 2018 in all sampling sites, and it was predominant in 2010, 2016 and 2020, followed by the congeners IUPAC #105, #156 and #167. The IUPAC #167, #169 and #123 were the most abundant hexachlorinated congeners, and the IUPAC #77 the most abundant tetrachlorinated congener. This work emphasises the importance of monitoring dioxins and mapping the congeners in Atlantic coastal ecosystems, to contribute to their elimination.