Decreases in contaminant loads and risk of adverse effects in harbour porpoises (Phocoena phocoena) from Inner Danish waters over three decades.

Abstract

We present temporal trends in juvenile harbour porpoises from Danish Waters collected during 1980-2019, and investigate effect concentrations for both juveniles and adults for a range of organochlorines (OCs), brominated flame retardants (BFRs), per- and polyfluoroalkyl substances (PFASs), organotins and total mercury (THg). We found declining concentrations for ?PCBs, ?DDTs, ?HCHs, HCB, Trans-nonachlor, ?PBDEs, TBT and ?BTs over the three periods 1987-1990, 1996-1999 and 2010-2019. Concentrations above effect thresholds were detected for ?PCBs, ?DDTs and THg. All adult males were above PCB effect thresholds for reproductive and immune system (9000 ng/g lw) effects during the first two periods, declining to 50% of effect levels in the last period. For ?DDTs, the highest concentrations were also detected among adults with all animals above effect threshold for immune system (1430 ng/g lw). while During the two first periods, all juveniles were also above the threshold, this proportion declined to 50% in the last period. Most animals were within the THg Low or No risk group (<64,00 ng/g ww) and no animals had concentrations above the Severe risk threshold (>126,000 ng/g ww). Concentrations of other OCs and BFRs and PFASs were below effect thresholds and only the first two groups decreased significantly over the study periods. Given our study's high concentrations of particularly PCBs and DDTs bordering the Baltic Proper, our results strongly indicates that these contaminants played a major role in the decimation of the Baltic Proper harbour porpoise population during 1960s-1980,s prior to national bans and implementation of the Stockholm Convention.