Are legacy POPs a threat to Iberian harbour porpoises (Phocoena phocoena)?

The Iberian harbour porpoise (Phocoena phocoena) has experienced a marked decline in genetic diversity decrease over recent decades. Apart from fisheries bycatch, anthropogenic pollution is a major threat to the population. Although environmental concentrations of persistent organic pollutants (POPs) have declined since their ban in the 1970s, these compounds remain of concern due to their bioaccumulation, particularly in long-lived top predators. This study assessed POP concentrations (PCB, DDT, HCB, HCH, heptachlor, heptachlor epoxide, drins) in blubber of 43 porpoises stranded in Portugal between 2005 and 2013. ΣPCB, ΣDDT and ΣDrins showed the highest concentrations (6.59, 2.26 and 0.53 μg g-1 lw, respectively). Among PCBs, congener CB153, CB138, and CB180 predominated. Patterns of higher ΣPCB, ΣDDT and ΣDrins concentrations in males and evidence of contaminant offloading in females were consistent with previously reported accumulation dynamics. Older males exhibited significantly higher concentrations of heptachlor epoxide and ΣDrins. In several individuals, ΣPCB concentrations exceeded the toxicity threshold associated with adverse health effects in marine mammals (17 μg g-1 lw, as Aroclor 1254). Additionally, p,p'-DDE concentrations in both sexes surpassed the threshold linked to for reduced lymphocyte proliferation (1.43 μg g-1 lw). The viability of the small Iberian harbour porpoise population is therefore of serious concern. Contaminant burdens associated with disease susceptibility and immune impairment indicate that legacy POPs remain a significant threat. Further contaminant analyses of recently stranded Iberian porpoises, combined with comprehensive health assessments, are urgently needed.